BACKGROUND: Fragile X syndrome (FXS), an X-linked disorder, is the most common cause of inherited mental retardation. This is caused by a trinucleotide CGG repeat expansion (>200) on the fragile X mental retardation 1 gene (FMR1) becoming methylated leading to a deficiency or absence of the FMR1 protein. Determining FXS prevalence in the mentally retarded individuals in the west of Iran was the aim of this study.

METHODS: 200 patients with moderate mental retardation who were clinically suspicious to FXS were screened using cytogenetic and molecular methods. Blood samples were collected and cultured in the specific culture media. The G-Banding method was used for karyotyping and DNA sequencing performed for verifying the results of the cytogenetic tests.

RESULTS: 16 patients (8%) were found to have fragile X syndrome. The results showed that there is no significant association between the fragile X syndrome and economic status and place of residence, however, the relationship between fragile X syndrome and mental retardation in the family history is significant.

CONCLUSION: The frequency of FXS was similar to other reports in the preselected patients. For diagnosis of FXS, chromosome analysis must be accompanied by molecular studies.