ABSTRACT
The present study deals with investigation of the biochemical abnormality and the metabolic disorders which may be the cause or contribute significantly to the cause of mental retardation [MR]. The study included 203 mentally retarded children who were subjected to qualitative chemical tests on urine for the detection of certain defects in amino acid and carbohydrate metabolism. Thin layer chromatographic detection of specific amino acids in plasma and urine, and the quantitative determination of urea, creatinine, ammonia and uric acid in plasma, argininosuccinase and argininase enzyme activities in erythrocytes; mucopolysaccharides and creatinine in urine were also investigated. It was found that in 92 patient, mental retardation is accompanied by metabolic disorders. These comprise disorders in amino acid transport [10.6%] urea cycle abnormalities [17.4%], generalized amino acid urea [10.8%], miscellaneous aminoacidopathies [25%] and defects in carbohydrate metabolism [26.1%]. The plasma levels of urea, uric acid and creatinine in patients with disorders in aminoacid transport were unchanged indicating normal kidney function. Patients with urea cycle abnormalities showed deficiency in different enzymes controlling urea formation with elevation in plasma ammonia and decrease in plasma urea. Patient with carbohydrate metabolism disorders showed increased urinary mucopolysaccharides. These metabolic disorders were discussed on the basis of the findings obtained and the genetic defect that led to the respective metabolic disorder. According to results of this work, it is highly recommended to carry out genetic counselling in calculating the possibilities for recurrence risk of hereditary disorders and in detecting any metabolic abnormality to prevent the onset of mental retardation. Early detection of these cases and evaluation of specific treatment will be valuable for the management of these cases