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FRAXA

Chr X

fragile site, folic acid type, rare, fra(X)(q27.3) A

Also known as: FMR1

NCBI Gene: 108684022

The FRAXA locus contains a CGG trinucleotide repeat in the 5' regulatory region of the FMR1 gene that encodes fragile X messenger ribonucleoprotein 1. Expansions of this repeat cause fragile X syndrome (the most common inherited cause of intellectual disability and autism spectrum disorder) when fully expanded beyond 200 repeats, and fragile X tremor/ataxia syndrome or premature ovarian insufficiency with intermediate expansions of 55-200 repeats. The condition follows X-linked inheritance with reduced penetrance in females due to X-inactivation, and repeat expansions show a bias toward further expansion during maternal transmission.

GeneReviews ResearchSummary from RefSeq, OMIM

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]

GeneReviews ResearchGenerating clinical summary…

Clinical highlights

Interpreting a novel variant

Curated mechanisms (Gene2Phenotype) include both loss of function and gain of function. Which applies is variant-dependent — do not assume a null variant is, or isn’t, the pathogenic class without checking the specific variant.Curated gene-level mechanism — a prior for triage, not a per-variant call.

Active trials

Pubs (1 yr)

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P/LP submissions

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P/LP missense

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LOEUF

Multiple*

Mechanism· G2P

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GeneReview available — FRAXA