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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed December 2009

What is the official name of the SMN2 gene?

The official name of this gene is “survival of motor neuron 2, centromeric.”

SMN2 is the gene's official symbol. The SMN2 gene is also known by other names, listed below.

What is the normal function of the SMN2 gene?

The SMN2 gene provides instructions for making the survival motor neuron (SMN) protein. The SMN protein is found throughout the body, with high levels in the spinal cord. This protein is particularly important for the maintenance of specialized nerve cells called motor neurons, which are located in the spinal cord and the part of the brain that is connected to the spinal cord (the brainstem). Motor neurons control muscle movements.

Several different versions of the SMN protein are produced from the SMN2 gene, but only one version (called isoform d) is full size and fully functional. The other versions are smaller and easily broken down. The full-size protein made from the SMN2 gene is identical to the protein made from a similar gene called SMN1; however, much less full-size SMN protein is produced from the SMN2 gene compared with the SMN1 gene.

In cells, the SMN protein plays an important role in processing molecules called messenger RNA (mRNA), which serve as genetic blueprints for making proteins. Messenger RNA begins as a rough draft (pre-mRNA) and goes through several processing steps to become a final, mature form. The SMN protein helps to assemble the cellular machinery needed to process pre-mRNA. The SMN protein may have additional functions in nerve cells. Research findings indicate that the SMN protein is important for the development of specialized outgrowths from nerve cells called dendrites and axons. Dendrites and axons are required for the transmission of impulses from nerve to nerve and from nerves to muscles.

How are changes in the SMN2 gene related to health conditions?

spinal muscular atrophy - course of condition modified by extra copies of the SMN2 gene

Typically, people have two copies of the SMN1 gene and up to two copies of the SMN2 gene in each cell. In people with spinal muscular atrophy, both copies of the SMN1 gene are altered or missing. In some cases, individuals have three or more copies of the SMN2 gene. In those with spinal muscular atrophy, additional copies of the SMN2 gene are associated with a milder course of the disorder.

When both copies of the SMN1 gene are altered or missing, little or no SMN protein is produced from this gene. Extra SMN2 genes can help replace some of the SMN protein that is lost due to mutations in the SMN1 genes. The symptoms of spinal muscular atrophy still occur, however, because only a small amount of the full-size SMN protein is produced from the SMN2 genes. In general, symptoms are less severe and begin later in life in affected individuals with three or more copies of the SMN2 gene compared with those who have two copies of this gene.

Where is the SMN2 gene located?

Cytogenetic Location: 5q13.2

Molecular Location on chromosome 5: base pairs 70,049,523 to 70,077,595

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The SMN2 gene is located on the long (q) arm of chromosome 5 at position 13.2.

The SMN2 gene is located on the long (q) arm of chromosome 5 at position 13.2.

More precisely, the SMN2 gene is located from base pair 70,049,523 to base pair 70,077,595 on chromosome 5.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about SMN2?

You and your healthcare professional may find the following resources about SMN2 helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the SMN2 gene or gene products?

  • BCD541
  • C-BCD541
  • centromeric SMN
  • SMNC

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding SMN2?

atrophy ; axons ; brainstem ; cell ; gene ; gene conversion ; messenger RNA ; motor ; motor neuron ; mRNA ; neuron ; protein ; RNA

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Boda B, Mas C, Giudicelli C, Nepote V, Guimiot F, Levacher B, Zvara A, Santha M, LeGall I, Simonneau M. Survival motor neuron SMN1 and SMN2 gene promoters: identical sequences and differential expression in neurons and non-neuronal cells. Eur J Hum Genet. 2004 Sep;12(9):729-37. (
  • Briese M, Esmaeili B, Sattelle DB. Is spinal muscular atrophy the result of defects in motor neuron processes? Bioessays. 2005 Sep;27(9):946-57. Review. (
  • Cartegni L, Hastings ML, Calarco JA, de Stanchina E, Krainer AR. Determinants of exon 7 splicing in the spinal muscular atrophy genes, SMN1 and SMN2. Am J Hum Genet. 2006 Jan;78(1):63-77. Epub 2005 Nov 16. (
  • Corcia P, Camu W, Halimi JM, Vourc'h P, Antar C, Vedrine S, Giraudeau B, de Toffol B, Andres CR; French ALS Study Group. SMN1 gene, but not SMN2, is a risk factor for sporadic ALS. Neurology. 2006 Oct 10;67(7):1147-50. Epub 2006 Aug 23. (
  • Corcia P, Camu W, Praline J, Gordon PH, Vourch P, Andres C. The importance of the SMN genes in the genetics of sporadic ALS. Amyotroph Lateral Scler. 2009 Oct-Dec;10(5-6):436-40. doi: 10.3109/17482960902759162. (
  • Gubitz AK, Feng W, Dreyfuss G. The SMN complex. Exp Cell Res. 2004 May 15;296(1):51-6. Review. (
  • Kolb SJ, Battle DJ, Dreyfuss G. Molecular functions of the SMN complex. J Child Neurol. 2007 Aug;22(8):990-4. Review. (
  • Mailman MD, Heinz JW, Papp AC, Snyder PJ, Sedra MS, Wirth B, Burghes AH, Prior TW. Molecular analysis of spinal muscular atrophy and modification of the phenotype by SMN2. Genet Med. 2002 Jan-Feb;4(1):20-6. doi: 10.1097/00125817-200201000-00004. (
  • NCBI Gene (
  • Ogino S, Wilson RB. Genetic testing and risk assessment for spinal muscular atrophy (SMA). Hum Genet. 2002 Dec;111(6):477-500. Epub 2002 Oct 3. Review. (
  • Ogino S, Wilson RB. Spinal muscular atrophy: molecular genetics and diagnostics. Expert Rev Mol Diagn. 2004 Jan;4(1):15-29. Review. (
  • Prior TW, Swoboda KJ, Scott HD, Hejmanowski AQ. Homozygous SMN1 deletions in unaffected family members and modification of the phenotype by SMN2. Am J Med Genet A. 2004 Oct 15;130A(3):307-10. (
  • Veldink JH, Kalmijn S, Van der Hout AH, Lemmink HH, Groeneveld GJ, Lummen C, Scheffer H, Wokke JH, Van den Berg LH. SMN genotypes producing less SMN protein increase susceptibility to and severity of sporadic ALS. Neurology. 2005 Sep 27;65(6):820-5. Epub 2005 Aug 10. (
  • Wirth B, Brichta L, Schrank B, Lochmüller H, Blick S, Baasner A, Heller R. Mildly affected patients with spinal muscular atrophy are partially protected by an increased SMN2 copy number. Hum Genet. 2006 May;119(4):422-8. Epub 2006 Mar 1. (
  • Wirth B. Spinal muscular atrophy: state-of-the-art and therapeutic perspectives. Amyotroph Lateral Scler Other Motor Neuron Disord. 2002 Jun;3(2):87-95. Review. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: December 2009
Published: February 8, 2016