X-linked recessive dystrophinopathies are the most common muscular dystrophies (MDs) in humans and dogs. To date, 20 breed-specific MD-associated variants are described in the canine dystrophin gene (DMD), including one associated with dystrophin-deficient MD in the Border Collie mixed breed. Here, we report the diagnosis and follow-up of mild dystrophin-deficient MD in a 5-month-old male Border Collie, associated with a novel DMD variant. Diagnosis was based on neurological examination and laboratory evaluations including creatine kinase activity, electromyography and muscle biopsies with immunofluorescent staining. Inspection of the Sashimi plots of the RNA-seq data from the affected muscle biopsy led to the discovery of a 162-bp���L1 pseudoexon in DMD intron 63, introducing a frameshift and a premature stop codon (NM_001003343.1: c.9271_9272insN[162] p.(Ala3091fs*21)). Reduced DMD mRNA levels were detected for both the non-pseudoexon (50�� less) and pseudoexon (3�� less) containing transcripts in the affected muscle, compared with the level of the non-pseudoexon containing transcript in a control muscle, resulting in very low dystrophin protein levels and the upregulation of utrophin. Because the variant was only found in the affected dog, not in the healthy mother and grandmother, or in 108 unrelated Border Collies from the Belgian population (46 males and 62 females), it was considered a de novo variant. Although the prognosis for dystrophinopathy is generally regarded as poor, the dog stabilised at the age of 6���months and is still clinically stable at the age of 2���years.
Aartsma���Rus, A., Van Deutekom, J.C., Fokkema, I.F., Van Ommen, G.J. & Den Dunnen, J.T. (2006) Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading���frame rule. Muscle & Nerve, 34(2), 135���144. Available from: https://doi.org/10.1002/mus.20586
Atencia���Fernandez, S., Shiel, R.E., Mooney, C.T. & Nolan, C.M. (2015) Muscular dystrophy in the Japanese Spitz: an inversion disrupts the DMD and RPGR genes. Animal Genetics, 46(2), 175���184. Available from: https://doi.org/10.1111/age.12266
Barth��l��my, I., Calmels, N., Weiss, R.B., Tiret, L., Vulin, A., Wein, N. et al. (2020) X���linked muscular dystrophy in a Labrador retriever strain: phenotypic and molecular characterisation. Skeletal Muscle, 10(1), 23. Available from: https://doi.org/10.1186/s13395���020���00239���0
Beckers, E., Cornelis, I., Bhatti, S.F.M., Smets, P., Shelton, G.D., Guo, L.T. et al. (2022) A nonsense variant in the DMD gene causes X���linked muscular dystrophy in the Maine coon cat. Animals (Basel), 12(21), 2928. Available from: https://doi.org/10.3390/ani12212928
Brunetti, B., Muscatello, L.V., Letko, A., Papa, V., Cenacchi, G., Grillini, M. et al. (2020) X���linked Duchenne���type muscular dystrophy in Jack Russell terrier associated with a partial deletion of the canine DMD gene. Genes (Basel), 11(10), 1175. Available from: https://doi.org/10.3390/genes11101175
Chemello, F., Bassel���Duby, R. & Olson, E.N. (2020) Correction of muscular dystrophies by CRISPR gene editing. Journal of Clinical Investigation, 130(6), 2766���2776. Available from: https://doi.org/10.1172/JCI136873
Duan, D., Goemans, N., Takeda, S., Mercuri, E. & Aartsma���Rus, A. (2021) Duchenne muscular dystrophy. Nature Reviews. Disease Primers, 7(1), 13. Available from: https://doi.org/10.1038/s41572���021���00248���3
Dubowitz, V., Sewry, C.A. & Oldfors, A. (2021) Histological and histochemical stains and reactions. In: Muscle biopsy: a practical approach, 5th edition. Amsterdam: Elsevier. Available from: https://doi.org/10.1016/C2016���0���00124���9
Gao, Q.Q. & McNally, E.M. (2015) The dystrophin complex: structure, function, and implications for therapy. Comprehensive Physiology, 5(3), 1223���1239. Available from: https://doi.org/10.1002/cphy.c140048
Garc��a���Rodr��guez, R., Hiller, M., Jim��nez���Gracia, L., van der Pal, Z., Balog, J., Adamzek, K. et al. (2020) Premature termination codons in the DMD gene cause reduced local mRNA synthesis. Proceedings of the National Academy of Sciences of the United States of America, 117(28), 16456���16464. Available from: https://doi.org/10.1073/pnas.1910456117
Gazzoli, I., Pulyakhina, I., Verwey, N.E., Ariyurek, Y., Laros, J.F.J., 't Hoen, P.A.C. et al. (2016) Non���sequential and multi���step splicing of the dystrophin transcript. RNA Biology, 13(3), 290���305. Available from: https://doi.org/10.1080/15476286.2015.1125074
Gon��alves, A., Oliveira, J., Coelho, T., Taipa, R., Melo���Pires, M., Sousa, M. et al. (2017) Exonization of an Intronic LINE���1 element causing Becker muscular dystrophy as a novel mutational mechanism in dystrophin gene. Genes (Basel), 8(10), 253. Available from: https://doi.org/10.3390/genes8100253
Gorokhova, S., Schessl, J., Zou, Y., Yang, M.L., Heydemann, P.T., Sufit, R.L. et al. (2023) Unusually severe muscular dystrophy upon in���frame deletion of the dystrophin rod domain and lack of compensation by membrane���localized utrophin. Medicamundi, 4(4), 245���251.e3. Available from: https://doi.org/10.1016/j.medj.2023.02.005
Guo, L.T., Moore, S.A., Forcales, S., Engvall, E. & Diane Shelton, G. (2010) Evaluation of commercial dysferlin antibodies on canine, mouse and human skeletal muscle. Neuromuscular Disorders, 20(12), 820���825. Available from: https://doi.org/10.1016/j.nmd.2010.07.278
Halo, J.V., Pendleton, A.L., Shen, F., Doucet, A.J., Derrien, T., Hitte, C. et al. (2021) Long���read assembly of a great Dane genome highlights the contribution of GC���rich sequence and mobile elements to canine genomes. Proceedings of the National Academy of Sciences of the United States of America, 118(11), e2016274118. Available from: https://doi.org/10.1073/pnas.2016274118
Hamosh, A., Amberger, J.S., Bocchini, C., Scott, A.F. & Rasmussen, S.A. (2021) Online Mendelian inheritance in man (OMIM��): victor McKusick's magnum opus. American Journal of Medical Genetics. Part A, 185(11), 3259���3265. Available from: https://doi.org/10.1002/ajmg.a.62407
Jenkins, C.A. & Forman, O.P. (2015) Identification of a novel frameshift mutation in the DMD gene as the cause of muscular dystrophy in a Norfolk terrier dog. Canine Genetics and Epidemiology, 2, 7. Available from: https://doi.org/10.1186/s40575���015���0019���4
Jones, B.R., Brennan, S., Mooney, C.T., Callanan, J.J., McAllister, H., Guo, L.T. et al. (2004) Muscular dystrophy with truncated dystrophin in a family of Japanese Spitz dogs. Journal of the Neurological Sciences, 217(2), 143���149. Available from: https://doi.org/10.1016/j.jns.2003.09.002
Jurka, J. & Klonowski, P. (1996) Integration of retroposable elements in mammals: selection of target sites. Journal of Molecular Evolution, 43(6), 685���689. Available from: https://doi.org/10.1007/BF02202117
Katz, Y., Wang, E.T., Silterra, J., Schwartz, S., Wong, B., Thorvaldsd��ttir, H. et al. (2015) Quantitative visualization of alternative exon expression from RNA���seq data. Bioinformatics, 31(14), 2400���2402. Available from: https://doi.org/10.1093/bioinformatics/btv034
Kohany, O., Gentles, A.J., Hankus, L. & Jurka, J. (2006) Annotation, submission and screening of repetitive elements in Repbase: RepbaseSubmitter and censor. BMC Bioinformatics, 7, 474. Available from: https://doi.org/10.1186/1471���2105���7���474
Kornegay, J.N., Bogan, J.R., Bogan, D.J., Childers, M.K., Li, J., Nghiem, P. et al. (2012) Canine models of Duchenne muscular dystrophy and their use in therapeutic strategies. Mammalian Genome, 23(1���2), 85���108. Available from: https://doi.org/10.1007/s00335���011���9382���y
Landrum, M.J., Lee, J.M., Benson, M., Brown, G.R., Chao, C., Chitipiralla, S. et al. (2018) ClinVar: improving access to variant interpretations and supporting evidence. Nucleic Acids Research, 46(D1), D1062���D1067. Available from: https://doi.org/10.1093/nar/gkx1153
Lefter, M., Vis, J.K., Vermaat, M., den Dunnen, J.T., Taschner, P.E.M. & Laros, J.F.J. (2021) Mutalyzer 2: next generation HGVS nomenclature checker. Bioinformatics, 37(18), 2811���2817. Available from: https://doi.org/10.1093/bioinformatics/btab051
Mata L��pez, S., Hammond, J.J., Rigsby, M.B., Balog���Alvarez, C.J., Kornegay, J.N. & Nghiem, P.P. (2018) A novel canine model for Duchenne muscular dystrophy (DMD): single nucleotide deletion in DMD gene exon 20. Skeletal Muscle, 8(1), 16. Available from: https://doi.org/10.1186/s13395���018���0162���1
Morales, J., Pujar, S., Loveland, J.E., Astashyn, A., Bennett, R., Berry, A. et al. (2022) A joint NCBI and EMBL���EBI transcript set for clinical genomics and research. Nature, 604(7905), 310���315. Available from: https://doi.org/10.1038/s41586���022���04558���8
National Center for Biotechnology Information (NCBI) [Internet]. Bethesda, MD: National Library of Medicine (US), National Center for Biotechnology Information; 1988. [cited 2024 May 24]. Available from: https://www.ncbi.nlm.nih.gov/.
Nghiem, P.P., Bello, L., Balog���Alvarez, C., L��pez, S.M., Bettis, A., Barnett, H. et al. (2017) Whole genome sequencing reveals a 7 base���pair deletion in DMD exon 42 in a dog with muscular dystrophy. Mammalian Genome, 28(3���4), 106���113. Available from: https://doi.org/10.1007/s00335���016���9675���2
Nicholas, F.W. (2021) Online Mendelian inheritance in animals (OMIA): a record of advances in animal genetics, freely available on the internet for 25���years. Animal Genetics, 52(1), 3���9. Available from: https://doi.org/10.1111/age.13010
Richardson, S.R., Doucet, A.J., Kopera, H.C., Moldovan, J.B., Garcia���Perez, J.L. & Moran, J.V. (2015) The influence of LINE���1 and SINE retrotransposons on mammalian genomes. Microbiology Spectrum, 3(2), MDNA3���0061���2014. Available from: https://doi.org/10.1128/microbiolspec.MDNA3���0061���2014
Robinson, J.T., Thorvaldsd��ttir, H., Wenger, A.M., Zehir, A. & Mesirov, J.P. (2017) Variant review with the integrative genomics viewer. Cancer Research, 77(21), e31���e34. Available from: https://doi.org/10.1158/0008���5472.CAN���17���0337
S��nchez, L., Beltr��n, E., de Stefani, A., Guo, L.T., Shea, A., Shelton, G.D. et al. (2018) Clinical and genetic characterisation of dystrophin���deficient muscular dystrophy in a family of miniature poodle dogs. PLoS One, 13(2), e0193372. Available from: https://doi.org/10.1371/journal.pone.0193372
Schatzberg, S.J., Olby, N.J., Breen, M., Anderson, L.V.B., Langford, C.F., Dickens, H.F. et al. (1999) Molecular analysis of a spontaneous dystrophin ���knockout��� dog. Neuromuscular Disorders, 9(5), 289���295. Available from: https://doi.org/10.1016/s0960���8966(99)00011���5
Sharp, N.J., Kornegay, J.N., Van Camp, S.D., Herbstreith, M.H., Secore, S.L., Kettle, S. et al. (1992) An error in dystrophin mRNA processing in golden retriever muscular dystrophy, an animal homologue of Duchenne muscular dystrophy. Genomics, 13(1), 115���121. Available from: https://doi.org/10.1016/0888���7543(92)90210���j
Shelton, G.D., Minor, K.M., Friedenberg, S.G., Cullen, J., Guo, L. & Mickelson, J. (2023) Current classification of canine muscular dystrophies and identification of new variants. Genes, 14(8), 1557. Available from: https://doi.org/10.3390/genes14081557
Shelton, G.D., Minor, K.M., Vieira, N.M., Kunkel, L.M., Friedenberg, S.G., Cullen, J.N. et al. (2022) Tandem duplication within the DMD gene in Labrador retrievers with a mild clinical phenotype. Neuromuscular Disorders, 32(10), 836���841. Available from: https://doi.org/10.1016/j.nmd.2022.08.001
Shrader, S.M., Jung, S., Denney, T.S. & Smith, B.F. (2018) Characterization of Australian labradoodle dystrophinopathy. Neuromuscular Disorders, 28(11), 927���937. Available from: https://doi.org/10.1016/j.nmd.2018.08.008
Smith, B.F., Yue, Y., Woods, P.R., Kornegay, J.N., Shin, J.H., Williams, R.R. et al. (2011) An intronic LINE���1 element insertion in the dystrophin gene aborts dystrophin expression and results in Duchenne���like muscular dystrophy in the corgi breed. Laboratory Investigation, 91(2), 216���231. Available from: https://doi.org/10.1038/labinvest.2010.146
van Putten, M., Hulsker, M., Young, C., Nadarajah, V.D., Heemskerk, H., van der Weerd, L. et al. (2013) Low dystrophin levels increase survival and improve muscle pathology and function in dystrophin/utrophin double���knockout mice. FASEB journal: official publication of the Federation of American Societies for Experimental Biology, 27(6), 2484���2495. Available from: https://doi.org/10.1096/fj.12���224170
Waldrop, M.A., Moore, S.A., Mathews, K.D., Darbro, B.W., Medne, L., Finkel, R. et al. (2022) Intron mutations and early transcription termination in Duchenne and Becker muscular dystrophy. Human Mutation, 43(4), 511���528. Available from: https://doi.org/10.1002/humu.24343
Walmsley, G.L., Arechavala���Gomeza, V., Fernandez���Fuente, M., Burke, M.M., Nagel, N., Holder, A. et al. (2010) A duchenne muscular dystrophy gene hot spot mutation in dystrophin���deficient cavalier king charles spaniels is amenable to exon 51 skipping. PLoS One, 5(1), e8647. Available from: https://doi.org/10.1371/journal.pone.0008647
Winand, N.J. (1994) Molecular genetic characterization of spontaneously occurring animal models of Duchenne muscular dystrophy [dissertation]. Ithaka: Cornell University.
Zaynitdinova, M.I., Lavrov, A.V. & Smirnikhina, S.A. (2021) Animal models for researching approaches to therapy of Duchenne muscular dystrophy. Transgenic Research, 30(6), 709���725. Available from: https://doi.org/10.1007/s11248���021���00278���3