Medical Hypoparathyroidism

Hypoparathyroidism is a metabolic disorder characterized by hypocalcemia, hyperphosphatemia, and inadequate levels of or function of parathyroid hormone (PTH). The authors review the nonsurgical or medical causes of hypoparathyroidism. The most common of the nonsurgical causes is autoimmune destruction of the parathyroid. Magnesium deficiency or excess can cause a functional hypoparathyroidism. Genetic conditions result in hypoparathyroidism as part of a syndrome or in isolation. Pseudohypoparathyroidism reflects a resistance to PTH. Infiltrative, metastatic, radiation destruction, mineral deposition, or idiopathic are uncommon causes of hypoparathyroidism. This article reviews the causes of hypoparathyroidism and an approach to the evaluation of this condition.

EAST syndrome: Clinical, pathophysiological, and genetic aspects of mutations in KCNJ10

EAST syndrome is a recently described autosomal recessive disorder secondary to mutations in KCNJ10 (Kir4.1), a gene encoding a potassium channel expressed in the brain, eye, ear and kidney. This condition is characterized by 4 cardinal features; Epilepsy, Ataxia, Sensorineural deafness, and (a renal salt-wasting) Tubulopathy, hence the acronym EAST syndrome. Here we review reported clinical manifestations, in particular the neurological signs and symptoms which typically have the most impact on the quality of life of patients. In addition we review the pathophysiology and genetic aspects of the disease. So far 14 different KCNJ10 mutations have been published which either directly affect channel function or may lead to mislocalisation. Investigations of the pathophysiology may provide clues to potential treatments.

Renal control of calcium, phosphate, and magnesium homeostasis

Calcium, phosphate, and magnesium are multivalent cations that are important for many biologic and cellular functions. The kidneys play a central role in the homeostasis of these ions. Gastrointestinal absorption is balanced by renal excretion. When body stores of these ions decline significantly, gastrointestinal absorption, bone resorption, and renal tubular reabsorption increase to normalize their levels. Renal regulation of these ions occurs through glomerular filtration and tubular reabsorption and/or secretion and is therefore an important determinant of plasma ion concentration. Under physiologic conditions, the whole body balance of calcium, phosphate, and magnesium is maintained by fine adjustments of urinary excretion to equal the net intake. This review discusses how calcium, phosphate, and magnesium are handled by the kidneys.

The sodium chloride cotransporter SLC12A3: new roles in sodium, potassium, and blood pressure regulation

SLC12A3 encodes the thiazide-sensitive sodium chloride cotransporter (NCC), which is primarily expressed in the kidney, but also in intestine and bone. In the kidney, NCC is located in the apical plasma membrane of epithelial cells in the distal convoluted tubule. Although NCC reabsorbs only 5 to 10% of filtered sodium, it is important for the fine-tuning of renal sodium excretion in response to various hormonal and non-hormonal stimuli. Several new roles for NCC in the regulation of sodium, potassium, and blood pressure have been unraveled recently. For example, the recent discoveries that NCC is activated by angiotensin II but inhibited by dietary potassium shed light on how the kidney handles sodium during hypovolemia (high angiotensin II) and hyperkalemia. The additive effect of angiotensin II and aldosterone maximizes sodium reabsorption during hypovolemia, whereas the inhibitory effect of potassium on NCC increases delivery of sodium to the potassium-secreting portion of the nephron. In addition, great steps have been made in unraveling the molecular machinery that controls NCC. This complex network consists of kinases and ubiquitinases, including WNKs, SGK1, SPAK, Nedd4-2, Cullin-3, and Kelch-like 3. The pathophysiological significance of this network is illustrated by the fact that modification of each individual protein in the network changes NCC activity and results in salt-dependent hypotension or hypertension. This review aims to summarize these new insights in an integrated manner while identifying unanswered questions.

Disorders of calcium and magnesium balance: a physiology-based approach

Disorders of calcium and magnesium balance are physiologically interesting and clinically challenging. In this review, we attempt to bridge the gap between physiology and practice by providing a physiology-based approach to understanding hypocalcemia, hypercalcemia and hypomagnesemia. Calcium and, to a lesser extent, magnesium balance is achieved through a complex interplay between the parathyroid gland, bone, the intestine and the kidney. Our understanding of the molecular physiology of calcium and magnesium balance has grown considerably following the discovery of the calcium-sensing receptor (CaSR) and the main intestinal and renal transporters for calcium and magnesium, namely, the transient receptor potential channels TRPV5, TRPV6 and TRPM6. The regulation of parathyroid hormone (PTH) secretion by CaSR and the subsequent effects of PTH and vitamin D on TRPV5 constitute an increasingly characterized regulatory loop. In contrast, no truly magnesiotropic hormones have been identified, although the recently established interactions between the epidermal growth factor and TRPM6 suggest a possible candidate. Overall, the aim of this review is to illustrate the clinical disorders of calcium and magnesium balance from the perspective of their integrated physiology.

Laxative abuse, eating disorders, and kidney stones: a case report and review of the literature

Kidney stones are listed among the complications of eating disorders; however, very few cases have been reported. We present an additional case of nephrolithiasis associated with laxative abuse, including detailed results of the patient's urine metabolic profiles, in a patient with idiopathic hypercalciuria. We review the literature and provide an explanation for the paucity of cases of nephrolithiasis associated with these disorders. Despite low urine volumes resulting from extracellular fluid volume depletion and hypocitraturia resulting from hypokalemia, both of which would tend to favor the formation of kidney stones, most patients with eating disorders are likely to be protected from stone formation by the hypocalciuric effect of extracellular fluid volume depletion and increased proximal tubular sodium reabsorption. However, patients with underlying idiopathic hypercalciuria who develop eating disorders may be at increased risk of stone formation in the setting of low urine volume and therefore high supersaturation of calcium oxalate and phosphate.

Regulation of transport in the connecting tubule and cortical collecting duct

The central goal of this overview article is to summarize recent findings in renal epithelial transport,focusing chiefly on the connecting tubule (CNT) and the cortical collecting duct (CCD).Mammalian CCD and CNT are involved in fine-tuning of electrolyte and fluid balance through reabsorption and secretion. Specific transporters and channels mediate vectorial movements of water and solutes in these segments. Although only a small percent of the glomerular filtrate reaches the CNT and CCD, these segments are critical for water and electrolyte homeostasis since several hormones, for example, aldosterone and arginine vasopressin, exert their main effects in these nephron sites. Importantly, hormones regulate the function of the entire nephron and kidney by affecting channels and transporters in the CNT and CCD. Knowledge about the physiological and pathophysiological regulation of transport in the CNT and CCD and particular roles of specific channels/transporters has increased tremendously over the last two decades.Recent studies shed new light on several key questions concerning the regulation of renal transport.Precise distribution patterns of transport proteins in the CCD and CNT will be reviewed, and their physiological roles and mechanisms mediating ion transport in these segments will also be covered. Special emphasis will be given to pathophysiological conditions appearing as a result of abnormalities in renal transport in the CNT and CCD.

The mechanism of hypocalciuria with NaCl cotransporter inhibition

Thiazide diuretics are used to prevent the recurrence of calcium-containing kidney stones. The ability of these drugs to reduce urinary calcium excretion has a key role in this process. Although studies have shown a reduction in the recurrence rate of calcium-containing stones in patients treated with thiazides, whether hypocalciuria results from increased calcium reabsorption in the proximal or distal nephron is still unclear. When extracellular fluid volume is considerably reduced, the proximal tubule is likely to have a major role in thiazide-induced hypocalciuria. This process frequently occurs when high doses of thiazides and sodium restriction are prescribed for the treatment of kidney stone disease. The distal tubule is predominantly involved in NaCl cotransporter inhibition-induced hypocalciuria when the extracellular fluid volume is not reduced, a clinical scenario observed in patients with Gitelman syndrome. In this Perspectives article, we discuss the evidence supporting the hypocalciuric effects of NaCl cotransporter inhibition in the proximal and distal nephron.