关键词：人类遗骸；验尸间隔（PMI）；脱氧核酸（DNA）；医药
摘 要：Estimating the post-mortem interval (PMI) is difficult due to the many factors that influence the decomposition process. Tissues such as nails, teeth and bones are more resilient to environmental factors. Measuring the rate of degradation of nucleic acids in these tissues could provide a method for estimating the PMI for longer time intervals, from days and weeks, through to months and years. These time intervals have not been studied before in a systematic manner using human tissues. Our initial focus has been on nails. Nails are hard tissues, relatively easy to sample and until now, have been under-utilized as a tissue that has forensic value. We have investigated the stability of nucleic acids in nails to determine if both DNA and RNA can be co-extracted in levels suitable for PCR analysis. Furthermore, multiple nail samples can be taken from the same individual so that measuring changes in nucleic acid degradation can be undertaken where there are a minimal number of external variables so that the nucleic acid degradation is a more likely representation of the PMI. Using different methods for extracting DNA and RNA from nails, we have found that by modifying the Promega DNA IQ method, both DNA and RNA are efficiently extracted. This modified method has been implemented into operational forensic casework at ESR and nails are now being utilized in more human identification cases. We have developed multiplex PCR assays to measure the rate of degradation of messenger RNA (mRNA), ribosomal RNA (rRNA) and DNA. Using nails placed in different environmental conditions (air, soil and water), we have found that nails are protected from other environmental factors and that nucleic acids (both DNA and RNA) can be amplified from samples left submerged in water or placed in soil for 120 days (1043 accumulated degree days). Nails from human cadavers have been collected, and the DNA and RNA co-extracted. Using our multiplex PCR assays, we have shown that DNA and RNA can be co-extracted from cadaver nails with a PMI up to 20,925 ADDs. Using statistical analyses, some of the nucleic acid amplified fragments (from DNA and mRNA) look promising to use for deriving a statistical model for estimating the PMI.