RESUMO
Mental retardation with both genetic and environmental causes affects about 3% of the population. Etiology cannot be determined in at least 30-50% of cases. The aim of this study was to identify the percentage of minor chromosomal abnormalities in the children with probably genetic mental retardation. Twenty two children, 13 males and 9 females aged 2.5 to 12 years [6.25 +/- 1.34] with mental retardation attending the genetic outpatient clinic; Minoufiya university hospitals and Medical Genetics Center; Ain Shams University; were studied, in the period from August 2004 to December 2006. Children with IQ less than 70 and had at least one of the following additional criteria: prenatal or postnatal growth retardation, dysmorphic facial features, multiple congenital anomalies or neuropsychiatric abnormalities were included in this study. All studied children were subjected to: detailed history and three generation family pedigree, thorough clinical examination, anthropometric measuremants, lQ assessment by Wechsler-revised scale, visual and audiological assessment and imaging studies including brain CT, pelvi-abdominal ultrasonography, and echocardiography when needed. Plasma and urine amino grams and cyto genetic evaluation including routine conventional karyotyping using G-banding technique and chromosome elongation study by synchronization using MTX, FUDR and thymidine release. The degree of mental retardation was assessed according to WHO classification and DSM-IV criteria, 63.6% of then had mild MR, 27.2% had moderate MR and 4.5% had severe MR. The pedigree analysis of studied cases revealed positive consanguinity in 5 cases [22.7%] [1st cousin marriage] and positive family history of mental retardation in 2 cases [9.1%], and maternal history of miscarriages in 7 cases [31.8%]. As regard clinical presentation of studied cases, 13 cases [59%] presented with developmental delay, 6 cases [2 7.3%] presented with dysmorphic facial features and 3 cases [13.6%] presented with epilepsy. Clinical data revealed that, 41% had short stature, 72.7% had dysmorphic facial features, 4.5% had congenital heart disease, 41% had hand and foot anomalies and 45.4% had neurological abnormalities. Accurate conventional cyto genetic study within 450 band resolution [G-banding] revealed that nineteen cases [86.3%] of the studied cases had normal karyotypes and three cases [13.7%] showed the following chromosomal abnormalities: 45 XY, t [13, 14], 46 XX, del [5] and 47 XX,+mar. Chromosome elongation techniques [more than 550 bands]; confirmed these informations. It can be concluded that: chromosomal abnormalities could be one of the etiological causes of mental retardation; accurate conventional cyto genetic study still has its important role in their diagnosis and that chromosome elongation and high resolution chromosome analyses may have a complementary role and should be reserved for diagnosis of undetected cases by conventional cyto genetic studies