spinal muscular atrophy

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spinal muscular atrophy (SMA) n. a hereditary condition in which cells of the spinal cord die and the muscles in the arms and legs become progressively weaker. Eventually the respiratory muscles are affected and death usually results from respiratory infection. There are three types of SMA (types 1, 2, and 3), based on the severity of symptoms and age of onset; type 1, which is evident soon after birth, is the most acute and aggressive form (see Werdnig-Hoffmann disease).

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