CHROMOSOME-21 DISOMY IN THE SPERMATOZOA OF THE FATHERS OF CHILDREN WITH TRISOMY-21, IN A POPULATION WITH A HIGH PREVALENCE OF DOWN-SYNDROME- INCREASED INCIDENCE IN CASES OF PATERNAL ORIGIN

Between April 1991 and December 1994, epidemiological studies detected a population with a high prevalence of Down syndrome in El Valles, Sp ain. Parallel double studies were carried out to determine the parenta l and the meiotic origins of the trisomy 21, by use of DNA polymorphis ms, and to establish the incidence of disomy 21 in the spermatozoa of the fathers of affected children, by use of multicolor FISH. Results s how that the overall incidence of chromosome 21 disomy in the fathers of affected children was not significantly different from that in the control population (0.31% vs. 0.37%). However, analysis of individual data demonstrates that two cases (DP-4 and DP-5) with significant incr eases of disomy 21 (0.75% and 0.78% vs. 0.37%) correspond to the fathe rs of the two individuals with Down syndrome of paternal origin. DP-5 also had a significant increase of sex-chromosome disomies (0.69% vs. 0.37%) and of diploid spermatozoa (1.13% vs. 0.24%).