Currently, deficiencies in eight enzymes have been associated with IEBAM (Table 1), five of which have been reported in Japan: 3β-hydroxy-Δ5-C27-steroid dehydrogenase/isomerase (HSD3B7) deficiency (OMIM 607765), Δ4-3-oxosteroid 5β-reductase (SRD5B1) deficiency (OMIM 235555), 27-sterol hydroxylase (CYP27A1) deficiency (OMIM 213700), oxysterol 7α-hydroxylase (CYP7B1) deficiency (OMIM 603711), and bile acid conjugation defect–1 caused by a bile acid-CoA:amino acid N-acyltransferase (BAAT) gene mutation (bile acid conjugation defect–1: BACD1, MIM 619232) (2–5). The gene discussed is HSD3B7; the disease is hyperinsulinemic hypoglycemia, familial, 4.