Identification of burnt human remains: DNA quantity and quality assessment

Identifying human remains in the aftermath of a disaster is a crucial yet complex task. This thesis delves into the challenges and methods associated with the medico- legal investigation of disaster victim identification. This research explores the different techniques employed depending on the condition of the remains, with a particular focus on the essential role of forensic DNA analysis through short tandem repeat (STR) and mitochondrial DNA (mtDNA) profiling, especially in cases involving burnt bodies. The first objective was to investigate recent studies that examine the correlation between the macroscopic (colorimetric) characteristics of burnt bones and teeth and the efficacy of forensic DNA genotyping. It was seen that the Commission of Illumination (CIE) L*a*b color space values, and in particular the a* coordinate, can be used as thresholds to build a decision tree to help the operator in the selection of the most promising samples for STR typing or mtDNA sequencing by discriminating between light (LB) /dark brown (DB) discolored bone and black (BL) /gray (G) /white (W) bone. The first group was suitable for STR analysis in 76% (LB) and 58% (DB) of tested samples, while the mtDNA sequencing success rate was 90% (LB) and 89% (DB). On the other hand, BL, G, and W bone samples resulted in non-viable for DNA analysis. The a* coordinate also appeared to be the best predictor of nuclear and mtDNA yield in burnt teeth up to 300°C, while exposure to temperatures ≥600°C (roughly corresponding to BL/G/W discoloration) was associated with complete DNA degradation. The aim of these studies was to identify selection procedures for human remains that can optimize the probability of identification. With this in mind, a recent study investigating an alternative source of genetic material, the fibrocartilage of the intervertebral discs, using a standard extraction protocol that did not require pulverization and demineralization as for bone/tooth samples, was also taken into consideration. It was shown that cartilage yielded nuclear DNA of enough quantity and quality to enable straightforward DNA profiling and identification in 9 different severely burnt human remains from casework, including car fires, uncontrolled explosions, and detonations.