Abstract
The incomplete development of mental capacities and associated behavioural abnormalities are referred to as mental retardation. It is single largest neuropsychiatric disorder in every civilised society af- fecting 2.5-3.0% of the total population. Chromo- somal abnormalities are the important cause of mental retardation. Cytogenetic investigations were carried out on 143 mentally subnormal individuals that were re- ferred to the Centre for Genetic Disorders, Guru Nanak Dev University, Amritsar, India, during 1996 to 2002. These cases were referred mainly as suspected Down syndrome, delayed milestones, mental retardation, etc. The age group of the patients ranged from 1 month to 18 years. Interestingly, maximum number of patients i.e., 58/143 (40.5%) were the firstborns and the aver- age maternal age was 27.6 years. Free trisomy 21 was found to be the most frequent autosomal aberration, both amongst males and females (45.4% males, 18.8% females). It was seen in 92/143 (64.3%) cases while translocations were seen in 2.7% cases. The latter in- cluded 45,XY,+t(13;14), 46,XY,+t(14;21), 45,XX,+t (14;21) and 46,XX,+t(14;21) karyotypes.
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