Successful treatment of hypercalcaemia associated with a CYP24A1 mutation with fluconazole

Mutations in CYP24A1, encoding the vitamin D 24-hydroxlase enzyme, are known to cause a range of clinical phenotypes and presentations including idiopathic infantile hypercalcaemia and adult-onset nephrocalcinosis and nephrolithiasis. In the context of raised or borderline high serum calcium levels, suppressed PTH and persistently elevated 1,25 dihydroxy vitamin D levels, this rare condition should be considered. We present a case where this biochemical pattern was seen and mutations in CYP24A1 were confirmed. We were able to successfully control serum calcium levels and reduce urinary calcium excretion by treatment with low-dose fluconazole, which inhibits vitamin D-synthesizing enzymes (including 25-hydroxylases and 1-α-hydroxylase) thereby reducing levels of 1,25–dihydroxy vitamin D.