Comprehensive landscape of non-CODIS STRs in global populations provides new insights into challenging DNA profiles

The worldwide implementation of short tandem repeats (STR) profiles in forensic genetics necessitated establishing and expanding the CODIS core loci set to facilitated efficient data management and exchange. Currently, the mainstay CODIS STRs are adopted in most general-purpose forensic kits. However, relying solely on these loci failed to yield satisfactory results for challenging tasks, such as bio-geographical ancestry inference, complex DNA mixture profile interpretation, and distant kinship analysis. In this context, non-CODIS STRs are potent supplements to enhance the systematic discriminating power, particularly when combined with the high-throughput next-generation sequencing (NGS) technique. Nevertheless, comprehensive evaluation on non-CODIS STRs in diverse populations was scarce, hindering their further application in routine caseworks. To address this gap, we investigated genetic variations of 178 historically available non-CODIS STRs from ethnolinguistically different worldwide populations and studied their characteristics and forensic potentials via high-coverage whole genome sequencing (WGS) data. Initially, we delineated the genomic properties of these non-CODIS markers through sequence searching, repeat structure scanning, and manual inspection. Subsequent population genetics analysis suggested that these non-CODIS STRs had comparable polymorphism levels and forensic utility to CODIS STRs. Furthermore, we constructed a theoretical next-generation sequencing (NGS) panel comprising 108 STRs (20 CODIS STRs and 88 non-CODIS STRs), and evaluated its performance in inferring bio-geographical ancestry origins, deconvoluting complex DNA mixtures, and differentiating distant kinships using real and simulated datasets. Our findings demonstrated that incorporating supplementary non-CODIS STRs enabled the extrapolation of multidimensional information from a single STR profile, thereby facilitating the analysis of challenging forensic tasks. In conclusion, this study presents an extensive genomic landscape of forensic non-CODIS STRs among global populations, and emphasized the imperative inclusion of additional polymorphic non-CODIS STRs in future NGS-based forensic systems.