Advancing forensic SNP typing: Insights from an interlaboratory study of the FORCE panel

This study evaluated the ability to produce FORensic Capture Enrichment (FORCE) genotypes using amplicon-based and capture-based enrichment assays. The FORCE panel is a standardized set of single nucleotide polymorphism (SNP) markers developed for forensic applications. Twelve DNA samples were prepared and distributed to the laboratories for testing: five control DNA samples, a dilution series ranging from 10 ng to 0.03 ng, two degraded DNA samples with 200 bp and 150 bp average fragment lengths, and one inhibited sample spiked with humic acid. Fifteen laboratories from three different continents participated in this study, choosing from one of four manufacturer-developed enrichment assays to complete the experiments, setting their own parameters for sequencing and other user-defined steps to accommodate their own preferences and expertise. A total of eighteen methods were evaluated, as three laboratories performed two methods. The results showed that all four assays were successful in producing full FORCE SNP genotypes from high quality samples. However, significant differences between and within assays and methods were observed. Read count variability and enrichment type led to significant differences in call rate. Robust SNP recovery was observed across all assays at 0.3 ng DNA input, with an amplicon-based assay producing high SNP call rates at 0.03 ng DNA input. Capture and single primer extension assays produced consistently high SNP call rates from degraded samples with 150-200 bp fragments. Future research to optimize laboratory parameters may reduce the variation in SNP data, so that labs may equitably adopt SNP methods to make use of these powerful forensic markers.