Mutations in these genes are associated with diseases, including cystic fibrosis (ABCC7/CFTR) [3], Tangier disease (ABCA1/CERP) [4], Dubin–Johnson syndrome [ABCC2/multidrug resistance‐associated protein (MRP2)] [5] and gout [ABCG2/breast cancer resistance protein (BCRP)] [6]. The gene discussed is ABCG2; the disease is Dubin-Johnson syndrome.