Acknowledgements: We acknowledge H. Luque, L. Phillips, J. Casement, O. Magnuson, D. Nguyen and Y. Hu for technical support; R. García-Tercero and C. Díaz for sample collection; E. Zorio, M.E. Leach, D. Bharucha-Goebel, J. Dastgir and C. Konersman for clinical expertise and M. Gautel for helpful advice. We also thank CureCMD for their help in patient recruitment and the patients for donating their samples. The research leading to these results has received funding from the European Community’s Seventh Framework Program (FP7/2007-2013; 2012-305121) ‘Integrated European—omics research project for diagnosis and therapy in rare neuromuscular and neurodegenerative diseases (NEUROMICS)’ (to A. Töpf, V.S., I.T.Z. and F.M.); the European Union’s Horizon 2020 research and innovation program (Solve-RD project; 779257 to A. Töpf); Muscular Dystrophy UK and Muscular Dystrophy Association US (mda577346 to F.M.); Päulon Säätiö (to M. Savarese); Academy of Finland, Sigrid Juselius Foundation (to B.U.); core funding to the Sanger Institute by the Wellcome Trust (098051 and 206194 to E.M.B.-N., J.P. and N.W.); EURO-NMD and Fundación Gemio (to J.J.V., N.M. and P.M.); Intramural Research Grant (2-5, 29-4) for Neurological and Psychiatric Disorders of NCNP and AMED (JP20ek0109490h0001 to I.N.); Inserm, CNRS, University of Strasbourg, Labex INRT (ANR-10-LABX-0030 and ANR-10-IDEX-0002-02), France Génomique (ANR-10-INBS-09) and Fondation Maladies Rares for the ‘Myocapture’ sequencing project, AFM-Téléthon (22734), the European Joint program (EJPRD2019-126 IDOLS-G and ANR-19-RAR4-0002 to J.L., X.L. and V.B.); Intramural funds from the NIH National Institute of Neurological Disorders and Stroke (to C.G.B.); the Dutch Princess Beatrix Muscle Fund and the Dutch Spieren voor Spieren Muscle fund (to C.E.E.); PI16/00316 supported by the Instituto de Salud Carlos III (ISCIII), Madrid and the Generalitat Valenciana (grant PROMETEO/2019/075 to N.M.); Australian NHMRC Neil Hamilton Fairley Early Career Research Fellowship (GNT1090428 to E.C.O.); Starship Foundation A+7340 (to G.L.O.); Early Career Award from the Thrasher Research Fund (to S.S.); U54 HD090255 from the NIH Eunice Kennedy Shriver National Institute of Child Health and Human Development (to A.H.B.); Wellcome Center for Mitochondrial Research (203105/Z/16/Z), the Mitochondrial Disease Patient Cohort (UK; G0800674), the Medical Research Council International Center for Genomic Medicine in Neuromuscular Disease (MR/S005021/1), the Medical Research Council (MR/W019027/1), the Lily Foundation, Mito Foundation, the Pathological Society, the UK NIHR Biomedical Research Center for Ageing and Age-related Disease award to the Newcastle upon Tyne Foundation Hospitals NHS Trust and the UK NHS Highly Specialized Service for Rare Mitochondrial Disorders of Adults and Children (to R.W.T.). MYO–SEQ was funded by Sanofi Genzyme, Ultragenyx, LGMD2I Research Fund, Samantha J Brazzo Foundation, LGMD2D Foundation, Kurt+Peter Foundation, Muscular Dystrophy UK and Coalition to Cure Calpain 3. Sequencing and analysis for relevant families (Supplementary Note) were provided by the Broad Institute of MIT and Harvard Center for Mendelian Genomics (Broad CMG) and were funded by the National Human Genome Research Institute, the National Eye Institute and the National Heart, Lung and Blood Institute under grant UM1 HG008900 and the National Human Genome Research Institute under grants U01HG0011755 and R01 HG009141. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. DNA samples for NeurOmics and MYO–SEQ were provided by the John Walton Muscular Dystrophy Research Center Biobank. This facility is supported by the NIHR Newcastle Biomedical Research Center. Newcastle University’s Electron Microscopy Research Services and equipment Hitachi HT7800 120 kV TEM microscope are funded by BBSRC grant reference BB/R013942/1.Funder: Genzyme (Genzyme Corporation); doi: https://doi.org/10.13039/100004329Funder: Ultragenyx Pharmaceutical (Ultragenyx Pharmaceutical Inc.); doi: https://doi.org/10.13039/100013220Funder: EC | EC Seventh Framework Programm | FP7 Ideas: European Research Council (FP7-IDEAS-ERC - Specific Programme: "Ideas" Implementing the Seventh Framework Programme of the European Community for Research, Technological Development and Demonstration Activities (2007 to 2013)); doi: https://doi.org/10.13039/100011199; Grant(s): 2012-305121In digenic inheritance, pathogenic variants in two genes must be inherited together to cause disease. Only very few examples of digenic inheritance have been described in the neuromuscular disease field. Here we show that predicted deleterious variants in SRPK3, encoding the X-linked serine/argenine protein kinase 3, lead to a progressive early onset skeletal muscle myopathy only when in combination with heterozygous variants in the TTN gene. The co-occurrence of predicted deleterious SRPK3/TTN variants was not seen among 76,702 healthy male individuals, and statistical modeling strongly supported digenic inheritance as the best-fitting model. Furthermore, double-mutant zebrafish (srpk3-/-; ttn.1+/-) replicated the myopathic phenotype and showed myofibrillar disorganization. Transcriptome data suggest that the interaction of srpk3 and ttn.1 in zebrafish occurs at a post-transcriptional level. We propose that digenic inheritance of deleterious changes impacting both the protein kinase SRPK3 and the giant muscle protein titin causes a skeletal myopathy and might serve as a model for other genetic diseases
