| Summary: | Body fluids such as blood are amongst the most important biological evidence recovered from crime scenes. Identification of the donor can be achieved through STR profiling; however, extracting additional information regarding the tissue type or the donor’s physical appearance such as age could prove very useful in police investigations. Firstly, the performance of existing tissue-specific mRNA-based systems was assessed via collaborative exercises. All proposed methods have shown to be highly sensitive; however, issues regarding markers’ specificity, especially for the vaginal detection, were observed. Analysing complex casework samples revealed the need for interpretation guidelines and the use of a scoring system when implementing mRNA profiling in casework. It was understood that developing DNA-based testing would overcome the limitations of existing methods so the main aim of this study was to evaluate the applicability of DNA methylation profiling in forensics. Using three approaches various tissue-specific differentially methylated CpG sites in 18 different loci were evaluated by analysing various forensically relevant body fluids and tissues. As a result, a set of suitable blood- and semen-specific markers were validated using aged and mock casework samples; however, the identification of other tissues like saliva, vaginal fluid and menstrual blood seemed to be challenging. Regarding age prediction, a set of age-associated CpG sites were selected from genome-wide DNA methylation studies and the correlation of their blood methylation levels with age was assessed on two sequencing platforms. Using a subset of 16 CpG sites and taking advantage of artificial neural networks’ capabilities, age could be accurately predicted in 1,156 blood samples (mean error of 4.1 years). The applicability of the proposed prediction model was also tested by means of next generation sequencing. Although further research is required prior to implementing these results in casework, it can be concluded that epigenetics could shed light on the proposed forensic applications.
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