Internal Validation of Mitochondrial DNA Control Region Using the Precision ID mtDNA Control Region Panel

Background/Objectives: The sequencing of mitochondrial DNA is a valuable tool in forensic genetics, particularly in cases involving degraded samples or those with low nuclear DNA content. In this study, we performed an internal validation for an NGS-based typing of the mitochondrial DNA control region using the Precision ID mtDNA Control Region Panel on the Ion S5^TM sequencer (Thermo Fisher Scientific, Waltham, MA, USA). This validation enhances the scientific robustness, reliability, and judicial admissibility of the results in forensic cases. Methods: Six parameters were evaluated: minimum read depth, sensitivity, repeatability, concordance with Sanger, reproducibility and heteroplasmy detection employing ten negative controls, nine reference samples, a bone sample, and six experimental mixtures. Libraries were prepared using the Ion Chef^TM system, quantified on the Quantstudio^TM 5 Real-Time PCR, sequenced on the Ion GeneStudio^TM S5, and analyzed with Converge^TM software. Results: In this study, we found that a read depth threshold of 100 reads per position, an optimal concentration of 20 pg/µL, and a detection threshold of heteroplasmies of 20% are appropriate to obtain reliable genetic profiles. This supports the application of this method in forensic casework, in which initial concentrations may be around the optimal concentration exposed here due to the provenience of the samples. Conclusions: The results indicate that the NGS platform is suitable for forensic mtDNA analysis, even under low-template conditions, and offers higher sensitivity compared to Sanger sequencing. However, some limitations were observed in the coverage of specific amplicons, the detections of polymorphisms in homopolymeric regions, and in the detection of low-level heteroplasmies.