Development of a 24-locus multiplex system to incorporate the core loci in the Combined DNA Index System (CODIS) and the European Standard Set (ESS)

The 24-locus multiplex system allows co-amplification and fluorescent detection of 24 loci (23 STR loci and Amelogenin), including STR loci in the Combined DNA Index System (CODIS) and the ESS (European Standard Set) as well as five additional loci (D2S1338, D6S1043, D19S433, Penta D and Penta E) commonly used in commercial kits. It facilitates data sharing and minimizes adventitious matches within national or between international DNA databases. Additionally, the system can amplify directly from blood and buccal samples spotted on filter paper and swabs and reduce the cycling time to less than one hour and a half. Primers, internal size standard, allelic ladders and matrix standard set were designed and created in-house with a design strategy to work in this multiplex. Developmental validation experiments followed the Scientific Working Group on DNA Analysis Methods (SWGDAM) and the Chinese National Standard (GA/T815-2009) guidelines. The system was evaluated by species specificity, sensitivity, stability, precision and accuracy, case-type samples, population, mixture and PCR-based studies. The results demonstrate that the 24-locus multiplex system is a robust and reliable identification assay as required for forensic DNA typing and databasing.