NDUFAF4 is a mitochondrial assembly factor essential for Complex I biogenesis. It associates with assembly intermediates of the Q-module of NADH:ubiquinone oxidoreductase complex I and is required for proper stoichiometric organization of complex I subunits 1. NDUFAF4 is myristoylated at its N-terminus, facilitating membrane targeting and Complex I assembly 2. Recessive NDUFAF4 mutations cause mitochondrial Complex I deficiency (nuclear type 15), presenting with severe neonatal lactic acidosis, encephalopathy, cardiomyopathy, and early death 3. Pathogenic variants also associate with autosomal recessive Leber Hereditary Optic Neuropathy (arLHON), characterized by subacute vision loss and optic atrophy 4. Loss of NDUFAF4 results in near-complete absence of assembled Complex I and supercomplexes, markedly reducing cellular respiratory capacity 3. In cancer, NDUFAF4 has emerged as therapeutically relevant. N-myristoyltransferase inhibitors selectively downregulate NDUFAF4 in cancer cells, causing Complex I loss and oxidative phosphorylation dysfunction 2. MYC-deregulated cancers show enhanced sensitivity to this mechanism 5. A functional NDUFAF4 variant (rs1854268) reducing gene expression confers decreased non-small cell lung cancer risk by disrupting NF-κB and PI3K-AKT pathways 6. Additionally, NDUFAF4 interacts with vesicular stomatitis virus matrix protein, affecting viral propagation 7.