Twins with Two Different Fathers Identified by HLA

WE recently reported 1000 cases of disputed paternity in which the HLA typing test proved to be substantially more powerful than the previously used red-cell tests.¹ The remarkable efficacy of HLA typing in paternity determinations is attributable to the fact that all HLA haplotypes are relatively rare in the population. Thus, if a putative father shares a combination of HLA types with a child, it is highly probable that he is in fact the true father. This circumstance of shared rare blood types arises in very few cases with red-cell tests because of the allele frequency distributions in these systems.