DNA quality and STR success rate in different formalin-fixed tissues

Formalin-fixed tissues possess irreplaceable value as a source of DNA for identification, especially when fresh samples are unavailable. Nonetheless, extracting and amplifying DNA from these tissues is challenging, primarily due to formaldehyde-induced cross-linking and nucleic acid fragmentation. In this study, two pre-extraction treatments, gradual dehydration using ethanol and pre-digestion heat treatments, and three DNA extraction methods, the Chelex-100 method, TIANamp FFPE DNA Kit, and ML Ultra-micro DNA extraction kit, were utilized to optimize DNA extraction from different tissues, which were fixed in 4% unbuffered formalin for different durations. The tissues include the heart, liver, spleen, lung, kidney, muscle, and brain. DNA quality was assessed, and quantification was conducted using Spectrophotometer and Quantifiler^® Trio DNA Quantification Kits, while the GSTAR™ 25 kit was employed for STR detection. The results indicated that the two pre-extraction treatments exhibited no significant effect on the STR success rate. On day 9, allelic dropout was observed in the heart, liver, spleen, lung, and kidney tissues. Furthermore, allelic dropout was observed in muscle and brain at 12 days and 15 days, respectively. In conclusion, the results underscore the feasibility of effectively extracting DNA from formalin-fixed tissues within 9 days for subsequent STR analysis.