Study to Evaluate the Efficacy of Riluzole in Children and Young Adults With Spinal Muscular Atrophy (SMA)

Inclusion Criteria: * Patients afflicted with spinal muscular atrophy, type II or III, with genetic defect confirmed. * Age between 6 and 20 years old. * Score MFM at least 12 * Negative pregnancy test for women of child-bearing age * Signing of an informed consent form, after appropriate information has been provided (if the patient is under 18 years old, both parents are required to sign the form too; otherwise, only her (his) agreement is necessary). Exclusion Criteria: * Patients already treated with Riluzole * Concomitant treatment with: GAPAPENTINE, DEXTROMETHORPHANE, amantadine, any hepatotoxic medication that cannot be stopped, any other experimental product * Hepatic insufficiency: SGPT and/or SGOT levels higher than or equal to twice the normal higher limit * Renal insufficiency (creatinine above 115 micromoles/l) * Severe cardiac insufficiency * Current pneumopathy (clinical signs of an acute episode, confirmed by pulmonary X-ray, requiring specific treatment) * Pregnancy or nursing for women; non-abstinence or absence of effective contraception for nubile women * Any pathology or other circumstance likely to interfere with a regular follow-up * No affiliation to any social insurance system