The following diseases were all diagnosed in a single patient: NR1H4 deficiency (PFIC5), primary bile acid synthesis deficiency due to delta 4-3-oxoid dehydrogenase deficiency (AKR1D1), primary bile acid synthesis deficiency due to bile acid conjugation defects (BAAT), cerebrotendinous xanthomatosis (CYP27A1) and tricho-hepato-enteric syndrome (TTC37 gene). The gene discussed is CYP27A1; the disease is hyperinsulinemic hypoglycemia, familial, 4.