FRAXA screening in Brazilian institutionalized individuals with nonspecific severe mental retardation

Individuals with mental disabilities are a heterogeneous group, mainly when we consider the etiology of mental retardation (MR). Recent advances in mo lecular genetics techniques have enabled us to unveil more about the molecu lar basis of several genetic syndromes associated with MR. In this study, w e surveyed 85 institutionalized individuals with severe MR, 38 males and 47 females, by two molecular techniques, to detect CGG amplifications in the FMR1 gene. No FRAXA mutations were found in the FMR1 gene, reinforcing the low prevalence of Fragile X syndrome among institutionalized individuals wi th severe MR. We considered the PCR protocol used adequate for screening ma les with mental retardation of unknown etiology. The use of the Southern bl ot is still necessary for the decisive diagnosis of the Fragile X syndrome. To exclude chromosomal abnormalities associated with MR as a possible caus e of the phenotype in these individuals, G-banded chromosome analyst was pe rformed in all patients and 7.3% of chromosomal aberrations were found. Our results are similar to those reported previously and point to the necessit y of expanding the molecular investigation toward other causes of MR, such as subtle chromosomal rearrangements, as suggested recent by a combination of fluorescence in situ hybridization (FISH) and PCR studies.