familial spinal muscular atrophy

spinal mus·cu·lar at·ro·phy type I

the early infantile form, characterized by profound muscle weakness and wasting with onset at or shortly after birth; death occurs usually before 2 years of age. Autosomal recessive inheritance, caused by mutation in the survival motor neuron gene (SMN1) on 5q. About half of affected patients are also missing both homologues of a neighboring gene that encodes neuronal apoptosis inhibitory protein (NAIP), the loss of which is thought to influence the severity of the disease.

familial spinal muscular atrophy

spinal muscular atrophy type 1

An autosomal recessive condition (OMIM:253300) 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 amounts of full-length transcripts that encode for a protein identical to SMN1. Only about 4% of SMA patients bear one SMN1 copy with an intragenic mutation. SMA1 is the severest form of the SMAs, with onset before age 6 months. Infants never achieve the ability to sit.

Molecular pathology
Defects of SMN1, which encodes a survival motor neuron protein, cause spinal muscular atrophy types 1–4.
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