Detection of the fragile X syndrome protein for the evaluation of FMR1 intermediate alleles

Molecular screening programs in mentally retarded individuals have been per formed in several populations worldwide. One finding has been an excess of FMR1 intermediate alleles in a population with learning difficulties. Howev er, other published reports with similar. characteristics did not corrobora te those previous results. In order to contribute additional data from our population, we studied 563 patients affected with nonspecific mental retard ation (MRX) that did not present a CGG expansion in the FMR1 gene and 208 i ndividuals as a control population. Forty MRX patients presented alleles wi thin the intermediate range. Among them, one case showed a pattern of expre ssion of the FMR1 protein (FMRP) concordant with a fragile X syndrome case with an intermediate allele/full mutation mosaicism, although it was not de tected by Southern blot analysis. Statistical analysis was performed again Showing no statistically significant difference regarding the intermediate allele frequency in the MRX and control populations. This finding is in agr eement with the hypothesis that the incidence of intermediate FMR1 alleles in MRX populations does not seem to be higher than in control populations, and it emphasizes the importance of FMRP detection as a diagnostic tool for fragile X syndrome.