PDSS2 encodes a subunit of decaprenyl diphosphate synthase, a heterotetrameric enzyme that catalyzes sequential condensation of isopentenyl diphosphate onto farnesyl diphosphate to produce prenyl diphosphates of varying chain lengths. This activity is essential for synthesis of ubiquinone-9 and ubiquinone-10, lipid-soluble electron transporters in the mitochondrial respiratory chain and cellular antioxidants. PDSS2 dysfunction impairs mitochondrial energy production. Loss-of-function mutations in PDSS2 cause primary coenzyme Q10 deficiency, manifesting as infantile multisystemic disease with nephropathy and encephalopathy, or cerebellar ataxia with marked cerebellar atrophy 1. In reproductive biology, reduced PDSS2 expression in aging oocytes associates with mitochondrial dysfunction and decreased ATP production; oocyte-specific Pdss2 disruption in mice recapitulated age-related infertility phenotypes including reduced ovarian reserve and increased meiotic spindle abnormalities, reversible by dietary coenzyme Q10 supplementation 2. Recent evidence suggests PDSS2 possesses non-catalytic tumor-suppressive functions independent of its enzymatic activity 3. PDSS2 is frequently downregulated in hepatocellular carcinoma and lung cancer, where low expression predicts poor prognosis; restoration of full-length PDSS2 inhibits cancer cell proliferation and promotes metabolic reorientation toward mitochondrial respiration 4. In tissue-resident memory T cells, PDSS2 overexpression enhances coenzyme Q synthesis, mitochondrial respiration, and antitumor immunity 5.