Allele frequencies and forensic efficiency of autosomal short tandem repeat loci in the Rwandan population

Although Rwanda has increasingly adopted DNA evidence in criminal investigations, paternity testing, and civil applications, comprehensive population-specific autosomal STR reference data remain limited. The first forensic STR study in Rwanda analyzed a relatively small cohort of unrelated individuals using a limited marker panel, and provided an initial allele frequency dataset with restricted population coverage. The present study provides nationally distributed allele frequency data and forensic efficiency parameters for 23 autosomal STR loci.

This retrospective study collected 815 autosomal STR profiles generated between 2005 and 2015. The profiles were obtained through database sampling whereby all archived STR genotype data meeting the inclusion criteria were retrieved. Because the study comprised autosomal STR profiles generated over a 10-year period, laboratory records were reviewed to verify the extraction and quantification methods, amplification systems, capillary electrophoresis platforms, allele-calling software, and quality assurance procedures used during the study period. DNA extraction was performed using Chelex® 100 method, followed by Quantification using Quantifiler Duo DNA Quantification kit on the ABI 7500 Real-Time PCR System (only for casework samples), and STR amplification with PowerPlex 16 in combination with PowerPlex ESI 17 Pro and/or PowerPlex ESX 17 kits to obtain a combined panel of 23 autosomal STR loci.

All 23 autosomal loci were polymorphic. The number of observed alleles per locus ranged from 7 (D16S539) to 50 (SE33). Forensic parameters indicated high informativeness across loci with very low combined match probability (CMP = 1.7239 × 10⁻³⁰). At most loci, one or two alleles predominated, while the remaining alleles occurred at relatively low frequencies. For example, allele 16 at D3S1358 (0.3392638), allele 7 at TH01 (0.37791411), allele 12 at D13S317 (0.36319018), allele 10 at D7S820 (0.40552147), allele 12 at D5S818 (0.36809816).

The present findings strengthen the forensic genetic resources available for Rwanda. Compared with previous Rwandan studies, the expanded characterization of highly polymorphic loci and detection of rare alleles provide more comprehensive allele frequency estimates and strengthen the statistical basis of forensic DNA interpretation.