Fragile X syndrome

Fragile X syndrome
Classification and external resources
Location of FMR1 gene
ICD-10Q99.2
ICD-9759.83
OMIM300624
DiseasesDB4973
MedlinePlus001668
eMedicineped/800
MeSHD005600

Fragile X syndrome (FXS) is a genetic syndrome that causes a range of intellectual disabilities as well as unusual physical and behavioural characteristics. Males and females can have FXS but it is more common, and often more serious, in males. It is one of the most common causes of autism and intellectual disability among boys. Individuals with this condition lack an important gene product.

Technical account

Fragile X syndrome occurs as a result of a mutation of the FMR1 gene on the X chromosome. This causes an increase an increase in the number of CGG repeats in the 5' untranslated region of FMR1.

In unaffected individuals, the FMR1 gene contains 5–44 repeats of the CGG codon, most commonly 29 or 30 repeats. Between 45 and 54 repeats is considered a "grey zone". Between 55 and 200 repeats in length is described as a premutation allele. Individuals with fragile X syndrome have a full mutation of the FMR1 allele, with over 200 repeats of the CGG codon.

In these individuals with a repeat expansion greater than 200, there is methylation of the CGG repeat expansion and FMR1 promoter. This silences the FMR1 gene, and its end-product is not made.

References

  1. 1 2 CDC (2022-06-03). "What is Fragile X Syndrome (FXS)? | CDC". Centers for Disease Control and Prevention. Retrieved 2023-01-11.
  2. 1 2 McLennan Y. et al 2011 (2011). "Fragile X Syndrome". Current Genomics. 12 (3): 216–224. doi:10.2174/138920211795677886. PMC 3137006. PMID 22043169.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  3. ↑ Budimirovic D.B. & Kaufmann W.E. 2011 (2011). "What can we learn about autism from studying fragile X syndrome?". Dev Neurosci. 33 (5): 379–94. doi:10.1159/000330213. PMC 3254037. PMID 21893949. Retrieved 26 January 2012.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  4. 1 2 Santoro M.R. et al 2012. Molecular mechanisms of Fragile X Syndrome: a twenty-year perspective. Annu. Rev. Pathol. Mech. Dis. 7: 219–45. Archived 2016-05-23 at the Wayback Machine
  5. 1 2 Maddalena A. et al 2001. (2001). "Technical Standards and Guidelines for Fragile X: the first of a series of disease-specific supplements to the Standards and Guidelines for Clinical Genetics Laboratories of the American College of Medical Genetics". Genetics in Medicine. 3 (3): 200–205. doi:10.1097/00125817-200105000-00010. PMC 3110344. PMID 11388762.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  6. ↑ Nolin S.L. et al 2003 (2003). "Expansion of the fragile X CGG repeat in females with premutation or intermediate alleles". American Journal of Human Genetics. 72 (2): 454–64. doi:10.1086/367713. PMC 379237. PMID 12529854.{{cite journal}}: CS1 maint: numeric names: authors list (link)