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FRAXA SCREENING IN BRAZILIAN INSTITUTIONALIZED INDIVIDUALS WITH NONSPECIFIC SEVERE MENTAL RETARDATION
Affilliation
Universidade do Estado do Rio de Janeiro. Departamento de Biologia Celular e Genética. Rio de Janeiro, RJ, Brasil
Fundação Oswaldo Cruz.Instituto Fernandes Figueira. Departamento de Genética Médica. Rio de Janeiro, RJ, Brasil
Universidade do Estado do Rio de Janeiro. Departamento de Biologia Celular e Genética. Rio de Janeiro, RJ, Brasil
Fundação Oswaldo Cruz.Instituto Fernandes Figueira. Departamento de Genética Médica. Rio de Janeiro, RJ, Brasil
Universidade do Estado do Rio de Janeiro. Departamento de Biologia Celular e Genética. Rio de Janeiro, RJ, Brasil
Abstract
Individuals with mental disabilities are a heterogeneous group, mainly when we consider the etiology of mental
retardation (MR). Recent advances in molecular genetics techniques have enabled us to unveil more about
the molecular basis of several genetic syndromes associated with MR. In this study, we 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 with severe MR. We considered the
PCR protocol used adequate for screening males with mental retardation of unknown etiology. The use of the
Southern blot is still necessary for the decisive diagnosis of the Fragile X syndrome. To exclude chromosomal
abnormalities associated with MR as a possible cause of the phenotype in these individuals, G-banded chromosome
analysis was performed in all patients and 7.3% of chromosomal aberrations were found. Our results
are similar to those reported previously and point to the necessity 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.
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