Forensic STR Identification of Human Teeth Samples Exposed to Various Acidic and Alkaline Chemical Conditions in the Iraqi Population

Abstract

Mohammad R. Abd Ali Al-Owaidi, Mona N. Al-Terehi, Ali Hmood Al-Saadi, Kazem Zibara.

Forensic odontology has transformed human identification of forensic applications. This study evaluated the effect of various acidic and alkaline chemical solutions on dental DNA STR loci used in human identification. Teeth samples were divided into 3 groups of hydrochloric acid (HCl), nitric acid (HNO3) and sodium hydroxide (NaOH), in comparison to control teeth or blood DNA samples of the same individual. Following DNA extraction, a total of ten STR loci (CSF1PO, FGA, D13S317, D16S539, D21S11, D2S1338, TH01, D18S51, D5S818 and D8S1179) were amplified and sequenced. Results showed that DNA concentrations and purities decreased significantly in HCl and HNO3chemical conditions, but were less affected in NaOH whereas only HNO3showed DNA degradation. In addition, amplification of dental STR loci showed lower size products than their control blood counterparts. Moreover, the number of amplified STR loci in samples exposed to HNO3 and HCl were fewer than those in NaOH. To evaluate STR loci, sequencings analysis was performed to compare STR motif frequency, DNA identity, and gaps between teeth and blood DNA. Results showed that the ratio of tooth/blood STR frequency was significantly different among HNO3, HCl and NaOH (25%, 8.5% and 33.4%, respectively). Moreover, gap percentages were lower in samples exposed to NaOH and HNO3 than HCl (9.8 and 9.3 vs 12.2%).Furthermore, NaOH alkaline solution had higher percent identities of STR loci, between teeth and blood DNA, than HNO3 or HCl acidic conditions (58.7 versus 48.9 and36.8%, respectively). The highest STR identity percentages was found for CSF, D18S5, and D2S1338(64.7, 59.1, and 57.1%; respectively) whereas D5S818 was the lowest (16.9%).The most stable human identifier in the Iraqi population was the CSF locus whereas D5S818 was the least stable. In conclusion, dental DNA STR loci are more sensitive to HNO3 than HCl or NaOH, which affected sequence STR frequency, identity and gap.