Phenotypic Differences in 2 Unrelated Cases Carrying Identical DOK7 Mutations

INTRODUCTION: Mutations in the Dok-7 gene (DOK7) underlie a congenital myasthenic syndrome (CMS) with a characteristic limb-girdle (LG) pattern of muscle weakness. Multiple clinical findings and a wide clinical heterogeneity have been identified in this form of CMS. METHODS: We describe here 2 unrelated adult patients who presented with a LG CMS, caused by 2 compound heterozygous pathogenic sequence variants in DOK7: c.1124_1127dupTGCC (P.Ala378Serfs*30) and c.480C> A (p.Tyr160*). RESULTS: Although both patients presented with severe proximal weakness consistent with LG myasthenia, one of the patients presented with additional distal muscle involvement in the lower extremities. By contrast, the other patient had severe bulbar and respiratory deficit requiring gastric tube feeding and mechanical ventilatory support for most parts of the day. DISCUSSION: These 2 cases illustrate the lack of phenotype-genotype correlation and the absence of geographic, genetic, and ethnic association in cases of LG CMS caused by DOK7 mutations.