Efficacy Trial of Zonisamide for Myoclonus Dystonia

Inclusion criteria : * Age \>18 and \< 60 * Diagnosis of myoclonus dystonia including the isolated myoclonus caused by epsilon-sarcoglycans mutation or deletion. * Myoclonus present in both hands * Myoclonus decrease quality of life * Insufficient efficiency of the benzodiazepine's tolerated maximal dose during one year * Agreement to use a medically acceptable method of contraception throughout the study for female of childbearing potential * Normal physical and neurological examination, except myoclonus dystonia * No hepatic disease * No renal disease * Able to comply with study visits and procedures * Has voluntarily signed consent form * Taking no medications or stable doses medication for 4 weeks prior to the Baseline visit Exclusion criteria : * Patients who are not enrolled at social security * Individual who have MMS ≤ 24/30 or patients legally protected or inability to provide an informed consent * Pregnancy, breast feeding women and women who are of childbearing age and not practicing adequate birth control * Weight \< 40 kg * history of serious psychiatric illness * history of renal stones * history of allergy to sulfonamides * taking medications : topiramate, rifampicin, ketoconazole, cimetidine