ABO genotyping of suspects from sperm DNA isolated from postcoital samples in sex crimes

In sexual assaults against women, one key to identifying the suspect is ABO phenotyping or the typing of other polymorphic markers of the seminal fluid in the victim's vagina. However, ABO phenotyping is frequently unsuccessful, since mixtures of fluids cannot be separated to be subjected to conventional methods for the detection of antibody or antigen material. We therefore studied ABO blood group genotyping of sperm DNA isolated from contaminating vaginal fluid by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Seminal samples of genotypes OO, AO, BO and AB were experimentally mixed with vaginal fluid (OO, AO, BO and AB), and were successfully separated and genotyped by this method. In practice, we also separated and genotyped the seminal DNA of suspects from contaminated postcoital vaginal fluid obtained in 4 sexual assaults. These forensic samples were easily separated and completely genotyped. This reliable ABO genotyping method by PCR-RFLP, using separated sperm DNA, should be of value in forensic identification in sexual assaults.