Global population variability in Qiagen Investigator HDplex STRs

Supplementary short tandem repeats (STRs) can be added to forensic analyses if the 15-24 core STRs in routine use fail to give sufficient discrimination power in complex identification or relationship testing scenarios. In this study, 10 of 12 supplementary STRs in the Qiagen Investigator HDplex kit (SE33, D2S1360, D3S1744, D4S2366, D5S2500, D6S474, D7S1517, D8S1132, D10S2325, D21S2055) were genotyped in 941 individuals from the 51 populations of the CEPH Human Genome Diversity Panel (HGDP-CEPH). The other two components of the 12-STR HDplex kit are established STRs D12S391 and D18S51 that we previously genotyped for the HGDP-CEPH panel. We describe the rare alleles identified and outline allele frequency distributions in the seven population groups of the HGDP-CEPH panel. The HDplex STRs novel to forensic application were found to be both highly informative and comparable in their power across all populations studied: at least six of the nine loci showing above average forensic discrimination power in each population group. In some rare instances certain low frequency alleles in D2S1360 were found to overlap in mobility with the neighbouring allele size ranges of D12S391, as well as those of D7S1517 with neighbouring D3S1744 and D10S2325 with neighbouring SE33. Lastly, since expanded five-dye multiplex kits of 20 STRs (Promega Powerplex 21) and 22 STRs (Promega Powerplex Fusion) have recently been introduced, we assess through simulations the increased power to analyse pairwise relationships in deficient pedigrees that can be expected from an optimum kit pair: combining HDplex with either of the above sets to provide 30 or 32 unique STRs and just two overlapping loci.