Adult-onset spinal muscular atrophy in a patient with SOD1 mutation: case report

Amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA) are distinct motor neuron disorders with overlapping molecular mechanisms. ALS involves progressive upper and lower motor neuron degeneration, while SMA primarily affects lower motor neurons. Mutations in SOD1 (superoxide dismutase 1), a well-established cause of familial ALS, have been identified in patients with atypical motor neuron disease phenotypes, suggestive of their broader role in motor neuron dysfunction. A 28-year-old male presented with progressive distal muscle weakness, atrophy, and a steppage gait, without upper motor neuron involvement. Electromyography confirmed chronic motor neuron dysfunction, raising suspicion of SMA. Genetic testing excluded SMN1 deletions but identified a pathogenic SOD1 mutation. Despite this, slow disease progression and phenotype were more consistent with adult-onset SMA type IV than ALS. This case highlights the diagnostic challenges posed by overlapping features of ALS and SMA. The findings emphasize the need for further research into the clinical features associated with SOD1 mutations and their potential contributions to SMA-like presentations, refining our understanding of motor neuron disorders.