Mitochondrial haplogroups

Mitochondrial haplogroups are clusters of maternally inherited mitochondrial DNA (mtDNA) haplotypes defined by shared polymorphisms, reflecting ancient migration patterns and geographic lineages. Because mtDNA encodes 13 essential respiratory-chain subunits and 22 tRNAs, haplogroup-defining variants can subtly alter oxidative phosphorylation efficiency, reactive oxygen species production, and mitochondrial morphology. Several studies have reported associations between specific haplogroups and longevity, most notably sub-haplogroups D4a and D5 among Japanese centenarians (Tanaka et al.), and haplogroup J in some European centenarian cohorts; however, replication across populations is inconsistent, sample sizes in the original studies were modest, and population stratification is a persistent confound. Mitochondrial haplogroups therefore represent plausible but not firmly established modulators of aging trajectory.