UQCC1 (ubiquinol-cytochrome c reductase complex assembly factor 1) is an essential mitochondrial protein required for the assembly of complex III of the respiratory chain 1. The protein functions as an assembly factor that interacts with UQCC2 and binds newly synthesized mitochondrial-encoded cytochrome b, facilitating its incorporation into the complex III holocomplex 1. UQCC1 works upstream in the complex III assembly pathway relative to UQCC3, as UQCC3 levels are reduced when UQCC1 is depleted 2. Beyond its mitochondrial role, UQCC1 has broader clinical significance. Genetic variants in UQCC1 show protective effects against non-alcoholic fatty liver disease, with the rs878639 G allele associated with lower liver fat content 3. However, elevated UQCC1 expression is causally associated with reduced muscle mass and function, contributing to sarcopenia pathogenesis 45. The gene also shows associations with developmental dysplasia of the hip and meniscus injury risk, where genetic variants may modulate TGF-β signaling pathways 67. These diverse associations suggest UQCC1 functions extend beyond mitochondrial complex III assembly to influence multiple pathological processes through both metabolic and signaling mechanisms.