A newly devised multiplex assay of novel polymorphic non-CODIS STRs as a valuable tool for forensic application

Area of Science:

• Forensic Genetics
• Molecular Biology
• Human Identification

Background:

• Current autosomal short tandem repeat (STR) kits lack sufficient markers for complex forensic cases.
• Increased STR loci are needed to achieve adequate likelihood ratios (LR) for relationship testing.
• Existing STR kits are insufficient for complex family scenarios or indirect forensic analyses.

Purpose of the Study:

• To discover and characterize new autosomal non-CODIS STR loci.
• To develop and validate a novel multiplex STR typing system for enhanced forensic analysis.
• To improve the accuracy and reliability of human DNA profiling and paternity testing.

Main Methods:

• Discovery of 18 new autosomal non-CODIS STR loci through web scanning and experimental screening.
• Development of the "SiFaSTR 21plex_NCII Typing System" including 18 non-CODIS STRs, D2S1338, Amelogenin, and DYS391.
• Forensic developmental validation following SWGDAM guidelines, including sensitivity, specificity, concordance, reproducibility, stability, and mixture testing.
• Investigation of allelic frequencies and forensic parameters in 259 Chinese Han individuals.

Main Results:

• The SiFaSTR 21plex_NCII Typing System demonstrated high accuracy, reliability, and suitability for human DNA profiling.
• Sensitivity analysis showed full profiles obtainable with as little as 125 pg of DNA.
• The system exhibited no cross-reactivity with common animal species, confirming species specificity.
• Stability tests confirmed reliable genotyping in the presence of common inhibitors like haematin, indigotin, urea, nigrosine, and humic acid.
• Mixture tests successfully identified minor alleles at mixed ratios of 1:1, 1:3, and 3:1.
• Forensic efficiency parameters, including total power of discrimination (TDP) and combined exclusion power (CPE), exceeded established thresholds for forensic applications.

Conclusions:

• The developed SiFaSTR 21plex_NCII Typing System is accurate, reliable, and suitable for forensic human DNA profiling.
• The 18 newly discovered non-CODIS STRs and the typing system provide a valuable supplementary tool for forensic genetics.
• This system will aid in resolving complex paternity cases, evolutionary studies, and population investigations.