SMN2 (Survival of motor neurone 2)

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Human Uniqueness Compared to "Great Apes": 
Likely Difference
MOCA Domain: 
MOCA Topic Authors: 

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.


Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Definite Appearance: 
6,000 thousand years ago
Genetics Topic Attributes
Gene symbols follow the HUGO Gene Nomenclature Committee standard.
Gene Symbol Type of Human-Specific Changes
SMN2 Copy Number Changes


  1. Correlation of SMN2, NAIP, p44, H4F5 and Occludin genes copy number with spinal muscular atrophy phenotype in Tunisian patients., Amara, Abdelbasset, Adala Labiba, Ben Charfeddine Ilhem, Mamaï Ons, Mili Amira, Ben Lazreg Taheni, H'mida Dorra, Amri Fathi, Salem Najla, Boughammura Lamia, et al. , Eur J Paediatr Neurol, 03/2012, Volume 16, Issue 2, p.167-74, (2012)
  2. Detecting gene duplications in the human lineage., Itan, Yuval, Bryson Kevin, and Thomas Mark G. , Ann Hum Genet, 2010 Nov, Volume 74, Issue 6, p.555-65, (2010)
  3. Diversity of human copy number variation and multicopy genes., Sudmant, Peter H., Kitzman Jacob O., Antonacci Francesca, Alkan Can, Malig Maika, Tsalenko Anya, Sampas Nick, Bruhn Laurakay, Shendure Jay, and Eichler Evan E. , Science, 10/2010, Volume 330, Issue 6004, p.641-6, (2010)
  4. A population-based study of genotypic and phenotypic variability in children with spinal muscular atrophy., Arkblad, Eva, Tulinius Már, Kroksmark Anna-Karin, Henricsson Mirja, and Darin Niklas , Acta Paediatr, 05/2009, Volume 98, Issue 5, p.865-72, (2009)
  5. Lineage-specific gene duplication and loss in human and great ape evolution., Fortna, A., Kim Y., MacLaren E., Marshall K., Hahn G., Meltesen L., Brenton M., Hink R., Burgers S., Hernandez-Boussard T., et al. , PLoS Biol, 07/2004, Volume 2, Issue 7, p.E207, (2004)