Paternity investigation among known false trios: ABO, Rh, MNSs, Kell, Duffy, Kidd, and HLA systems

This paternity study was performed with trios in which the putative father was not the biological father (NBF), in order to evaluate adjustment of genetic markers employed to disclose non biological fathers for the population, and the biological meaning of likelihood of paternity in casework. All 923 generated trios had ABO, Rh, MNS, Kell and HLA systems tested; 372 of them also had Duffy and Kidd systems tested. The most powerful exclusion system was HLA, followed, in this order, by ABO, Rh, Duffy, MNSs, Kidd, and Kell. Taking into account the Indian/black/white historical miscegenation background in the population, an improvement in the performance of red blood cells as disclosers of non biological fathers could be achieved, if particular additional sera were used. In the group tested with seven different systems, direct exclusions were observed in 90.31%, and they were single system exclusions in 26.61%. In order to avoid the remote possibility of mutation, it is suggested that the number of used systems be increased. Indirect exclusions were verified in 8.87% and only 0.81% of NBF were not excluded at all. In this last group, probabilities of paternity were calculated and two values greater than 95% were obtained. To be able to accomplish the "visum et repertum" duty and to assist the court, the expert should equally emphasize: a) the probability of paternity of the alleged father and the possibility of finding an unexcluded NBF; b) the actual performance of systems used to uncover NBF, together with the probabilities of paternity of those who were not discovered; c) the previous referenced trend of probabilities of paternity of true and of non-biological fathers to cluster in distinct class intervals of likelihood of paternity.