Peter J. Tebben

Hypercalcemia, Hypercalciuria, and Elevated Calcitriol Concentrations with Autosomal Dominant Transmission Due to CYP24A1 Mutations: Effects of Ketoconazole Therapy

BACKGROUND Mutations of the CYP24A1 gene, which encodes the 1,25-dihydroxyvitamin D-24-hydroxylase cytochrome P450, Cyp24A1, are predicted to result in elevated 1,25-dihydroxyvitamin D concentrations, hypercalcemia, hypercalciuria, nephrolithiasis, and bone disease. Treatment of hypercalcemia associated with CYP24A1 gene mutations has not been described. METHODS The genetic basis of a syndrome in a 44-yr-old Caucasian male characterized by intermittent hypercalcemia, hypercalciuria, elevated serum 1,25-dihydroxyvitamin D, undetectable serum 24,25-dihydroxyvitamin D, metabolically active nephrolithiasis, and reduced bone mineral density of the lumbar spine was examined. Sequencing of the CYP24A1 gene and biochemical and genetic analysis of seven family members in three generations was carried out. Because of hypercalcemia, hypercalciuria, and metabolically active nephrolithiasis, the patient was treated with a cytochrome 3A inhibitor, ketoconazole, 200 mg orally every 8 h, for 2 months. RESULTS The sequence of the CYP24A1 gene showed two canonical splice junction mutations in the proband. Analysis of family members showed a phenotype associated one or both mutations, suggesting autosomal dominant transmission with partial penetrance of the trait. After therapy with ketoconazole, statistically significant reductions in previously elevated urinary calcium into the normal range were noted. Previously elevated serum 1,25-dihydroxyvitamin D and calcium concentrations decreased, and previously decreased PTH concentrations increased into the normal range, but the differences were not statistically significant. CONCLUSIONS In a syndrome characterized by intermittent hypercalcemia, hypercalciuria, elevated 1,25-dihydroxyvitamin D, undetectable 24,25-dihydroxyvitamin D concentrations, splice junction mutations of the CYP24A1 gene, and autosomal dominant transmission of the trait, treatment with ketoconazole is useful in reducing urinary calcium.

Fibroblast Growth Factor 23, Parathyroid Hormone, and 1α,25-Dihydroxyvitamin D in Surgically Treated Primary Hyperparathyroidism

OBJECTIVE To determine whether fibroblast growth factor 23 (FGF23) contributes to the hypophosphatemia of primary hyperparathyroldism. PATIENTS AND METHODS Thirteen adult patients with primary hyperparathyroidism had serum collected before and after parathyroidectomy for analysis of inorganic phosphorus, calcium, 1alpha,25-dihydroxyvitamin D (1alpha,25[OH]2D), parathyroid hormone (PTH), FGF23, creatinine, and bone-specific alkaline phosphatase (BSAP). Patients were recruited between July 24, 2003, and February 11, 2004. RESULTS Before surgery, patients had elevated serum calcium and PTH concentrations. Serum phosphorus concentrations were in the low-normal range. The FGF23 concentrations were not elevated in patients with primary hyperparathyroidism compared with healthy controls. Within 24 hours of surgery, serum calcium, PTH, 1alpha,25(OH)2D, and BSAP concentrations were lower (P < .002 for all) and phosphorus concentrations were higher (P = .003) than in the preoperative state. The FGF23 concentrations were similar 1 day and 6 weeks after surgery. The FGF23 concentrations did not correlate with serum phosphorus, calcium, PTH, 1alpha,25(OH)2D, creatinine, or BSAP concentrations in the preoperative or postoperative state. CONCLUSION Parathyroid hormone is the major regulator of serum phosphorus concentrations in patients with primary hyperparathyroidism. Fibroblast growth factor 23 does not appear to play a role in phosphorus homeostasis in patients with surgically treated primary hyperparathyroidism.

Increasing Incidence of Nutritional Rickets: A Population-Based Study in Olmsted County, Minnesota

OBJECTIVE To determine temporal trends in incidence and risk factors of nutritional rickets in a community-based population. PATIENTS AND METHODS Rochester Epidemiology Project data were used to identify all children (aged <18 years) residing in Olmsted County, Minnesota, between January 1, 1970, and December 31, 2009, with diagnostic codes corresponding to rickets, vitamin D deficiency, hypovitaminosis D, rachitis, osteomalacia, genu varum, genu valgum, craniotabes, hypocalcemia, hypocalcemic seizure, and tetany. Record abstraction was performed to select individuals with radiographic confirmation of rickets. Age- and sex-matched controls were identified for the evaluation of risk factors. The main outcome measure was radiographic evidence of rickets without identifiable inherited, genetic, or nonnutritional causes. Incidence rates were calculated using Rochester Epidemiology Project census data. RESULTS Of 768 children with eligible diagnostic codes, 23 had radiographic evidence of rickets; of these, 17 children had nutritional rickets. All 17 children were younger than 3 years, and 13 (76%) were of nonwhite race/ethnicity. Clinical presentation included poor growth (n=12), leg deformity (n=8), motor delay (n=5), leg pain (n=3), weakness (n=3), and hypocalcemia or tetany (n=2). The incidence of nutritional rickets in children younger than 3 years was 0, 2.2, 3.7, and 24.1 per 100,000 for the decades beginning in 1970, 1980, 1990, and 2000, respectively (P=.003 for incidence trend). Nutritional rickets was associated with black race, breast-feeding, low birth weight, and stunted growth (P<.05 for all). Four of 13 patients (31%) who underwent 25-hydroxyvitamin D testing had values less than 10 ng/mL. CONCLUSION Nutritional rickets remains rare, but its incidence has dramatically increased since 2000. Not all cases of rickets can be attributed to vitamin D deficiency.

Secreted frizzled-related protein-4 reduces sodium–phosphate co-transporter abundance and activity in proximal tubule cells

The phosphatonin, secreted frizzled-related protein-4 (sFRP-4), induces phosphaturia and inhibits 25-hydroxyvitamin D 1α-hydroxylase activity normally induced in response to hypophosphatemia. To determine the mechanism by which sFRP-4 alters renal phosphate (Pi) transport, we examined the effect of sFRP-4 on renal brush border membrane (BBMV) Na+-dependent Pi uptake, and the abundance and localization of the major Na+–Pi-IIa co-transporter in proximal tubules and opossum kidney (OK) cells. Infusion of sFRP-4 increased renal fractional excretion of Pi and decreased renal β-catenin concentrations. The increase in renal Pi excretion with sFRP-4 infusion was associated with a 21.9±3.4% decrease in BBMV Na+-dependent Pi uptake (P<0.001) compared with a 39.5±2.1% inhibition of Na+-dependent Pi transport in renal BBMV induced by PTH (P<0.001). sFRP-4 infusion was associated with a 30.7±4.8% decrease in Na+–Pi-IIa co-transporter protein abundance (P<0.01) assessed by immunoblotting methods compared to a 45.4±8.8% decrease induced by PTH (P<0.001). In OK cells, sFRP-4 reduced surface expression of a heterologous Na+–Pi-IIa co-transporter. We conclude that sFRP-4 increases renal Pi excretion by reducing Na+–Pi-IIa transporter abundance in the brush border of the proximal tubule through enhanced internalization of the protein.

Vitamin D and the kidney

The kidney is essential for the maintenance of normal calcium and phosphorus homeostasis. Calcium and inorganic phosphorus are filtered at the glomerulus, and are reabsorbed from tubular segments by transporters and channels which are regulated by 1α,25-dihydroxyvitamin (1α,25(OH)(2)D) and parathyroid hormone (PTH). The kidney is the major site of the synthesis of 1α,25(OH)(2)D under physiologic conditions, and is one of the sites of 24,25-dihydroxyvitamin D (24,25(OH)(2)D) synthesis. The activity of the 25(OH)D-1α-hydroxylase, the mixed function oxidase responsible for the synthesis of 1α,25(OH)(2)D, is regulated by PTH, 1α,25(OH)(2)D, fibroblast growth factor 23 (FGF23), inorganic phosphorus and other growth factors. Additionally, the vitamin D receptor which binds to, and mediates the activity of 1α,25(OH)(2)D, is widely distributed in the kidney. Thus, the kidney, by regulating multiple transport and synthetic processes is indispensible in the maintenance of mineral homeostasis in physiological states.

Pediatric Endocrine Surgery: A 20-Year Experience at the Mayo Clinic

CONTEXT Surgically managed endocrinopathies are rare in children. Most surgeons have limited experience in this field. Herein we report our operative experience with pediatric patients, performed over two decades by high-volume endocrine surgeons. SETTING The study was conducted at the Mayo Clinic (a tertiary referral center). PATIENTS Patients were <19 years old and underwent an endocrine operation (1993-2012). MAIN OUTCOME MEASURES Demographics, surgical procedure, diagnoses, morbidity, and mortality were retrospectively reviewed. RESULTS A total of 241 primary cases included 177 thyroid procedures, 13 neck dissections, 24 parathyroidectomies, 14 adrenalectomies, 7 paragangliomas, and 6 pancreatic procedures. Average age of patients was 14.2 years. There were 133 total thyroidectomies and 40 hemithyroidectomies. Fifty-three cases underwent a central or lateral neck dissection. Six-month follow-up was available for 98 total thyroidectomy patients. There were four cases of permanent hypoparathyroidism (4%) and no permanent recurrent laryngeal nerve (RLN) paralyses. Sequelae of neck dissections included temporary RLN neurapraxia and Horners syndrome. Parathyroidectomy was performed on 24 patients: 20 with primary hyperparathyroidism (HPT), three with tertiary HPT, and one with familial hypocalciuric hypocalcemia. Three patients (16%) had recurrent HPT, all with multiglandular disease. One patient had temporary RLN neurapraxia. We performed seven bilateral and seven unilateral adrenalectomies; eight were laparoscopic. Indications included pheochromocytoma, Cushings syndrome, adrenocortical carcinoma, congenital adrenal hyperplasia, and ganglioneuroma. One death was due to adrenocortical carcinoma. Five paraganglioma patients had succinate dehydrogenase subunit B mutations, and one recurred. Six patients with insulinoma underwent enucleation (n = 5) or distal pancreatectomy (n = 1). A single postoperative abscess was managed nonoperatively. CONCLUSION Pediatric endocrine procedures are uncommon but can be safely performed with complication rates comparable to those of the adult population. It is imperative that these operations be performed by high-volume surgeons.

Germline TGF-β receptor mutations and skeletal fragility: A report on two patients with Loeys–Dietz syndrome†

Loeys–Dietz syndrome (LDS, OMIM # 609192) caused by heterozygous mutations in TGFBR1 and TGFBR2 has recently been described as an important cause of familial aortic aneurysms. These patients have craniofacial and skeletal features that overlap with the Marfan syndrome (MFS), and more importantly, have significant vascular fragility as is seen in MFS and Ehlers–Danlos syndrome Type IV (EDS‐IV). The skeletal phenotype with respect to low bone mineral density and skeletal fragility is not clear. We present two patients with LDS with significant skeletal fragility. The first is a 17‐year‐old male who had talipes equinovarus, diaphragmatic and inguinal and herniae, aortic root dilatation necessitating surgical repair, craniofacial and skeletal dysmorphism consistent with LDS, and a history of numerous fragility fractures leading to significant skeletal deformity. He was found to be heterozygous for a c.923T > C transition in exon 4 of TGFBR2. The second is a 26‐year‐old male with submucous cleft palate, talipes equinovarus, pectus excavatum requiring surgery, inguinal hernia, and aneurysms in the ascending aorta, abdominal aorta, carotid, subclavian, vertebral and brachial arteries requiring surgical repairs. He also had craniofacial and skeletal dysmorphism consistent with LDS, multiple fractures in childhood, low bone mineral density, and was found to be heterozygous for a c.1561 T > C transition in exon 7 of TGFBR2. These case studies highlight the importance of paying close attention to fractures and bone density in patients with LDS. Osteopenia or osteoporosis may become increasingly important issues as earlier detection and treatment of the vascular complications of LDS improves life expectancy in these patients.

Oncogenic osteomalacia: localization of underlying peripheral mesenchymal tumors with use of Tc 99m sestamibi scintigraphy.

OBJECTIVE To highlight a strategy for potential detection of mesenchymal tumors in oncogenic malacia, as illustrated by 3 cases. METHODS Three case reports are presented in which successful localization of the offending neoplasm was accomplished by using whole-body Tc 99m sestamibi scanning. Alternative localization techniques are also reviewed. RESULTS Oncogenic osteomalacia occurs infrequently and is caused by neoplasms that secrete phosphatonins, substances that interfere with proximal tubular resorption of phosphorus and can result in phosphaturia, hypophosphatemia, reduced 1,25-dihydroxyvitamin D concentration, and osteomalacia. Removal of the underlying neoplasm results in complete resolution of all biochemical, pathologic, and physical manifestations of this disorder, as shown in our 3 patients. Because the neoplasms are small and can occur in any tissue compartment, they are difficult to localize, a feature that often results in therapeutic failure. CONCLUSION We conclude that use of whole-body Tc 99m sestamibi scanning may be an appropriate and cost-effective initial strategy for the localization of peripheral phosphatonin-secreting tumors.

Granulomatous adenohypophysitis after interferon and ribavirin therapy

OBJECTIVE To describe a case of granulomatous hypophysitis occurring after treatment with interferon alfa-2b and ribavirin for hepatitis C. METHODS Clinical, radiologic, laboratory, and pathologic assessments of a woman with granulomatous hypophysitis and interferon-induced thyroiditis are presented. RESULTS A 42-year-old woman with hepatitis C was treated with interferon alfa-2b and ribavirin for 5 months. She was referred after symptoms of thyrotoxicosis developed, in conjunction with laboratory and radiographic evidence of thyroiditis. During the initial evaluation, she was weak and hypotensive; biochemical evaluation showed undetectable plasma cortisol and corticotropin concentrations. Magnetic resonance imaging revealed diffuse enlargement of the pituitary gland, which encroached on but did not compress the optic chiasm. Treatment with supraphysiologic doses of prednisone resulted in clinical and radiographic improvement. Once physiologic doses of glucocorticoids were instituted, however, follow-up magnetic resonance imaging showed substantial progression of the diffuse pituitary enlargement and mild compression of the optic chiasm. Surgical debulking of the mass and histologic evaluation showed chronic, noncaseating granulomatous hypophysitis. An extensive evaluation for secondary causes of granulomatous inflammation of the pituitary revealed only an elevated angiotensin-converting enzyme level; no organisms were identified. After 2 courses of high-dose glucocorticoids, she had radiographic evidence of decreased size of the pituitary lesion but continued to have multiple anterior pituitary hormone deficiencies. CONCLUSION Granulomatous hypophysitis and sarcoidosis of the pituitary are rare disorders. Hypophysitis should be considered in patients receiving interferon and ribavirin therapy who have symptoms consistent with pituitary dysfunction.

Elevated Fibroblast Growth Factor 23 in Women With Malignant Ovarian Tumors

OBJECTIVE To determine whether fibroblast growth factor 23 (FGF23) concentrations are altered in women with ovarian cancers in which FGF physiology is known to be abnormal. PATIENTS AND METHODS Between May 2002 and September 2003 at the Mayo Clinic in Rochester, Minn, plasma or serum FGF23 concentrations were measured in 39 healthy women and in 14 with benign ovarian tumors, 14 with early-stage ovarian cancer, and 13 with advanced-stage ovarian cancer. Immunohistochemistry using anti-human FGF23 antibodies was performed on tissue from benign masses and advanced-stage tumors. RESULTS Serum or plasma FGF23 concentrations were significantly higher in women with advanced-stage ovarian cancer compared with concentrations in women with early-stage ovarian cancer or benign disease or in healthy women. A significant positive correlation was seen between serum iFGF23 and cFGF23 concentrations and stage of disease. Serum iFGF23 and cFGF23 concentrations were positively correlated with serum phosphorus among women with ovarian cancer. No patients with elevated iFGF23 or cFGF23 concentrations had hypophosphatemia. Immunohistochemistry detected FGF23 tissue staining in malignant ovarian cancer cells. CONCLUSION Serum or plasma FGF23 concentrations are elevated in patients with advanced-stage epithellal ovarian cancer without reductions in serum phosphate concentrations. The presence of elevated FGF23 concentrations in patients with an ovarian mass should suggest advanced-stage disease.