cytogenetic stidy of 366 affected children with down’s syndrome in iran

down’s syndrome, or 21 trisomy, is the most common autosomal abnormality, with incidence of 1 per 815 live births in iran. worldwide reports indicate that about 95% are regular trisomy, or nondisjunction, 1% are mosaic and 4% due to translocation. however, these values show a geographical variation. a cytogenetic study of down's syndrome, or trismoy 21, was carried out on 366 cases (202 males and 164 females) during a 10 year period (1974-1983) in akbarabadi maternity hospital in tehran. the lymphocyte chromosomes were stained with g-banding technique. free trisomy 21 constituted 93.44%, d/g translocation 3.55% and g/g translocation 3.01%. reciprocal translocation and mosaic were not observed. the values are compared with other studies in some of the countries of the countries of the region.