Inclusion Criteria:  Genetic testing confirms the diagnosis of FXS Participate in the study with the informed consent of the guardian BMI>the 3rd percentile Not taking more than 2 therapeutic drugs Able to receive regular follow-up visits  Exclusion Criteria:  Malnutrition Primary heart disease Severe infection or acute clinical illness Gastrointestinal, renal, or hepatic disease Previous history of lactic acidosis previous use of metformin intolerant Use of angiotensin converting enzyme inhibitors, use of anticoagulants, vitamin B12 deficiency, alcohol consumption Unstable systemic diseases other than FXS Changes in clinical medication