As mentioned, several small observational studies have led to authorization of cholic acid as an orphan drug in the EU for 3β-HSD, AKR1D1, CTX, AMACR and CYP7A1 defects, and in the United States for ZSD as well [15, 16, 20]. The gene discussed is AKR1D1; the disease is peroxisome biogenesis disorder.