Cytogenetic diagnosis of fragile X syndrome: Study of 305 suspected cases in Saudi Arabia

Background: Fragile X syndrome is the most common cause of inherited mental retardation. Patients with fragile X syndrome show variable mental disabil ity, typical long and narrow facial appearance with large ears and prominen t fontanelle and frequent macro-orchidism. It is generally associated with a fragile site at Xq 27.3, which can be observed in the metaphase chromosom e following selective culture conditions. At the molecular level, the fragi le X syndrome is associated with an amplification of CGG repeat sequence of the FMR1 gene. The prevalence estimates are reported as one per 1500 males and one per 2500 females. Estimated prevalence rates of fragile X syndrome in different ethnic groups range from 0.4-0.8 per 1000 in males and 0.2-0. 6 per 1000 in females. In this study, we have determined the frequency of f ragile X-positive cases in 305 preselected patients. Materials and Methods: Three hundred and five Saudi patients with mental re tardation/developmental delay/clinical suspicion of fragile X syndrome were screened for fragile X chromosome by cytogenetic methods. The majority of patients (95.59%) screened were under the age of 20 years. Results: Two hundred and ninety-nine patients (98.03%) were in the category of mild to moderate mental retardation. Twenty-four males (7.86%) and two females (0.65%) were found to express fragile X site at q27.3. The frequenc y of fragile X-positive cells in males ranged between 7% and 58% (mean 26 /- 13.11), while in the females it was between 14% and 21% (mean 12.5 +/- 3 5), respectively. Conclusion: The frequency of fragile X positive cases found in this study i s similar to other reports of fragile X syndrome in preselected patients.