X-linked spinal muscular atrophy type 2

X-linked spinal muscular atrophy type 2 (SMAX2, XLSMA), also known as arthrogryposis multiplex congenita X-linked type 1 (AMCX1), is a rare neurological disorder involving death of motor neurons in the anterior horn of spinal cord resulting in generalised muscle wasting (atrophy). The disease is caused by a mutation in UBA1 gene and is passed in a X-linked recessive manner by carrier mothers to affected sons.[1][2]

X-linked spinal muscular atrophy type 2
Other namesSpinal muscular atrophy with arthrogryposis
This condition is inherited in an X-linked recessive manner

Affected babies have general muscle weakness, weak cry and floppy limbs; consequently, the condition is usually apparent at or even before birth. Symptoms resemble the more severe forms of the more common spinal muscular atrophy (SMA); however, SMAX2 is caused by a different genetic defect and only genetic testing can correctly identify the disease.

The disorder is usually fatal in infancy or early childhood due to progressive respiratory failure, although survival into teenage years have been reported.[3] As with many genetic disorders, there is no known cure to SMAX2. Appropriate palliative care may be able to increase quality of life and extend lifespan.

See also


  1. Ramser, J.; Ahearn, M. E.; Lenski, C.; Yariz, K. O.; Hellebrand, H.; Von Rhein, M.; Clark, R. D.; Schmutzler, R. K.; Lichtner, P.; Hoffman, E. P.; Meindl, A.; Baumbach-Reardon, L. (2008). "Rare Missense and Synonymous Variants in UBE1 Are Associated with X-Linked Infantile Spinal Muscular Atrophy". The American Journal of Human Genetics. 82 (1): 188–193. doi:10.1016/j.ajhg.2007.09.009. PMC 2253959. PMID 18179898.
  2. Dressman, D.; Ahearn, M. E.; Yariz, K. O.; Basterrecha, H.; Martínez, F.; Palau, F.; Barmada, M. M.; Clark, R. D.; Meindl, A.; Wirth, B.; Hoffman, E. P.; Baumbach-Reardon, L. (2007). "X-linked infantile spinal muscular atrophy: Clinical definition and molecular mapping". Genetics in Medicine. 9 (1): 52–60. doi:10.1097/GIM.0b013e31802d8353. PMID 17224690.
  3. Kobayashi, H.; Baumbach, L.; Matise, T. C.; Schiavi, A.; Greenberg, F.; Hoffman, E. (1995). "A gene for a severe lethal form of X-linked arthrogryposis (X-linked infantile spinal muscular atrophy) maps to human chromosome Xp11.3–q11.2". Human Molecular Genetics. 4 (7): 1213–1216. doi:10.1093/hmg/4.7.1213. PMID 8528211.

Further reading

  • Dlamini, N.; Josifova, D. J.; Paine, S. M. L.; Wraige, E.; Pitt, M.; Murphy, A. J.; King, A.; Buk, S.; Smith, F.; Abbs, S.; Sewry, C.; Jacques, T. S.; Jungbluth, H. (2013). "Clinical and neuropathological features of X-linked spinal muscular atrophy (SMAX2) associated with a novel mutation in the UBA1 gene". Neuromuscular Disorders. 23 (5): 391–398. doi:10.1016/j.nmd.2013.02.001. PMID 23518311.
  • Baumbach-Reardon L.; Sacharow S.; Ahearn M. E. "Spinal Muscular Atrophy, X-Linked Infantile." 30 Oct 2008 [Updated 13 Sep 2012]. In: Pagon R. A.; Adam M. P.; Ardinger H. H.; et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2014. Available from: www.ncbi.nlm.nih.gov/books/NBK2594.
External resources

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