Developing a DNA methylation-based multiplex SNP assay for the identification of semen in mixed stains

Abstract

In forensic investigations, especially in sexual assault cases, biological samples are often mixed stains of different types of body fluids. Highly uneven proportions DNA of male and female makes the detection for stains more difficult. Recently, DNA methylation was proposed to be a promising maker for body fluid identification, and successfully applied to mixed DNA samples. In this study, 7 semen-specific sites were selected from the dataset GSE59509. Methylation-specific polymerase chain reaction and SNaPshot technology were then used to detect the genotype of SNPs in these sites. The results showed that 7-plex SNP typing system was specific in semen samples. In mixed stains, when semen and vaginal fluid in volume ratios of 1:25, the analyses for 7-plex SNP showed that the semen derived genotype could be determined correctly. Meanwhile, unambiguous profiles can be obtained when the input DNA was 0.25 ng. In addition, the 7-plex assay may be useful in the identification of semen even in the degraded samples and complex mixtures.