HSD3B7 (3β-hydroxy-Δ5-steroid dehydrogenase type 7) is a key metabolic enzyme catalyzing sequential dehydrogenation and isomerization reactions essential for bile acid synthesis 1. The enzyme converts 7α-hydroxylated oxysterols, including 7α,25-dihydroxycholesterol (7α,25-OHC), through NAD+-dependent sequential ordered bi-bi kinetics and requires membrane localization for full activity 1. Beyond steroid metabolism, HSD3B7 regulates immune cell positioning in lymphoid tissues by controlling 7α,25-OHC levels, which acts as a ligand for the chemotactic receptor GPR183/EBI2, directing B cell migration 2. Functionally, HSD3B7 maintains cholesterol homeostasis critical for cellular survival across multiple tissues 3. Clinically, biallelic HSD3B7 mutations cause congenital bile acid synthesis defect 1, manifesting as neonatal cholestasis in 82% of patients, with renal cysts occurring in 29% 4. Treatment with chenodeoxycholic acid (CDCA) normalizes liver biochemistries in 73% of patients and remarkably resolves renal lesions 4. Elevated HSD3B7 expression correlates with poor prognosis in clear cell renal cell carcinoma (ccRCC), promoting tumor proliferation and invasion, identifying it as a therapeutic target 5. Genetic variants in HSD3B7 also associate with reduced late-onset Parkinson's disease risk 6 and represent a potential hypertension drug target 7.