ABSTRACT
Mental retardation [MR] is a common problem in the world especially in the developing countries. Nearly 2-3% of total population have IQ below 70 but only 0.3% of them have severe mental retardation. The purpose of this study is to evaluate the etiologic factors of mental retardation. In a retrospective study, we collected 160 cases referring to the pediatric neurologic out patient of Imam Khomeini Hospital with the chief complaint of mental retardation between 1996-2000, and documented their IQ with the help of Ravon test. The causes of MR were divided into pre/ peri / postnatal and unknown ones. The causes were prenatal in 24[15%], perinatal in 82[51.3%], postnatal in 31[19.4%] and unknown in 23[14.4%] of the cases. In the first group [prenatal causes] fragile X syndrome was the most frequent one 5 cases [3/1%]. But hypoxic- ischemic encephalopathy 31 cases [19.37%], neonatal infection 25 cases [15. 61%], hyperbilirubinemia 16cases [10%] and RDS 12 cases [7.5%] were the most frequent causes in the perinatal group, and epilepsy 16 cases [10%], C.N.S. infection 5 cases [3.1%], trauma 5 [3.1%] were the most frequent causes among the postnatal groups. As the result, we conclude that in the majority of our patients, the cause of MR were perinatal accidents. Secondly perinatal causes were the most important and common causes [51.2%]. Moreover, it appears that these factors were preventable and preventive medicine could be an effective measure in the reducing the incidence of MR