Objectives: The fragile X syndrome (FXS) is the most frequent cause of inherited mental retardation (MR). It is caused by the progressive expansion of (CGG)n trinucleotide repeats located in the promoter region of the (Fragile X mental retardation 1 gene) FMR1 gene at Xq27.3. The aim of the study is to estimate the prevalance of the FXS and other chromosomal aberrations by cytogenetic and molecular analysis in patients with MR and language disorders.

Material and Method: 72 cases with MR who were sent to our laboratory for molecular and cytogenetic search in term of fragile X. The lymphocyte culture was carried out according to standard methods. DNA extraction was done using whole blood DNA extraction kit (Bangalore Genei, Bangalore). This was followed by bisulphite treatment and PCR amplification.

Results: Chromosome abnormality was found in 12 cases (16.7%). 7 cases (9.7%) were detected fragile X positive in molecular analysis. The mutations were detected such a full mutation and abnormal methylation in (4.1%) and a premutation carrier (5.5%). We concluded that chromosomal studies in mentally retarded patients help in accurate diagnosis and proper prognosis followed by genetic counseling and management rehabilitation.

Conclusion: Due to recent molecular advances, our understanding of the perplexing genetic issues surrounding fragile X syndrome has grown and diagnostic techniques have become both reliable and readily available. ©2007, Fırat University, Medical Faculty