Effective use of the degradation index from human DNA quantification kits to improve STR and Y-STR profiling

Short tandem repeat (STR) genotyping is primarily used for human identification in various forensic biological samples. However, samples collected from crime scenes or mass disasters are often exposed to environmental factors that cause considerable DNA degradation. As a result, degraded DNA yields significantly less polymorphic information than non-degraded DNA due to a reduction in the effective copy number of STR loci available for amplification. To obtain reliable STR results, it is crucial to consider the degree of DNA degradation alongside accurate DNA quantification. In this study, we investigated the impact of DNA degradation on allele detection in STR and Y-chromosome STR (Y-STR) analyses to improve the estimation of degraded DNA quantity for PCR amplification and enhance allele detection rates. Specifically, we analyzed the relationship between the degradation index (DI) provided by the Quantifiler HP DNA Quantification Kit and allele detection rates in STR and Y-STR analyses using various amounts of artificially fragmented or UV-irradiated DNA. Our results demonstrate that the DI serves as a valuable indicator of DNA degradation, aiding in the estimation of the appropriate amount of degraded DNA for PCR amplification. Furthermore, STR and Y-STR profiles and allele detection rates vary depending on the degradation pattern, such as fragmentation or UV irradiation, even when the DI remains the same. Our findings underscore the importance of incorporating DI into forensic workflows to maximize allele recovery from a limited amount of degraded DNA, ultimately enhancing forensic and disaster victim identification.