Abstract Background Congenital myasthenic syndrome is a heterogeneous group of inherited neuromuscular transmission disorders. Variants in RAPSN are a common cause of CMS, accounting for approximately 14%–27% of all CMS cases. Whether preimplantation genetic testing for monogenic disease (PGT‐M) could be used to prevent the potential birth of CMS‐affected children is unclear. Methods Application of WES (whole‐exome sequencing) for carrier testing and guidance for the PGT‐M in the absence of a genetically characterized index patient as well as assisted reproductive technology were employed to prevent the occurrence of birth defects in subsequent pregnancy. The clinical phenotypes of stillborn fetuses were also assessed. Results The family carried two likely pathogenic variants in RAPSN(NM_005055.5): c.133G>A (p.V45M) and c.280G>A (p.E94K). And the potential birth of CMS‐affected child was successfully prevented, allowing the family to have offspring devoid of disease‐associated variants and exhibiting a normal phenotype. Conclusion This report constitutes the first documented case of achieving a CMS‐free offspring through PGT‐M in a CMS‐affected family. By broadening the known variant spectrum of RAPSN in the Chinese population, our findings underscore the feasibility and effectiveness of PGT‐M for preventing CMS, offering valuable insights for similarly affected families.
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