FDXR (ferredoxin reductase) is a mitochondrial flavoprotein that serves as the first electron transfer component in mitochondrial cytochrome P450 systems, playing essential roles in steroidogenesis and coenzyme Q biosynthesis 1. The protein facilitates cholesterol side chain cleavage in steroidogenic tissues, steroid 11-beta hydroxylation in the adrenal cortex, and vitamin D3 hydroxylation in the kidney by transferring electrons from NADPH to ferredoxin 2. FDXR also functions in coenzyme Q biosynthesis by transferring electrons required for COQ6-mediated hydroxylation reactions. Pathogenic variants in FDXR cause a multisystem mitochondrial disorder characterized primarily by optic atrophy (89% of cases) and auditory neuropathy, along with developmental delay, movement disorders, and hypotonia 34. The disorder can present with acute-onset peripheral neuropathy that may mimic inflammatory conditions 4. Some FDXR variants also cause adrenal insufficiency and atypical sexual development due to impaired steroidogenesis, particularly affecting glucocorticoid and mineralocorticoid production 2. Additionally, FDXR expression is radiation-inducible and serves as a biomarker for radiation dose estimation in biodosimetry applications 5. The gene is located on chromosome 17 and represents a critical component of mitochondrial electron transport systems.