spinal muscular atrophy type 3
spinal muscular atrophy type 3An autosomal recessive condition (OMIM:253400) characterised by degeneration of the anterior horn cells of the spinal cord, leading to symmetrical 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. SMA3 is a more banal form than SMA1 or SMA2, with onset after 18 months of age; patients can stand, walk and survive into adulthood.
Defects of SMN1, which encodes a survival motor neuron protein, cause spinal muscular atrophy types 1–4.