We report the medical histories and personal attitudes of 5 unrelated German patients, 2 following autosomal recessive inheritance (case 1; most likely and case 2; confirmed Becker disease) and 3 following autosomal dominant inheritance (case 3; CLCN1 mutation, cases 4-5; SCN4A mutations), who delivered a total of 9 children.
Both recessive (Becker's disease) or dominant (Thomsen's disease) MC are caused by mutations in the CLCN1 gene encoding the voltage-dependent chloride ClC-1 channel, which is quite exclusively expressed in skeletal muscle.
Mutations in the gene encoding this chloride channel (CLCN1) are responsible for both human purely myotonic disorders, autosomal recessive generalized myotonia (Becker's disease, GM) and autosomal dominant myotonia congenita (Thomsen's disease, MC).