SCN4A and Myotonia: Cold as an exacerbating factor for symptoms was most commonly reported in individuals with non-dystrophic myotonias, with 40.7% (n = 11) of individuals with CLCN1 variants and 46.7% (n = 7) of individuals with SCN4A variants reporting this compared to 36.4% (n = 4) of individuals with CNBP expansions and in 7.9% (n = 7) of individuals with DMPK expansions.