Massively parallel sequencing of 25 autosomal STRs including SE33 in four population groups for forensic applications

The introduction of massively parallel sequencing (MPS) in forensic investigation enables sequence-based large-scale multiplexing beyond size-based analysis using capillary electrophoresis (CE). For the practical application of MPS to forensic casework, many population studies have provided sequence data for autosomal short tandem repeats (STRs). However, SE33, a highly polymorphic STR marker, has little sequence-based data because of difficulties in analysis. In this study, 25 autosomal STRs were analyzed, including SE33, using an in-house MPS panel for 350 samples from four populations (African-American, Caucasian, Hispanic, and Korean). The barcoded MPS library was generated using a two-step PCR method and sequenced using a MiSeq System. As a result, 99.88% genotype concordance was obtained between length- and sequence-based analyses. In SE33, the most discordances (eight samples, 0.08%) were observed because of the 4 bp deletion between the CE and MPS primer binding sites. Compared with the length-based CE method, the number of alleles increased from 332 to 725 (2.18-fold) for 25 autosomal STRs in the sequence-based MPS method. Notably, additional 129 unique alleles, a 4.15-fold increase, were detected in SE33 by identifying sequence variations. This population data set provides sequence variations and sequence-based allele frequencies for 25 autosomal STRs.