Loss of function mutations in the CLCN1 gene encoding ClC‐1 cause myotonia congenita (MC) [12, 13], a rare disease characterized by sarcolemma hyper‐excitability responsible for muscle stiffness after voluntary muscle contraction, which improves with consecutive movements and worsens with inactivity [14]. This evidence concerns the gene CLCN1 and Thomsen and Becker disease.