Integrated Detection Techniques for Forensic DNA and DNA Methylation Markers

DNA genetic markers have always played important roles in individual identification, kinship analysis, ancestry inference and phenotype characterization in the field of forensic medicine. DNA methylation has unique advantages in biological age inference, body fluid identification and prediction of phenotypes. The majority of current studies independently examine DNA and DNA methylation markers using various workflows, and they use various analytical procedures to interpret the biological information these two markers present. Integrated methods detect DNA and DNA methylation markers simultaneously through a single experimental workflow using the same preparation of sample. Therefore, they can effectively reduce consumption of time and cost, streamline experimental procedures, and preserve valuable DNA samples taken from crime scenes. In this paper, the integrated detection approaches of DNA and DNA methylation markers on different detection platforms were reviewed. In order to convert methylation modifications to detectable forms, several options were available for pretreatment of genomic DNA, including digestion with methylation-sensitive restriction enzyme, affinity enrichment of methylated fragments, conversion of methylated or unmethylated cytosine. Multiplexed primers can be designed for DNA markers and converted DNA methylation markers for co-amplification. The schemes of using capillary electrophoresis platform for integrated detection add the pretreatment of genomic DNA on the basis of detecting DNA genetic markers. DNA and DNA methylation markers are then integrated by co- amplification. But the limited number of fluorescent options available and the length of amplicons restrict the type and quantity of markers that can be integrated into a panel. Pyrophosphate sequencing also supports integrated detection of DNA and DNA methylation markers. On this platform, due to the conversion of unmethylated cytosine to thymine after treatment with bisulfite, the methylation level of CpG site can be directly calculated using the peak height ratio of cytosine bases and thymine bases. Therefore, the methylation levels and SNP typing can be simultaneously obtained. However, due to the limited read length of sequencing, the detection of markers with longer amplicons is restricted. It is not conducive to fully interpret the complete information of the target sequence. Next-generation sequencing also supports integrated detection of DNA and DNA methylation markers. A preliminary experimental process including DNA extraction, pretreatment of genomic DNA, co-preparation of DNA and DNA methylation library and co-sequencing, has been formed based on the next-generation sequencing platform. It confirmed the feasibility of next-generation sequencing technology for integrated detection of DNA and DNA methylation markers. In field of biomedicine, various integrated detection schemes and corresponding data analysis approaches of DNA and DNA genetic markers developed based on the above detection process. Co-analysis can simultaneously obtain the genomic genetic and epigenetic information through a single analytic process. These schemes suggest that next-generation sequencing may be an effective method for achieving more accurate and highly integrated detection, helping to explore the potential for application in forensic biological samples. We finally explore the impact of interactions between sites and different pretreatment methods on the integrated detection of DNA and DNA methylation markers, and also propose the challenge of applying third- generation sequencing for integrated detection in forensic samples.