spinal muscular atrophy type 4
spinal muscular atrophy type 4An autosomal recessive condition (OMIM:271150) characterised by symmetrical proximal muscle weakness and atrophy. Disease severity is inversely proportional to the copy number of SMN2, a copy gene which predominantly produces exon 7-skipped transcripts and only low amount of full-length transcripts that encode for a protein identical to SMN1. SMA4 is the most banal SMA; it is of adult onset with normally long-term survival.
Defects of SMN1, which encodes a survival motor neuron protein, cause spinal muscular atrophy types 1–4.
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