Myotonia congenita has been reported in humans [4], mice [10,11,12] and eight non-laboratory animal species (OMIA:000698), with likely causal variants identified in the CLCN1 gene in all species except cattle for which a single affected calf was reported and a likely causative variant not determined [13,14,15,16,17,18,19,20,21,22,23,24,25]. This evidence concerns the gene CLCN1 and Thomsen and Becker disease.