PARENTAL ORIGIN OF THE EXTRA CHROMOSOME-18 IN EDWARDS-SYNDROME

Trisomy 18 (Edwards syndrome) is the second most common trisomy in hum an. The parental origin of the additional chromosome leading to meioti c errors is imperative to understand the etiology of trisomy 18. We co mpiled the data on 171 cases (table I) where meiotic error is provided . The paternal meiotic error occurred in 7 % of the cases while in 93 % of the cases nondisjunction took place in the mother, There were 28 cases (16 %) where nondisjunction took place in meiosis I (MI), 53 cas es (31 %) in meiosis II (MII) and in 90 cases (53 %) either the error was postzygotic mitosis or the dysfunctional stages could not be deter mined. The age distribution could be found in 119 cases (table II) and a conclusion could not be drawn as there were only 11 cases where pat ernal nondisjunction was noted.