A 1-year forensic evaluation of DNA degradation and STR typing in embalmed human tissues: Muscle, brain, liver, and...

Postmortem perfusion is a procedure which provides in-vivo fixation of the human body and prevents organ and tissue decomposition after biological death occurs. Formaldehyde-based embalming solutions influence nucleic acid degradation, which reduces the quality and quantity of DNA extracted and the effectiveness of short tandem repeat (STR) typing. This research is a 1-year study aimed at determining the timeframe within which viable DNA profiles can be generated from different tissue types, post-embalming. Samples from the bone marrow (tibia), trapezius and quadriceps muscles, liver, and brain tissues were collected before embalming and at seven time points post-embalming. DNA extraction and quantification were performed on each sample to assess whether sufficient DNA was available for testing. Samples with DNA quantities over 0.05 ng/μL underwent amplification and STR analysis to produce DNA profiles. Quantification values and profile quality were compared across tissue types and time points. Results showed that prolonged exposure to embalming solutions significantly reduced DNA quality, leading to less discernible profiles. Statistically significant differences were detected among all tissue types at all time periods. Liver and brain samples retained more DNA than bone marrow, trapezius, and quadricep muscle samples. Qualitative evaluation of ski slope patterns in liver STR profiles demonstrated increasing signal degradation over time and was consistent across loci, suggesting predictable fragment length-dependent decline. This study suggests that after embalming, the liver is the preferential tissue for recovering DNA for forensic analysis, as the liver samples were the most robust and the only sample type to yield DNA profiles up to 1 year.