Evaluation of the Efficacy and Safety of Metformin in the Myotonic Dystrophy Type 1 (Steinert's Disease)

Treatment (Metformin or placebo) will be administered orally and titrated following the same guideline that metformin in diabetic patient: start with a daily dose of 500 mg twice a day, given during or after meals; then increase to 1000 mg twice a day after a week. If digestive tolerance is good, treatment will be increased to a maximum of 1000 mg three times a day i.e. 3000 mg/day after another week.