The genetic causes of mental retardation in Estonia: fragile X syndrome and creatine transporter defect

The present study was initiated to characterize two most common X-linked MR disorders: fragile X syndrome (FXS) and creatine transporter deficiency in Estonia. Within years 1997 to 2006 in the Department of Genetics of United Laboratories of Tartu University Hospital there were 676 patients (516 children and 160 adults) investigated for FXS. The prevalence of FXS among the MR population in Estonia was 2.7%, which was similar to the results of previously reported studies that were performed on Caucasian males. Furthermore, the overall live-birth prevalence rate of FXS from 1984 to 2005 was 1:27,115. The clinical phenotype of the boys with FXS was similar to previously reported cases. The main clinical feature of the females with FXS premutation was premature ovarian insufficiency or irregular menstruation (43%). In collaboration with Department of Genetics of United Laboratories of Tartu University Hospital, Children’s Clinic of Tartu University Hospital, and Tallinn Children’s Hospital DNA material and phenotype data from 83 Estonian families were collected. From this study group familial XLMR group that consist 49 families where probands in the families were mainly boys were chosen. The prevalence of creatine transporter deficiency among investigated families with suspicion of XLMR was found to be 2 %. In three related brothers and their mother a missense mutation – c.1271G>A (p.Gly424Asp) was identified. This mutation has not been previously reported. The phenotype of patients with creatine transporter defect was somewhat different from published cases and the clinical expression varied widely among affected brothers. In addition, our aim was to evaluate the correlation between clinical features and molecular finding in cases of rare submicroscopic chromosomal aberration, which causes MR in complicated dysmorphic patients. In this study, two patients with submicroscopic copy number variation in chromosomes X and 17q were being described. Uuringus analüüsitakse kahte sagedasemat X-liitelise vaimse arengu mahajäämuse sündroomi – fragiilse X sündroomi (FXS) ja kreatiini transporteri defekti. FXS uuringu teostamisel võeti aluseks 1997-2006 aastal SA Tartu Ülikooli Kliinikumi Ühendlabori geneetikakeskuses teostatud FXS-i positiivsete DNA analüüside tulemused. Sel ajavahemikul oli Eestis FXS uuring teostatud 676 patsiendil (516 lapsel ja 160 täiskasvanul). FXS esinemissageduseks Eesti vaimse arengu mahajäämusega patsientide hulgas oli 2,7%, mis sarnanes esinem