NDUFAF5 encodes an arginine hydroxylase that functions as a critical assembly factor for mitochondrial respiratory chain Complex I. The protein mediates hydroxylation of arginine-111 in the NDUFS7 subunit and is essential for early stages of Complex I assembly 1. NDUFAF5 contains a putative methyltransferase domain that is essential for its function, and site-directed mutagenesis studies confirm this motif's importance 2. The protein has been identified as a substrate for pp60Src kinase, with phosphorylation playing a role in Complex I activity and assembly 3. Biallelic mutations in NDUFAF5 cause mitochondrial Complex I deficiency leading to Leigh syndrome, with significant phenotypic heterogeneity observed among patients 14. The p.Met279Arg variant shows particular population specificity in Chinese ancestry and demonstrates age-dependent clinical severity, with early-onset cases presenting with severe neurodegeneration and late-onset cases showing progressive dystonia with preserved cognition 4. NDUFAF5 deficiency is also associated with increased autophagy activation, suggesting novel pathways beyond traditional AMPK-mediated mechanisms in mitochondrial disease pathology 2. Additionally, NDUFAF5 may play roles in cancer chemoresistance through ROS regulation pathways 5.