Mexiletine hydrochloride for treating myotonia in children and adolescents with myotonic disorders

Mexiletine is currently in clinical development for the treatment of children and adolescents with myotonic disorders. Myotonic disorders comprise both myotonic dystrophy (DM1 and DM2) and non-dystrophic myotonia (NDM). A common symptom of both conditions is myotonia, during which muscles relax slowly and with difficulty after a voluntary contraction. Muscles affected can include those in the hands, arms, legs, eyelids, face and jaw and muscles in the neck. For patients with symptoms of myotonia, they can appear anytime between the first decade of life and old age. Myotonic disorder patient symptoms may include muscle stiffness (myotonia) pain, weakness, clouding of the eye lens, a slow and irregular heartbeat, slurred speech, problems with swallowing, behavioural and personality problems and excessive sleepiness or tiredness. Life expectancy can vary for people with DM1 and 2; while some have a normal life expectancy, those with more severe congenital forms present from birth might die at a very young age. With NDM, life expectancy is not impaired. There is a medical need for a novel therapy in treatment of children and adolescents with myotonic disorders.