Quantitation of human mitochondrial DNA and whole mtGenomes sequencing of fingernail/hair shaft samples

The analysis of mitochondrial DNA (mtDNA) is suitable for fingernail/hair shaft samples in forensic science. A successful mtDNA forensic analysis depends on the quantity and quality of the mtDNA. The application of massively parallel sequence techniques to the analysis of mtDNA has the potential to improve the recovery of genetic information from difficult forensic specimens and to increase the discrimination potential of mtDNA by capturing and comparing full mtGenomes. In this study, we constructed mtDNA-specific standard curves using real-time PCR. The 105-base pair target sequence facilitates the amplification of degraded DNA and is minimally homologous to non-human mtDNA. The results indicated that the assay enables the absolute quantification of down to 10 copies of mtDNA and provides a dynamic range of eight orders of magnitude. Whole mtGenome sequencing experiments demonstrated that as few as 2 000 mtDNA copies resulted in a successful full region amplification and sequencing. Moreover, the frequency of point heteroplasmy from one donor showed that hairs from the same donor have been found to differ within and among themselves and from other tissues, which could impact the interpretation of the results obtained in a forensic investigation.