Therapy for spinal muscular atrophy

Spinal muscular atrophy is a term applied to both a specific and common disorder, and to a group of related but individually rare disorders. The specific, common disorder is also known as childhood spinal muscular atrophy, proximal spinal muscular atrophy, and historically has been broken up into several subgroups labeled SMA 1 (Werdnig Hoffmann disease), SMA 2 (intermediate childhood SMA), and SMA 3 (Kugelberg Welander disease). All of these labels refer to a recessively inherited genetic disorder caused by mutation of the survival motor neuron gene, SMN. The group of disorders collectively known as the spinal muscular atrophies (Table 1) is diverse in many respects. Some are well characterized genetically by defined mutations in known genes, some are clearly genetic from their inheritance pattern but as yet involve unknown genes, and others affect single patients in a manner that suggests a genetic etiology that yet remains unproven. Both the specific SMN-related SMA and the broad range of SMA disorders share in common certain clinical features including slow progressive, symmetric and often diffuse weakness caused by degeneration of the primary motor neurons. Symmetric dysfunction and degeneration of spinal and bulbar motor neurons may be a feature of other disorders (Table 2).