Paternity exclusion using 18 genetic systems in 2124 cases in four South African population groups.

Using 18 different blood group systems, 2,124 cases of doubtful paternity, unevenly distributed among four different population groups--South African Negroes (Xhosas) 645 (30%); South African Caucasians 264 (13%); Cape Coloureds (non-Malay) 1,156 (54%), and Cape Malays 59 (3%)--were analysed. Tests for red cell antigen, plasma protein, red cell enzyme and HLA polymorphisms were done on all subjects. The overall exclusion rate was 38,23%, i.e. 812 of the 2,124 men were not biological fathers of the children ascribed to them. The capability of the individual systems to exclude a man from specific paternity was also evaluated. The polymorphic HLA system was the most useful and alone--depending on the particular population group--excluded between 93.5% and 97.8% of falsely accused men. The proportion of men excluded also varied between different population groups using the different systems, e.g. the Rhesus system alone excluded 43.9% of South African Caucasian non-fathers and only 14% of the Xhosa non-fathers. This is a reflection of the gene frequencies within a particular population. The analysis showed that the genetic systems tested in this laboratory were extremely efficient in providing evidence in proof of non-paternity.