NDUFB11 encodes an accessory subunit of mitochondrial complex I (NADH:ubiquinone oxidoreductase) that is essential for proper enzyme assembly and function 1. This X-linked gene produces a small integral membrane protein required for complex I assembly, with reduced NDUFB11 expression leading to isolated complex I deficiency 1. The protein functions in the mitochondrial electron transport chain, facilitating electron transfer from NADH to ubiquinone as part of oxidative phosphorylation 2. Pathogenic variants in NDUFB11 cause diverse clinical phenotypes including neonatal lethal cardiomyopathy, hypertrophic cardiomyopathy with lactic acidosis, and optic atrophy 134. The gene shows incomplete penetrance, with pathogenic variants sometimes inherited from asymptomatic parents 5. Clinically, NDUFB11 deficiency can present as histiocytoid cardiomyopathy, congenital sideroblastic anemia, or isolated optic neuropathy, though phenotypic expression is highly variable even with identical mutations 14. The gene's role in mitochondrial metabolism also makes it relevant in other conditions, with reduced expression associated with atherosclerosis and chrX stress 6. Therapeutic targeting of complex I, including NDUFB11, shows promise in treating DNMT3A-mutant clonal hematopoiesis 7.