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Zebra of the Week: Spinal muscular atrophy (SMA)
Spinal muscular atrophy (SMA) is a group of inherited neuromuscular disorders characterized by degeneration of motor neurons in the spinal cord and brainstem, leading to progressive muscle weakness and atrophy. Core clinical features include hypotonia, impaired motor milestones, and difficulty with walking, sitting, and head control; respiratory and swallowing dysfunction often develop as the disease advances. SMA types 1–4 are caused by pathogenic variants in the survival motor neuron 1 (SMN1) gene and follow an autosomal recessive inheritance pattern. Disease severity is influenced by the number of SMN2 gene copies, which partially compensate for SMN1 loss. Additional rare forms include SMA with progressive myoclonic epilepsy, SMA with respiratory distress type 1, and X-linked infantile SMA. Diagnosis of SMA is suspected by symptoms and confirmed by genetic testing.
FDA recently approved Itvisma (onasemnogene abeparvovec-brve) for the treatment of SMA in adult and pediatric patients ≥2 years of age with a confirmed SMN1 gene mutation.
Source:
(Accessed 2025, December 5). NIH: Genetic and Rare Diseases Information Center. Spinal muscular atrophy. https://rarediseases.info.nih.gov/diseases/7674/spinal-muscular-atrophy