SLC22A9 encodes organic anion transporter 7 (OAT7), a sodium-independent hepatic membrane transporter with high specificity for sulfated conjugates of xenobiotics and steroid hormones, particularly estrone 3-sulfate and dehydroepiandrosterone sulfate 1. The transporter is uniquely activated by short-chain fatty acids including propionate, butyrate, and valerate, and may operate an exchange mechanism between sulfated organic components and short-chain fatty acids at the hepatocyte sinusoidal membrane 1. OAT7 transports the statin pravastatin and may contribute to its hepatic disposition when other organic anion transporting polypeptides are compromised 1. Recent studies have identified SLC22A9 as a transporter for the thyroid hormone analog TRIAC, with uptake inhibited by the known substrate estrone-3-sulfate 2. The transporter exhibits substantial inter-individual variability in hepatic expression (28-fold mRNA, 15-fold protein), primarily regulated by hepatic nuclear factor 4-alpha (HNF4α) 1. Genome-wide association studies have linked SLC22A9 variants to total thyroid hormone levels and renal urate handling, suggesting broader physiological roles beyond xenobiotic transport 34. However, variants do not appear to significantly impact osteoporosis risk in Europeans 5.