Comparison of hard tissues that are useful for DNA analysis in forensic autopsy
Graphical abstract
Introduction
Forensic autopsy is an important process for personal identification and investigation of cause of death. In recent years in Japan, the number of corpses handled by police has been increasing steadily, being 169,047 in 2013 and thus 1.24 times the number handled in 2004. This has resulted in an increase in the number of autopsies, having increased 1.68-fold from 4969 in 2004 to 8356 in 2013. Against this background, legislation to promote the investigation of causes of death has been introduced.
DNA testing at autopsy is a highly effective approach for personal identification [1], [2], [3]. DNA testing is used when antemortem records are missing and corpses are in a poor state of preservation. DNA identification becomes essential at times of mass disasters. When putrefaction has occurred after a corpse has remained undiscovered for a long period, DNA testing using soft tissue becomes difficult. However, hard tissues such as tooth and bone tend to remain better preserved, even after long periods have elapsed. In comparison with soft tissues, hard tissues are resistant to autolysis and putrefaction resulting from environmental exposure. For this reason, bones, teeth and nails may be the only source of DNA in many forensic cases [4], [5], [6], [7]. Therefore, DNA extraction from hard tissue is employed when investigating a variety of cases involving crimes and disasters.
A number of reports have indicated that DNA testing using teeth is very useful and practical [8], [9], [10], [11], [12]. However, we often encounter situations in which teeth cannot be used for DNA testing, for example in aged individuals who are edentulous or young infants in whom tooth eruption has not yet occurred. There are many situations in which DNA testing using teeth cannot be performed, such as burnout of teeth in charred corpses, mixing of DNA due to root canal treatment, or paucity of DNA in the remaining root. In particular, tooth desorption or loss is frequently observed in corpses that have remained undiscovered for long periods or in corpses of elderly individuals, or infants less than 6 months old in which tooth eruption has not yet occurred. Thus, cases in which tooth samples cannot be collected for DNA analysis are not uncommon.
Here we examined methods for collection and extraction of DNA from hard tissues that can be used an alternative to teeth when DNA testing using teeth is not possible.
Section snippets
Materials and methods
Cleaning of samples, DNA extraction and amplification were conducted following the generally accepted safety and DNA typing guidelines.
Results
Samples of hard tissue, i.e. teeth, nails, skull, and rib, were obtained from 42 forensic autopsy cases (male 30, female 12; time elapsed from death: 2 days to 2 years). Skull and rib samples were obtained from all cases, but tooth samples were obtained from 37 cases and nail samples from 39.
In this study, we examined 13 out of 42 cases for which DNA was extracted from all four hard tissues. Sample profiles are listed in Table 1.
The average DNA concentration of each sample per microliter was:
Discussion
Samples of teeth, nails, skull and rib were collected as examples of hard tissue. We compared the DNA concentrations for 13 cases in which DNA had been extracted from all four of the hard tissues, and verified that such hard tissues can be an alternative material to teeth for use in DNA testing at the time of autopsy.
The average DNA concentration in tooth samples was 48.5 ng/μl. STR analysis of 13 samples was possible for all of the loci using four types of hard tissue. Therefore, it was
Conflict of interest
The authors have declared no conflict of interest.
Acknowledgements
We would like to thank the members of the Department of Disaster Relief Medicine/Dentistry, Division of Forensic Dentistry, Graduate School of Kanagawa Dental University, for their helpful comments.
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