Resolving relationship tests that show ambiguous STR results using autosomal SNPs as supplementary markers

Area of Science:

• Forensic Genetics
• Human Identification
• Molecular Biology

Background:

• Standard short tandem repeat (STR) analysis in relationship testing can yield ambiguous results, particularly when a brother of the true father is tested.
• Ambiguous results may stem from minor genotype discrepancies interpreted as mutations, complicating relationship confirmation.
• While additional STRs exist, their validation is limited, and hypervariable loci like SE33 increase mutation risks.

Purpose of the Study:

• To evaluate the efficacy of single nucleotide polymorphisms (SNPs) in resolving ambiguous relationship testing cases.
• To compare the reliability of SNPs versus STRs in forensic identification, especially with degraded DNA.
• To assess the statistical efficiency of SNPs in distinguishing first-degree relatives in complex pedigrees.

Main Methods:

• Utilized large multiplex SNP panels for relationship testing.
• Analyzed eight historical relationship cases with ambiguous STR results that were resolved with SNP data.
• Conducted simulations to determine the frequency of inconclusive paternity results with different marker sets when a brother of the father was tested.

Main Results:

• SNPs proved more informative than STRs in cases with low initial probabilities or ambiguous exclusions.
• SNP genotyping provided a more reliable approach for highly degraded DNA samples.
• Simulations confirmed that SNPs are statistically more efficient than STRs for resolving cases involving first-degree relatives.

Conclusions:

• SNPs are a valuable tool for enhancing the accuracy and reliability of forensic relationship testing.
• SNP analysis offers a robust alternative to STRs for overcoming challenges posed by degraded DNA and complex familial relationships.
• The findings support the integration of SNP data to improve outcomes in forensic genetic analyses.