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.
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.
While mutations in the telomeric copy are associated with spinal muscular atrophy, mutations in this gene, the centromeric copy, do not lead to disease. This gene may be a modifier of disease caused by mutation in the telomeric copy.
The full-length SMN protein encoded by this gene, accounting for approximately 10-20% of its total transcripts, localizes to both the cytoplasm and the nucleus. Within the nucleus, the protein localizes to subnuclear bodies called gems which are found near coiled bodies containing high concentrations of small ribonucleoproteins (snRNPs). This protein forms heteromeric complexes with proteins such as SIP1 and GEMIN4, and also interacts with several proteins known to be involved in the biogenesis of snRNPs, such as hnRNP U protein and the small nucleolar RNA binding protein. Four transcript variants encoding distinct isoforms have been described.
Corcia P, Camu W, Praline J, Gordon PH, Vourch P, Andres C (2009). "The importance of the SMN genes in the genetics of sporadic ALS". Amyotrophic Lateral Sclerosis. 10 (5-6): 436–40. doi:10.3109/17482960902759162. PMID19922137.
Jedrzejowska M, Milewski M, Zimowski J, Borkowska J, Kostera-Pruszczyk A, Sielska D, Jurek M, Hausmanowa-Petrusewicz I (2009). "Phenotype modifiers of spinal muscular atrophy: the number of SMN2 gene copies, deletion in the NAIP gene and probably gender influence the course of the disease". Acta Biochimica Polonica. 56 (1): 103–8. PMID19287802.
Arkblad E, Tulinius M, Kroksmark AK, Henricsson M, Darin N (May 2009). "A population-based study of genotypic and phenotypic variability in children with spinal muscular atrophy". Acta Paediatrica. 98 (5): 865–72. doi:10.1111/j.1651-2227.2008.01201.x. PMID19154529.
Farooq F, Balabanian S, Liu X, Holcik M, MacKenzie A (November 2009). "p38 Mitogen-activated protein kinase stabilizes SMN mRNA through RNA binding protein HuR". Human Molecular Genetics. 18 (21): 4035–45. doi:10.1093/hmg/ddp352. PMID19648294.
Hasanzad M, Golkar Z, Kariminejad R, Hadavi V, Almadani N, Afroozan F, Salahshurifar I, Shafeghati Y, Kahrizi K, Najmabadi H (February 2009). "Deletions in the survival motor neuron gene in Iranian patients with spinal muscular atrophy". Annals of the Academy of Medicine, Singapore. 38 (2): 139–41. PMID19271042.
Song F, Qu YJ, Zou LP, Wang LW, Long MJ, Wang X, Yang YL, Chen Q, Wang H, Jin YW (December 2008). "[Molecular analysis of survival motor neuron gene in 338 suspicious children patients with spinal muscular atrophy]". Zhonghua Er Ke Za Zhi = Chinese Journal of Pediatrics. 46 (12): 919–23. PMID19134255.
Irimura S, Kitamura K, Kato N, Saiki K, Takeuchi A, Matsuo M, Nishio H, Lee MJ (2009). "HnRNP C1/C2 may regulate exon 7 splicing in the spinal muscular atrophy gene SMN1". The Kobe Journal of Medical Sciences. 54 (5): E227–36. PMID19628962.
Cogulu O, Durmaz B, Pehlivan S, Alpman A, Ozkinay F (June 2009). "Evaluation of the SMN and NAIP genes in a family: homozygous deletion of the SMN2 gene in the fetus and outcome of the pregnancy". Genetic Testing and Molecular Biomarkers. 13 (3): 287–8. doi:10.1089/gtmb.2008.0139. PMID19397406.