Application of mtDNA SNP Analysis in Forensic Casework

Introduction

  • Forensic genetics has seen optimization in analyzing challenging DNA samples.

  • Analysis techniques are time-consuming and expensive, leading to the use of the SNaPshot technique for mtDNA analysis.

mtDNA SNP Analysis Overview

  • The study discusses six cases where traditional STR analysis and mtDNA HVR I sequencing failed, but mtDNA SNP analysis succeeded.

  • Key findings highlight the capability of analyzing 32 SNPs in a single PCR and SNaPshot reaction, particularly in mixed stain cases.

Materials and Methods

  • Sample Types: Saliva, sperm, blood, hair, teeth, and bones.

  • Sample Processing:

    • Extraction of hair follows methods specified in selected references.

    • DNA extraction procedures detailed according to specific references for blood, teeth, etc.

  • SNP Analysis:

    • Multiplex PCR setup and thermal cycling conditions match established references.

    • Internal database contains over 1000 German mtDNA samples for comparison.

Haplogroup Assignment

  • Haplogroups assigned based on mandatory tagging SNPs (tSNPs) that allow haplogroup discrimination among populations.

  • Example mutations discussed:

    • Haplogroup X: Discriminated by tSNPs 10873T and 14470C.

    • Haplogroup HV: Characterized by tSNPs 10873T, 12705C, and 14766C.

  • Haplogroup Identification Process: Decision trees assist in systematically identifying haplogroups.

  • Limitations discussed in haplogroup identification when certain SNPs are not detected.

Quality Control in SNP Analysis

  • Multiple analyses are performed on samples to ensure reliability (2-3 runs).

  • Criteria for interpreting SNP peaks:

    • Relative Fluorescence (RFU) threshold set above 125 for acceptance.

    • Key SNPs have defined issues with artefact peaks, particularly influenced by the analysis machine used.

  • Recommendations given for minimizing potential artefacts and misinterpretations.

Case Studies Summary

Case 1

  • An unknown male body discovered; hair analysis failed using prior methods but succeeded using mtDNA SNPs comparing with a putative brother.

Case 2

  • Analysis of hair from a homicide victim in 1981; mtDNA results successfully discerned the suspect's connection.

Case 3

  • Hairs from a victim analyzed; mtDNA SNPs ruled out suspects and presented unidentified DNA profiles.

Case 4

  • Analysis of buried bones revealed haplogroup characteristics, verifying identity links to historical remains.

Case 5

  • Ancient teeth analysis yielded clear haplogroup profiles, confirming historical identities and excluding relations among remains.

Case 6

  • Mixed stain analysis on a bed sheet detected multiple haplogroups, ruling out victim contributions based on SNP differences.

Conclusion

  • The study underscores the efficacy of mtDNA SNP analysis in forensic genetics.

  • Highlights the method's utility for challenging and degraded DNA samples, reinforcing its value as a rapid screening technique for biological material.

  • Emphasizes the technological advancements in SNP analysis for improving forensic outcomes and addressing limitations of traditional methods.