Evaluation of mental retardation - Part 1: Etiologic classification of 4659 patients with mental retardation or multiple congenital abnormality and mental retardation

Patients with multiple congenital abnormalities and mental retardation are the most frequent patient group who are referred to a genetic clinic. Specific diagnosis for these patients will provide a better understanding of the possible reasons of pathogenesis, thereby providing more true information to families on recurrence risk, prognosis, possible treatment options and prenatal diagnosis. With the aim of finding out the etiology of the genetic diseases, 4659 patients who were classified into mental retardation or multiple congenital anomaly and mental retardation (MR or MCA/MR) group who were referred to Istanbul University, Departments of Medical Genetics of Cerrahpasa Medical Faculty and Istanbul Medical Faculty in between 1985 and 2005 were analyzed retrospectively and a two step study was generated: first step involved the etiologic classification of MR or MCA/MR group and the second evaluation of the factors that help in finding out the etiologies such as age at first observation, number and periods of observations and completion of laboratory tests. In the first part of the study, etiologic classification of the patients with MR or MCA/MR who were referred to genetic clinics of the two medical faculty of Istanbul University were mentioned. 2847 patients have had an etiological diagnosis (61.10%): from these patients, 1541 out of them had a chromosomal abnormality (33.07%), 555 were known single gene mutations (11.91%), 20 were recognized syndromes (00.42%), 567 were sequences (12.16%), 6 were associations (00.12%), 29 had spectrums (00.62%), 98 had structural abnormality of CNS (2.10%), and finally, 31 suffered from prematurity and its complications, toxic drugs, infections and hypoxic ischemic encephalopathy. This study will be the one of the biggest studies in Turkey and also around the world, evaluating the most frequent patient group referred to genetic clinics: MCA or MR.