COMPOSITIONS AND METHODS FOR MUSCLE DISORDERS Sequence Listing This application contains a sequence listing in electronic form as an eXtensible Markup Language (XML) form filed via the Patent Center and is hereby incorporated by reference in its entirety. The XML-formatted sequence listing, created on April 6, 2023, is named KATE-013- 02WO-Seq.xml, and is 1.13 MB in size. Field of the Invention The invention relates to the medical treatment of muscle weakening disorders, including facioscapulohumeral muscular dystrophy. Background Genetic disorders are a major source of disease burden, and many of them have few or no medical or curative treatments. Along with other genetically linked muscle wasting disorders, Facioscapulohumeral Muscular Dystrophy (“FSHD”) is a genetic disorder that causes progressively increasing weakness and atrophy of the muscles. FSHD is so named because the muscles in the face, shoulder, and upper arm are the most affected, but it also affects other muscles in the body, including the legs, eyes, heart, hip, or abdominal muscles. FSHD causes progressively worsening symptoms that may result in asymmetric weakness FSHD is a genetic disorder caused by a genetic mutation that leads to inappropriate expression of the DUX4 gene on chromosome 4. DUX4 is the double homeobox protein 4 gene. FSHD can be inherited by just one parent because it is an autosomal dominant genetic disorder. FSHD often affects patients before the age of 20 and has an estimated prevalence in the United States of 4 cases per 100,000 individuals. There is currently no medical treatment to arrest or reverse the muscular effects of FSHD. Summary Aspects of the invention provide a method of inhibiting expression of a gene in a cell, the method comprising administering to a subject the adeno-associated virus (AAV) vector comprising a promoter sequence, a miRNA strand that binds to DUX4-FL, and a capsid protein comprising at least one modification that is an insertion between any two contiguous amino acids between amino acids 262-269, 327-332, 382-386, 452-460, 488-505, 527-539, 545-558, 581-593, 704-714, or any combination thereof in an AAV9 capsid polypeptide or in an analogous position in an AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV rh.74, AAV rh.10 capsid polypeptide. Methods of inhibiting that gene expression may include providing the AAV vector with any of the indicated permutations of the embodiment of the invention. For example. the promoter sequence is a promoter sequence transcribed by RNA polymerase II or III, U6 promoter sequence, MHCK7 promoter sequence, CK6 promoter sequence, tMCK promoter sequence, CK5 promoter sequence, MCK promoter sequence, HAS promoter sequence, MPZ promoter sequence, desmin promoter sequence, APOA2 promoter sequence, hAAT promoter sequence, INS promoter sequence, IRS2 promoter sequence, MYH6 promoter sequence, MYL2 promoter sequence, TNNI3 promoter sequence, SYN1 promoter sequence, GFAP promoter sequence, NES promoter sequence, MBP promoter sequence, or TH promoter sequence. The miRNA strand or miRNA scaffold may be selected from the group of miDUX4, miRN92, miRNA-17, miRNA-18a, miRNA-19a, miRNA-20a, miRNA-19b-1, mi-RNA-26a, miRNA-126, miRNA-335, let-7a and let-7b, miRNA-34, miR-34a, miRNA-10b, miRNA-208, miRNA-499, miRNA-195, miRNA-29a, miRNA-29b, or miRNA-29c. The miRNA strand may be selected from the group of SEQ ID NOs.1250-1305. The miRNA strand may further comprise 5-6 thymidines at the 5’ end. Advantageously, the capsid protein comprises at least one modification that results in reduced liver-tropism of the AAV vector. The capsid protein may comprise at least one modification that results in preferential targeting of the AAV vector to muscle tissue. The capsid protein may be selected from the sequences in Tables 1 - 4. The vector may further comprises a nuclear export sequence enabling nuclear spreading. Aspects of the invention also provide a methods of inhibiting expression of a gene in a cell by administering AAV vectors of the invention. Methods may comprise administering to a subject an adeno-associated virus (AAV) vector comprising a promoter sequence, a miRNA strand that binds to DUX4-FL, and a capsid protein comprising at least one modification that is an insertion between any two contiguous amino acids between amino acids 262-269, 327-332, 382-386, 452-460, 488-505, 527-539, 545-558, 581-593, 704-714, or any combination thereof in an AAV9 capsid polypeptide or in an analogous position in an AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV rh.74, AAV rh.10 capsid polypeptide. Table 1:

Table 2: Table 3: Table 4: Table 5 Exemplary nucleic acids comprising the mature guide strand of miDUX4, mi405 or mi1155 and the miR-122 binding site or the miR-208 binding site are provided below . Table 6 Additional exemplary miRNA. Detailed Description The invention discloses the combination of a truncated portion of the full-length DUX4 protein, a promoter that increases translation of the truncated DUX4 protein in muscle cells specifically, and a capsid protein that helps to deliver the genome to the appropriate cells. There are multiple methods for truncating the DUX4-FL protein to make the protein less pathogenic, wherein a single or possibly combinations of mutations, deletions, and fusions of the genome yield possible therapeutic sequences. The invention utilizes a recombinant AAV virus; recombinant viruses can be used to express therapeutic proteins in a subject as a form of genetic therapy. The therapy seeking to deliver that protein may utilize a recombinant viral genome that has the region of interest that will code the desired protein along with untranslated regions at the 5’ and 3’ ends of the genome. It may also include a promoter that will drive the gene of interest and it may include uninteresting that enhances stability and exportation out of the nucleus. The promoter may be used to identify preferential cellular transcription sites, so whether the gene is translated more often in skin, blood, bone, muscle, nervous, or other tissue types. For example, and non-exclusively, DUX4-S is the first 159 amino acids of DUX4-FL (SEQ ID NO.3). This version of the truncated portion of the full-length DUX4-FL sequence may result in reduced pathogenesis of muscle disorders because the full DUX4 amino acid sequence is no longer translated, and thus would not yield harmful effects to the myocytes. Furthermore, the invention may be delivered to a subject by any pharmaceutically acceptable dosage delivery method, which may be preferentially parenteral or another method that accomplishes successful delivery of the genome to a cell that can transcribe and translate a truncated DUX4 sequence. Adeno Associated Virus Vector AAVs are particularly appropriate viral vectors for delivery of genetic material into mammalian cells. AAVs are not known to cause disease in mammals and cause a very mild immune response. Additionally, AAVs are able to infect cells in multiple stages whether at rest or in a phase of the cell replication cycle. Advantageously, AAV DNA is not regularly inserted into the host’s genome at random sites, reducing the oncogenic properties of this vector. AAVs have been engineered to deliver a variety of treatments, especially for genetic disorders caused by single nucleotide polymorphisms (“SNP”). Genetic diseases that have been studied in conjunction with AAV vectors include Cystic fibrosis, hemophilia, arthritis, macular degeneration, muscular dystrophy, Parkinson’s disease, congestive heart failure, and Alzheimer’s disease. The AAV can be used as a vector to deliver engineered nucleic acid to a host and utilize the host’s own ribosomes to transcribe that nucleic acid into the desired proteins. See, e.g., West et al., Virology 160:38-47 (1987); U.S. Pat. No.4,797,368; WO 93/24641; Kotin, Human Gene Therapy 5:793-801 (1994); and Muzyczka, J. Clin. Invest.94:1351 (1994). AAVs have some deficiency in their replication and/or pathogenicity and thus can be safer that adenoviral vectors. In some embodiments, the AAV can integrate into a specific site on chromosome 19 of a human cell with no observable side effects. In some embodiments, the capacity of the AAV vector, system thereof, and/or AAV particles can be up to about 4.7 kb. The AAV vector or system thereof can include one or more engineered capsid polynucleotides described herein. AAVs are small, replication-defective, nonenveloped viruses that infect humans and other primate species and have a linear single-stranded DNA genome. Naturally occurring AAV serotypes exhibit liver tropism. As a result, transfection of non-liver tissue with traditional AAV vectors is impeded by the virus’s natural liver tropism. Moreover, because the liver acts to break down substances delivered to a subject, transfection of non-liver tissue with unmodified AAV vectors requires higher dosing to provide sufficient viral load to overcome the liver and reach non-liver tissue. More than 30 naturally occurring serotypes of AAV are available. Many natural variants in the AAV capsid exist. AAV serotypes include, but are not limited to, AAV serotypes AAV1, AAV2, AAV3, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV10, AAV11, AAV 12, AAV13. AAVs may be engineered using conventional molecular biology techniques, making it possible to optimize these particles, for example, for cell specific delivery, for minimizing immunogenicity, for tuning stability and particle lifetime, for efficient degradation, for accurate delivery to the nucleus. AAV vectors can be specifically targeted to one or more types of cells by choosing the appropriate combination of AAV serotype, promoter, and delivery method. Previous approaches to identify AAV sequences correlated with tropism have relied upon the comparison of highly related extant serotypes with distinct characteristics, random domain swaps between unrelated serotypes, or consideration of higher-order structure, to identify motifs that define liver tropism. For example, mapping determinants of AAV tropism have been carried out by comparing highly related serotypes. One such example is the single-amino acid change (E531K) between AAV1 and AAV6 that improves murine liver transduction in AAV1. See Wu et al. (2006) J. Virol., 80(22):11393-7, incorporated by reference herein. Another example is a reciprocal domain swap between AAV2 and AAV8 that alters tropism, but fails to define any robust specific tissue- targeting motifs. See Raupp et al. (201) J. Virol., 86(l7):9396-408, incorporated by reference herein. Further, global consideration of structure has only highlighted gross differences between better- or worse-liver-transducers that are more observational than useful in practice. Nam et al (2007) J. Virol., 81(22):12260-71. AAVs exhibiting modified tissue tropism that may be used with the present invention are described in U.S. Patent No.9,695,220, U.S. Patent No.9,719,070; U.S. Patent No.10,119,125; U.S. Patent No.10,526,584; U.S. Patent Application Publication No.2018-0369414; U.S. Patent Application Publication No.2020-0123504; U.S. Patent Application Publication No.2020-0318082; PCT International Patent Application Publication No. WO 2015/054653; PCT International Patent Application Publication No. WO 2016/179496; PCT International Patent Application Publication No. WO 2017/100791; and PCT International Patent Application Publication No. WO 2019/217911, the entirety of the contents of each of which are incorporated by reference herein. The AAV vector or system thereof may include one or more regulatory molecules, such as promoters, enhancers, repressors and the like. In some embodiments, the AAV vector or system thereof can include one or more polynucleotides that can encode one or more regulatory proteins. In some embodiments, the one or more regulatory proteins can be selected from Rep78, Rep68, Rep52, Rep40, variants thereof, and combinations thereof. In some embodiments, the muscle specific promoter can drive expression of an engineered AAV capsid polynucleotide. The AAV vector or system thereof can include one or more polynucleotides that can encode one or more capsid proteins, such as the engineered AAV capsid proteins described elsewhere herein. The engineered capsid proteins can be capable of assembling into a protein shell (an engineered capsid) of the AAV virus particle. The engineered capsid can have a cell-, tissue-, and/or organ-specific tropism. The AAV vector or system thereof can be configured to produce AAV particles having a specific serotype. In some embodiments, the serotype can be AAV-1, AAV-2, AAV-3, AAV-4, AAV-5, AAV-6, AAV-8, AAV-9 or any combinations thereof. In some embodiments, the AAV can be AAV1, AAV-2, AAV-5, AAV-9 or any combination thereof. One can select the AAV of the AAV with regard to the cells to be targeted; e.g., one can select AAV serotypes 1, 2, 5, 9 or a hybrid capsid AAV-1, AAV-2, AAV-5, AAV-9 or any combination thereof for targeting brain and/or neuronal cells; and one can select AAV-4 for targeting cardiac tissue; and one can select AAV-8 for delivery to the liver. Thus, in some embodiments, an AAV vector or system thereof capable of producing AAV particles capable of targeting the brain and/or neuronal cells can be configured to generate AAV particles having serotypes 1, 2, 5 or a hybrid capsid AAV-1, AAV-2, AAV-5 or any combination thereof. In some embodiments, an AAV vector or system thereof capable of producing AAV particles capable of targeting cardiac tissue can be configured to generate an AAV particle having an AAV-4 serotype. In some embodiments, an AAV vector or system thereof capable of producing AAV particles capable of targeting the liver can be configured to generate an AAV having an AAV-8 serotype. See also Srivastava.2017. Curr. Opin. Virol.21:75-80. It will be appreciated that while the different serotypes can provide some level of cell, tissue, and/or organ specificity, each serotype still is multi-tropic and thus can result in tissue-toxicity if using that serotype to target a tissue that the serotype is less efficient in transducing. Thus, in addition to achieving some tissue targeting capacity via selecting an AAV of a particular serotype, it will be appreciated that the tropism of the AAV serotype can be modified by an engineered AAV capsid described herein. As described elsewhere herein, variants of wild-type AAV of any serotype can be generated via a method described herein and determined to have a particular cell-specific tropism, which can be the same or different as that of the reference wild-type AAV serotype. In some embodiments, the cell, tissue, and/or specificity of the wild-type serotype can be enhanced (e.g., made more selective or specific for a particular cell type that the serotype is already biased towards). For example, wild-type AAV-9 is biased towards muscle and brain in humans (see e.g., Srivastava.2017. Curr. Opin. Virol.21:75-80.) By including an engineered AAV capsid and/or capsid protein variant of wild-type AAV-9 as described herein, the tropism for nervous cells might be reduced or eliminated and/or the muscle specificity increased such that the nervous specificity appears reduced in comparison, thus enhancing the specificity for muscle as compared to the wild- type AAV-9. As previously mentioned, inclusion of an engineered capsid and/or capsid protein variant of a wild-type AAV serotype can have a different tropism than the wild-type reference AAV serotype. For example, an engineered AAV capsid and/or capsid protein variant of AAV-9 can have specificity for a tissue other than muscle or brain in humans. In some embodiments, the AAV vector is a hybrid AAV vector or system thereof. Hybrid AAVs are AAVs that include genomes with elements from one serotype that are packaged into a capsid derived from at least one different serotype. For example, if it is the rAAV2/5 that is to be produced, and if the production method is based on the helper-free, transient transfection method discussed above, the 1st plasmid and the 3rd plasmid (the adeno helper plasmid) will be the same as discussed for rAAV2 production. However, the 2nd plasmid, the pRepCap will be different. In this plasmid, called pRep2/Cap5, the Rep gene is still derived from AAV2, while the Cap gene is derived from AAV5. The production scheme is the same as the above-mentioned approach for AAV2 production. The resulting rAAV is called rAAV2/5, in which the genome is based on recombinant AAV2, while the capsid is based on AAV5. It is assumed the cell or tissue-tropism displayed by this AAV2/5 hybrid virus should be the same as that of AAV5. It will be appreciated that wild-type hybrid AAV particles suffer the same specificity issues as with the non-hybrid wild-type serotypes previously discussed. Advantages achieved by the wild-type based hybrid AAV systems can be combined with the increased and customizable cell-specificity that can be achieved with the engineered AAV capsids can be combined by generating a hybrid AAV that can include an engineered AAV capsid described elsewhere herein. It will be appreciated that hybrid AAVs can contain an engineered AAV capsid containing a genome with elements from a different serotype than the reference wild-type serotype that the engineered AAV capsid is a variant of. For example, a hybrid AAV can be produced that includes an engineered AAV capsid that is a variant of an AAV-9 serotype that is used to package a genome that contains components (e.g., rep elements) from an AAV-2 serotype. As with wild-type based hybrid AAVs previously discussed, the tropism of the resulting AAV particle will be that of the engineered AAV capsid. In some embodiments, the AAV vector or system thereof is configured as a “gutless” vector, similar to that described in connection with a retroviral vector. In some embodiments, the “gutless” AAV vector or system thereof can have the cis-acting viral DNA elements involved in genome amplification and packaging in linkage with the heterologous sequences of interest (e.g., the engineered AAV capsid polynucleotide(s)). The vectors described herein can be constructed using any suitable process or technique. In some embodiments, one or more suitable recombination and/or cloning methods or techniques can be used to the vector(s) described herein. Suitable recombination and/or cloning techniques and/or methods can include, but not limited to, those described in U.S. Application publication No. US 2004-0171156 A1. Other suitable methods and techniques are described elsewhere herein. Construction of recombinant AAV vectors are described in a number of publications, including U.S. Pat. No.5,173,414; Tratschin et al., Mol. Cell. Biol.5:3251-3260 (1985); Tratschin, et al., Mol. Cell. Biol.4:2072-2081 (1984); Hermonat & Muzyczka, PNAS 81:6466-6470 (1984); and Samulski et al., J. Virol.63:03822-3828 (1989). Any of the techniques and/or methods can be used and/or adapted for constructing an AAV or other vector described herein. AAV vectors are discussed elsewhere herein. In some embodiments, the vector can have one or more insertion sites, such as a restriction endonuclease recognition sequence (also referred to as a “cloning site”). In some embodiments, one or more insertion sites (e.g., about or more than about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more insertion sites) are located upstream and/or downstream of one or more sequence elements of one or more vectors. Delivery vehicles, vectors, particles, nanoparticles, formulations and components thereof for expression of one or more elements of a engineered AAV capsid system described herein are as used in the foregoing documents, such as International Patent Application Publications WO WO 2021/050974 and WO 2021/077000 and PCT International Application No. PCT/US2021/042812, the contents of which are incorporated by reference herein. Additional AAV vectors are described in International Patent Application Publication WO 2019/2071632, the contents of which are incorporated by reference herein. Further AAV vectors are described in International Patent Application Publications WO 2020/086881 and WO 2020/235543, the contents of each of which are incorporated by reference herein. Further AAV vectors are described in International Patent Application Publications WO 2005/033321; WO 2006/110689; WO 2007/127264; WO 2008/027084; WO 2009/073103; WO 2009/073104; WO 2009/105084; WO 2009/134681; WO 2009/136977; WO 2010/051367; WO 2010/138675; WO 2001/038187; WO 2012/112832; WO 2015/054653; WO 2016/179496; WO 2017/100791; WO 2017/019994; WO 2018/209154; WO 2019/067982; WO 2019/195701; WO 2019/217911; WO 2020/041498; WO 2020/210839; U.S. Patent No.7,906,111; U.S. Patent No. 9,737,618; U.S. Patent No.10,265,417; U.S. Patent No.10,485,883; U.S. Patent No.10,695,441; U.S. Patent No.10,722,598; U.S. Patent No.8,999,678; U.S. Patent No.10,301,648; U.S. Patent No. 10,626,415; U.S. Patent No.9,198,984; U.S. Patent No.10,155,931; U.S. Patent No.8,524,219; U.S. Patent No.9,206,238; U.S. Patent No.8,685,387; U.S. Patent No.9,359,618; U.S. Patent No. 8,231,880; U.S. Patent No.8,470,310; U.S. Patent No.9,597,363; U.S. Patent No.8,940,290; U.S. Patent No.9,593,346; U.S. Patent No.10,501,757; U.S. Patent No.10,786,568; U.S. Patent No. 10,973,928; U.S. Patent No.10,519,198; U.S. Patent No.8,846,031; U.S. Patent No.9,617,561; U.S. Patent No.9,884,071; U.S. Patent No.10,406,173; U.S. Patent No.9,596,220; U.S. Patent No. 9,719,010; U.S. Patent No.10,117,125; U.S. Patent No.10,526,584; U.S. Patent No.10,881,548; U.S. Patent No.10,738,087; U.S. Patent Publication No.2011-023353; U.S. Patent Publication No.2019- 0015527; U.S. Patent Publication No.2020-155704; U.S. Patent Publication No 2017-0191079; U.S. Patent Publication No.2019-0218574; U.S. Patent Publication No.2020-0208176; U.S. Patent Publication No.2020-0325491; U.S. Patent Publication No.2019-0055523; U.S. Patent Publication No.2020-0385689; U.S. Patent Publication No.2009-0317417; U.S. Patent Publication No.2016- 0051603; U.S. Patent Publication No.2016-00244783; U.S. Patent Publication No.2017-0183636; U.S. Patent Publication No.2020-0263201; U.S. Patent Publication No.2020-0101099; U.S. Patent Publication No.2020-0318082; U.S. Patent Publication No.2018-0369414; U.S. Patent Publication No.2019-0330278; U.S. Patent Publication No.2020-0231986, the contents of each of which are incorporated by reference herein. Promoter The invention may contain a muscle specific promoter or another promoter. The promoter may be linked to the nucleic acid sequence so that the transcription preferably occurs within myocytes. Promoter regions enable the host cells to replicate the AAV delivered nucleic acid only in those cell types and tissues or organs in which the desired protein should be created. Here, the muscle specific promoter is included because it is principally desired that the proteins only be translated in myocytes. Specificity of the cell type into which the nucleic acid is delivered and thus the proteins translated is desired because of the adverse effects that may ensue from delivering the nucleic acid and having it translated in cells in which that nucleic acid and thus protein is not needed. The myocyte specific promoter may be coupled or otherwise associated with a truncated DUX4 sequence. In some embodiments, the promoter may be directly attached, and in others there may be a linker molecule or another indirect coupling method to attach to the truncated DUX4 sequence. In some embodiments, there may be an associated polypeptide or other particle that is coupled to the truncated DUX4 sequence. In some embodiments, the muscle specific promoter yields increased muscle cell potency, muscle cell specificity, reduced immunogenicity, or any combination thereof. As used herein the terms “muscle-specific”, “muscle cell specificity”, “muscle cell potency,” “myocyte specific” and the like, refer to the increased specificity, selectivity, or potency, of the muscle-specific targeting moieties and compositions incorporating said muscle-specific targeting moieties of the present invention for myocytes relative to non-muscle cells. In some embodiments, the cell specificity, or selectivity, or potency, or a combination thereof of a muscle-specific targeting moiety or composition incorporating a muscle-specific targeting moiety described herein is at least 2 to at least 500 times more specific, selective, and/or potent for/in a muscle cell relative to a non-muscle cell. In some embodiments, the myocyte-selective promoter utilized is MHCK7. MHCK7is a 770 base pair length promoter that is small enough to be included in an AAV vector. MHCK7 directs expression in fast and slow skeletal and cardiac muscle, with low expression in the liver, lung, and spleen. It is less active in smooth muscle. The MHCK7 promoter is associated with high levels of expression in skeletal muscles, including the diaphragm, and includes an enhancer to especially drive expression in the heart, whereas expression in off-target tissues is minimal. In some embodiments, the promoters described herein are inserted into an AAV protein (e.g., an AAV capsid protein) that has reduced specificity (or no detectable, measurable, or clinically relevant interaction) for one or more non-muscle cell types. Exemplary non-muscle cell types include, but are not limited to, liver, kidney, lung, heart, spleen, central or peripheral nervous system cells, bone, immune, stomach, intestine, eye, skin cells and the like. In some embodiments, the non- muscle cells are liver cells. The term “operably linked” refers to the association of two or more nucleic acid molecules on a single nucleic acid fragment so that the function of one is affected by the other. Further exemplary tissue specific promoters include U6 promoter sequence, MHCK7 promoter sequence, CK6 promoter sequence, tMCK promoter sequence, CK5 promoter sequence, MCK promoter sequence, HAS promoter sequence, MPZ promoter sequence, desmin promoter sequence, APOA2 promoter sequence, hAAT promoter sequence, INS promoter sequence, IRS2 promoter sequence, MYH6 promoter sequence, MYL2 promoter sequence, TNNI3 promoter sequence, SYN1 promoter sequence, GFAP promoter sequence, NES promoter sequence, MBP promoter sequence, or TH promoter sequence. Muscle specific promoters are described in International Patent Application Publications WO 2020/006458 and WO 2021/126880, the contents of each of which are incorporated by reference herein. Further muscle specific promoters are described in U.S. Patent No.9,133,482; U.S. Patent No.10,105,453; U.S. Patent No.10,301,367; U.S. Patent Publication No.2020-0360534; PCT International Patent Publication Nos. WO 2020/006458; WO 2021/035120; WO 2021/053124; and WO 2021/077000, the contents of each of which are incorporated by reference herein. It may be convenient to use an RNA polymerase II or III promoter; these are known to the person skilled in the art and reviewed in e.g. Kornberg 1999. However, transcripts from an RNA II polymerase often have complex transcription terminators and transcripts are polyadenylated; this may hamper with the requirements of the miRNA strand which because both its 5' and 3' ends need to be precisely defined in order to achieve the required secondary structure to produce a functional molecule. These drawbacks can however be circumvented. In case an RNA polymerase II or III promoter is used, the polynucleotide encoding the miRNA strand may also encode self-processing ribozymes and may be operably linked to an RNA polymerase II or III promoter; as such the polynucleotide encodes a pre- miRNA strand comprising the miRNA strand and self-processing ribozymes, wherein, when transcribed, the miRNA strand is released by the self-processing ribozymes from the pre- miRNA strand de transcript. Preferably, in a composition according to the present invention the AAV vector is comprised of an RNA polymerase II promoter or III promoter, and encodes a pre- miRNA strand comprising the miRNA strand and self-processing ribozymes, wherein, when transcribed, the miRNA strand is released by the self-processing ribozymes from the pre- miRNA strand transcript. Conveniently, multiple pre-miRNA strands and multiple self-processing ribozymes may be encoded by a single polynucleotide, operably linked to one or more RNA polymerase II promoters. RNA polymerase II or III promoters that are inducible and/or tissue-specific have been previously described. RNA polymerase promoters are known in the art and further described in U.S. Patent Publication 11,149,288, the contents of which is incorporated by reference herein. Capsid Protein The capsid protein is the shell or coating of the virus that enables its delivery into the host. Without the protein, the nucleic acids would be destroyed by the host without entering into the host cells and beginning transcription and translation. The capsid protein may be in the natural conformation of a naturally occurring AAV, or it may be modified. In certain example embodiments, the AAV capsid protein is an engineered AAV capsid protein having reduced or eliminated uptake in a non-muscle cell as compared to a corresponding wild-type AAV capsid polypeptide. In some embodiments, the engineered AAV capsid encoding polynucleotide can be included in a polynucleotide that is configured to be an AAV genome donor in an AAV vector system that can be used to generate engineered AAV particles described elsewhere herein. In some embodiments, the engineered AAV capsid encoding polynucleotide can be operably coupled to a poly adenylation tail. In some embodiments, the poly adenylation tail can be an SV40 poly adenylation tail. In some embodiments, the AAV capsid encoding polynucleotide can be operably coupled to a promoter. In some embodiments, the promoter can be a tissue specific promoter. In some embodiments, the tissue specific promoter is specific for muscle (e.g., cardiac, skeletal, and/or smooth muscle), neurons and supporting cells (e.g., astrocytes, glial cells, Schwann cells, etc.), fat, spleen, liver, kidney, immune cells, spinal fluid cells, synovial fluid cells, skin cells, cartilage, tendons, connective tissue, bone, pancreas, adrenal gland, blood cell, bone marrow cells, placenta, endothelial cells, and combinations thereof. In some embodiments, the promoter can be a constitutive promoter. Suitable tissue specific promoters and constitutive promoters are discussed elsewhere herein and are generally known in the art and can be commercially available. Suitable muscle specific promoters include, but are not limited to CK8, MHCK7, Myoglobin promoter (Mb), Desmin promoter, muscle creatine kinase promoter (MCK) and variants thereof, and SPc5-12 synthetic promoter. Described herein are various embodiments of engineered viral capsids, such as adeno- associated virus (AAV) capsids, that can be engineered to confer cell-specific tropism, such as muscle specific tropism, to an engineered viral particle. Engineered viral capsids can be lentiviral, retroviral, adenoviral, or AAV capsids. The engineered capsids can be included in an engineered virus particle (e.g., an engineered lentiviral, retroviral, adenoviral, or AAV virus particle), and can confer cell-specific tropism, reduced immunogenicity, or both to the engineered viral particle. The engineered viral capsids described herein can include one or more engineered viral capsid proteins described herein. The engineered viral capsids described herein can include one or more engineered viral capsid proteins described herein that can contain a muscle-specific targeting moiety containing or composed of an n-mer motif described elsewhere herein. The engineered viral capsid and/or capsid proteins can be encoded by one or more engineered viral capsid polynucleotides. In some embodiments, the engineered viral capsid polynucleotide is an engineered AAV capsid polynucleotide, engineered lentiviral capsid polynucleotide, engineered retroviral capsid polynucleotide, or engineered adenovirus capsid polynucleotide. In some embodiments, an engineered viral capsid polynucleotide (e.g., an engineered AAV capsid polynucleotide, engineered lentiviral capsid polynucleotide, engineered retroviral capsid polynucleotide, or engineered adenovirus capsid polynucleotide) can include a 3’ polyadenylation signal. The polyadenylation signal can be an SV40 polyadenylation signal. The engineered viral capsids can be variants of wild-type viral capsid. For example, in some embodiments, the engineered AAV capsids can be variants of wild-type AAV capsids. In some embodiments, the wild-type AAV capsids can be composed of VP1, VP2, VP3 capsid proteins or a combination thereof. In other words, the engineered AAV capsids can include one or more variants of a wild-type VP1, wild-type VP2, and/or wild-type VP3 capsid proteins. In some embodiments, the serotype of the reference wild-type AAV capsid can be AAV-1, AAV-2, AAV-3, AAV-4, AAV- 5, AAV-6, AAV-8, AAV-9 or any combination thereof. In some embodiments, the serotype of the wild-type AAV capsid can be AAV-9. The engineered AAV capsids can have a different tropism than that of the reference wild-type AAV capsid. The engineered viral capsid can contain 1-60 engineered capsid proteins. In some embodiments, the engineered viral capsids can contain 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, or 60 engineered capsid proteins. In some embodiments, the engineered viral capsid can contain 0-59 wild-type viral capsid proteins. In some embodiments, the engineered viral capsid can contain 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, or 59 wild-type viral capsid proteins. In some embodiments, the engineered AAV capsid can contain 1-60 engineered capsid proteins. In some embodiments, the engineered AAV capsids can contain 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, or 60 engineered capsid proteins. In some embodiments, the engineered AAV capsid can contain 0-59 wild-type AAV capsid proteins. In some embodiments, the engineered AAV capsid can contain 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, or 59 wild-type AAV capsid proteins. In some embodiments, the engineered viral capsid protein can have an n-mer amino acid motif, where n can be at least 3 amino acids. In some embodiments, n can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 amino acids. In some embodiments, an engineered AAV capsid can have a 6- mer or 7-mer amino acid motif. In some embodiments, the n-mer amino acid motif can be inserted between two amino acids in the wild-type viral protein (VP) (or capsid protein). In some embodiments, the n-mer motif can be inserted between two amino acids in a variable amino acid region in a viral capsid protein. In some embodiments, the n-mer motif can be inserted between two amino acids in a variable amino acid region in an AAV capsid protein. The core of each wild-type AAV viral protein contains an eight-stranded beta-barrel motif (betaB to betaI) and an alpha-helix (alphaA) that are conserved in autonomous parvovirus capsids (see e.g., DiMattia et al.2012. J. Virol.86(12):6947- 6958). Structural variable regions (VRs) occur in the surface loops that connect the beta-strands, which cluster to produce local variations in the capsid surface. AAVs have 12 variable regions (also referred to as hypervariable regions) (see e.g., Weitzman and Linden.2011. “Adeno-Associated Virus Biology.” In Snyder, R.O., Moullier, P. (eds.) Totowa, NJ: Humana Press). In some embodiments, one or more n-mer motifs can be inserted between two amino acids in one or more of the 12 variable regions in the wild-type AVV capsid proteins. In some embodiments, the one or more n- mer motifs can be each be inserted between two amino acids in VR-I, VR-II, VR-III, VR-IV, VR-V, VR-VI, VR-VII, VR-III, VR-IX, VR-X, VR-XI, VR-XII, or a combination thereof. In some embodiments, the n-mer can be inserted between two amino acids in the VR-III of a capsid protein. In some embodiments, the engineered capsid can have an n-mer inserted between any two contiguous amino acids between amino acids 262 and 269, between any two contiguous amino acids between amino acids 327 and 332, between any two contiguous amino acids between amino acids 382 and 386, between any two contiguous amino acids between amino acids 452 and 460, between any two contiguous amino acids between amino acids 488 and 505, between any two contiguous amino acids between amino acids 545 and 558, between any two contiguous amino acids between amino acids 581 and 593, between any two contiguous amino acids between amino acids 704 and 714 of an AAV9 viral protein. In some embodiments, the engineered capsid can have an n-mer inserted between amino acids 588 and 589 of an AAV9 viral protein. In some embodiments, the engineered capsid can have a 7-mer motif inserted between amino acids 588 and 589 of an AAV9 viral protein. In other embodiments, the motif inserted is a 10-mer motif, with replacement of amino acids 586-88 and an insertion before 589. SEQ ID NO.2 is a reference AAV9 capsid sequence for at least referencing the insertion sites discussed above. It will be appreciated that n- mers can be inserted in analogous positions in AAV viral proteins of other serotypes. In some embodiments as previously discussed, the n-mer(s) can be inserted between any two contiguous amino acids within the AAV viral protein and in some embodiments the insertion is made in a variable region. In some embodiments, the first 1, 2, 3, or 4 amino acids of an n-mer motif can replace 1, 2, 3, or 4 amino acids of a polypeptide into which it is inserted and preceding the insertion site. In some embodiments, the amino acids of the n-mer motif that replace 1 or more amino acids of the polypeptide into which the n-mer motif is inserted come before or immediately before an “RGD” in an n-mer motif. For example, in one or more of the 10-mer inserts shown in e.g., Tables 2-3, the first three amino acids shown can replace 1-3 amino acids into a polypeptide to which they may be inserted. Using an AAV as another non-limiting example, one or more of the n-mer motifs can be inserted into e.g., and AAV9 capsid prolylpeptide between amino acids 588 and 589 and the insert can replace amino acids 586, 587, and 588 such that the amino acid immediately preceding the n-mer motif after insertion is residue 585. It will be appreciated that this principle can apply in any other insertion context and is not necessarily limited to insertion between residues 588 and 589 of an AAV9 capsid or equivalent position in another AAV capsid. It will further be appreciated that in some embodiments, no amino acids in the polypeptide into which the n-mer motif is inserted are replaced by the n-mer motif. In some embodiments, the AAV capsids or other viral capsids or compositions can be muscle-specific. In some embodiments, muscle-specificity of the engineered AAV or other viral capsid or other composition is conferred by a muscle specific n-mer motif incorporated in the engineered AAV or other viral capsid or other composition described herein. While not intending to be bound by theory, it is believed that the n-mer motif confers a 3D structure to or within a domain or region of the engineered AAV capsid or other viral capsid or other composition such that the interaction of the viral particle or other composition containing the engineered AAV capsid or other viral capsid or other composition described herein has increased or improved interactions (e.g., increased affinity) with a cell surface receptor and/or other molecule on the surface of a muscle cell. In some embodiments, the cell surface receptor is AAV receptor (AAVR). In some embodiments, the cell surface receptor is a muscle cell specific AAV receptor. In some embodiments, the cell surface receptor or other molecule is a cell surface receptor or other molecule selectively expressed on the surface of a muscle cell. In some embodiments, the cell surface receptor or molecule is an integrin or dimer thereof. In some embodiments, the cell surface receptor or molecule is an Vb6 integrin heterodimer. In some embodiments, a muscle specific engineered viral particle or other composition described herein containing the muscle-specific capsid, n-mer motif, or muscle-specific targeting moiety described herein can have an increased uptake, delivery rate, transduction rate, efficiency, amount, or a combination thereof in a muscle cell as compared to other cells types and/or other virus particles (including but not limited to AAVs) and other compositions that do not contain the muscle-specific n-mer motif of the present invention. First- and second-generation muscle specific AAV capsids were developed using a muscle specific promoter and the resulting capsid libraries were screened in mice and non-human primates as described elsewhere herein and/or in e.g., U.S. Provisional Application Serial Nos.62/899,453, 62/916,207, 63/018,454, and 63/242,008. First and second generation myoAAV capsids were further optimized in mice and non-human primates as previously described to generate enhanced myoAAV capsids. Tables 1 and 2 show the top hits of enhanced muscle specific n-mer motifs and their encoding sequence in rank order within each table. Enhanced MyoAAV (eMyoAAV) capsid variants can transduce mouse muscle more effectively as compared to the first generation MyoAAV after systemic delivery. First and second generation myoAAV capsid variants are dependent on the aVb6 integrin heterodimer for transduction of human primary myotubes. Tables 3 and 4 show top-ranking capsid variants produced in rounds of directed evolution of capsid variants for skeletal muscle specificity. As shown in the Tables above with respect to those variant n-mer inserts containing P-motifs, the first three amino acids of the variant sequences shown are amino acids that replaced amino acids corresponding to positions 596, 597, and 598 of an AAV9 capsid polypeptide. Thus, the P-motif, for example, was inserted between amino acids at positions 598 and 599 of an AAV9 vector. DUX4-FL and Truncated Versions Thereof DUX4 is the double homeobox protein 4, and is expressed in myocytes. DUX4-FL (SEQ ID NO.1) is the double homeobox protein 4 gene; DUX4-FL is the wild type of the gene that is pathogenic in patients with FSHD. DUX4-FL causes pathogenesis by overproduction of the DUX4 protein. DUX4-FL is located on the D4Z4 region of the chromosome 4. Together with a linker and a V5 epitope 17 amino acids long, truncated versions of the DUX4 protein include DUX4-S, which is the first 159 amino acids of DUX4-FL (SEQ ID NO.3), delMid, which is amino acids 1-159, 343-424, delDC2, which is amino acids 1-374, delDC1/2, which is amino acids 1-342, S+DC1, which is amino acids 1-159, 343-374, S+DC2, which is 1-159, 375- 424, S+375-397, which is amino acids 1-159, 375-397, S+398-424, which is amino acids 1-159, 398- 424, or del405-424, which is amino acids 1-404. The linker is amino acid sequence LEGTRFE, and the V5 epitope is amino acid sequence GKPIPNPLLGLDSTRTG. These truncations are described in Mitsuhashi et al., (Biology Open (2018 Apr.26; 7(4), bio033977, doi:10.1242/bio.033977), which is incorporated by reference herein as if expressed in its entirety Advantageously, truncated DUX4 genes may cause reduced expression of the DUX4 protein. Truncated DUX4 genes do not result in the same pathology, wherein the DUX4 protein is not over expressed. In aspects of the invention, truncated forms of DUX4 are expressed by a nucleic acid molecule. “Nucleic acid molecule” or “polynucleotide” refers to a polymeric compound including covalently linked nucleotides comprising natural subunits (e.g., purine or pyrimidine bases). Purine bases include adenine and guanine, and pyrimidine bases include uracil, thymine, and cytosine. Nucleic acid molecules include polyribonucleic acid (RNA) and polydeoxyribonucleic acid (DNA), which includes cDNA, genomic DNA, and synthetic DNA, either of which may be single or double-stranded. A nucleic acid molecule encoding an amino acid sequence includes all nucleotide sequences that encode the same amino acid sequence. The term “expression,” as used herein, refers to the process by which a polypeptide is produced based on the encoding sequence of a nucleic acid molecule, such as a gene. The process may include transcription, post-transcriptional control, post-transcriptional modification, translation, post-translational control, post-translational modification, or any combination thereof. An expressed nucleic acid molecule is typically operably linked to an expression control sequence (e.g., a promoter). In aspects of the invention, the truncated form of DUX4 may be a functional variant of the polypeptide. A “functional variant” refers to a polypeptide or polynucleotide that is structurally similar or substantially structurally similar to a parent or reference compound of this disclosure, but differs, in some contexts slightly, in composition (e.g., one base, atom, or functional group is different, added, or removed; or one or more amino acids are substituted, mutated, inserted, or deleted), such that the polypeptide or encoded polypeptide is capable of performing at least one function of the encoded parent polypeptide with at least 50% efficiency of activity of the parent polypeptide. In aspects of the invention, the functional variant may have at least 70% homology, at least 80% homology, at least 90% homology, at least 95% homology, or at least 99% homology with the reference/parent polypeptide disclosed herein. As used herein, a “functional portion” or “functional fragment” refers to a polypeptide or polynucleotide that comprises only a domain, motif, portion, or fragment of a parent or reference compound, and the polypeptide or encoded polypeptide retains at least 50% activity associated with the domain, portion, or fragment of the parent or reference compound. In specific aspects, variants are at least 60% as efficient, at least 70% as efficient, at least 80% efficient, at least 90% as efficient, at least 95% as efficient, or at least 99% as efficient as the reference/parent polypeptides disclosed herein. The invention discloses compositions and methods for treating Facioscapulohumeral Muscular Dystrophy (“FSHD”) that comprise a nucleic acid sequence encoding a modified copy of the double homeobox protein 4 (“DUX4”). Without being bound to a mechanism of action, the present invention benefits from the insight that the DUX4 gene presents in FSHD patients as a full- length form, known as DUX4-FL, and that modifications to the DUX4-FL gene can result in non- pathogenic expression of a truncated DUX4 protein. The invention further benefits from the discovery that adeno-associated virus (“AAV”) vectors may be modified to target muscle tissue and detarget liver tissue in vivo, allowing for effective delivery of the gene product to a subject. Accordingly, aspects of the invention provide an adeno-associated virus (AAV) vector comprising: a nucleic acid sequence encoding a truncated portion of the full-length DUX-4FL sequence operably linked to a muscle specific promoter, and a capsid protein. The full-length sequence of the DUX-4FL protein (SEQ ID NO.1) and variants of the protein are discussed in Mitsuhashi et al. (2018) Biology Open 7(4):bio033977, the entirety of the contents of which are incorporated by reference herein in their entirety. For example, the truncated portion of the full-length DUX-4FL sequence may comprise amino acids 1-159 of the full-length amino acid sequence of DUX-4FL (SEQ ID NO.3). The truncated portion of the full-length DUX-4FL sequence may comprise amino acids 19-159 of a full- length amino acid sequence of DUX-4FL (SEQ ID NO.4). The truncated portion of the full-length DUX-4FL sequence may comprise amino acids 1-343 of a full-length amino acid sequence of DUX- 4FL (SEQ ID NO.: 5). Specific portions of the DUX-4FL sequence may be removed. For example, the truncated portion of the full-length DUX-4FL sequence may comprise a full-length amino acid sequence of DUX-4FL (SEQ ID NO.1) in which amino acids 344-404 and 405-424 have been removed. In aspects of the invention, the capsid protein may comprise at least one modification that results in reduced liver-tropism of the AAV vector. The capsid protein may comprise at least one modification that results in preferential targeting of the AAV vector to muscle tissue. The capsid protein may comprise at least one modification that results in reduced liver-tropism of the AAV vector, and at least one modification that results in preferential targeting of the AAV vector to muscle tissue. For example, the capsid protein may comprise at least one modification that is an insertion between any two contiguous amino acids between amino acids 262-269, 327-332, 382-386, 452-460, 488-505, 527-539, 545-558, 581-593, 704-714, or any combination thereof in an AAV9 capsid polypeptide or in an analogous position in an AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV rh.74, AAV rh.10 capsid polypeptide. The capsid protein may comprise at least one modification that is a replacement of amino acids 586-88 and an insertion between amino acids 588 and 589 in an AAV9 capsid polypeptide or in an analogous position in an AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV rh.74, AAV rh.10 capsid polypeptide. For example, the capsid protein may comprise at least one modification that is a replacement of amino acids 586-88 and an insertion between amino acids 588 and 589 in an AAV9 capsid polypeptide and the insertion may be selected from the sequences in Table 1 or Table 2, hereinbelow. In aspects of the invention, the muscle specific promoter may be MHCK7. For example, the AAV vector may comprise the truncated DUX-4FL sequence that comprises amino acids 1-159 of a full-length amino acid sequence of DUX-4FL (SEQ ID NO.1), a capsid protein comprising at least one modification that is a replacement of amino acids 586-88 and an insertion between amino acids 588 and 589 in an AAV9 capsid polypeptide wherein the insertion is selected from the sequences in Tables 1-4, and the muscle specific promoter may be MHCK7. Aspects of the invention further provide a method of treating a DUX-4 associated disorder in a subject, the method comprising: administering to a subject a composition comprising a nucleic acid sequence encoding a truncated portion of the full-length DUX-4FL sequence or an amino acid sequence expressed by the truncated portion of the full-length DUX-4FL sequence. The adeno-associated virus (AAV) vector may comprise a nucleic acid sequence encoding the truncated portion of the full-length DUX-4FL sequence operably linked to a muscle specific promoter, and a capsid protein. For example, the truncated portion of the full-length DUX-4FL sequence may comprise amino acids 1-159 of the full-length amino acid sequence of DUX-4FL (SEQ ID NO.3). The truncated portion of the full-length DUX-4FL sequence may comprise amino acids 19-159 of a full- length amino acid sequence of DUX-4FL (SEQ ID NO.4). The truncated portion of the full-length DUX-4FL sequence may comprise amino acids 1-343 of a full-length amino acid sequence of DUX- 4FL (SEQ ID NO.5). Specific portions of the DUX-4FL sequence may be removed. For example, the truncated portion of the full-length DUX-4FL sequence may comprise a full-length amino acid sequence of DUX-4FL (SEQ ID NO.1) in which amino acids 344-404 and 405-424 have been removed. In aspects of the invention, the capsid protein may comprise at least one modification that results in reduced liver-tropism of the AAV vector. The capsid protein may comprise at least one modification that results in preferential targeting of the AAV vector to muscle tissue. The capsid protein may comprise at least one modification that results in reduced liver-tropism of the AAV vector, and at least one modification that results in preferential targeting of the AAV vector to muscle tissue. For example, the capsid protein may comprise at least one modification that is an insertion between any two contiguous amino acids between amino acids 262-269, 327-332, 382-386, 452-460, 488-505, 527-539, 545-558, 581-593, 704-714, or any combination thereof in an AAV9 capsid polypeptide or in an analogous position in an AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV rh.74, AAV rh.10 capsid polypeptide. The capsid protein may comprise at least one modification that is a replacement of amino acids 586-88 and an insertion between amino acids 588 and 589 in an AAV9 capsid polypeptide or in an analogous position in an AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV rh.74, AAV rh.10 capsid polypeptide. For example, the capsid protein may comprise at least one modification that is a replacement of amino acids 586-88 and an insertion between amino acids 588 and 589 in an AAV9 capsid polypeptide and the insertion may be selected from the sequences in Tables 1-4, hereinbelow. In aspects of the invention, the muscle specific promoter may be MHCK7. For example, the AAV vector may comprise the truncated portion of the full-length DUX-4FL sequence that comprises amino acids 1-159 of a full-length amino acid sequence of DUX-4FL (SEQ ID NO.: 3), a capsid protein comprising at least one modification that is a replacement of amino acids 586-88 and an insertion between amino acids 588 and 589 in an AAV9 capsid polypeptide wherein the insertion is selected from the sequences in Tables 1-4, and the muscle specific promoter may be MHCK7. In aspects of the method, the DUX4 associated disorder may be facioscapulohumeral muscular dystrophy (FSHD). In aspects of the method, the composition may be administered to the subject intramuscularly. In aspects of the method, transcription of the nucleic acid results in expression of a truncated DUX4 protein. Expression of the truncated DUX4 protein may inhibit activity and/or expression of the full-length DUX4 protein. The truncated DUX4 protein may inhibit Trim36 and Wfdc3 expression. Further embodiments of the invention comprise an adeno-associated virus (AAV) vector comprising a promoter sequence, a miRNA strand that binds to DUX4-FL, and a capsid protein comprising at least one modification that is an insertion between any two contiguous amino acids between amino acids 262-269, 327-332, 382-386, 452-460, 488-505, 527-539, 545-558, 581-593, 704- 714, or any combination thereof in an AAV9 capsid polypeptide or in an analogous position in an AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV rh.74, AAV rh.10 capsid polypeptide. In aspects of the invention, the promoter sequence may be a promoter sequence transcribed by RNA polymerase II or III, U6 promoter sequence, MHCK7 promoter sequence, CK6 promoter sequence, tMCK promoter sequence, CK5 promoter sequence, MCK promoter sequence, HAS promoter sequence, MPZ promoter sequence, desmin promoter sequence, APOA2 promoter sequence, hAAT promoter sequence, INS promoter sequence, IRS2 promoter sequence, MYH6 promoter sequence, MYL2 promoter sequence, TNNI3 promoter sequence, SYN1 promoter sequence, GFAP promoter sequence, NES promoter sequence, MBP promoter sequence, or a TH promoter sequence. The miRNA strand may be selected from the group of miDUX4, miRN92, miRNA-17, miRNA-18a, miRNA-19a, miRNA-20a, miRNA-19b-1, mi-RNA-26a, miRNA-126, miRNA-335, let-7a and let-7b, miRNA-34, miR-34a, miRNA-10b, miRNA-208, miRNA-499, miRNA-195, miRNA-29a, miRNA-29b, or miRNA-29c. The miRNA strand may also be selected from the group of SEQ ID NOs.1250-1305. The miRNA strand may also comprise 5-6 thymidines at the 5’ end. In an embodiment of the invention, the capsid protein comprises at least one modification that results in reduced liver-tropism of the AAV vector, or at least one modification that results in preferential targeting of the AAV vector to muscle tissue, or both. The capsid protein may be selected from the sequences in Tables 1 - 4. In an embodiment of the invention, the vector further comprises a nuclear export sequence enabling nuclear spreading. Micro RNA MiRNA-based therapies, including miRNA inhibition and miRNA replacement, may be used to treat many diseases such as hepatitis C viral infection, muscular dystrophies, neurodegenerative diseases, peripheral neuropathies, chronic heart failure and post-myocardial infarction remodeling and cancers. In addition, miRNA directed regulation of gene expression may improve traditional gene therapy approaches in which the vector payload is a protein coding gene. Systemically delivered AAV vectors preferentially transduce the liver, resulting in high-level transgene expression in that organ if a liver-active promoter is used. As described in detail herein, the insertion of liver-specific miR-122 binding sites reduce transgene expression in the liver when a liver-specific promoter is used. The nucleic acid molecule of the disclosure comprises a mature guide strand of a miRNA to knockdown expression of the DUX4 gene. This system may be used with any tissue specific promoter or gene expression control element and any miRNA sequences. For example, in order to promote expression of miRNA sequence in skeletal muscle and to detarget expression of the miRNA in liver and heart tissue, the nucleic acid molecule comprises the mature guide stand of the miRNA in which the binding sites for liver specific miR-122 and/or the binding site for heart specific miR-208 are inserted within the loop of the mature guide strand or at the 5' or 3' end of the mature guide strand of the miRNA . There are two miR-208 sequences in the human and mouse genome (miR-208a and miR- 208b). To avoid a run of 5 U's (pol III promoter termination sequence), in the above exemplary sequences, a single base in the binding site was mutated to a "c" (lower-case bolded "c"). This change was included because it creates a perfect binding site for mir-208b, but will have a mismatch with mir-208a. If detargeting expression of a miRNA in skeletal muscle is desired, binding sites for miR-1, miR-206 or miR-133 are inserted within the loop of the mature guide strand of the miRNA or at the 5' or 3' end of the mature guide strand of the miRNA. There are two miR-208 sequences in the human and mouse genome (miR-208a and miR- 208b). To avoid a run of 5 U's (pol III promoter termination sequence), in the following exemplary sequences, a single base in the binding site was mutated to a "c" (lower-case bolded "c"). This change was included because it creates a perfect binding site for mir-208b, but will have a mismatch with mir-208a. The nucleic acid molecules of the disclosure may comprise the sequence of the mature guide strand of any miRNA transcript sequence desired to have tissue-specific expression. For example, in one embodiment, skeletal expression of DUX4 miRNA is contemplated. Exemplary DUX4 miRNA sequences are provided in International Patent Application No. PCT/US2012/047999 (WO 2013/016352) and US patent publication no. US 2012-20225034 incorporated by reference herein in their entirety. Two examples of miDUX4 are miDUX4-1: and miDUX4-2. Exemplary nucleotide sequences comprising the DUX4 miRNA and the binding site for either miR-122 or miR-208 are provided in Table 5. Any human miRNA may be expressed using the nucleic acid molecules of the disclosure , including those set out in the miRBase: the microRNA database websites (miRBase.org), which are incorporated by reference herein in its entirety. Examples include but not limited to the following: miR-122, miR-124, miR-142, miR-155, miR-21, miR-17-92, miR-17, miR-18a, miR-19a, miR-20a, miR-19b-1, miR-26a, miR-126, miR-335, let-7 family: let-7a and let-7b, miR-34 (miR-34a), miR-10b, miR-208, miR-499, miR-195, miR-29a, miR-29b, and miR-29c. Additional exemplary miRNA are set out below in Table 6 above. Any of these miRNA may be used with different detargeting sequences, depending of the desired tissue specificity and desired detargeting. The AAV vector of claim 35, wherein the miRNA strand is selected from the group of in table 5. The AAV vector of claim 35, wherein the miRNA strand further comprises 5-6 thymidines at the 5’ end. The AAV vector of claim 35, wherein the miRNA strand is the binding site for miRNA-122 or miRNA 208. Embodiments of the invention further provide methods of decreasing gene expression in a cell. The method may include providing the AAV vector to a subject, the vector comprised as noted within this section. Further microRNA sequences are described in U.S. Patent Publication Nos.2020-0248179, 2019-0300903, 2019-0136235, 2019-0024083, 2017-0029849, and 2014-0322169, the contents of each of which are incorporated by reference herein. Pharmaceutical Composition Some embodiments of the invention may include any acceptable form of providing the AAV vector to a subject. For example, the AAV vector may be provided to the subject in the form of a composition or formulation comprising the AAV vector. The expression vector of this invention can be formulated and administered to treat a variety of disease states by any means that produces contact of the active ingredient with the agent's site of action in the body of the subject. The compositions, polynucleotides, polypeptides, particles, cells, vector systems and combinations thereof described herein can be contained in a formulation, such as a pharmaceutical formulation. In some embodiments, the formulations can be used to generate polypeptides and other particles that include one or more muscle-specific targeting moieties described herein. In some embodiments, the formulations can be delivered to a subject in need thereof. In some embodiments, component(s) of the engineered AAV capsid system, engineered cells, engineered AAV capsid particles, and/or combinations thereof described herein can be included in a formulation that can be delivered to a subject or a cell. In some embodiments, the formulation is a pharmaceutical formulation. One or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein can be provided to a subject in need thereof or a cell alone or as an active ingredient, such as in a pharmaceutical formulation. As such, also described herein are pharmaceutical formulations containing an amount of one or more of the polypeptides, polynucleotides, vectors, cells, or combinations thereof described herein. In some embodiments, the pharmaceutical formulation can contain an effective amount of the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein. The pharmaceutical formulations described herein can be administered to a subject in need thereof or a cell. In some embodiments, the amount of the one or more of the polypeptides, polynucleotides, vectors, cells, virus particles, nanoparticles, other delivery particles, and combinations thereof described herein contained in the pharmaceutical formulation can range from about 1 pg/kg to about 10 mg/kg based upon the bodyweight of the subject in need thereof or average bodyweight of the specific patient population to which the pharmaceutical formulation can be administered. The amount of the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein in the pharmaceutical formulation can range from about 1 pg to about 10 g, from about 10 nL to about 10 ml. In embodiments where the pharmaceutical formulation contains one or more cells, the amount can range from about 1 cell to 1 x 10 ² , 1 x 10 ³ , 1 x 10 ⁴ , 1 x 10 ⁵ , 1 x 10 ⁶ , 1 x 10 ⁷ , 1 x 10 ⁸ , 1 x 10 ⁹ , 1 x 10 ¹⁰ or more cells. In embodiments where the pharmaceutical formulation contains one or more cells, the amount can range from about 1 cell to 1 x 10 ² , 1 x 10 ³ , 1 x 10 ⁴ , 1 x 10 ⁵ , 1 x 10 ⁶ , 1 x 10 ⁷ , 1 x 10 ⁸ , 1 x 10 ⁹ , 1 x 10 ¹⁰ or more cells per nL, µL, mL, or L. In embodiments, were engineered AAV capsid particles are included in the formulation, the formulation can contain 1 to 1 x 10 ² , 1 x 10 ³ , 1 x 10 ⁴ , 1 x 10 ⁵ , 1 x 10 ⁶ , 1 x 10 ⁷ , 1 x 10 ⁸ , 1 x 10 ⁹ , 1 x 10 ¹⁰ , 1 x 10 ¹¹ , 1 x 10 ¹² , 1 x 10 ¹³ , 1 x 10 ¹⁴ , 1 x 10 ¹⁵ , 1 x 10 ¹⁶ , 1 x 10 ¹⁷ , 1 x 10 ¹⁸ , 1 x 10 ¹⁹ , or 1 x 10 ²⁰ transducing units (TU)/mL of the engineered AAV capsid particles. In some embodiments, the formulation can be 0.1 to 100 mL in volume and can contain 1 to 1 x 10 ² , 1 x 10 ³ , 1 x 10 ⁴ , 1 x 10 ⁵ , 1 x 10 ⁶ , 1 x 10 ⁷ , 1 x 10 ⁸ , 1 x 10 ⁹ , 1 x 10 ¹⁰ , 1 x 10 ¹¹ , 1 x 10 ¹² , 1 x 10 ¹³ , 1 x 10 ¹⁴ , 1 x 10 ¹⁵ , 1 x 10 ¹⁶ , 1 x 10 ¹⁷ , 1 x 10 ¹⁸ , 1 x 10 ¹⁹ , or 1 x 10 ²⁰ transducing units (TU)/mL of the engineered AAV capsid particles. Pharmaceutically Acceptable Carriers and Auxiliary Ingredients and Agents In embodiments, the pharmaceutical formulation containing an amount of one or more of the polypeptides, polynucleotides, vectors, cells, virus particles, nanoparticles, other delivery particles, and combinations thereof described herein can further include a pharmaceutically acceptable carrier. Suitable pharmaceutically acceptable carriers include, but are not limited to, water, salt solutions, alcohols, gum arabic, vegetable oils, benzyl alcohols, polyethylene glycols, gelatin, carbohydrates such as lactose, amylose or starch, magnesium stearate, talc, silicic acid, viscous paraffin, perfume oil, fatty acid esters, hydroxy methylcellulose, and polyvinyl pyrrolidone, which do not deleteriously react with the active composition. The pharmaceutical formulations can be sterilized, and if desired, mixed with auxiliary agents, such as lubricants, preservatives, stabilizers, wetting agents, emulsifiers, salts for influencing osmotic pressure, buffers, coloring, flavoring and/or aromatic substances, and the like which do not deleteriously react with the active composition. In some embodiments, the pharmaceutical formulations described herein may be in a dosage form. The dosage forms can be adapted for administration by any appropriate route. Appropriate routes include, but are not limited to, oral (including buccal or sublingual), rectal, epidural, intracranial, intraocular, inhaled, intranasal, topical (including buccal, sublingual, or transdermal), vaginal, intraurethral, parenteral, intracranial, subcutaneous, intramuscular, intravenous, intraperitoneal, intradermal, intraosseous, intracardiac, intraarticular, intracavernous, intrathecal, intravitreal, intracerebral, gingival, subgingival, intracerebroventricular, and intradermal. Such formulations may be prepared by any method known in the art. Dosage forms adapted for oral administration can be discrete dosage units such as capsules, pellets or tablets, powders or granules, solutions, or suspensions in aqueous or non- aqueous liquids; edible foams or whips, or in oil-in-water liquid emulsions or water-in-oil liquid emulsions. In some embodiments, the pharmaceutical formulations adapted for oral administration also include one or more agents which flavor, preserve, color, or help disperse the pharmaceutical formulation. Dosage forms prepared for oral administration can also be in the form of a liquid solution that can be delivered as foam, spray, or liquid solution. In some embodiments, the oral dosage form can contain about 1 ng to 1000 g of a pharmaceutical formulation containing a therapeutically effective amount or an appropriate fraction thereof of the targeted effector fusion protein and/or complex thereof or composition containing the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein. The oral dosage form can be administered to a subject in need thereof. Where appropriate, the dosage forms described herein can be microencapsulated. The dosage form can also be prepared to prolong or sustain the release of any ingredient. In some embodiments, the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein can be the ingredient whose release is delayed. In other embodiments, the release of an optionally included auxiliary ingredient is delayed. Suitable methods for delaying the release of an ingredient include, but are not limited to, coating or embedding the ingredients in material in polymers, wax, gels, and the like. Delayed release dosage formulations can be prepared as described in standard references such as "Pharmaceutical dosage form tablets," eds. Liberman et. al. (New York, Marcel Dekker, Inc., 1989), "Remington - The science and practice of pharmacy", 20th ed., Lippincott Williams & Wilkins, Baltimore, MD, 2000, and "Pharmaceutical dosage forms and drug delivery systems", 6th Edition, Ansel et al., (Media, PA: Williams and Wilkins, 1995). These references provide information on excipients, materials, equipment, and processes for preparing tablets and capsules and delayed release dosage forms of tablets and pellets, capsules, and granules. The delayed release can be anywhere from about an hour to about 3 months or more. Examples of suitable coating materials include, but are not limited to, cellulose polymers such as cellulose acetate phthalate, hydroxypropyl cellulose, hydroxypropyl methylcellulose, hydroxypropyl methylcellulose phthalate, and hydroxypropyl methylcellulose acetate succinate; polyvinyl acetate phthalate, acrylic acid polymers and copolymers, and methacrylic resins that are commercially available under the trade name EUDRAGIT® (Roth Pharma, Westerstadt, Germany), zein, shellac, and polysaccharides. Coatings may be formed with a different ratio of water-soluble polymer, water insoluble polymers, and/or pH dependent polymers, with or without water insoluble/water soluble non- polymeric excipient, to produce the desired release profile. The coating is either performed on the dosage form (matrix or simple) which includes, but is not limited to, tablets (compressed with or without coated beads), capsules (with or without coated beads), beads, particle compositions, "ingredient as is" formulated as, but not limited to, suspension form or as a sprinkle dosage form. Dosage forms adapted for topical administration can be formulated as ointments, creams, suspensions, lotions, powders, solutions, pastes, gels, sprays, aerosols, or oils. In some embodiments for treatments of the eye or other external tissues, for example the mouth or the skin, the pharmaceutical formulations are applied as a topical ointment or cream. When formulated in an ointment, the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein can be formulated with a paraffinic or water-miscible ointment base. In some embodiments, the active ingredient can be formulated in a cream with an oil-in-water cream base or a water-in-oil base. Dosage forms adapted for topical administration in the mouth include lozenges, pastilles, and mouth washes. Dosage forms adapted for nasal or inhalation administration include aerosols, solutions, suspension drops, gels, or dry powders. In some embodiments, the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein is contained in a dosage form adapted for inhalation is in a particle-size-reduced form that is obtained or obtainable by micronization. In some embodiments, the particle size of the size reduced (e.g., micronized) compound or salt or solvate thereof, is defined by a D50 value of about 0.5 to about 10 microns as measured by an appropriate method known in the art. Dosage forms adapted for administration by inhalation also include particle dusts or mists. Suitable dosage forms wherein the carrier or excipient is a liquid for administration as a nasal spray or drops include aqueous or oil solutions/suspensions of an active ingredient (e.g., the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein and/or auxiliary active agent), which may be generated by various types of metered dose pressurized aerosols, nebulizers, or insufflators. In some embodiments, the dosage forms can be aerosol formulations suitable for administration by inhalation. In some of these embodiments, the aerosol formulation can contain a solution or fine suspension of the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein and a pharmaceutically acceptable aqueous or non- aqueous solvent. Aerosol formulations can be presented in single or multi-dose quantities in sterile form in a sealed container. For some of these embodiments, the sealed container is a single dose or multi-dose nasal, or an aerosol dispenser fitted with a metering valve (e.g., metered dose inhaler), which is intended for disposal once the contents of the container have been exhausted. Where the aerosol dosage form is contained in an aerosol dispenser, the dispenser contains a suitable propellant under pressure, such as compressed air, carbon dioxide, or an organic propellant, including but not limited to a hydrofluorocarbon. The aerosol formulation dosage forms in other embodiments are contained in a pump-atomizer. The pressurized aerosol formulation can also contain a solution or a suspension of one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein. In further embodiments, the aerosol formulation can also contain co-solvents and/or modifiers incorporated to improve, for example, the stability and/or taste and/or fine particle mass characteristics (amount and/or profile) of the formulation. Administration of the aerosol formulation can be once daily or several times daily, for example 2, 3, 4, or 8 times daily, in which 1, 2, or 3 doses are delivered each time. For some dosage forms suitable and/or adapted for inhaled administration, the pharmaceutical formulation is a dry powder inhalable formulation. In addition to the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein, an auxiliary active ingredient, and/or pharmaceutically acceptable salt thereof, such a dosage form can contain a powder base such as lactose, glucose, trehalose, mannitol, and/or starch. In some of these embodiments, the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein is in a particle-size reduced form. In further embodiments, a performance modifier, such as L-leucine or another amino acid, cellobiose octaacetate, and/or metals salts of stearic acid, such as magnesium or calcium stearate. In some embodiments, the aerosol dosage forms can be arranged so that each metered dose of aerosol contains a predetermined amount of an active ingredient, such as the one or more of the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein. Dosage forms adapted for vaginal administration can be presented as pessaries, tampons, creams, gels, pastes, foams, or spray formulations. Dosage forms adapted for rectal administration include suppositories or enemas. Dosage forms adapted for parenteral administration and/or adapted for any type of injection (e.g. intravenous, intraperitoneal, subcutaneous, intramuscular, intradermal, intraosseous, epidural, intracardiac, intraarticular, intracavernous, gingival, subgingival, intrathecal, intravitreal, intracerebral, and intracerebroventricular) can include aqueous and/or non-aqueous sterile injection solutions, which can contain anti-oxidants, buffers, bacteriostats, solutes that render the composition isotonic with the blood of the subject, and aqueous and non-aqueous sterile suspensions, which can include suspending agents and thickening agents. The dosage forms adapted for parenteral administration can be presented in a single- unit dose or multi-unit dose containers, including but not limited to sealed ampoules or vials. The doses can be lyophilized and resuspended in a sterile carrier to reconstitute the dose prior to administration. Extemporaneous injection solutions and suspensions can be prepared in some embodiments, from sterile powders, granules, and tablets. Dosage forms adapted for ocular administration can include aqueous and/or nonaqueous sterile solutions that can optionally be adapted for injection, and which can optionally contain anti- oxidants, buffers, bacteriostats, solutes that render the composition isotonic with the eye or fluid contained therein or around the eye of the subject, and aqueous and nonaqueous sterile suspensions, which can include suspending agents and thickening agents. For some embodiments, the dosage form contains a predetermined amount of the one or more of the polypeptides, polynucleotides, vectors, cells, and combinations thereof described herein per unit dose. In some embodiments, the predetermined amount of the Such unit doses may therefore be administered once or more than once a day. Such pharmaceutical formulations may be prepared by any of the methods well known in the art. DUX4 and Facioscapulohumeral Muscular Dystrophy Muscular dystrophies (MDs) are a group of genetic diseases. The group is characterized by progressive weakness and degeneration of the skeletal muscles that control movement or breathing. Some forms of MD develop in infancy or childhood, while others may not appear until middle age or later. The disorders differ in terms of the distribution and extent of muscle weakness (some forms of MD also affect cardiac muscle), the age of onset, the rate of progression, and the pattern of inheritance. Facioscapulohumeral muscular dystrophy (FSHD) is a complex autosomal dominant disorder characterized by progressive and asymmetric weakness of facial, shoulder and limb muscles. Symptoms typically arise in adulthood with most patients showing clinical features before age thirty. About five percent of patients develop symptoms as infants or juveniles and these are generally more severely affected. Clinical presentation can vary from mild (some limited muscle weakness) to severe (wheelchair dependence). Historically, FSHD was classified as the third most common MD, affecting one in 20,000 individuals worldwide. However, recent data indicate FSHD is the most common MD in Europe, suggesting its worldwide incidence could be as high as 1 in 8,333.Typical FSHD cases (FSHD1A, heretofore referred to as FSHD) are linked to heterozygous chromosomal deletions that decrease the copy number of 3.3 kilobase (kb) D4Z4 repeats on human chromosome 4q35. Simplistically, normal individuals have 11-100 tandemly-repeated D4Z4 copies on both 4q35 alleles, while patients with FSHD have one normal and one contracted allele containing 1-10 repeats. In addition, FSHD-associated D4Z4 contractions must occur on specific disease-permissive chromosome 4q35 backgrounds (called 4qA). Importantly, no genes are completely lost or structurally mutated as a result of FSHD-associated deletions. Instead, genetic changes associated with FSHD give rise to expression of the toxic DUX4 gene, which is damaging to muscle. FSHD2 (also known as FSHD1B) is phenotypically identical to FSHD1, is associated with DUX4 expression, and requires the 4qA chromosomal background. FSHD2 is not associated with D4Z4 repeat contraction, but is instead caused by mutation in the SMCHD1 gene, which is a chromatin regulator normally involved in repressing the DUX4 locus at 4qA. Mutated SMCHD1 proteins fail to participate in adding heterochromatin to the 4qA DUX4 allele, thereby allowing DUX4 gene expression. In the leading FSHD pathogenesis model, D4Z4 contractions are proposed to cause epigenetic changes that permit expression of the DUX4 gene. As a result, the aberrant over- expression of otherwise silent or near-silent DUX4 gene, and the genes it regulates, may ultimately cause FSHD. This model is consistent with data showing normal 4q35 D4Z4 repeats have heterochromatin characteristics, while FSHD-linked D4Z4 repeats contain marks more indicative of actively transcribed euchromatin. These transcription-permissive epigenetic changes, coupled with the observation that complete monosomic D4Z4 deletions (i.e., zero repeats) do not cause FSHD, support the hypothesis that D4Z4 repeats harbor potentially myopathic open reading frames (ORFs), which are abnormally expressed in FSHD muscles. This notion was initially considered in 1994, when a D4Z4-localized ORF, called DUX4, was first identified. However, the locus had some characteristics of an unexpressed pseudogene and DUX4 was therefore summarily dismissed as an FSHD candidate. For many years thereafter, the search for FSHD-related genes was mainly focused outside the D4Z4 repeats, and although some intriguing candidates emerged from these studies, no single gene had been conclusively linked to FSHD development. This slow progress led to the re- emergence of DUX4 as an FSHD candidate in 2007. The role of DUX4 in FSHD pathogenesis can be explained as follows. First, D4Z4 repeats contain identical DUX4 coding regions, and D4Z4 repeats also harbor smaller sense and antisense transcripts, including some resembling microRNAs. Over-expressed DUX4 transcripts and a .about.50 kDa full-length DUX4 protein are found in biopsies and cell lines from FSHD patients. These data are consistent with a transcriptional de-repression model of FSHD pathogenesis. In addition, unlike pseudogenes, D4Z4 repeats and DUX4 likely have functional importance, since tandemly-arrayed D4Z4 repeats are conserved in at least eleven different placental mammalian species (non-placental animals lack D4Z4 repeats), with the greatest sequence conservation occurring within the DUX4 ORF. Second, over-expressed DUX4 is toxic to tissue culture cells and embryonic progenitors of developing lower organisms in vivo. This toxicity occurs at least partly through a pro-apoptotic mechanism, indicated by Caspase-3 activation in DUX4 transfected cells, and presence of TUNEL-positive nuclei in developmentally arrested Xenopus embryos injected with DUX4 mRNA at the two-cell stage. These findings are consistent with studies showing some pro- apoptotic proteins, including Caspase-3, are present in FSHD patient muscles. In addition to stimulating apoptosis, DUX4 may negatively regulate myogenesis. Human DUX4 inhibits differentiation of mouse C2C12 myoblasts in vitro, potentially by interfering with PAX3 and/or PAX7, and causes developmental arrest and reduced staining of some muscle markers when delivered to progenitor cells of zebrafish or Xenopus embryos. Finally, aberrant DUX4 function is directly associated with potentially important molecular changes seen in FSHD patient muscles. Specifically, full-length human DUX4 encodes an approximately 50 kDa double homeodomain transcription factor, and DUX4 targets can be found at elevated levels in FSHD patient muscles. These data support that DUX4 catalyzes numerous downstream molecular changes that are incompatible with maintaining normal muscle integrity. Application of Nuclear Spreading to Facioscapulohumeral Muscular Dystrophy (FSHD) A DUX4 Dominant Negative can compete with full-length DUX4 to prevent DUX4- mediated transcription. One such construct is S+375-397 DUX4, which contains HOXl and HOX2 DNA binding domains, which but only part of the C-terminal domain (FIG.8A). This construct was identified by Mitsuhashi et al. as a potential inhibitory construct which can bind the DUX4 promoter without being toxic to cells. Muscle cells include cells including multiple nuclei, thus a DUX4 dominant negative may require efficient spreading to multiple myonuclei. Thus, if delivered by AAV, not all myonuclei will generate DUX4 dominant negative RNA, and if the DUX4 dominant negative has nuclear localization activity, then activity of the dominant negative will be limited to only a few nuclei. Addition of nuclear export sequences may enable the DUX4 dominant negative to spread across the myofiber. In an experiment, C2C12 mouse myoblast stable cell lines were created and used: reporter cell line containing Zscan4 promoter driving tdTomato (Zscan4 is a promoter activated by DUX4); cell line that contains tet-inducible DUX4-Halo (Halo is a fluorescent protein that can be visualized upon addition of a small molecule dye); cell line that stably expresses S+375-397 DUX4 dominant negative fused to GFP; and cell line that stably expresses S+375-397 DUX4 dominant negative fused to GFP and an ALYREF nuclear export signal. Cell lines were plated at varying ratios onto a gelatin substrate that facilitates formation of myotubes. The cells were then differentiated into myotubes; each myotube contains a mixture of nuclei from all the different cell lines. Once differentiated (7 days post serum withdrawal), DUX4-Halo is induced with doxycycline-containing media (500 nanograms per milliliter (ng/ml)). Myotubes were imaged 72 hours following doxycycline induction. S+375- 397 dominant negative prevents binding of DUX4-Halo to the Zscan promoter, limiting expression of tdTomato, with the ALYREF construct performing more efficiently. The ALYREF dominant negative fusion prevents tdTomato expression more effectively than the dominant negative without the ALYREF sequence providing enhanced nuclear­ cytoplasmic trafficking which is beneficial to limit DUX4 transcriptional activation. Nuclear spreading is further described in the patent application PCT/US2021/033680, the entirety of the contents of which is incorporated by reference herein in its entirety. Examples Adeno-associated viral vectors comprising a nucleic acid sequence encoding Dux4 and adeno-associated viral vectors comprising a nucleic acid sequence encoding truncated forms of Dux4 were administered to mice. Expression of Dux4 regulated genes were analyzed. FIG.1 shows the expression rates of protein coding gene Wfdc3 in response to full and truncated forms of Dux4. Wfdc3 is the Whey Acidic Four-Disulfide Core Domain Protein 3; it functions as a protease inhibitor and contains eight cysteines forming four disulfide bonds at the core of the protein. Expression of the gene may be associated with FSHD. Experimental mice were intramuscularly administered an inert control, the full-length DUX4-FL sequence, the truncated DUX4-S sequence, a 1:1 co-administered mixture of DUX4-FL and DUX4-S, and a 1:101 co- administered mixture of DUX4-FL and DUX4-S. Wfdc3 was found to be upregulated in those mice that received only the DUX4-FL full sequence, as well as upregulated to a lesser degree in those mice that received a 1:1 co-administered mixture of DUX4-FL and DUX4-S. Wfdc3 was not upregulated in mice that received the inert control, DUX4-S alone, or the 1:101 mixture of DUX4- FL and DUX4-S. FIG.2 shows the expression rates of protein coding gene Trim36 in response to varying forms of the DUX4 sequence. Trim36 is the tripartite motif containing 36 gene; it includes three zinc-binding domains, a ring, B-box type 1 and B-box type 2, and a coiled-coil region. Expression of the gene is related to the innate immune system pathway, and the gene is involved in chromosome segregation and regulation of the cell cycle. Experimental mice were intramuscularly administered an inert control, the full-length DUX4-FL sequence, the truncated DUX4-S sequence, a 1:1 co- administered mixture of DUX4-FL and DUX4-S, and a 1:101 co-administered mixture of DUX4- FL and DUX4-S. Trim36 was found to be upregulated in those mice that received only the DUX4- FL full sequence, as well as upregulated to a lesser degree in those mice that received a 1:1 co- administered mixture of DUX4-FL and DUX4-S. Trim36 expression matched the inert control in mice receiving DUX4S alone. Trim36 expression was lower than the vehicle in mice that received the 1:101 mixture of DUX4-FL and DUX4-S. Conclusion Expression of truncated forms of DUX4 inhibit the expression of DUX4 controlled genes, even in the presence of full-length DUX4. Accordingly, DUX4 associated conditions, such as FSHD, may be treated by expression of truncated forms of DUX4. Incorporation by Reference References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made throughout this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes. Equivalents Various modifications of the invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including references to the scientific and patent literature cited herein. The subject matter herein contains important information, exemplification and guidance that can be adapted to the practice of this invention in its various embodiments and equivalents thereof. Select Sequences SEQ ID NO.1: Full-length DUX4-FL amino acid sequence. MALPTPSDSTLPAEARGRGRRRRLVWTPSQSEALRACFERNPYPGIATRERLAQAIGIPE PR VQIWFQNERSRQLRQHRRESRPWPGRRGPPEGRRKRTAVTGSQTALLLRAFEKDRFPGIA AREELARETGLPESRIQIWFQNRRARHPGQGGRAPAQAGGLCSAAPGGGHPAPSWVAFA HTGAWGTGLPAPHVPCAPGALPQGAFVSQAARAAPALQPSQAAPAEGISQPAPARGDFA YAAPAPPDGALSHPQAPRWPPHPQKSREDRDPQRDGLPGPCAVAQPGPAQAGPQGQGV LAPPTSQGSPWWGWGRGPQVAGAAWEPQAGAAPPPQPAPPDASASARQGQMQGIPAPS QALQEPAPWSALPCGLLLDELLASPEFLQQAQPLLETEAPGELEASEEAASLEAPLSEEE Y RALLEEL SEQ ID NO.2: AAV9 Capsid Reference Sequence MAADGYLPDWLEDNLSEGIREWWALKPGAPQPKANQQHQDNARGLVLPGYKYLGPG NGLDKGEPVNAADAAALEHDKAYDQQLKAGDNPYLKYNHADAEFQERLKEDTSFGG NLGRAVFQAKKRLLEPLGLVEEAAKTAPGKKRPVEQSPQEPDSSAGIGKSGAQPAKKRL NFGQTGDTESVPDPQPIGEPPAAPSGVGSLTMASGGGAPVADNNEGADGVGSSSGNWH CDSQWLGDRVITTSTRTWALPTYNNHLYKQISNSTSGGSSNDNAYFGYSTPWGYFDFNR FHCHFSPRDWQRLINNNWGFRPKRLNFKLFNIQVKEVTDNNGVKTIANNLTSTVQVFT DSDYQLPYVLGSAHEGCLPPFPADVFMIPQYGYLTLNDGSQAVGRSSFYCLEYFPSQMLR TGNNFQFSYEFENVPFHSSYAHSQSLDRLMNPLIDQYLYYLSKTINGSGQNQQTLKFSVA GPSNMAVQGRNYIPGPSYRQQRVSTTVTQNNNSEFAWPGASSWALNGRNSLMNPGPAM ASHKEGEDRFFPLSGSLIFGKQGTGRDNVDADKVMITNEEEIKTTNPVATESYGQVATN HQSAQAQAQTGWVQNQGILPGMVWQDRDVYLQGPIWAKIPHTDGNFHPSPLMGGFG MKHPPPQILIKNTPVPADPPTAFNKDKLNSFITQYSTGQVSVEIEWELQKENSKRWNPEI QYTSNYYKSNNVEFAVNTEGVYSEPRPIGTRYLTRNL SEQ ID NO.3: DUX4-FL Truncated MALPTPSDSTLPAEARGRGRRRRLVWTPSQSEALRACFERNPYPGIATRERLAQAIGIPE PR VQIWFQNERSRQLRQHRRESRPWPGRRGPPEGRRKRTAVTGSQTALLLRAFEKDRFPGIA AREELARETGLPESRIQIWFQNRRARHPGQGGRAPAQ SEQ ID NO.4: DUX4-FL Truncated GRRRRLVWTPSQSEALRACFERNPYPGIATRERLAQAIGIPEPRVQIWFQNERSRQLRQH R RESRPWPGRRGPPEGRRKRTAVTGSQTALLLRAFEKDRFPGIAAREELARETGLPESRIQ I WFQNRRARHPGQGGRAPAQ SEQ ID NO.5: DUX4-FL Truncated MALPTPSDSTLPAEARGRGRRRRLVWTPSQSEALRACFERNPYPGIATRERLAQAIGIPE PR VQIWFQNERSRQLRQHRRESRPWPGRRGPPEGRRKRTAVTGSQTALLLRAFEKDRFPGIA AREELARETGLPESRIQIWFQNRRARHPGQGGRAPAQAGGLCSAAPGGGHPAPSWVAFA HTGAWGTGLPAPHVPCAPGALPQGAFVSQAARAAPALQPSQAAPAEGISQPAPARGDFA YAAPAPPDGALSHPQAPRWPPHPQKSREDRDPQRDGLPGPCAVAQPGPAQAGPQGQGV LAPPTSQGSPWWGWGRGPQVAGAAWEPQAGAAPPPQPAPPDASAS