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SMN2 (Survival of motor neurone 2)

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What is MOCA?
MOCA FAQ...
Human Uniqueness Compared to "Great Apes": 
Likely Difference
MOCA Domain: 
Genetics
MOCA Topic Authors: 
Majesta O'Bleness
James Sikela

Survival of motor neuron 2 (SMN2) is a human specific copy of SMN1 which has a mutation leading to the loss of exon 7 in SMN2 transcripts. The function of SMN2 is not understood as loss is not associated with spinal muscular atrophy, an autosomal recessive neuromuscular disorder that leads to loss and dysfunction of motor neurons. However, higher copy number of SMN2 in conjunction with loss of SMN1 is associated with less severe forms of the disease indicating that SMN2 can supplement some of the SMN1 function. SMN2 copies are found within a 500kb 15q13 inverted duplication region that is highly prone to rearrangements and deletions. Humans have 1-3 more copies of SMN2 than any other primate, although the significance of these copies is unknown.

Genetics Topic Attributes

Gene symbols follow the HUGO Gene Nomenclature Committee standard.

Gene Symbol:
SMN2 (SMN2: survival of motor neuron 2, centromeric)
Type of Human-Specific Changes:
Copy Number Changes
Related MOCA Topics
Timing

Timing of Appearance of the Difference in the Hominin Lineage.

For this entry assume that

  • the common ancestor of humans and old world monkeys was 25000 thousand (25 million) years ago
  • the common ancestor of humans and chimpanzees was 6000 thousand (6 million) years ago
  • the emergence of the genus Homo was 2000 thousand (2 million) years ago
  • the common ancestor of modern humans was 100 thousand years ago

 

Definite Appearance: 
6000 Thousand Years
References: 

Amara A, Adala L, Ben Charfeddine I, Mamaï O, Mili A, Lazreg TB, H'mida D, Amri F, Salem N, Boughammura L, Saad A, Gribaa M. Correlation of SMN2, NAIP, p44, H4F5 and Occludin genes copy number with spinal muscular atrophy phenotype in Tunisian patients. Eur J Paediatr Neurol. 2011 Aug 5. [Epub ahead of print] PMID:21821450

 

Itan Y, Bryson K, Thomas MG. (2010) Detecting gene duplications in the human lineage. Ann Hum Genet. 74(6):555-65. PMID: 20946257

 

Sudmant PH, Kitzman JO, Antonacci F, Alkan C, Malig M, Tsalenko A, Sampas N, Bruhn L, Shendure J; 1000 Genomes Project, Eichler EE. Diversity of human copy number variation and multicopy genes. Science. 2010 Oct 29;330(6004):641-6. PMID:21030649



Arkblad E, Tulinius M, Kroksmark AK, Henricsson M, Darin N. (2009) A population-based study of genotypic and phenotypic variability in children with spinal muscular atrophy. Acta Paediatr. 98(5):865-72. PMID: 19154529

 

Fortna A, Kim Y, MacLaren E, Marshall K, Hahn G, Meltesen L, Brenton M, Hink R, Burgers S, Hernandez-Boussard T, Karimpour-Fard A, Glueck D, McGavran L, Berry R, Pollack J, Sikela JM. (2004) Lineage-specific gene duplication and loss in human and great ape evolution. PLoS Biol 2(7):E207. PMID: 15252450
 

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