Postmortem miscoding lesions in sequence analysis of human ancient mitochondrial DNA.

Genetic miscoding lesions can cause inaccuracies during the interpretation of ancient DNA sequence data. In this study, genetic miscoding lesions were identified and assessed by cloning and direct sequencing of degraded, amplified mitochondrial DNA (mtDNA) extracted from human remains. Forty-two individuals, comprising nine collections from five geographic locations, were analyzed for the presence of DNA damage that can affect the generation of a correct mtDNA profile. In agreement with previous studies, high levels (56.5% of all damage sites) of proposed hydrolytic damage products were observed. Among these, type 2 transitions (cytosine --> thymine or guanine --> adenine), which are highly indicative of hydrolytic deamination, were observed in 50% of all misincorporations that occurred. In addition to hydrolytic damage products, oxidative damage products were also observed in this study and were responsible for approximately 43.5% of all misincorporations. This level of misincorporation is in contrast to previous studies characterizing miscoding lesions from the analysis of bone and teeth, where few to no oxidative damage products were observed. Of all the oxidative damage products found in this study, type 2 transversions (cytosine --> adenine/guanine --> thymine or cytosine --> guanine/guanine --> cytosine), which are commonly formed through the generation of 8-hydroxyguanine, accounted for 30.3% of all genetic miscoding lesions observed. This study identifies the previously unreported presence of oxidative DNA damage and proposes that damage to degraded DNA templates is highly specific in type, correlating with the geographic location and the taphonomic conditions of the depositional environment from which the remains are recovered.