A Case of Delayed Diagnosis of Idiopathic Infantile Hypercalcemia Due to CYP24A1 Mutation: A 10-Year Journey

The parathyroid gland is responsible for the synthesis and secretion of parathyroid hormone, which is synthesized and released at an inverse relationship to the level of ionized calcium in the blood. Primary hyperparathyroidism affects women more than men. There are various causes for hyperparathyroidism-induced hypercalcemia and the most common cause is parathyroid adenoma. A less common cause of vitamin D-mediated parathyroid hormone-independent hypercalcemia is the loss of function mutation of the CYP24A1 gene. The CYP24A1 gene encodes the vitamin D 24-hydroxylase enzyme, responsible for hydroxylating the active form of vitamin D into an inactive form, and mutations in the CY24A1 gene can lead to elevated active vitamin D metabolite levels. It can result in hypercalcemia and hypercalciuria-related complications. We present a case of a 72-year-old male patient referred to the endocrine clinic, who had repeated treatments for hypercalcemia and recurrent renal calculi. He underwent ultrasound, computerized tomography, and sestamibi scans, all reported as normal. Following this, the patient underwent a positron emission tomography (PET) scan, which was also normal. He then finally underwent genetic testing and tested positive for the CYP24A1 gene. He was started on fluconazole 50mg once a day and cinacalcet 30mg twice with normalization of calcium level. Three of his family members also tested positive for the condition.