Heteroplasmy in mtDNA and the weight of evidence in forensic mtDNA analysis: a case report

Mitochondrial DNA (mtDNA) sequencing has been validated as a useful tool fo r forensic analysis. However, there are several aspects of the analysis whi ch need to be considered in order to evaluate the value of the evidence. On e of these aspects is related to heteroplasmy which is the state when two o r more mtDNA populations occur in a single individual, cell or mitochondrio n. In this report a case is described where the mtDNA profile of the blood sample of a raped woman was compared with the mtDNA profile of a single hai r found in the suspect's car. The results obtained show differences in sequ ence between different portions of the hair and the victim's sequence. Thes e differences are related to various heteroplasmy events. The concordance b etween the hair sample and the potential source (victim) of this sample is questionable and the strength of the evidence depends on how the sequence i nformation is interpreted by the expert. The discussion of the results emph asises the necessity to evaluate heteroplasmic events in routine forensic w ork.