MANAGEMENT OF ENDOCRINE DISEASE: Postsurgical hypoparathyroidism: current treatments and future prospects for parathyroid allotransplantation.

BACKGROUND: Permanent postsurgical hypoparathyroidism (POSH) is a major complication of anterior neck surgery in general and of thyroid surgery in particular. Depending on diagnostic criteria, up to 10% of patients undergoing bilateral thyroid surgery develop POSH. This leads to a multitude of symptoms that decrease the quality of life and burden the healthcare provision through complex needs for medication and treatment of specific complications, such as seizures and laryngospasm. METHODS: Narrative review of current medical treatments for POSH and of the experience accumulated with parathyroid allotransplantation. RESULTS: In most patients, POSH is controlled with regular use of calcium supplements and active vitamin D analogues but a significant proportion of patients continue to experience severe symptoms requiring repeated emergency admissions. Replacement therapy with synthetic PTH compounds (PTH1-34, Natpara® and PTH1-84, teriparatide, Forsteo®) has been assessed in multicentre trials, but the use of this medication is restricted by costs and concerns related to the risk of development of osteosarcoma. Based on recent case reports of successful allotransplantation of parathyroid tissue between siblings, there is renewed interest in this technique. Data on selection of donors, parathyroid cell preparation before allotransplantation, site and timing of transplantation, need for immunosuppression and long-term outcomes are reviewed. CONCLUSION: A prospective trial to assess the efficacy of parathyroid allotransplantation in patients with severely symptomatic protracted post-surgical hypoparathyroidism is warranted.

Case report: a 10-year-old girl with primary hypoparathyroidism and systemic lupus erythematosus.

Objectives Hypoparathyroidism is a rare disease in children that occurs as a result of autoimmune destruction of the parathyroid glands, a defect in parathyroid gland development or secondary to physical parathyroid gland disturbance. Typical symptoms of hypoparathyroidism present as hypocalcaemia and hyperphosphatemia due to decreased parathyroid hormone secretion and may lead to nerve and muscles disturbances resulting in clinical manifestation of tetany, arrhythmias and epilepsy. Currently, there is no conventional hormone replacement treatment for hypoparathyroidism and therapeutic approaches include normalising mineral levels using an oral calcium supplement and active forms of vitamin D. Case presentation We present the case of a 10-year-old girl with primary hypoparathyroidism who had no prior history of autoimmune disorders, but who subsequently developed systemic lupus erythematosus.

Genetic variants of calcium and vitamin D metabolism in kidney stone disease.

Kidney stone disease (nephrolithiasis) is a major clinical and economic health burden with a heritability of ~45-60%. We present genome-wide association studies in British and Japanese populations and a trans-ethnic meta-analysis that include 12,123 cases and 417,378 controls, and identify 20 nephrolithiasis-associated loci, seven of which are previously unreported. A CYP24A1 locus is predicted to affect vitamin D metabolism and five loci, DGKD, DGKH, WDR72, GPIC1, and BCR, are predicted to influence calcium-sensing receptor (CaSR) signaling. In a validation cohort of only nephrolithiasis patients, the CYP24A1-associated locus correlates with serum calcium concentration and a number of nephrolithiasis episodes while the DGKD-associated locus correlates with urinary calcium excretion. In vitro, DGKD knockdown impairs CaSR-signal transduction, an effect rectified with the calcimimetic cinacalcet. Our findings indicate that studies of genotype-guided precision-medicine approaches, including withholding vitamin D supplementation and targeting vitamin D activation or CaSR-signaling pathways in patients with recurrent kidney stones, are warranted.

Current and emerging therapies for PNETs in patients with or without MEN1.

Pancreatic neuroendocrine tumours (PNETs) might occur as a non-familial isolated endocrinopathy or as part of a complex hereditary syndrome, such as multiple endocrine neoplasia type 1 (MEN1). MEN1 is an autosomal dominant disorder characterized by the combined occurrence of PNETs with tumours of the parathyroids and anterior pituitary. Treatments for primary PNETs include surgery. Treatments for non-resectable PNETs and metastases include biotherapy (for example, somatostatin analogues, inhibitors of receptors and monoclonal antibodies), chemotherapy and radiological therapy. All these treatments are effective for PNETs in patients without MEN1; however, there is a scarcity of clinical trials reporting the efficacy of the same treatments of PNETs in patients with MEN1. Treatment of PNETs in patients with MEN1 is challenging owing to the concomitant development of other tumours, which might have metastasized. In recent years, preclinical studies have identified potential new therapeutic targets for treating MEN1-associated neuroendocrine tumours (including PNETs), and these include epigenetic modification, the ß-catenin-wingless (WNT) pathway, Hedgehog signalling, somatostatin receptors and MEN1 gene replacement therapy. This Review discusses these advances.

Hypoparathyroidism.

Hypoparathyroidism is a disease characterized by inadequately low circulating concentrations of parathyroid hormone (PTH) resulting in low calcium levels and increased phosphate levels in the blood. Symptoms of the disease result from increased neuromuscular irritability caused by hypocalcaemia and include tingling, muscle cramps and seizures. The most common cause of the disease is inadvertent removal of, or injury to, the parathyroid glands during neck surgery, followed by genetic, idiopathic and autoimmune aetiologies. Conventional treatment includes activated vitamin D and/or calcium supplements, but this treatment does not fully replace the functions of PTH and can lead to short-term problems (such as hypocalcaemia, hypercalcaemia and increased urinary calcium excretion) and long-term complications (which include nephrocalcinosis, kidney stones and brain calcifications). PTH replacement has emerged as a new treatment option. Clinical trials using human PTH(1-34) and PTH(1-84) showed that this treatment was safe and effective in studies lasting up to 6 years. Recombinant human PTH(1-84) has been approved in the United States and Europe for the management of hypoparathyroidism; however, its effect on long-term complications is still being evaluated. Clinical practice guidelines, which describe the consensus of experts in the field, have been published and recognize the need for more research to optimize care. In this Primer, we summarize current knowledge of the prevalence, pathophysiology, clinical presentation and management of hypoparathyroidism.

Mouse models for inherited endocrine and metabolic disorders.

In vivo models represent important resources for investigating the physiological mechanisms underlying endocrine and metabolic disorders, and for pre-clinical translational studies that may include the assessments of new treatments. In the study of endocrine diseases, which affect multiple organs, in vivo models provide specific advantages over in vitro models, which are limited to investigation of isolated systems. In recent years, the mouse has become the popular choice for developing such in vivo mammalian models, as it has a genome that shares ∼85% identity to that of man, and has many physiological systems that are similar to those in man. Moreover, methods have been developed to alter the expression of genes in the mouse, thereby generating models for human diseases, which may be due to loss- or gain-of-function mutations. The methods used to generate mutations in the mouse genome include: chemical mutagenesis; conventional, conditional and inducible knockout models; knockin models and transgenic models, and these strategies are often complementary. This review describes some of the different strategies that are utilised for generating mouse models. In addition, some mouse models that have been successfully generated by these methods for some human hereditary endocrine and metabolic disorders are reviewed. In particular, the mouse models generated for parathyroid disorders, which include: the multiple endocrine neoplasias; hyperparathyroidism-jaw tumour syndrome; disorders of the calcium-sensing receptor and forms of inherited hypoparathyroidism are discussed. The advances that have been made in our understanding of the mechanisms of these human diseases by investigations of these mouse models are described.

CLC-5 and KIF3B interact to facilitate CLC-5 plasma membrane expression, endocytosis, and microtubular transport: relevance to pathophysiology of Dent's disease.

Renal tubular reabsorption is important for extracellular fluid homeostasis and much of this occurs via the receptor-mediated endocytic pathway. This pathway is disrupted in Dent's disease, an X-linked renal tubular disorder that is characterized by low-molecular-weight proteinuria, hypercalciuria, nephrolithiasis, and renal failure. Dent's disease is due to mutations of CLC-5, a chloride/proton antiporter, expressed in endosomes and apical membranes of renal tubules. Loss of CLC-5 function alters receptor-mediated endocytosis and trafficking of megalin and cubilin, although the underlying mechanisms remain to be elucidated. Here, we report that CLC-5 interacts with kinesin family member 3B (KIF3B), a heterotrimeric motor protein that facilitates fast anterograde translocation of membranous organelles. Using yeast two-hybrid, glutathione-S-transferase pull-down and coimmunoprecipitation assays, the COOH terminus of CLC-5 and the coiled-coil and globular domains of KIF3B were shown to interact. This was confirmed in vivo by endogenous coimmunoprecipitation of CLC-5 and KIF3B and codistribution with endosomal markers in mouse kidney fractions. Confocal live cell imaging in kidney cells further demonstrated association of CLC-5 and KIF3B, and transport of CLC-5-containing vesicles along KIF3B microtubules. KIF3B overexpression and underexpression, using siRNA, had reciprocal effects on whole cell chloride current amplitudes, CLC-5 cell surface expression, and endocytosis of albumin and transferrin. Clcn5(Y/-) mouse kidneys and isolated proximal tubular polarized cells showed increased KIF3B expression, whose effects on albumin endocytosis were dependent on CLC-5 expression. Thus, the CLC-5 and KIF3B interaction is important for CLC-5 plasma membrane expression and for facilitating endocytosis and microtubular transport in the kidney.