Humoral Hypercalcemia of Malignancy in a Patient with Large Cell Carcinoma of the Lung: Report of Case and Review of Literature

ObjectiveTo report a case of hypercalcemia associated with parathyroid hormone-related protein (PTHrP) in large cell carcinoma of the lung.MethodsWe present a case of PTHrP-mediated hypercalcemia in a patient with a large cell carcinoma of the lung and review the related literature.ResultsA 43-year-old African American man required medical attention because of lethargy, confusion, and poor oral intake. He had bullous emphysema attributable to a 50-pack-year smoking history. On physical examination, vital signs were normal, he was oriented to place and person but not time, and he had cachexia. Breath sounds were decreased in the left lower lung field. Findings on cardiac and abdominal examination were normal. Results of laboratory studies (and corresponding reference ranges) were as follows: calcium 12.1 mg/dL (8.5 to 10.5), albumin 2.0 g/dL (3.5 to 5.0), phosphorus 2 mg/dL (2.5 to 4.5), alkaline phosphatase 68 U/L (40 to 150), intact parathyroid hormone 5 pg/mL (10 to 60), PTHrP 7.0 pmol/L (0.0 to 1.5), 1,25-dihydroxyvitamin D 20.8 pg/mL (25.1 to 66.1), and 25-hydroxyvitamin D 3.7 ng/mL (10 to 60). Computed tomographic scans of the chest showed a large complex lesion in the left lower hemithorax, a small right pleural effusion, and extensive pulmonary emphysema bilaterally. Open lung biopsy revealed a large cell undifferentiated carcinoma. Abdominal and pelvic computed tomographic scans showed no evidence of metastatic involvement. A bone scan was negative for osseous metastatic lesions.ConclusionAlthough the finding is rare, patients with large cell carcinoma of the lung and hypercalcemia may have humoral hypercalcemia mediated by PTHrP. (Endocr Pract. 2007;13:389-395)     

Clonal rat parathyroid cell line expresses a parathyroid hormone-related peptide but not parathyroid hormone itself

A novel parathyroid hormone-related peptide has been identified in tumors associated with the syndrome of humoral hypercalcemia of malignancy. Subsequently, mRNAs encoding this peptide have been found to be expressed in a number of normal tissues, including the parathyroids. Using Northern blotting, RNase protection, and immunochemical techniques, we examined a clonal rat parathyroid cell line originally developed as a model system for studying parathyroid cell physiology. We found that this line expresses the parathyroid hormone-related peptide but not parathyroid hormone itself. Secretion of the parathyroid hormone-related peptide varied inversely with extracellular calcium concentration, but neither calcium nor 1,25-dihydroxyvitamin D3 appeared to influence steady-state parathyroid hormone-related peptide mRNA levels. This clonal line may prove to be an interesting system for studying the factors responsible for tissue-specific parathyroid hormone and parathyroid hormone-related peptide gene expression.     

Hypercalcemia Secondary to Gastrointestinal Stromal Tumors: Parathyroid Hormone-Related Protein Independent Mechanism?

ObjectiveHypercalcemia is a common paraneoplastic manifestation of many malignancies like breast, ovarian, and squamous-cell cancers of head and neck; however, there have been only a few case reports of hypercalcemia associated with gastrointestinal stromal tumors (GISTs). We report a case of GIST presenting with hypercalcemia without any osseous metastasis and provide a literature review regarding the mechanisms of hypercalcemia and therapeutic strategies.MethodsWe present a report of case and a review of the relevant literature.ResultsA 52-year-old woman with history of localized breast cancer in remission and a pelvic 13 × 12 cm GIST with peritoneal, liver, and lung metastases presented with hypercalcemia of 14.3 mg/dL (8.5-10.5 mg/dL). Parathyroid hormone-related protein (PTHrP) was undetectable, intact parathyroid hormone (PTH) was appropriately low at 1 pg/mL (10-65 pg/mL), and 1,25 dihydroxy vitamin D (1,25 OH₂ vit D) was elevated at 131 pg/mL (18-78 pg/mL) with normal renal function. Calcium responded transiently to tyrosine kinase inhibitor therapy and bisphosphonates but within a year, she expired due to tumor progression.ConclusionGIST is a rare cause of hypercalcemia. In addition to PTHrP expression, direct tumor production of 1,25(OH)₂ vit D or 1-α hydroxylase enzyme resulting in activation of 25-hydroxy vitamin D may be an alternative mechanism in GIST-related hypercalcemia. Therapy with tyrosine kinase inhibitors and bisphosphonates is recommended, though prognosis is poor. Further investigations are needed to characterize the etiology and management of hypercalcemia in these patients. (Endocr. Pract. 2013;19: e158-e162)     

Active Crohn Disease and Hypercalcemia Treated With Infliximab: Case Report and Literature Review

ObjectiveTo report a case of 1,25-dihydroxyvitamin D–mediated hypercalcemia caused by active Crohn disease that improved with infliximab therapy.MethodsWe present the clinical and laboratory findings and describe the clinical course of a patient who had hypercalcemia during Crohn disease exacerbations. The literature is reviewed regarding 1,25-dihydroxyvitamin D production in Crohn disease, and the 3 cases of hypercalcemia in individuals with Crohn disease reported in the literature are described.ResultsA 50-year-old man with long-standing Crohn disease treated with multiple bowel resections presented for take-down ileostomy. He was hypercalcemic and had suppressed parathyroid hormone and parathyroid hormone–related peptide levels. Histopathology of the resected ileostomy site and adjacent small bowel indicated active Crohn disease. Hypercalcemia promptly resolved after a few days of treatment with intravenous glucocorticoids. One month later, hypercalcemia recurred in the presence of an inappropriately high 1,25-dihydroxyvitamin D level and increased urinary calcium and serum angiotensin-converting enzyme levels. The serum and urinary calcium levels became normal with infliximab therapy. Three previous reports of hypercalcemia caused by active Crohn disease describe effective treatment with glucocorticoids. This is the first report of successful response to infliximab in this setting.ConclusionHypercalcemia mediated by 1,25-dihydroxyvitamin D in the setting of Crohn disease may respond to glucocorticoid-sparing immunomodulators. (Endocr Pract. 2008;14:87-92)     

1,25-Dihydroxyvitamin D-Mediated Hypercalcemia in Oleogranulomatous Mastitis (Paraffinoma), Ameliorated by Glucocorticoid Administration

ObjectiveTo report a case of oleogranulomatous mastitis (paraffinoma) in which both the hypercalcemia and the inappropriately elevated 1,25-dihydroxyvitamin D [1,25(OH)2D] levels were successfully reduced by administration of prednisone.MethodsWe describe the clinical, imaging, and laboratory findings in the study patient. Furthermore, we review the relevant literature regarding hypercalcemia in oleogranulomatous mastitis.ResultsA 58-year-old man with oleogranulomatous mastitis (paraffinoma)-related hypercalcemia, renal failure, and inappropriately elevated levels of 1,25(OH)2D presented to our institution. Treatment with prednisone—0.5 mg/kg of body weight or 30 mg daily—for 10 days resulted in a reduction of his serum calcium and 1,25(OH)2D levels to near-normal or normal values and a substantial improvement of his renal function. Nevertheless, the patient ultimately died 11 months later of multiple paraffinomarelated complications.ConclusionIn selected cases, treatment with glucocorticoids may offer a temporary relief from paraffinomarelated hypercalcemia until definitive treatment options are feasible. (Endocr Pract. 2010;16:102-106)     

Hypercalcemia in malignancy.

The pathogenesis of hypercalcemia in malignancy has been enigmatic until recent years. Since the realization in 1980 that bioassays for parathyroid hormone detected a cross-reacting substance in malignancy, progress has been remarkably rapid. A parathyroid hormone-related protein was purified and identified by molecular cloning as a 141-amino acid peptide with limited homology to parathyroid hormone itself. Nonetheless, both peptides activate the parathyroid hormone receptor to produce hypercalcemia. It is now clear that the parathyroid hormone-related protein is the cause of hypercalcemia in most solid tumors, particularly squamous and renal carcinomas. New assays for the hormone as well as the related peptide have greatly simplified the differential diagnosis of hypercalcemia. At the same time, new agents for the treatment of hypercalcemia are becoming available, most notably the bisphosphonate drugs.     

The Emerging Role of Denosumab in the Long-Term Management of Parathyroid Carcinoma-Related Refractory Hypercalcemia

Objective: The main cause of death in patients with parathyroid carcinoma is parathyroid hormone (PTH)-induced hypercalcemia. To date, the management of hypercalcemia has been based on the use of bisphosphonates and calcimimetic agents. In recent reports, the use of denosumab has shown encouraging results in cases of refractory hypercalcemia of malignancy. Our objective is to present a case of successful management of resistant hypercalcemia due to parathyroid carcinoma with denosumab, to review similar cases from the literature, and to propose denosumab's use in the clinical management of PTH-induced refractory hypercalcemiaMethods: Presentation of a case report and review of the literature for cases of parathyroid carcinoma–mediated hypercalcemia successfully treated with denosumab.Results: A 71-year-old man with metastatic parathyroid carcinoma was referred to our department for uncontrolled hypercalcemia, resistant to treatment with bisphosphonates and cinacalcet. Treatment with denosumab (120 mg per month) in addition to cinacalcet (180 mg per day) resulted in normalization of calcium levels and maintenance within the normal range for an observation period of 11 months. Review of the literature revealed 4 case reports and a letter to the editor, all of which reported the successful treatment of resistant hypercalcemia associated with parathyroid carcinoma.Conclusion: Based on the above findings of the effectiveness of denosumab in controlling refractory hypercalcemia, its safety in renal failure and the fact that denosumab may reduce PTH-induced bone loss, we endorse its use in the management of hypercalcemia in patients with parathyroid carcinoma and perhaps other conditions with PTH-induced hypercalcemia.Abbreviations: CT = computed tomography IV = intravenous PTH = parathyroid hormone     

Splenic Sarcoidosis without Focal Nodularity: A Case of 1,25-Dihydroxyvitamin D-Mediated Hypercalcemia Localized with FDG PET/CT

ObjectiveTo report an uncommon cause of 1,25-dihydroxyvitamin D (1,25[OH]₂D)-mediated hypercalcemia associated with splenic sarcoidosis and illustrate the evaluation and potential role of fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) in such patients.MethodsWe present detailed clinical features, laboratory results, imaging results, and pathology results for this rare entity, discuss evaluation and management options, and review previous literature.ResultsA 65-year-old male presented with symptomatic hypercalcemia, with a serum calcium level of 14.1 mg/dL 3 months after being initiated on ergocalciferol for vitamin D deficiency. He was found to have a suppressed parathyroid hormone level, normal 25-hydroxyvitamin D (25[OH]D) level, and elevated 1,25(OH)₂D level. Extensive evaluation did not yield a definitive diagnosis. Hiscalcium levels normalized and symptoms resolved on prednisone then recurred when prednisone was discontinued. FDG PET/CT showed intense uptake in the spleen. Splenectomy was performed, which resulted in resolution of hypercalcemia and yielded a diagnosis of splenic sarcoidosis.Conclusion:Splenic sarcoidosis causing hypercalcemia has been rarely reported. Our case is unique in that the spleen lacked typical focal nodularity on cross-sectional CT imaging, which is expected in sarcoid involvement of the spleen. Our case adds to an emerging literature documenting the potential value of FDG PET/CT in localizing otherwise occult 1,25(OH)₂D-mediated hypercalcemia. (Endocr Pract. 2014;20:e28-e33)     

Suppressibility of Parathyroid Hormone in Primary Hyperparathyroidism

ObjectiveTo describe an unusual case of pathologically confirmed primary hyperparathyroidism in a patient presenting with severe hypercalcemia and an undetectable parathyroid hormone (PTH) level.MethodsWe present a detailed case report and outline the serial laboratory findings. In addition, the possible causes of low serum PTH levels in the setting of primary hyperparathyroidism are discussed.ResultsA 16-year-old female patient presented with severe epigastric pain, found to be attributable to acute pancreatitis. At hospital admission, her serum calcium concentration was high (14.0 mg/dL); the patient also had a normal serum phosphorus level of 3.6 mg/dL and an undetectable PTH level (< 0.2 pmol/L). An evaluation for non-PTH-mediated causes of hypercalcemia revealed a partially suppressed thyroid-stimulating hormone concentration and a below normal 1,25-dihydroxyvitamin D level, consistent with her suppressed PTH. One week after the patient was dismissed from the hospital, repeated laboratory studies showed a serum calcium value of 11.1 mg/dL, a serum phosphorus level of 2.8 mg/dL, and an elevated PTH concentration of 11.0 pmol/L, consistent with primary hyperparathyroidism. A repeated 1,25-dihy-droxyvitamin D measurement was elevated. A parathyroid scan showed a parathyroid adenoma in the left lower neck area, and she subsequently underwent successful surgical resection of a pathologically confirmed parathyroid adenoma.ConclusionThis case demonstrates that the serum PTH level can be suppressed in patients with primary hyperparathyroidism. Moreover, it emphasizes the need for careful evaluation of the clinical context in which the PTH measurement is determined. Consideration should be given to repeating measurement of PTH and serum calcium levels when the initial laboratory evaluation of hypercalcemia is unclear because dynamic changes in calcium metabolism may occur in the presence of secondary contributing factors. (Endocr Pract. 2007;13:785-789)     

Humoral hypercalcemia of malignancy: Some enigmas on the clinical features

Humoral hypercalcemia of malignancy (HHM) is a common paraneoplastic syndrome mediated by tumor-derived parathyroid hormone-related peptide (PTHRP), which bears structural and functional similarities to PTH. Thus the clinical features of HHM are very similar to those of primary hyperparathyroidism (1° HPT), a prototype of humoral hypercalcemia caused by PTH. On the other hand, HHM syndrome differs from 1° HPT in several aspects, including serum 1,25(OH)₂D levels, acid-base balance, and bone remodeling process, the reason of which remains largely unknown. We approached these questions using a unique animal model of HHM, nude rats implanted with PTHRP-overproducing human carcinomas. In this review we will summarize the results and discuss the implications in understanding the disease mechanism.     

Phosphatonins: From Discovery to Therapeutics

ObjectivePhosphate is crucial for cell signaling, energy metabolism, nucleotide synthesis, and bone mineralization. The gut-bone-parathyroid-kidney axis is influenced by parathyroid hormone, 1,25-dihydroxyvitamin D, and phosphatonins, especially fibroblast growth factor 23 (FGF23). These hormones facilitate maintenance of phosphate homeostasis. This review summarizes current knowledge regarding the phosphate homeostasis, phosphatonin pathophysiology, and clinical implications of FGF23-related hypophosphatemic disorders, with specific focus on burosumab treatment.MethodA focused literature search of PubMed was conducted.ResultsPhosphatonins including FGF23, secreted frizzled-related protein 4, matrix extracellular phosphoglycoprotein, and fibroblast growth factor 7 play a pathogenic role in several hypophosphatemic disorders. Excess FGF23 inhibits sodium-dependent phosphate cotransporters (NaPi-2a and NaPi-2c), resulting in hyperphosphaturia and hypophosphatemia. Additionally, FGF23 suppresses 1,25-dihydroxyvitamin D synthesis in the proximal renal tubule, and thus, it indirectly inhibits intestinal phosphate absorption. Disorders of FGF23-related hypophosphatemia include X-linked hypophosphatemia (XLH), autosomal dominant hypophosphatemic rickets, autosomal recessive hypophosphatemic rickets, fibrous dysplasia/McCune-Albright syndrome, and tumor-induced osteomalacia (TIO). Complications of conventional therapy with oral phosphate and vitamin D analogs comprise gastrointestinal distress, hypercalcemia, nephrocalcinosis, and secondary/tertiary hyperparathyroidism. In both children and adults with XLH and TIO, the anti-FGF23 antibody burosumab exhibits a favorable safety profile and is associated with healing of rickets in affected children and improvement of osteomalacia in both children and adults.ConclusionThe treatment paradigm for XLH and TIO is changing based on data from recent clinical trials. Research suggest that burosumab is effective and safe for pediatric and adult patients with XLH or TIO.     

Vitamin D–Mediated Hypercalcemia and Cushing Syndrome as Manifestations of Malignant Pleural Mesothelioma

ObjectiveTo report a case of coincident hypercalcemia and Cushing syndrome arising from mesothelioma.MethodsWe describe the clinical, laboratory, imaging, and pathologic findings of a patient with malignant pleural mesothelioma and elucidate the underlying biologic mechanisms resulting in concurrent overexpression of steroid and polypeptide hormones.ResultsA 62-year-old woman presented with chest discomfort and cough. Radiologic imaging revealed a diffuse pleural-based mass encasing the right lung. There was no invasion into the chest wall, diaphragm, or mediastinum, and there was no distant disease. Laboratory analyses documented hypercalcemia and Cushing syndrome, which were due to ectopic overproduction of 1,25-dihydroxyvitamin D (1,25[OH]₂D) and corticotropin. Surgical resection resulted in normocalcemia with normalization of serum 1,25(OH)₂D and reduction in hypercortisolemia. The extrapleural pneumonectomy specimen revealed overexpression of the 1,25(OH)₂D synthetic enzyme 25- hydroxyvitamin-D-1α-hydroxylase (1α-hydroxylase) and underexpression of the 1,25(OH)₂D catabolic enzyme 24- hydroxylase. Immunohistochemistry and electron microscopy demonstrated corticotropin and secretory granules in the tumor tissue.ConclusionThese findings support the evidence for a paracrine role of vitamin D in the resistance of the human host to antigen. (Endocr Pract. 2008;14:1011-1016)     

Hypercalcemia Associated with Mineral Oil-Induced Sclerosing Paraffinomas

ObjectiveGranuloma-forming diseases such as sarcoidosis are associated with extrarenal synthesis of 1,25-dihydroxyvitamin D [1,25(OH)₂D]. We describe a case of extensive skin lesions associated with mineral oil injections in which we provide evidence for cutaneous granuloma synthesis of 1,25(OH)₂D in the pathogenesis of the patient's hypercalcemia.MethodsAnalysis of expression of the 25(OH)D-1a-hydroxylase (1-a OHase [CYP27b1]) was carried out by immunohistochemical analysis of involved skin.ResultsIn involved skin, expression of CYP27b1 was found in the dermis, where it is not normally expressed. Successful management of hypercalcemia was achieved with glucocorticoids.ConclusionsHypercalcemia associated with mineral oil induced skin lesions is likely driven by unregulated expression of CYP27b1 by inflammatory monocytes and macrophages infiltrating the dermis. (Endocr Pract. 2013;19:e50-e56)     

Calcium Carbonate Toxicity: The Updated Milk-Alkali Syndrome; Report of 3 Cases and Review of the Literature

ObjectiveTo describe 3 patients with calcium carbonate-induced hypercalcemia and gain insights into the cause and management of the milk-alkali syndrome.MethodsWe report the clinical and laboratory data in 3 patients who presented with severe hypercalcemia (corrected serum calcium ≥ 14 mg/dL) and review the pertinent literature on milk-alkali syndrome.ResultsThe 3 patients had acute renal insufficiency, relative metabolic alkalosis, and low parathyroid hormone (PTH), PTH-related peptide, and 1,25-dihydroxyvitamin D concentrations. No malignant lesion was found. Treatment included aggressive hydration and varied amounts of furosemide. The 2 patients with the higher serum calcium concentrations received pamidronate intravenously (60 and 30 mg, respectively), which caused severe hypocalcemia. Of the 3 patients, 2 were ingesting acceptable doses of elemental calcium (1 g and 2 g daily, respectively) in the form of calcium carbonate. In addition to our highlighted cases, we review the history, classification, pathophysiologic features, and treatment of milk-alkali syndrome and summarize the cases reported from early 1995 to November 2003.ConclusionMilk-alkali syndrome may be a common cause of unexplained hypercalcemia and can be precipitated by small amounts of orally ingested calcium carbonate in susceptible persons. Treatment with hydration, furosemide, and discontination of the calcium and vitamin D source is adequate. Pamidronate treatment is associated with considerable risk for hypocalcemia, even in cases of initially severe hypercalcemia. (Endocr Pract. 2005;11: 272-280)     

Acid-catalyzed esterification of lysozyme in methanol. Reactivities of individual carboxyl groups

Rats maintained on a diet low in phosphorus produce 1,25-dihydroxyvitamin D₃ from 25-hydroxyvitamin D₃ whether they have been thyroparathyroidectomized or not. On the other hand, rats maintained on low-calcium diets produce 1,25-dihydroxyvitamin D₃, but lose this ability within 48 hr after thyroparathyroidectomy. This loss of ability to synthesize 1,25-dihydroxyvitamin D₃ can be prevented or be restored by replacing their drinking water with calcium gluconate-glucose solution which returns their high serum inorganic phosphorus to normal levels. In thyroparathyroidectomized rats under a variety of conditions, the ability to synthesize 1,25-dihydroxyvitamin D₃ correlates with serum inorganic phosphorus values below 7–8 mg/100 ml while the ability to synthesize 24,25-dihydroxyvitamin D₃ correlates with serum phosphorus values above 7–8 mg/100 ml. There is in addition a close correlation between reduced kidney cortex inorganic phosphorus levels and the synthesis of 1,25-dihydroxyvitamin D₃. It is suggested that the renal tubular cell inorganic phosphorus level underlies the regulation of synthesis of 1,25-dihydroxyvitamin D₃ in the kidney and that the parathyroid hormone and calcitonin regulate 1,25-dihydroxyvitamin D₃ synthesis via their effects on renal cell inorganic phosphorus levels.     

Unusual Recurrence of Hypercalcemia Due to Concurrent Parathyroid Adenoma and Parathyroid Sarcoidosis with Lymph Node Involvement

ObjectiveTo describe a patient presenting with the rare findings of synchronous parathyroid adenoma and parathyroid sarcoidosis.MethodsWe describe the clinical history, physical examination findings, laboratory values, imaging findings, and pathologic data of a man who developed recurrent se- vere hypercalcemia after successful parathyroidectomy.ResultsA 67-year-old man had the following initial blood test results: calcium, 11.1 mg/dL (reference range, 8.5-10.6 mg/dL); albumin 4.0 g/dL (reference range, 3.2-5.2 g/dL); intact parathyroid hormone, 166 pg/mL (refer- ence range, 10-69 pg/mL); creatinine, 1.9 mg/dL; 25-hy- droxyvitamin D, 15 ng/mL (reference range, 30-80 ng/ mL); and 1, 25-dihydroxyvitamin D, 44 pg/mL (reference range, 16-72 pg/mL). Chest x-ray was normal, and delayed images from a technetium Tc 99m sestamibi scan showed increased activity in the right lower pole of the thyroid. Two months after successful parathyroidectomy, the pa- tient was admitted to the hospital with a serum calcium concentration of 17 mg/dL. Pathologic examination of the resected gland confirmed the diagnosis of parathyroid ad- enoma, and subsequent review disclosed the presence of noncaseating granulomas within the adenoma.ConclusionsSarcoidosis with parathyroid involve- ment causing severe hypercalcemia is unique to this case.Recurrent hypercalcemia after successful resection of a parathyroid adenoma may require consideration of poten- tial causes other than the initial diagnosis. (Endocr Pract. 2010;16:463-467)     

1,25-Dihydroxyvitamin D downregulation of TGFalpha/EGFR expression and growth signaling: a mechanism for the antiproliferative actions of the sterol in parathyroid hyperplasia of renal failure

Elevated serum levels of parathyroid hormone (PTH) contribute to the increased morbidity and mortality in renal failure patients. Parathyroid gland hyperplasia is a major cause of high serum PTH. The present studies used the rat model of renal failure to address the mechanisms underlying uremia-induced parathyroid hyperplasia and the antiproliferative properties of vitamin D therapy (1,25-dihydroxyvitamin D (1,25(OH)(2)D(3)) or its less calcemic analogs). Enhanced TGFalpha/EGFR co-expression is the major mitogenic signal in uremic parathyroid glands. At early stages of renal failure, vitamin D therapy efficiently counteracts uremia- and high phosphorus-induced hyperplasia by inhibiting the increases in parathyroid-TGFalpha/EGFR co-expression. In established hyperparathyroidism, characterized by highly enhanced-TGFalpha/EGFR co-expression, vitamin D therapy arrests growth by suppressing EGFR-growth signals from the plasma membrane and nuclear EGFR actions as a transactivator of the cyclin D1 gene, an important contributor to parathyroid hyperplasia in humans. In advanced renal failure, reduced-parathyroid vitamin D receptor levels limits the antiproliferative efficacy of vitamin D therapy. However, non-antiproliferative doses of 1,25-dihydroxyvitamin D enhance the anti-EGFR actions of EGFR-tyrosine kinase inhibitors (TKI). In fact, combined 1,25-dihydroxyvitamin D/TKI therapy inhibits parathyroid hyperplasia more efficiently than phosphorus restriction, the most powerful promoter of parathyroid growth arrest available at present.     

A Case of “Late-Onset” Idiopathic Infantile Hypercalcemia Secondary to Mutations in the CYP24A1 Gene

ObjectiveMutations in the 24-hydroxylase gene, CYP24A1, have recently been reported to cause idiopathic infantile hypercalcemia (IIH), a rare disease presenting in the first year of life that is characterized by increased sensitivity to vitamin D, leading to severe symptomatic hypercalcemia.MethodsWe present a case report and review the relevant literature.ResultsA 24-year-old Caucasian man presented with repetitive signs of nephrolithiasis since the age of 18 years, hypercalciuria (17.1 mmol/24 h), slightly elevated serum calcium concentration (2.64 mmol/L), and inappropriately high levels of 1,25-dihydroxyvitamin D (101 pg/mL) in combination with suppressed levels of circulating parathormone (7.9 pg/mL). Exogenous vitamin D intoxication as well as granulomatous disease or malignancy were excluded. Genetic analysis revealed a loss-of-function mutation in CYP24A1. Of note, our patient denied any prior clinical signs of impaired calcium homeostasis during childhood.ConclusionHere, we describe the exceptional case of a patient with hypercalciuria and recurrent nephrolithiasis secondary to mutations in CYP24A1, without any signs of IIH in childhood, indicating that the phenotypic spectrum includes mild “late-onset” disease that becomes symptomatic in adolescence. Therefore, reduced CYP24A1 activity should be considered as a possible reason for recurrent nephrolithiasis in adults. (Endocr Pract. 2014;20: e91-e95)