Sequencing of mtDNA in Shed Hairs: A Retrospective Analysis of Material from Forensic Cases and a Pre-Screening Method

In crime scene investigations, shed hairs are one of the most frequently found types of biological evidence material. DNA analysis of hair can be of great significance in forensic investigations, and the sequencing of the hypervariable regions I (HVI) and II (HVII) of the mitochondrial genome has become a useful tool in this field. This paper describes a retrospective evaluation of the potential of sequence analysis of mitochondrial DNA. We examined evidentiary hair and reference samples obtained from 25 criminal investigations conducted over a ten year period and determined the number of matches and exclusions between samples in the investigation. In total, the study includes the results of 129 samples obtained between 1999 and 2008. Analysis resulted in high quality sequence data from most of the evidentiary hairs, allowing comparison to reference samples. On the basis of matches between mitochondrial DNA sequences from evidentiary hairs and those from reference samples, inclusions were obtained in 16 of the 25 cases (64%). Thus, sequencing of mitochondrial DNA was informative in many cases in this data set. In addition, we conducted an initial evaluation of a strategy for estimating the mitochondrial DNA and nuclear DNA contents of plucked and shed hair samples. The strategy is based on staining both the nuclear DNA and the mitochondria, and may be useful when trying to identify an optimal DNA profiling approach for a given hair sample.