ND2 (mitochondrially encoded NADH dehydrogenase 2) is a core subunit of mitochondrial Complex I that catalyzes electron transfer from NADH through the respiratory chain using ubiquinone as an electron acceptor, essential for complex I catalytic activity and assembly 1. ND2 supports mitochondrial oxidative phosphorylation and ATP synthesis, with expression patterns linked to cellular differentiation and developmental processes 2. The protective ND2 m.5178C>A mutation enhances mitochondrial functions, increasing ATP synthesis, oxygen consumption rates, and Complex I activity while decreasing reactive oxygen species production and apoptosis 3. ND2 expression shows sex-dependent regulation in human spinal cord oligodendrocytes, with higher levels in females 4, and increases during post-weaning developmental transitions in the pig cecum 5. ND2 upregulation participates in parthanatos-mediated glioma cell death through respiratory Complex I activation 6. Clinical relevance includes associations with Leber hereditary optic neuropathy, Leigh syndrome, and Alzheimer disease, though ND2 variants show no significant association with reproductive outcomes in in vitro fertilization 7. ND2 also serves as a biomarker for intervertebral disc degeneration 8.