Becker syndrome is a congenital myotonia of autosomal recessive inheritance that is produced by mutations in the skeletal muscle chlorine gene (CLCN1) leading to a defect in its function. It generally begins in childhood and myotonia is the main clinical manifestation, which consists of a sensation of immobility after voluntary muscle contraction that is usually accompanied by a ‘‘warm-up’’ effect in which patients present an improvement in myotonia with repeated muscle contraction. . Myotonias can be painful, associated with transient or fixed weakness, and an athletic phenotype is generally seen from infancy. At present, only a symptomatic treatment of myotonias can be offered since there is no modifying pharmacological management of the disease.
