Paramyotonia congenita (OMIM 168300) is a non-dystrophic myopathy caused by mutations in the SCN4A gene that sometimes can be confused with myotonia congenita.
One Brugada family carried an SCN4A variant that is predicted to probably affect function, one family suffered from a not genetically confirmed non-dystrophic myotonia, one family was diagnosed with myotonic dystrophy (DMPK gene) and one family had a Thomsen diseasemyotonia congenita (CLCN1 variant that affects function).
They are caused by mutations in either the CLCN1 gene in myotonia congenita or in the SCN4A gene in paramyotonia congenita and sodium channel myotonias.
We performed linkage analysis using chromosome 17q polymorphisms at D17S74, SCN4A, and GH1, two chromosome 7q31 restriction fragment length polymorphisms, and a dinucleotide repeat polymorphism within the CFTR gene (CFTR-DNR), in three pedigrees with ADMC.