High polymorphism detected by massively parallel sequencing of autosomal STRs using old blood samples from a Chinese Han population

The development of massively parallel sequencing (MPS) has quickly changed forensic short tandem repeat (STR) genotyping. By providing detailed sequence information, MPS technology may be used as an alternative or additional method to overcome the limitations of capillary electrophoresis-based STR profiling. Most current NGS processes are labour-intensive with regard to library preparation and require high-quality DNA template. In this study, a 16-plex STR typing system (SeqType®R16) was used to achieve direct library preparation without DNA extraction and adaptor ligation. The efficiency of this system was tested in 601 individuals, including 593 old blood samples from the Chinese Han population and eight positive controls. It took approximately 4 hours for library preparation, including blood direct multiplex PCR (1.5 hours), mixing of the product (15 minutes), single tube purification (2 hours) and quantification (15 minutes). The results showed that MPS presented a broader allele range and higher discrimination power. Except for FGA and D19S433, the allele number almost doubled or more than doubled at all complex STR loci and simple STR loci, including D13S317, D16S539, D5S818, and D7S820. The range of discrimination power increased from 0.8008–0.9572 to 0.8401–0.9753, and the culminated matching probability decreased from 1.7 × 10−15 to 1.1 × 10−17.