Clinical Trial: Parathyroid Hormone (PTH) Homeostasis in Bartter Syndrome
Study Status: Not yet recruiting
Recruit Status: Unknown status
Study Type: Observational
Official Title: Case-control Study of the PTH Homeostasis in Adolescents and Young Adults With Bartter Syndrome
Brief Summary:
Parathyroid hormone (PTH) gland calcium sensing receptor (CASR) regulates PTH secretion. CASR is also expressed in nephron thick ascending limb (TAL). Bartter syndrome (BS), a normotensive hypokalemic tubulopathy, may be due to mutations in different TAL channels, including the potassium channel ROMK. Mutations in CASR may also cause BS through its effects on ROMK function. However, it is unknown whether ROMK mutations exert any effects on CASR function and PTH physiology. Preliminary data from our center shows that PTH levels were specifically elevated in type II (where ROMK is mutated) and not in type IV (where another gene, Barttin is defective) BS, without a common explanation. We assume that the mutation in ROMK may cause a dysregulation of PTH secretion via possible interaction with CASR.
The purpose of this study is: to investigate the PT-gland function and regulation in BS.
Methods: Patients with BS type II and IV and normal controls will undergo a standard protocol of controlled ionic hypo- and hypercalcemia, during which PTH secretion, phosphate balance and calcium excretion will be followed. Calcium Vs PTH response curves will be generated and compared.
Expected impact and benefit: the results of this study will help understand the mechanisms of PTH regulation beyond CASR.
Detailed Summary:
The parathyroid glands play a pivotal physiological function by maintaining blood calcium levels, specifically blood ionized calcium concentrations, within a very narrow range. They do so by modulating the minute-to-minute release of parathyroid hormone (PTH) into the circulation. Such changes have almost immediate effects on calcium excretion in the urine and on calcium efflux from bone and, if sustained for hours or days, affect renal vitamin D metabolism and ultimately the efficiency of intestinal calcium absorption. The capacity of chief cells of the parathyroid to detect small changes in blood ionized calcium levels, modify PTH release accordingly, and initiate these adaptive responses is mediated by a calcium-sensing receptor (CaSR) located at the cell surface.
The importance of the CaSR in parathyroid tissue extends beyond its traditional role as a modifier of calcium-regulated PTH secretion to involve other key components of parathyroid gland function that are frequently abnormal in clinical disorders characterized by excess parathyroid gland activity such as hyperparathyroidism. These include disturbances in the control of PTH gene transcription and hormone synthesis and the development of parathyroid gland enlargement due to tissue hyperplasia.
PTH acts mainly on renal proximal tubule phosphorus (Pi) reabsorption and bone osteoclast calcium and Pi resorption. CASR is also expressed in nephron thick ascending limb (TAL), where it interacts with luminal potassium ROMK channel. Mutations in several TAL channels and proteins (including ROMK, NKCC2, ClCKb, Barttin and CASR) cause Bartter syndrome (BS), a normotensive hypokalemic tubulopathy. Whereas the effects of CASR mutations on ROMK function in the kidney have been described , it is unknown whether ROMK mutations exert any effects on CASR function or PTH regulatio
Sponsor: Soroka University Medical Center
Current Primary Outcome:
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Information By: Soroka University Medical Center
Dates:
Date Received: November 25, 2009
Date Started: January 2013
Date Completion: June 2014
Last Updated: June 13, 2012
Last Verified: June 2012
