Fragile X syndrome is the most common cause of hereditary mental retardation (MR) in humans. It is the second reason of hereditary and non hereditary MR after Down syndrome. The aim of the study is to estimate the prevalance of the fragile X and other chromosomal aberrations by cytogenetic screening in 72 patients with MR and language disorders.

Fragile X can be diagnosed cytogenetically by searching metaphases chromosomes in the culture of lymphocytes using basal medium without folic acid. In this study, 72 cases with MR who were sent to our laboratory for cytogenetic search in term of fragile X. At all of the cases, the chromosomes from the metaphases that obtained by either standart methods or basal medium without folic acid for fragile X were evaluated. For each case at least 100 metaphases were evaluated for fragile X.

The majority of the 72 cases sent from Firat University Medical Center Neurology were passed from clinical observation. The first two complications of the cases were MR and perservative speech. Seven of the all cases (72 cases) were diagnosed as fragile X syndrome cytogenetically. In conclusion, the incidence of fragile X was consistent with the result of the fragile screening studies made in the societies with MR. It has been concluded that cases must have been selected after a good clinical observation for cytogenetic analyses.