spinal muscular atrophy type 2(redirected from muscular atrophy, spinal, infantile chronic form)
spinal muscular atrophy type 2An autosomal recessive condition (OMIM:253500) 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. SMA2 is a more banal form than SMA1, with onset between age 6 and 18 months; patients do not reach the developmental milestone of standing, but survive into adulthood.
Defects of SMN1, which encodes a survival motor neuron protein, cause spinal muscular atrophy types 1–4.