Molecular study of time dependent changes in DNA stability in soil buried skeletal residues

In the past years, many publications about identification and sex-determination of dry human bones by means of DNA analysis have been published. However, few studies exist that investigate the potential use of DNA technique to determine the postmortem interval (PMI). In the present study we analyzed the rate of increasingly smaller fragments of chromosomal DNA and PMI. We examined DNA degradation in human bones with postmortem intervals ranging between 1 and more than 200 years that had been kept under comparable conditions concerning weather and soil. Following bone separation into the three different zones of interest of inner/middle/outer segments the quantity of total DNA was determined in each region. Subsequently, the degree of DNA fragmentation was estimated by searching for PCR products of defined size (150, 507 and 763 bp) with primers of the human-specific multicopy beta-actin-gene. Concerning DNA quantity we detected a significant correlation between the zone of interest and the amount of DNA. However, there was no correlation between the amount of DNA and PMI. In contrast to this, analyzing DNA using PCR showed a significant inverse correlation between fragment length and PMI. Thus, postmortem DNA degradation into increasingly smaller fragments reveals a time-dependent process. It has the potential to be used as a predictor of PMI in human bone findings, provided that environmental conditions are known.