Identification of a novel X-linked arginine-vasopressin receptor 2 mutation in nephrogenic diabetes insipidus: Case report and pedigree analysis.

INTRODUCTION: The clinical and genetic characteristics of nephrogenic diabetes insipidus (NDI) were described via assessing 2 cases of NDI patients from a Chinese family. PATIENT CONCERNS: Two patients who manifest polyuria and polydipsia were admitted to hospital for definite diagnosis. DIAGNOSIS: Water deprivation-vasopressin tests showed that the patients may possess renal-origin diabetes insipidus. All the levels of thyroid-stimulating hormone, luteinizing hormone, follicle stimulation hormone, adrenocorticotropic hormone, prolactin, and growth hormone in both patients were normal. These results were certified that both patients possess a nephropathy-type diabetes insipidus. B-mode ultrasonography and urinalysis test demonstrated that the patient's diabetes insipidus is unlikely to originate from renal organic disease. Remarkably, by nucleotide sequencing, we found a novel mutation c.414_418del in arginine-vasopressin receptor 2 (AVPR2) was related to the disease of NDI. INTERVENTIONS: Two patients were treated with oral hydrochlorothiazide and indomethacin. In addition, low salt diet and potassium supplementation throughout the patients' treatment. OUTCOMES: The clinical symptoms of 2 patients were significantly reduced after targeted therapy. CONCLUSION: A mutation in AVPR2 was discovered to be associated with NID. It provides a new target for molecular diagnosis of NDI, enabling families to undergo genetic counseling and obtain prenatal diagnoses.

Diverse vasopressin V2 receptor functionality underlying partial congenital nephrogenic diabetes insipidus.

X-linked congenital nephrogenic diabetes insipidus (CNDI) is characterized by a defective renal response to the antidiuretic hormone (AVP) due to variations in the arginine vasopressin receptor 2 (AVPR2) gene. In a unique group of patients, the renal insensitivity to the effects of AVP is incomplete resulting in a partial phenotype. To investigate the molecular defects, two previously published variations in the AVPR2 gene, known to cause a partial CNDI phenotype, were expressed in transiently transfected human embryonic kidney cells. One variation (p.Arg104Cys) is located in the first extracellular loop and the other variation (p.Ser329Arg) is located in the intracellular COOH terminal of the receptor protein. Western blotting showed almost equal amounts of WT-V2R and Arg104Cys-V2R protein at steady state, whereas the level of Ser329Arg-V2R protein was lower. Confocal microscopy established that WT-V2R and Arg104Cys-V2R are localized on the cellular surface while the Ser329Arg-V2R primarily accumulates within the endoplasmic reticulum resulting in reduced surface expression. Ligand binding analysis demonstrated that the B(max) for cells expressing Arg104Cys-V2R and Ser329Arg-V2R were 14.8- and 2.5-fold lower than B(max) for WT-V2R, respectively. AVP affinity (1/K(d)) for WT-V2R and the Ser329Arg-V2R was similar while 1/K(d) for Arg104Cys-V2R was increased. cAMP assay revealed that cells expressing p.Arg104Cys-V2R or p.Ser329Arg-V2R produced 1.7- and 6.8-fold lower amounts of cAMP compared with WT-V2R, respectively. In conclusion, ligand binding and signal transduction capability are dependent on localization of the amino acid variation. Striking divergences at the level of receptor functionality may thus underlie similar clinical phenotypes in CNDI.

Water in health and disease: new aspects of disturbances in water metabolism.

Vasopressin is a critical regulator of water homeostasis. There are two major receptors for vasopressin: V1 and V2 receptors. Disturbances in water balance are commonly encountered in clinical practice and can be divided into disorders of urinary dilution and concentration. The major representatives of such disorders are diabetes insipidus and the syndrome of inappropriate secretion of antidiuretic hormone (SI ADH). Recent studies show that genetic forms of nephrogenic diabetes insipidus are due to mutations in the genes coding for the vasopressin V2 receptor (V2R) or aquaporin-2 (AQP2). Identification of the genes involved and analysis of the cellular fate of the V2R and AQP2 mutants are relevant for understanding the functioning of the V2R and AQP2 protein. These developments also have implications for future therapeutic options. The development of nonpeptide vasopressin receptor antagonists (VRAs) offers prospects for the treatment of euvolaemic (SI ADH) or hypervolaemic hyponatraemia (congestive heart failure or cirrhosis). Several nonpeptide VRAs are now in various stages of clinical trials. At present, only conivaptan is registered by the FD A for intravenous treatment of euvolaemic and hypervolaemic hyponatremia. A recent long-term study comparing tolvaptan with placebo in patients with chronic heart failure showed no reduction in risk of death and hospitalisation.

Altered expression of selected genes in kidney of rats with lithium-induced NDI.

Lithium treatment is associated with development of nephrogenic diabetes insipidus, caused in part by downregulation of collecting duct aquaporin-2 (AQP2) and AQP3 expression. In the present study, we carried out cDNA microarray screening of gene expression in the inner medulla (IM) of lithium-treated and control rats, and selected genes were then investigated at the protein level by immunoblotting and/or immunohistochemistry. The following genes exhibited significantly altered transcription and mRNA expression levels, and these were compatible with the changes in protein expression. 11beta-Hydroxysteroid dehydrogenase type 2 protein expression in the IM was markedly increased (198 +/- 25% of controls, n = 6), and immunocytochemistry demonstrated an increased labeling of IM collecting duct (IMCD) principal cells. This indicated altered renal mineralocorticoid/glucocorticoid responses in lithium-treated rats. The inhibitor of cyclin-dependent kinases p27 (KIP) protein expression was significantly decreased or undetectable in the IMCD cells, pointing to increased cellular proliferation and remodeling. Heat shock protein 27 protein expression was decreased in the IM (64 +/- 6% of controls, n = 6), likely to be associated with the decreased medullary osmolality in lithium-treated rats. Consistent with this, lens aldose reductase protein expression was markedly decreased in the IM (16 +/- 2% of controls, n = 6), and immunocytochemistry revealed decreased expression in the thin limb cells in the middle and terminal parts of the IM. Ezrin protein expression was upregulated in the IM (158 +/- 16% of controls, n = 6), where it was predominantly expressed in the apical and cytoplasmic domain of the IMCD cells. Increased ezrin expression indicated remodeling of the actin cytoskeleton and/or altered regulation of IMCD transporters. In conclusion, the present study demonstrates changes in gene expression not only in the collecting duct but also in the thin limb of the loop of Henle in the IM, and several of these genes are linked to altered sodium and water reabsorption, cell cycling, and changes in interstitial osmolality.

Identification and characterization of aquaporin-2 water channel mutations causing nephrogenic diabetes insipidus with partial vasopressin response.

Congenital nephrogenic diabetes insipidus (NDI) is a rare disease caused most often by mutations in the vasopressin V2 receptor (AVPR2). We studied a family which included a female patient with NDI with symptoms dating from infancy. The patient responded to large doses of desmopressin (dDAVP) which decreased urine volume from 10 to 4 I/day. Neither the parents nor the three sisters were polyuric. The patient was found to be a compound heterozygote for two novel recessive point mutations in the aquaporin-2 (AQP2) gene: L22V in exon 1 and C181W in exon 3. Residue Cys181 in AQP2 is the site for inhibition of water permeation by mercurial compounds and is located near to the NPA motif conserved in all aquaporins. Osmotic water permeability (Pf) in Xenopus oocytes injected with cRNA encoding C181W-AQP2 was not increased over water control, while expression of L22V cRNA increased the Pf to approximately 60% of that for wild-type AQP2. Co-injection of the mutant cRNAs with the wild-type cRNA did not affect the function of the wild-type AQP2. Immunolocalization of AQP2-transfected CHO cells showed that the C181W mutant had an endoplasmic reticulum-like intracellular distribution, whereas L22V and wild-type AQP2 showed endosome and plasma membrane staining. Water permeability assays showed a high Pf in cells expressing wild-type and L22V AQP2. This study indicates that AQP2 mutations can confer partially responsive NDI.