Maternal lineage tracing using mtDNA from unbuffered formalin-fixed autopsy tissues in India.

Abstract

Background: In India, autopsy tissues are routinely preserved in 10% unbuffered formalin, which induces extensive deoxyribonucleic acid (DNA) damage through cross-linking and fragmentation. However, mitochondrial DNA (mtDNA), owing to its high copy number and polymorphic regions, may remain recoverable when nuclear DNA profiling is not feasible.

Aim: This study evaluated the feasibility of obtaining HV1 and HV2 mtDNA sequences from unbuffered formalin-fixed autopsy tissues and explored maternal lineage diversity within the study cohort.

Subjects and methods: Seventy pairs of formalin-fixed autopsy tissues and reference samples (blood/buccal swabs) from first-degree maternal relatives were analysed. Total DNA was extracted using an organic method. HV1 and HV2 regions were amplified and sequenced using Sanger sequencing. Sequence variants were determined relative to the revised Cambridge Reference Sequence (rCRS), and haplogroups were assigned using the EMPOP haplogrouping tool.

Results: The formalin-fixed samples yielded complete HV1 and HV2 mtDNA sequences that were concordant with their corresponding maternal reference samples. A total of 34 haplogroups were observed, indicating maternal lineage diversity within the study cohort.

Conclusion: These findings support the feasibility of mtDNA sequencing in unbuffered formalin-fixed tissues under routine mortuary conditions and provide exploratory mtDNA data relevant for forensic genetic research in the Indian context.