A Novel SNP-STR System Based on a Capillary Electrophoresis Platform

Area of Science:

• Forensic genetics
• Molecular biology
• Biomarker development

Background:

• Generalized microhaplotypes, including SNP-STRs, are valuable forensic tools for DNA mixture deconvolution and ancestry inference.
• Existing SNP-STR markers often lack compatibility with established short tandem repeat (STR) databases.
• The amplification refractory mutation system (ARMS) PCR combined with capillary electrophoresis (CE) is a standard forensic technique.

Purpose of the Study:

• To develop and validate novel SNP-STR markers compatible with existing forensic DNA databases.
• To establish stable and sensitive multiplex PCR panels for SNP-STR analysis on the CE platform.
• To evaluate the performance of SNP-STRs in analyzing unbalanced DNA mixtures and in casework applications.

Main Methods:

• Screening of 18 SNP-STR loci, with 14 derived from the expanded CODIS core loci set.
• Development of stable and sensitive SNP-STR multiplex PCR panels for capillary electrophoresis.
• Testing on simulated two-person DNA mixtures, including high-ratio mixtures (1:500).
• Population data collection from 113 unrelated Chengdu Han individuals.
• Development of a Bayesian framework for likelihood ratio (LR) evaluation.

Main Results:

• Established stable and sensitive SNP-STR multiplex PCR panels.
• Demonstrated detection of minor DNA components in simulated 1:500 mixtures.
• Achieved a combined likelihood ratio of 7.14 × 10^7 in a casework example, significantly higher than autosomal STR kits (2.86 × 10^3).
• Collected population data for forensic interpretation.

Conclusions:

• SNP-STRs offer enhanced discriminatory power and compatibility with existing forensic DNA databases.
• The developed SNP-STR panels are effective for analyzing unbalanced DNA mixtures and show significant advantages in casework.
• SNP-STR technology represents a valuable advancement for forensic identification and mixture analysis.