FRAXA

This biological region is found near the 5' regulatory region of the Fragile X messenger ribonucleoprotein 1 (FMR1) gene on the q arm of chromosome X, and contains a CGG trinucleotide repeat with AGG repeat interruptions. This region is highly polymorphic, and alleles with varying numbers of repeats have been observed. Alleles with repeat sizes of 5-44 tend to show mitotic and meiotic stability, while those with about 45-54 repeats are at a higher risk for instability, but show no phenotype. Individuals with alleles that are expanded to 55-200 repeats are at risk for a number of disorders, including fragile X-associated tremor/ataxia syndrome (FXTAS), fragile X-associated premature ovarian insufficiency (FXPOI), and adult-onset neurodegenerative disorder. These alleles tend to be unstable upon transmission, with a bias for expansion during maternal transmission. Alleles containing more than 200 CGG repeats are considered full mutation alleles, and are associated with fragile X syndrome. These alleles display hypermethylation of the FMR1 promoter region. It has been shown that the presence of AGG interruptions reduce the risk of repeat instability. [provided by RefSeq, Apr 2022]