Efficacy of reduced-size short tandem repeat PCR analysis for degraded DNA samples

Background Short tandem repeats (STR) typing is an essential analysis method for human identification in forensic field. When DNAs obtained from the field as evidences are severely degraded or in too small amounts, STR analysis often shows allele drop-out. Objective To improve STR analysis for degraded DNA or trace DNA, reduced-size STR (rSTR) polymerase chain reaction (PCR) system was devised by selecting relatively large-size STR loci. Methods The rSTR PCR system consisted of 8 loci (amelogenin, SE33, CSF1PO, D7S820, D13S317, D2S1338, TPOX, and FGA). The size of PCR product was reduced by designing new primers in the flanking region. The efficiency of this system was verified against existing kits through concordance study, sensitivity study, efficiency study, and casework sample study. Results The size of PCR product in the rSTR PCR system was reduced to be less than 322 bp. The amplicon of each locus was reduced by about 100 bp on average. Results of this rSTR PCR system were confirmed using 146 Korean samples and other commercial kits. The rSTR PCR system was capable of analyzing DNA samples with a minimum amount of DNA of 16 pg and a degradation index of 4.215. Conclusion The rSTR PCR system was more effective than other PCR kits for obtaining genetic profiles from a small amount of DNA or degraded DNA. The combination of this new system and other commercial kits is more effective than existing systems. This combination is expected to be helpful for the identification of unidentified bodies and skeletal samples.