Ability of Muscle Imaging and Motor Function Measure (MFM) to Detect Changes in Disease Progression in Ambulant Spinal Muscular Atrophy Patients Compared to Healthy Volunteers.

Inclusion Criteria: * Male and female subjects, aged \>/= 10 years at screening * For SMA patients: Confirmed clinical diagnosis of 5q-autosomal recessive SMA, ambulant at time of screening, and prefereably without spinal cord fixation Exclusion Criteria: * Previous (3 months or less) or concomitant participation in any other therapeutic trial * Known or suspected cancer * Other chronic disease or inadequate renal, liver, or heart function * Contraindications for MRI scans, including but not limited to: claustrophobia, pacemaker, artifical heart valves, cochlear implants, presence of foreign metal objects in the body, intracranial vascular clips, etc. Any contraindications to MRI found on a standard radiography scan.