An evaluation of ForenSeq DNA Signature Prep iiSNP mixture interpretation using a probabilistic genotyping method.

Area of Science:

• Forensic genetics
• Molecular biology
• Biostatistics

Background:

• Autosomal short tandem repeat (STR) markers analyzed via capillary electrophoresis (CE) are standard in global forensics.
• Next-generation sequencing (NGS) offers simultaneous amplification of STR and single-nucleotide polymorphism (SNP) loci, presenting advantages over traditional methods.
• SNPs, while biallelic and less polymorphic individually than STRs, offer simpler interpretation of mixed DNA evidence due to lack of stutter and fewer genotype combinations.

Purpose of the Study:

• To investigate the application of the STRmix™ NGS probabilistic genotyping model for interpreting mixed SNP profiles.
• To compare the performance of STRmix™ NGS on SNP profiles against established methods for STR analysis.
• To assess the utility of SNP markers as a complementary tool to STRs in forensic investigations.

Main Methods:

• Utilized the STRmix™ NGS probabilistic genotyping software.
• Applied the software to interpret mixed DNA profiles generated from 94 identity-informative SNPs (iiSNPs) on the ForenSeq kit.
• Compared likelihood ratios (LRs) for true and false donors in both single-source and mixed profiles.

Main Results:

• STRmix™ NGS demonstrated expected trends for single-source SNP profiles.
• The system's ability to differentiate true from false donors decreased significantly in complex SNP mixtures.
• This limitation is consistent with the theoretical constraints of biallelic markers in complex scenarios.

Conclusions:

• Simple SNP profiles can be interpreted using the existing STRmix™ NGS framework.
• This provides a valuable tool for SNP profile analysis and supports future joint interpretation of STR and SNP markers.
• Further research with larger SNP panels is warranted to enhance interpretation capabilities for complex forensic samples.