Spinal muscular atrophy with progressive myoclonic epilepsy: report of new cases and review of the literature.

Spinal muscular atrophy (SMA) is a clinically and genetically heterogeneous disease characterised by loss of motor function and muscle atrophy due to anterior horn cell degeneration. The most common variant is chromosome 5-linked proximal SMA, ranging in severity from congenital onset and infantile death to onset in adult life. Genetically separate variants with different distribution of weakness and/or additional features such as central nervous system involvement have been described.