Thus, calcifediol may be an alternative to optimize 25(OH)D status and should beconsidered in specific situations, including obesity, malabsorption syndromes(e.g., Crohn’s disease, celiac disease, and cystic fibrosis),bariatric surgery, chronic liver diseases, and the use of drugs that interfere withthe hepatic cytochrome P-450 enzyme system, such as corticosteroids,anticonvulsants, and antiretrovirals (8,11,15). The gene discussed is CYP4F3; the disease is obesity due to melanocortin 4 receptor deficiency.