Spinal muscular atrophy.

The history of the spinal muscular atrophies (SMA) began in the 1890s with Guido Werdnig and Johann Hoffmann. Together, their papers present a rather complete picture of the clinical and pathologic aspects of infantile SMA: onset during the first year of life, occurrence in siblings with normal parents, progressive floppiness and weakness, hand tremor, and death from pneumonia in early childhood. Based on the work of an international collaboration, the following is current nomenclature: SMA type 1 (or I) for onset of symptoms before age 6 months, SMA type 2 (II) for onset between 6 and 18 months, and SMA type 3 (III) for onset after age 18 months. Linkage of autosomal recessive SMA to chromosome 5q11.2-13.3 was reported by Gilliam et al in 1990. A novel gene, whose function remains unknown, called the survival motor neuron gene (SMN) at 5q13, contains deletions in more than 98% of SMA patients. Some patients with atypical forms of SMA have been shown to have mutations in SMN. Because there is no effective therapy for SMA, management consists of preventing or treating the complications of severe weakness, such as restrictive lung disease, poor nutrition, orthopedic deformities, immobility, and psychosocial problems.