Myotonia congenita in a Greek cohort: Genotype spectrum and impact of the CLCN1:c.501C > G variant as a genetic modifier.

The large number of patients in whom a diagnosis was established allowed the characterization of genotype-phenotype correlations with respect to both previously reported and novel findings. For the c.501C > G (p.Phe167Leu) variant a likely nonpathogenic property is suggested, as it only seems to act as an aggravating modifying factor in cases in which a pathogenic variant triggers phenotypic expression.