This project provides proof-of-concept that nucleic acid degradation can be used in estimating the postmortem interval (PMI) over longer time periods than is possible with traditional methods.
This research clearly demonstrates that DNA and RNA can be extracted from nails, and the process has been validated and implemented into operational forensic casework in determining PMI and human identification. Nucleic acid degradation was determined by using tissues that are less influenced by environmental factors over time, such as fingernails and toenails, as well as bone material. The project developed multiplex PCR assays in order to measure the rate of degradation of messenger RNA (mRNA), ribosomal RNA (rRNA), and DNA so as to estimate the PMI. Using nails placed in different environmental conditions (air, soil, and water), researchers found that nails are protected from various 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. Nails from human cadavers were collected, and the DNA and RNA co-extracted. Researchers amplified nucleic acids from human cadaver nails up to 1,310 days PMI, i.e., 20.295 accumulated degree days (ADD). Researchers found that this co-extraction from bone material (rib samples) was more difficult due to the lower levels of DNA and RNA in bone compared to the nail material. Researchers were unable to amplify mRNA or rRNA from the rib samples; this could be due to the co-extraction method requiring further refinement or that the mRNA and rRNA were too degraded to be amplified in the PCR assays. RNA was extracted from nail samples collected during the same time period. 7 tables, 18 figures, and 22 references
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Date Published: January 1, 2013