For 33 missense variants the assessment of pathogenicity or inheritance was complicated by co-allelic CLCN1 variants, the presence of variants in other myotonia-associated genes, by the variant not segregating with myotonia congenita symptoms, or by reported dominant inheritance in compound heterozygous probands where it could not be determined which of the variants was associated with dominant inheritance. Here, CLCN1 is linked to Thomsen and Becker disease.