Myotonia congenita, recessive (Q89056)

Autosomal recessive myotonia congenita (Becker disease) is caused by mutation in the gene encoding skeletal muscle chloride channel-1 (CLCN1). It is a non-dystrophic skeletal muscle disorder characterised by muscle stiffness and an inability of the muscle to relax after voluntary contraction. Most patients have symptom onset in the legs, which later progresses to the arms, neck, and facial muscles. Many patients show marked hypertrophy of the lower limb muscles. Some patients show transient muscle weakness.