CYP24A1 and hyperinsulinemic hypoglycemia, familial, 4: Measurement of 1,25(OH)2D is helpful in the investigation of patients with unexplained hypercalcaemia, sarcoidosis, granulomatous disorders, pseudo-vitamin D deficiency, rickets, tumour-induced osteomalacia, hyperparatiroidism, and CYP24A1 deficiency [20].