Gallstone formation is regulated by the balance between biliary cholesterol, biliary phospholipids, and bile acids, the secretion of which are regulated by ABCG5/8 heterodimers, bile salt export pump (BSEP, also known as ABC subfamily B [ABCB]11), and multidrug resistance protein 2 (MDR2, also known as ABCB4), respectively [1]. The gene discussed is ABCG5; the disease is gallstones.