Mild Idiopathic Infantile Hypercalcemia-Part 2: A Longitudinal Observational Study

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.

One half-century of advances in the evaluation and management of disorders of bone and mineral metabolism in children and adolescents

The past 50 years of research in pediatric bone and mineral metabolism have led to remarkable progress in the identification and characterization of disorders that affect the developing skeleton. Progress has been facilitated through advances in both technology and biology and this paper provides a brief description of some but not all of the key findings, including identification of the calcium sensing receptor and the polypeptides parathyroid hormone and parathyroid hormone-related protein as well as their shared receptor and signal generating pathways; the elucidation of vitamin D metabolism and actions; discovery of fibroblast growth factor 23 (FGF23), the sodium-phosphate co-transporters and the other components that regulate phosphate metabolism. Moreover, the past half-century of research has led to the delineation of the molecular bases for genetic forms of hypoparathyroidism, pseudohypoparathyroidism, and primary hyperparathyroidism as well as the determination of the genetic causes of osteogenesis imperfecta, osteopetrosis, hypophosphatasia, and other disorders of mineral/bone homeostasis. During the next decade we expect that many of these fundamental discoveries will lead to the development of innovative treatments that will improve the lives of children with these disorders.

Long-term Efficacy and Safety of Rifampin in the Treatment of a Patient Carrying a CYP24A1 Loss-of-Function Variant

BACKGROUND

Pharmacological therapy may be useful in the treatment of moderate to severe hypercalcemia in patients with infantile hypercalcemia-1 (HCINF1) due to pathogenic variants in the cytochrome P450 24 subfamily A member 1 (CYP24A1). Rifampin is an antituberculosis drug that is a potent inducer of cytochrome P450 3 subfamily A member 4, which is involved in an alternative catabolic pathway of vitamin D. The efficacy of rifampin in improving hypercalcemia was previously reported, but many questions remain on the long-term efficacy and safety. The aim of the study is to test the long-term efficacy and safety of rifampin in a patient with HCINF1.

METHODS

We report clinical, biochemical, and imaging features of a 23-year-old man affected by HCINF1 with moderate hypercalcemia (12.9 mg/dL), symptomatic nephrolithiasis, nephrocalcinosis, and impaired kidney function [estimated glomerular filtration rate (eGFR) 60 mL/min/1.73 m2] treated with rifampin for an overall period of 24 months. Kidney, liver, and adrenal function were evaluated at every follow-up visit.

RESULTS

In 2 months, rifampin induced a normalization of serum calcium (9.6 mg/dL) associated with an improvement of kidney function (eGFR 92 mL/min/1.73 m2) stable during the treatment. After 15 months, rifampin was temporally withdrawn because of asthenia, unrelated to impairment of adrenal function. After 3 months, the timing of drug administration was shifted from the morning to the evening, obtaining the remission of asthenia. At the end of follow-up, the nephrolithiasis disappeared and the nephrocalcinosis was stable.

CONCLUSIONS

Rifampin could represent an effective choice to induce a stable reduction of calcium levels in patients with HCINF1, with a good safety profile.