Sex identification of normal persons and sex reverse cases from bloodstains using FISH and PCR

Sex identification of dry blood is of crucial importance in forensic medicine.

Sixty normal (with matching phenotypic and genotypic sex) persons (36 males and 24 females), and 7 cases of sex reverse, i.e., persons with one genotypic sex and ambiguous or external genitalia of the opposite sex (3 phenotypic females with Swyer syndrome and the 46,XY karyotype, and 4 phenotypic Klinefelter-like males with the 46,XX karyotype) were subjected to sex identification by FISH and PCR using bloodstains.

The FISH technique using an X/Y cocktail probe (DXZI & DYZI, Oncor) has identified the sex correctly in 91.69% of interphase nuclei of the 36 males of the study, and in 92.29% of cells of the 24 females and incorrectly identified the 3 phenotypic females with Swyer syndrome as males and the 4 Klinefelter-like males as females. The 60 normal individuals in the study were correctly typed to their phenotypic sex by the 2 PCR methods used, i.e., the single PCR using the amelogenin sequence specific for the X and Y chromosomes and the multiplex PCR using SRY gene (male-specific) and the AR gene (X-specific). Out of the 7 sex reverse cases, one Klinefelter-like male was incorrectly identified by PCR as female due to the absence of amplification of the SRY gene and the amelogenin male-specific 788 bp fragment.

The present study demonstrates that both FISH and PCR techniques are fast, easy to perform, reliable and efficient for sex identification but PCR is more accurate. It also emphasises that the sex identified is the genotypic sex which does not necessarily correspond to the phenotypic one and if evidences at the scene of crime indicate opposite sex of the accused, persons with sex reverse have to be ruled out using different X- and Y-specific probes and PCR.