FRAXE - fragile site, folic acid type, rare, fra(X)(q28) E Gene

This biological region is found near the 5' regulatory region of the AF4/FMR2 family member 2 (AFF2) gene on the q arm of the X chromosome. This region is a rare folate-sensitive fragile site and contains a highly polymorphic (CCG)n repeat, with most normal alleles containing less than 25 triplet repeat units. Expansion of the CCG/CGG repeat to copy numbers greater than 200 has been observed and causes fragility at this site. Hypermethylation of a CpG island near the expanded allele can lead to transcriptional silencing of the AFF2 gene. Intellectual disability has been observed in some individuals with the expanded allele, but a wide range of clinical manifestations have also been reported. [provided by RefSeq, Dec 2016]