An Assessment of the Effect of X-ray Radiation on DNA Marker Profiles Obtained from Human Teeth

X-ray radiation is known to destroy cells and damage DNA, yet human remains from forensic anthropology cases are routinely exposed to X-ray radiation as part of the documentation and evidence collection process. If X-ray radiation significantly impacts the quality of DNA extracted from human remains in forensic cases, then the validity of a resulting genetic profile is called into question. To better understand how X-ray radiation affects DNA profiles, specifically profiles consisting of short tandem repeat (STR) markers, this study followed standard forensic X-ray and genetic profiling protocols to obtain DNA profiles on individual molar teeth, before and after they were exposed to a single X-ray dosage event. The results of the study demonstrate that X-ray radiation did indeed affect DNA profiles, in two ways. First, the total number of DNA markers recovered pre-and post-X-ray radiation decreased significantly between the pre- (control) and post-(experimental) irradiation. Second, the overall amount of DNA per genetic marker recovered was significantly reduced, as measured by Relative Fluorescence Units (RFUs). Interestingly, contrary to expectations, the DNA markers recovered did not exhibit significant shortened fragments lengths post- irradiation, otherwise known as “allelic stutter.” Thus, it seems that X-ray exposure tended to damage DNA marker variants to such an extent that DNA markers were completely unrecoverable post-irradiation, rather than simply damaged to a point of producing allelic stutter. Importantly, X-ray radiation altered DNA marker profiles of individual cases before and after X-ray radiation. The post-radiation sample exhibited a significant amount of “allelic dropout,” leading to a condition known as “false homozygosity,” when one only DNA variant for a given locus is represented in a genetic profile instead of the two different variants that may actually be found in the sample. These results indicate further research is required to understand the stochastic effects of X-ray irradiation on DNA, and suggest that forensic samples undergo DNA analysis prior to exposure to X-ray radiation