[FMR1 PREMUTATION CARRIERS - ARE THEY REALLY ASYMPTOMATIC?]

Fragile X Syndrome (FXS), the most common form of inherited mental retardation, is caused by a trinucleotide repeat expansion (CGG) in the 5'-untranslated region of the Fragile X Mental Retardation 1 (FMR1) gene located at Xq27.3. Patients with fragile X -related mental retardation, carry the full mutation CGG-repeat expansions (>200 CGG repeats), which are generally accompanied by hypermethylation of the promoter region, with the consequent transcriptional silencing of the FMR1 gene and absence of the encoded FMR1 protein (FMRP). Expansion of the CGG triplet number above the normal range (n=5-54) towards the so-called premutation status (n=55-199) is associated with increased risk for Fragile X-Associated Premature Ovarian Insufficiency (FXPOI) in females and Fragile X-Associated Tremor/ Ataxia Syndrome (FXTAS) predominantly in males. In addition, premutation women carriers are at increased risk for learning disabilities, as well as psychologic, endocrine, autoimmune and metabolic disorders. The observation that premutation carriers, both males and females, have increased FMR1 transcript levels, led researchers to suggest a similar molecular pathogenesis in both FXPOI and FXTAS. Two models have been proposed as the culprits of FXTAS and FXPOI: The toxic RNA gain-of-function model and the Repeat Associated Non-AUG initiated (RAN) translation protein toxicity model. The Fragile X Multidisciplinary Center in Sheba Medical Center, at Tel Hashomer includes a team of geneticists, fertility specialists, endocrinologists, psychologists and neurologists who work together in order to provide early detection of FMR1 premutation carriers and offer FMR1 premutation carriers and their families adequate multidisciplinary medical consultation, follow-up and care.