Application of mtDNA SNP analysis in forensic casework.

Area of Science:

• Forensic science
• Molecular biology
• Genetics

Background:

• Routine forensic DNA analysis methods, including short tandem repeats (STRs) and mitochondrial DNA (mtDNA) hypervariable region I (HVR I) sequencing, can fail on challenging samples.
• Older and degraded samples, as well as various biological materials, pose significant difficulties for standard forensic DNA profiling.

Purpose of the Study:

• To evaluate the efficacy of mitochondrial DNA (mtDNA) single nucleotide polymorphisms (SNPs) analysis using the SNaPshot technique on forensic samples where conventional methods failed.
• To demonstrate the application of mtDNA SNP analysis in complex forensic cases, including mixed-person stains and ancient samples.
• To establish criteria for haplogroup assignment and quality control for mtDNA SNaPshot analysis in forensic casework.

Main Methods:

• Analysis of six forensic cases with failed STR and HVR I sequencing.
• Mitochondrial DNA (mtDNA) single nucleotide polymorphisms (SNPs) analysis using the SNaPshot technique on samples ranging from 2 months to 1400 years old.
• Investigation of various sample types: saliva, blood, sperm, hair, tooth, and bone.
• Analysis of a mixed-person stain to discriminate between different haplogroups.

Main Results:

• Successful DNA profiling was achieved using mtDNA SNP analysis via SNaPshot in all cases where STR and HVR I methods failed.
• The technique was effective across a wide range of sample ages (2 months to 1400 years) and types.
• Two distinct haplogroups were successfully discriminated within a mixed-person stain, and specific SNPs from a hair sample were identified within this mixture.
• Criteria for haplogroup assignment and quality control for mtDNA SNaPshot analysis were proposed.

Conclusions:

• Mitochondrial DNA (mtDNA) SNP analysis using the SNaPshot technique is a robust and valuable tool for forensic casework, especially when conventional methods are unsuccessful.
• This method offers a reliable approach for analyzing diverse and degraded forensic samples, including ancient DNA.
• The proposed criteria enhance the reliability and interpretability of mtDNA SNP data in forensic investigations.