The major spliceosome contains five small nuclear RNAs (snRNAs; U1, U2, U4, U5 and U6) essential for splicing. Variants in RNU4-2, encoding U4, cause a neurodevelopmental disorder called ReNU syndrome. We investigated de novo variants in 50 snRNA-encoding genes in a French cohort of 23,649 individuals with rare disorders and gathered additional cases through international collaborations. Altogether, we identified 145 previously unreported probands with (likely) pathogenic variants in RNU4-2 and 21 individuals with de novo and/or recurrent variants in RNU5B-1 and RNU5A-1, encoding U5. Pathogenic variants typically arose de novo on the maternal allele and cluster in regions critical for splicing. RNU4-2 variants mainly localize to two structures, the stem III and T-loop/quasi-pseudoknot, which position the U6 ACAGAGA box for 5' splice site recognition and associate with different phenotypic severity. RNU4-2 variants result in specific defects in alternative 5' splice site usage and methylation patterns (episignatures) that correlate with variant location and clinical severity. This study establishes RNU5B-1 as a neurodevelopmental disorder gene, suggests RNU5A-1 as a strong candidate and highlights the role of de novo variants in snRNAs.
GrantsInserm Cancer Research UK Medical Research Council National Human Genome Research Institute Care4Rare Canada Consortium Genome Canada Ontario Genomics Institute Canadian Institutes of Health Research Ontario Research Fund Genome Alberta Genome British Columbia Genome Quebec Children's Hospital of Eastern Ontario Foundation Wellcome Trust NHS England French Ministry of Health European Union's Horizon 2020 research and innovation program Deutsche Forschungsgemeinschaft (DFG) Inserm as part of the 2022 MESSIDORE program (project Inserm-MESSIDORE 19) European Joint Programme on Rare Diseases by the Austrian Science Fund FWF Centre for Population Genomics (Garvan Institute of Medical Research) - Medical Research Future Fund (MRFF) Genomics Health Futures Mission grant Centre for Population Genomics (Murdoch Children's Research Institute) - Medical Research Future Fund (MRFF) Genomics Health Futures Mission grant RNU-SPLICE project - health philanthropic program of Mutuelles AXA Priority Research Programme on Rare Diseases of the French Investments for the Future Programme, project MultiOmixCare ERC Starting Grant project 'SPLIFEM' Region Normandie GIRCI Nord-Ouest National Institute for Health Research CIHR Foundation Tier 1 Canada Research Chair in Rare Disease Precision Health CIHR European Commission Royal Society Novo Nordisk Stiftung Michael through Canger-Janz Fellowship ZonMw Vidi Stichting 12q Estonian Research Council Manton Center for Orphan Disease Research postdoctoral fellowship La Fondation pour la Recherche medicale Royal Children's Hospital Foundation AP-HP German Research Foundation (DFG) Alberta Innovates Alberta Children's Hospital Foundation BCH Children's Rare Disease Collaborative Robinson Fund for Transformative Research in Epilepsy BCH Office of Faculty Development/Basic & Clinical Translational Research Executive Committees Faculty Career Development Fellowship Victorian Government's Operational Infrastructure Support Program Australian Government's MRFF Undiagnosed Rare Diseases Program of Catalonia from the Autonomous Government of Catalonia Biomedical Research Networking Center on Rare Diseases (CIBERER) Hesperia Foundation (Royal House of Spain) La Marato de TV3 Foundation IMPACT-Genomica