Q&A on Spinraza Treatment for Spinal Muscular Atrophy (SMA) Patients. ABOUT SMA. What is spinal muscular atrophy (SMA) and what causes it? SMA is a genetic disorder that presents with weakness of arm and leg muscles as well as breathing difficulties. SMA is caused by mutations in a gene called SMN1 (survival motor neuron 1) that encodes for the …

