This non-drug, single center, 24-week, longitudinal study in ambulant spinal muscular atrophy (SMA) patients and in age- and gender-matched healthy volunteers will assess the detection of disease progression by magnetic resonance imaging (MRI) and the Muscle Function Measure (MFM) test.

Each participant will be evaluated in three testing sessions: at baseline, at Week 12 and at Week 24. Both patients and volunteers will undergo MRI scans. Patients will additionally undergo testing of motor function and have blood samples taken for Survival of the Motor Neuron (SMN) genes, proteins and mRNA analysis.

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.

Ambulant patients with spinal muscular atrophy (SMA) and age- and gender-matched healthy volunteers.