COQ8B is an atypical kinase essential for coenzyme Q10 (ubiquinone) biosynthesis, a critical lipid-soluble electron transporter required for aerobic respiration in mitochondria 123. Its precise catalytic mechanism remains unclear; while it may phosphorylate COQ3 protein or prenyl lipid intermediates in the ubiquinone pathway, direct small molecule kinase activity has not been definitively confirmed 3. COQ8B is a mitochondrial matrix protein peripherally associated with the inner membrane 4. Biallelic COQ8B mutations cause primary Coenzyme Q10 deficiency, clinically manifesting as steroid-resistant focal segmental glomerulosclerosis with a predominantly renal-limited phenotype 56. Disease typically presents in adolescence (median age 9.8 years), distinguishing it from COQ2/COQ6 deficiencies with earlier onset 5. Notably, COQ8B mutations also cause non-syndromic retinitis pigmentosa through impaired mitochondrial oxidative phosphorylation 7. Unlike COQ2 mutations, clinical severity in COQ8B disease does not correlate with residual CoQ biosynthesis, suggesting genetic redundancy through COQ8A compensation 4. CoQ10 supplementation combined with ACE inhibitors effectively slows renal dysfunction progression and preserves long-term renal function, particularly when initiated early 86, making COQ8B nephropathy one of the few treatable genetic kidney diseases.