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Survival of motor neuron 2 (SMN2) is a gene that encodes the SMN protein (full and truncated) in humans.[1][2]


The SMN2 gene is part of a 500 kb inverted duplication on chromosome 5q13. This duplicated region contains at least four genes and repetitive elements which make it prone to rearrangements and deletions. The repetitiveness and complexity of the sequence have also caused difficulty in determining the organization of this genomic region. The telomeric (SMN1) and centromeric (SMN2) copies of this gene are nearly identical and encode the same protein. The critical sequence difference between the two genes is a single nucleotide in exon 7, which is thought to be an exon splice enhancer. The nucleotide substitution in SMN2 results in around 80-90% of its transcripts to be a truncated, unstable protein of no biological function (Δ7SMN) and only 10-20% of its transcripts being full-length protein (fl-SMN).[citation needed]

Note that the nine exons of both the telomeric and centromeric copies are designated historically as exon 1, 2a, 2b, and 3–8. It is thought that gene conversion events may involve the two genes, leading to varying copy numbers of each gene.[2]

Clinical significance

Mechanisms of regulation of SMN2 gene expression in SMA[3]

While mutations in the telomeric copy are associated with spinal muscular atrophy, mutations in this gene, the centromeric copy, do not lead to disease.[citation needed]

This gene may be a modifier of disease caused by mutation in the telomeric copy.[citation needed]


  1. Lefebvre S, Bürglen L, Reboullet S, Clermont O, Burlet P, Viollet L, Benichou B, Cruaud C, Millasseau P, Zeviani M (January 1995). "Identification and characterization of a spinal muscular atrophy-determining gene". Cell. 80 (1): 155–65. doi:10.1016/0092-8674(95)90460-3. PMID 7813012. S2CID 14291056.
  2. 2.0 2.1 "Entrez Gene: SMN2 survival of motor neuron 2, centromeric". Archived from the original on 2023-11-29. Retrieved 2024-02-06.
  3. Ahmad, Saif; Bhatia, Kanchan; Kannan, Annapoorna; Gangwani, Laxman (2016). "Molecular Mechanisms of Neurodegeneration in Spinal Muscular Atrophy". Journal of Experimental Neuroscience. 10: 39–49. doi:10.4137/JEN.S33122. ISSN 1179-0695.

Further reading

This article incorporates text from the United States National Library of Medicine, which is in the public domain.