Recommendations for consistent treatment of length variants in the human mitochondrial DNA control region

Human mitochondrial DNA (mtDNA) analysis is a valuable forensic tool, useful in cases where the amount of extracted DNA is low or highly degraded. Population databases are used to determine the relative rarity of a particular profile obtained in a forensic case. Rather than full DNA sequence information, sequence profiles are compared to a reference sequence, and the differences from the reference are recorded in forensic databases. A standard method is proposed for characterizing length variants, and examples are described using actual human control region mtDNA profiles. Consistency in alignment and nomenclature avoids inadvertently describing two sequences as different when in fact they are the same.