Developmental Validation of the Microreader 23HS Plex ID System: A Novel Supplementary Non-CODIS STR Multiplex Assay for Forensic Application

A novel supplementary non-CODIS STR multiplex assay designated as the “Microreader 23HS Plex ID System” was developed. The Microreader 23HS Plex ID System enables simultaneous profiling of 23 STR loci and the amelogenin locus. The majority of these loci are non-CODIS STRs (D4S2408, D9S2157, D20S161, D3S2459, D18S1364, D13S305, D1S2142, D19S400, D6S1017, D7S1517, D2S1776, D2S1360, D3S1744, D16S3391, D3S1545, D11S4463, D20S85, D1S549, D10S2325, D21S2055), with the exception of three CODIS STRs (D2S441, D12S391, and D22S1045). Followed the recommendations of Scientific Working Group on DNA Analysis Methods (SWGDAM) and the Chinese validation standards, a comprehensive set of validation studies were conducted, encompassing PCR conditions, stutter ratio and peak height balance, sensitivity, precision and accuracy, reproducibility, species specificity, inhibition, as well as mixture testing. The results demonstrated that the Microreader 23HS Plex ID System is a reliable and robust assay, with well-balanced peak heights, high precision and accuracy, species specificity, and resistance to common inhibitors. The sensitivity of the assay was determined to be 0.125 ng of template DNA. In mixture study, all minor alleles were detected in two-sample mixtures across various ratios (1:19, 1:9, 1:4, 3:7, 2:3, 1:1, 3:2, 4:1, 9:1, and 19:1). In population study, a total of 500 unrelated individuals of Han ethnicity from East China were genotyped. The allele frequencies and forensic population genetic parameters were calculated, with a cumulative random match probability of 7.757 × 10⁻²⁷, and a total power of discrimination exceeding 0.999,999,999,999,999,999,999,999,99. In conclusion, the Microreader 23HS Plex ID System shows promise as a valuable supplementary tool for forensic applications, particularly in addressing complex kinship testing and challenges posed by STR mutation.