SCREEN FOR FRAGILE X MUTATION EXPANSION IN A PRIMATE MODEL

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Fragile X syndrome (FXS), the most common inherited form of mental retardation, arises in individuals with more than 200 CGG repeats in the 5' untranslated region of the fragile X mental retardation 1 (FMR1) gene. In humans, approximately 1 in 260 women is a carrier of the expanded (55 to 200; premutation) CGG repeat. We have identified a rhesus macaque pedigree with 7 subject carriers of an expanded CGG region in the premutation range. Human subject carriers of fragile X premutations express higher levels of FMR1-mRNA, between 2 to 10 fold in blood samples. The increased FMR1 expression can lead to cell toxicity over the years and be the cause of fragile X-associated tremor/ataxia syndrome (FXTAS), a newly described neurodegenerative disease. FXTAS often involves intention tremor, gait ataxia, and dementia, and affects at least 1/3 of males over 50 years of age who carry small CGG-repeat expansions of the FMR1. The neuropathological hallmark of FXTAS is the presence of intranuclear inclusions in neural cells, found in the brains of all individuals examined to date who had suffered from the neurodegenerative disorder. It has also been observed that premutation carriers often express lower levels of fragile X protein (FMRP) that presumably causes social phobia, autistic-like behavior, anxiety, OCD, psychotic traits and learning disability. This rhesus macaque pedigree represents the first animal model that spontaneously carries expanded triplet repeats. By examining the expression of the FMR1 gene and related proteins in this pedigree of non human primates, we expect to make progress in the understanding of the molecular mechanisms leading to the expansion of the CGG repeats in succeeding generations, which in humans leads to impaired neurodevelopment (FXS) as well as identifying factors involved in transcriptional regulation in premutation carriers, which can result in a toxic levels of FMR1-mRNA that are known to predispose to late onset neurodegeneration (FXTAS).