Applicability of DNA methylation markers used in age determination in artificial constructed crime scene blood samples

One of the epigenetic mechanisms that has been used in many fields recently is DNA methylation. In forensic research, DNA methylation can be used in tissue/cell type identification, gender determination, age estimation and discrimination of monozygotic twins. In recent years, age estimation panels specific to different body tissues have been developed by various researchers regarding age estimation. The panels developed in these studies are generally tested under different environmental conditions to test the profiling success of samples from the crime scene. Because biological evidence collected in forensic cases often contains trace amounts of DNA that has been stored for a long time and has been degraded due to various environmental factors. In this thesis study, the success of the age estimation panel containing 8 CpG sites developed in the R&D laboratory of Istanbul University-Cerrahpaşa-Forensic Medicine and Forensic Sciences Institute on blood samples taken from 3 people of different ages and samples kept on 3 different surfaces for different periods of time and the success of various environmental factors such as UV and heat. In addition to finding limit ranges, significant concentrations of PCR inhibitors have been determined. The age of all these designed samples was estimated by determining their methylation profiles using the SNaPshot method with the developed age determination model with 8 CpG sites (ELOVL2, ASPA, TOM1L1, C1orf132, RASSF5, FHL2, CCDC102B and cg07082267). According to the results obtained, age estimation analysis was performed on samples stored on different surfaces for up to 6 months. Although age estimation could not be made for one sample due to locus losses observed in 30 minutes of UV exposure, age estimation was made in the other two samples because there was no loss. It was observed that after 60 minutes of exposure to UV, age estimation could not be made except for a single sample, and after 15 minutes of exposure to 95 °C, age estimation could not be made due to locus losses. While age estimation was made at every concentration examined from 4 mM to 100 mM indigo concentration, age estimation could not be made at humic acid concentrations of 125 ng/μL and above. Although results were obtained at a humic acid concentration of 100ng/μl, a reliable result could not be obtained due to the high rate of deviation in age estimation. Considering the data obtained, results can also be obtained from samples kept for 6 months. When we look at the effect of inhibitors, even small concentrations of humic acid have a great effect, while results can be obtained even at high concentrations of indigo. Exposure to 95 °C heat affects age estimation analysis more than UV. It is thought that a more comprehensive study should be conducted in terms of different environmental factors.