Development of Quantitative Muscle Imaging as a Biomarker of Disease Endpoints in Myotonic Dystrophy

Inclusion Criteria: DM subjects * Age 18 - 65 years * Diagnosis of DM1 or DM2 by clinical or genetic criteria. If DM1 or DM2 was diagnosed by clinical criteria, a first-degree relative must have genetic testing confirmation and sign a genetic consent form to release their genetic information * Clinically affected, as defined by muscle weakness or myotonia * Ambulate independently (a walker is not permitted) * Able to provide informed consent for participation in the study Control subjects * Age 18 - 65 years old * Healthy as defined by no significant medical or neurological conditions * Able to provide informed consent for participation in the study Exclusion Criteria: * Cardiac pacemaker, defibrillator, metal implants, or other contraindications for MRI * Use of anabolic or catabolic agents within one year of entry * History of lumbar spine or leg surgery, lumbar radiculopathy, or peripheral neuropathy * BMI \> 35 because obesity compromises positioning on the MR scanner * Pregnancy * For muscle biopsy, history of bleeding disorders or on anticoagulation. Subjects taking nonsteroidal anti- inflammatory agents will be asked to discontinue these medications 7 days prior to muscle biopsy.