A Rare Case of Congenital Nephrogenic Diabetes Insipidus Associated with Aquaporin 2 Gene Mutation and Subsequent Acute Lymphoblastic Leukemia: Impact of Steroids on Kidney Function.

BACKGROUND Nephrogenic diabetes insipidus (NDI) is a rare renal disorder that can be congenital, and is caused by mutations in either aquaporin 2 or arginine vasopressin receptor 2, or it can be secondary to kidney disease or electrolyte imbalance. The clinical signs of NDI include polyuria, compensatory polydipsia, hypernatremic dehydration, and growth retardation without prompt treatment. In this report, we present the case of a patient with congenital NDI who was later diagnosed with acute lymphoblastic leukemia (ALL). With dexamethasone treatment, he had uncontrolled polyuria and polydipsia. Our aim was to concentrate on the impact of steroids on the kidneys. CASE REPORT Our patient presented at the age of 9 months with signs of severe dehydration that were associated with polyuria. His laboratory examinations revealed hypernatremia and decreased urine osmolality. He was diagnosed with NDI and his exome sequence revealed a homozygous mutation at the nucleotide position AQP2 NM_000486.6: c.374C>T (p.Thr125Met). He was treated with hydrochlorothiazide and amiloride. Then, at age 19 months, he presented with gastroenteritis and a complete blood count (CBC) showed high white blood cell count and blast cells. He was diagnosed with (ALL) and began receiving chemotherapy, during which again developed polydipsia and polyuria, which could not be controlled with an increased dosage of hydrochlorothiazide. CONCLUSIONS We report a rare case of NDI caused by a missense mutation in the aquaporin 2 gene. One year later, the child developed ALL, and treatment with dexamethasone led to an uncompensated state of polydipsia and polyuria.

Therapeutic potentials of nonpeptidic V2R agonists for partial cNDI-causing V2R mutants.

Loss-of-function mutations in the type 2 vasopressin receptor (V2R) are a major cause of congenital nephrogenic diabetes insipidus (cNDI). In the context of partial cNDI, the response to desmopressin (dDAVP) is partially, but not entirely, diminished. For those with the partial cNDI, restoration of V2R function would offer a prospective therapeutic approach. In this study, we revealed that OPC-51803 (OPC5) and its structurally related V2R agonists could functionally restore V2R mutants causing partial cNDI by inducing prolonged signal activation. The OPC5-related agonists exhibited functional selectivity by inducing signaling through the Gs-cAMP pathway while not recruiting ß-arrestin1/2. We found that six cNDI-related V2R partial mutants (V882.53M, Y1283.41S, L1614.47P, T2736.37M, S3298.47R and S3338.51del) displayed varying degrees of plasma membrane expression levels and exhibited moderately impaired signaling function. Several OPC5-related agonists induced higher cAMP responses than AVP at V2R mutants after prolonged agonist stimulation, suggesting their potential effectiveness in compensating impaired V2R-mediated function. Furthermore, docking analysis revealed that the differential interaction of agonists with L3127.40 caused altered coordination of TM7, potentially contributing to the functional selectivity of signaling. These findings suggest that nonpeptide V2R agonists could hold promise as potential drug candidates for addressing partial cNDI.

Diabetes insipidus: Vasopressin deficiency .

Diabetes insipidus is a disorder characterized by hypo-osmotic polyuria secondary to abnormal synthesis, regulation, or renal action of antidiuretic hormone. Recently, an expert group, with the support of patient associations, proposed that diabetes insipidus be renamed to avoid confusion with diabetes mellitus. The most common form of diabetes insipidus is secondary to a dysfunction of the neurohypophysis (central diabetes insipidus) and would be therefore named 'vasopressin deficiency'. The rarer form, which is linked to renal vasopressin resistance (nephrogenic diabetes insipidus), would then be named 'vasopressin resistance'. The etiology of diabetes insipidus is sometimes clear, in the case of a neurohypophyseal cause (tumoral or infiltrative damage) or a renal origin, but in some cases diabetes insipidus can be difficult to distinguish from primary polydipsia, which is characterized by consumption of excessive quantities of water without any abnormality in regulation or action of antidiuretic hormone. Apart from patients' medical history, physical examination, and imaging of the hypothalamic-pituitary region, functional tests such as water deprivation or stimulation of copeptin by hyperosmolarity (induced by infusion of hypertonic saline) can be proposed in order to distinguish between these different etiologies. The treatment of diabetes insipidus depends on the underlying etiology, and in the case of a central etiology, is based on the administration of desmopressin which improves patient symptoms but does not always result in an optimal quality of life. The cause of this altered quality of life may be oxytocin deficiency, oxytocin being also secreted from the neurohypophysis, though this has not been fully established. The possibility of a new test using stimulation of oxytocin to identify alterations in oxytocin synthesis is of interest and would allow confirmation of a deficiency in those patients presenting with diabetes insipidus linked to neurohypophyseal dysfunction.

Tubular Diseases and Stones Seen From Pediatric and Adult Nephrology Perspectives.

The tubular system of the kidneys is a complex series of morphologic and functional units orchestrating the content of tubular fluid as it flows along the nephron and collecting ducts. Renal tubules maintain body water, regulate electrolytes and acid-base balance, reabsorb precious organic solutes, and eliminate specific metabolites, toxins, and drugs. In addition, decisive mechanisms to adjust blood pressure are governed by the renal tubules. Genetic as well as acquired disorders of these tubular functions may cause serious diseases that manifest both in childhood and adulthood. This article addresses a selection of tubulopathies and the underlying pathomechanisms, while highlighting the important differences in pediatric and adult nephrology care. These range from rare monogenic conditions such as nephrogenic diabetes insipidus, cystinosis, and Bartter syndrome that present in childhood, to the genetic and acquired tubular pathologies causing hypertension or nephrolithiasis that are more prevalent in adults. Both pediatric and adult nephrologists must be aware of these conditions and the age-dependent manifestations that warrant close interaction between the two subspecialties.

Tamoxifen Affects Aquaporin-3 Expression and Subcellular Localization in Rat and Human Renal Collecting Ducts.

Sex hormones play an important role in the regulation of water homeostasis, and we have previously shown that tamoxifen (TAM), a selective estrogen receptor modulator (SERM), affects the regulation of aquaporin (AQP)-2. In this study, we investigated the effect of TAM on the expression and localization of AQP3 in collecting ducts using various animal, tissue, and cell models. The impact of TAM on AQP3 regulation was studied in rats subjected to 7 days of unilateral ureteral obstruction (UUO), with the rats fed a lithium-containing diet to induce nephrogenic diabetes insipidus (NDI), as well as in human precision-cut kidney slices (PCKS). Moreover, intracellular trafficking of AQP3 after TAM treatment was investigated in Madin-Darby Canine Kidney (MDCK) cells stably expressing AQP3. In all models, the expression of AQP3 was evaluated by Western blotting, immunohistochemistry and qPCR. TAM administration attenuated UUO-induced downregulation of AQP3 and affected the localization of AQP3 in both the UUO model and the lithium-induced NDI model. In parallel, TAM also affected the expression profile of other basolateral proteins, including AQP4 and Na/K-ATPase. In addition, TGF-ß and TGF-ß+TAM treatment affected the localization of AQP3 in stably transfected MDCK cells, and TAM partly attenuated the reduced AQP3 expression in TGF-ß exposed human tissue slices. These findings suggest that TAM attenuates the downregulation of AQP3 in a UUO model and a lithium-induced NDI model and affects the intracellular localization in the collecting ducts.

Iatrogenic endocrine complications of lithium therapy.

Lithium is a cation, similar to sodium and potassium, affecting ion transport. It is used in the medical field as a treatment of bipolar disorders. The main endocrine complications of lithium treatment affect thyroid and parathyroid glands, in association with renal complications. Thyroid adverse effects, which are more frequent in women, comprise hypothyroidism, goiter, or sometimes hyperthyroidism, through interference with the iodine symporter. The increase in thyroid volume is early. Prevalence of goiter is 4 times higher than in the general population and hypothyroidism (8-20%) more frequent in case of pre-existing thyroid autoimmunity. Hyperthyroidism likely to worsen mood is reported in 5% of cases but the causal link to lithium is unproven. An increase in serum calcium and PTH occurs in 30% of cases, as lithium stimulates parathyroid cell proliferation by activating the Wnt pathway. The risk of hyperparathyroidism, by adenoma and especially by hyperplasia, is 5 times higher than in the general population, with the particularity of frequent low urine calcium by action on the calcium-sensing receptor (CaSR). Renal complications include risk of acute or chronic renal failure and nephrogenic diabetes insipidus, which is a factor for hypernatremia and hypercalcemia through dehydration. Nephrogenic diabetes insipidus is not always reversible after lithium therapy discontinuation. Metabolically, weight gain can be observed, but rather less than with other psychotropic drugs, and lithium does not in itself induce diabetes. At pituitary level, corticotropic activation is frequent, but implicating the disease rather than lithium. Lithium treatment induces little or no hyperprolactinemia. Regular monitoring of serum calcium, the ionogram, creatinine and TSH is recommended in lithium treatment.

Central Diabetes Insipidus in the Background of Lithium Use: Consider Central Causes Despite Nephrogenic as the Most Common.

BACKGROUND Nephrogenic diabetes insipidus is a well-known adverse effect of lithium use. Albeit rare, there have also been documented cases of central diabetes insipidus (CDI) associated with lithium use. CASE REPORT A 31-year-old woman with a past medical history of bipolar disorder, managed with lithium 300 mg by mouth every day for 3 years, was assessed for a 1-year history of polyuria with accompanying polydipsia. During her initial hospital stay, her estimated urine output was more than 4 L per day. Initial labs showed elevated serum sodium (149 mmol/L; reference range 135-145), elevated serum osmolality (304 mOsm/kg; reference range 275-295), urine osmolality of 99 mOsm/kg (reference range 50-1200), and urine specific gravity (1.005; reference range 1.005-1.030). Lithium was at a subtherapeutic level of 0.05 mEq/L (reference range 0.6-1.2). Magnetic resonance imaging of the brain revealed no abnormalities of the pituitary gland. Two different occasions of desmopressin administration resulted in >50% increase in urine osmolality, confirming the diagnosis of CDI. Common causes of CDI, including trauma, tumors, and familial CDI, were ruled out and chronic lithium use was determined as the most probable cause for the patient's CDI. CONCLUSIONS CDI in the background of chronic lithium use is rarely reported. We present this case to consider CDI as a differential diagnosis when evaluating polyuria and hypernatremia in patients with long-term lithium use. These presentations warrant the consideration of both types of diabetes insipidus in the differential diagnoses.

A case of nephrogenic diabetes insipidus likely caused by anti-neutrophil cytoplastic antibody-associated vasculitis.

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a relatively rare form of autoimmune disease. Diabetes insipidus (DI) is characterized by diluted polyuria and thirstiness, and is clinically categorized into central and nephrogenic DI depending on damaged organs. In most previously reported cases, ANCA-related disorders have been implicated in central DI, which is attributed to impaired secretion of arginine vasopressin (AVP) from the posterior pituitary. However, no previous case of AAV-related nephrogenic DI has been reported in the English literature. Herein, we report a case of nephrogenic DI likely caused by AAV. A 76-year-old man was admitted to our hospital for acute kidney injury. He showed dehydration, polyuria, and polydipsia. Laboratory tests demonstrated elevated levels of serum urea and creatinine and a high myeloperoxidase ANCA titer. In the present case, both plasma AVP concentration and response of AVP secretion to 5% saline load test were normal. In addition, 1-desmino-8-arginine vasopressin administration could not increase urinary osmolarity. Kidney biopsy specimen revealed tubulointerstitial nephritis with findings that appeared to indicate peritubular capillaritis. Therefore, the patient was diagnosed with nephrogenic DI likely owing to ANCA-associated tubulointerstitial nephritis. Immediately after prednisolone administration, urinary volume decreased, urinary osmolarity increased, and kidney function was improved. This case demonstrates that AAV that extensively affects the tubulointerstitial area can result in nephrogenic DI.

Young Adults With Hereditary Tubular Diseases: Practical Aspects for Adult-Focused Colleagues.

Recent advances in the management of kidney tubular diseases have resulted in a significant cohort of adolescents and young adults transitioning from pediatric- to adult-focused care. Most of the patients under adult-focused care have glomerular diseases, whereas rarer tubular diseases form a considerable proportion of pediatric patients. The purpose of this review is to highlight the clinical signs and symptoms of tubular disorders, as well as their diagnostic workup, including laboratory findings and imaging, during young adulthood. We will then discuss more common disorders such as cystinosis, cystinuria, distal kidney tubular acidosis, congenital nephrogenic diabetes insipidus, Dent disease, rickets, hypercalciuria, and syndromes such as Bartter, Fanconi, Gitelman, Liddle, and Lowe. This review is a practical guide on the diagnostic and therapeutic approach of tubular conditions affecting young adults who are transitioning to adult-focused care.

X-Linked Kidney Disorders in Women.

A number of genes that cause inherited kidney disorders reside on the X chromosome. Given that males have only a single active X chromosome, these disorders clinically manifest primarily in men and boys. However, phenotypes in female carriers of X-linked kidney conditions are becoming more and more recognized. This article reviews the biology of X inactivation as well as the kidney phenotype in women and girls with a number of X-linked kidney disorders including Alport syndrome, Fabry disease, nephrogenic diabetes insipidus, X-linked hypophosphatemic rickets, Dent disease, and Lowe syndrome.

Whole-exome sequencing and variant spectrum in children with suspected inherited renal tubular disorder: the East India Tubulopathy Gene Study.

BACKGROUND: Inherited tubulopathies are a heterogeneous group of genetic disorders making whole-exome sequencing (WES) the preferred diagnostic methodology. METHODS: This was a multicenter descriptive study wherein children (< 18 years) with clinically suspected tubular disorders were recruited for molecular testing through WES. Multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing were done when required. Variants were classified as per American College of Medical Genetics 2015 guidelines and pathogenic (P)/likely pathogenic (LP) variants were considered causative. RESULTS: There were 77 index cases (male =73%). Median age at diagnosis was 48 months (IQR 18.5 to 108 months). At recruitment, the number of children in each clinical group was as follows: distal renal tubular acidosis (dRTA) = 25; Bartter syndrome = 18; isolated hypophosphatemic rickets (HP) = 6; proximal tubular dysfunction (pTD) = 12; nephrogenic diabetes insipidus (NDI) = 6; kidney stone/nephrocalcinosis (NC) = 6; others = 4. We detected 55 (24 novel) P/LP variants, providing genetic diagnoses in 54 children (70%). The diagnostic yield of WES was highest for NDI (100%), followed by HP (83%; all X-linked HP), Bartter syndrome (78%), pTD (75%), dRTA (64%), and NC (33%). Molecular testing had a definite impact on clinical management in 24 (31%) children. This included revising clinical diagnosis among 14 children (26% of those with a confirmed genetic diagnosis and 18% of the overall cohort), detection of previously unrecognized co-morbidities among 8 children (sensorineural deafness n = 5, hemolytic anemia n = 2, and dental changes n = 1) and facilitating specific medical treatment for 7 children (primary hyperoxaluria n = 1, cystinosis n = 4, tyrosinemia n = 2). CONCLUSION: WES is a powerful tool in the diagnosis and management of children with inherited tubulopathies in the Indian population. A higher resolution version of the Graphical abstract is available as Supplementary information.

Lithium and endocrine dysfunction.

Lithium carbonate is a commonly prescribed drug for bipolar disorders. In addition to its action on the central nervous system, lithium has systemic effects on multiple organs such as kidney, heart, motor end plate, thyroid and parathyroid glands. It can cause hypothyroidism, hyperthyroidism, goiter and ophthalmopathy by different mechanisms. It increases intrathyroid iodine content or compete for iodine transport, resulting in low iodine uptake by the thyroid. It also inhibits the coupling of iodotyrosine residues to form iodothyronines and inhibits the release of T4 and T3. Lithium has direct actions on parathyroid glands by antagonizing the calcium sensing receptor, which may induce hypercalcemia or even hyperparathyroidism, requiring surgery in some cases. Furthermore, it inhibits the expression of aquaporins, mainly aquaporin 2, in the renal collecting tubule by unknown mechanisms leading to nephrogenic diabetes insipidus. This adverse effect is usually reversible after drug withdrawal. However, some patients may present irreversible kidney damage due to chronic interstitial nephropathy.

El carbonato de litio es un fármaco que se prescribe comúnmente para el tratamiento de trastornos bipolares. Además de su acción sobre el sistema nervioso central, el litio tiene repercusiones sistémicas, afectando a múltiples órganos como el riñón, el corazón, la placa motora terminal y glándulas tiroides y paratiroides. Puede causar hipotiroidismo, hipertiroidismo, bocio y oftalmopatía por diferentes mecanismos; también aumentar el contenido de yodo intratiroideo o competir por el transporte de yodo, lo que resulta en una baja captación tiroidea de yodo. Inhibe el acoplamiento de residuos de yodotirosina para formar yodotironinas e inhibe la liberación de T4 y T3. Tiene acciones directas sobre las glándulas paratiroides antagonizando el receptor sensor de calcio, lo que puede inducir hipercalcemia e incluso hiperparatiroidismo, y puede requerir cirugía en algunos casos. Inhibe la expresión de acuaporinas en el túbulo colector renal, principalmente acuaporina 2, por mecanismos que aún no se conocen, produciendo diabetes insípida nefrogénica; este efecto adverso suele ser reversible tras la suspensión del fármaco. Sin embargo, algunos pacientes pueden presentar daño renal irreversible por nefropatía intersticial crónica.

What an endocrinologist should know for patients receiving lithium therapy.

Lithium is an efficient treatment of bipolar disorder. Besides renal insufficiency, many endocrine side effects are described such as the occurrence of thyroid disorders, hypercalcaemia and nephrogenic diabetes insipidus. Lithium inhibits the secretion of thyroid hormones. The prevalence of goiter is 4 times more common in Lithium-treated patients compared as to the general population. Hypothyroidism (8-20%) is more frequent in women and in case of pre-existing thyroid autoimmunity. Grave's disease and other hyperthyroidisms are sometimes reported. Lithium stimulates the proliferation of parathyroid cells by activating the Wnt pathway. An increase in serum calcium and PTH is described in patients treated with Lithium with a 4 to 6-fold higher risk of primary hyperparathyroidism than in the general population. Nevertheless, 24-hour urine calcium is not often increased, and the phenotype can mimic a hypercalcemia-hypocalciuria syndrome that may regress with Lithium discontinuation. Surgery should be cautious since parathyroid hyperplasia is more common than parathyroid adenoma. Nephrogenic diabetes insipidus is frequently reported and may be debilitating, sometimes intricated with severe dehydration, hypernatremia, and acute renal insufficiency. Nephrogenic diabetes insipidus is not generally reversible after Lithium discontinuation, especially in patients who have chronic kidney disease due to interstitial tubule nephritis. In conclusion, clinical assessment (goiter, diuresis) and biological monitoring of serum calcium, sodium creatinine, TSH and lithium are recommended in patients receiving Lithium therapy. The risk of Lithium discontinuation in case of side effects should be weighed against the psychological risk, and must be discussed with the psychiatrist.

Bendamustine-induced nephrogenic diabetes insipidus - A case report.

INTRODUCTION: In patients with relapsed or refractory lymphoma, high-dose chemoimmunotherapy with subsequent autologous hematopoietic cell transplantation (HCT) is a standard of care. Bendamustine, an alkylating agent, is used in the BeEAM (bendamustine, etoposide, cytarabine, melphalan) protocol for conditioning therapy before autologous HCT in patients with relapsed or refractory lymphoma who are eligible for transplant. There is no consensus regarding an optimal salvage regimen and the approach varies according to toxicity. CASE REPORT: We present a case of partial nephrogenic diabetes insipidus after receiving bendamustine, as part of the BeEAM protocol.Management and outcome: The patient was managed with parenteral fluid administration and intranasal desmopressin before the condition resolved on its own. DISCUSSION: We summarize published reports of bendamustine-induced diabetes insipidus.

Adipsic Diabetes Insipidus in Children: A Case Report and Practical Guide.

BACKGROUND Diabetes insipidus (DI) is a clinical syndrome characterized by polyuria and polydipsia that result from a deficiency of antidiuretic hormone (ADH), central DI, or resistance to ADH, nephrogenic DI. In otherwise healthy patients with DI, normal thirst mechanism, and free access to water, the thirst system can maintain plasma osmolality in the near-normal range. However, in cases where DI presents with adipsia, cognitive impairment, or restricted access to water, true hypernatremia may occur, leading to severe morbidity and mortality. CASE REPORT We report a case of a 2-year-old boy who had global developmental delay and post-brain debulking surgery involving the hypothalamic region, which resulted in central DI and thirst center dysfunction. We describe the clinical presentation, the current understanding of adipsic DI, and a new practical approach for management. The main guidelines of treatment include (1) fixed desmopressin dosing that allows minimal urinary breakthroughs in-between the doses; (2) timely diaper weight-based replacement of water; (3) bodyweight-based fluid correction 2 times a day, and (4) providing the nutritional and water requirements in a way similar to any healthy child but at fixed time intervals. CONCLUSIONS This plan of management showed good effectiveness in controlling plasma sodium level and volume status of a child with adipsic DI without interfering with his average growth. This home treatment method is practical and readily available, provided that the family remains very adherent.

Activation of AQP2 water channels by protein kinase A: therapeutic strategies for congenital nephrogenic diabetes insipidus.

BACKGROUND: Congenital nephrogenic diabetes insipidus (NDI) is primarily caused by loss-of-function mutations in the vasopressin type 2 receptor (V2R). Renal unresponsiveness to the antidiuretic hormone vasopressin impairs aquaporin-2 (AQP2) water channel activity and water reabsorption from urine, resulting in polyuria. Currently available symptomatic treatments inadequately reduce patients' excessive amounts of urine excretion, threatening their quality of life. In the past 25 years, vasopressin/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) has been believed to be the most important signaling pathway for AQP2 activation. Although cAMP production without vasopressin is the reasonable therapeutic strategy for congenital NDI caused by V2R mutations, the efficacy of candidate drugs on AQP2 activation is far less than that of vasopressin. RESULTS: Intracellular distribution and activity of PKA are largely controlled by its scaffold proteins, A-kinase anchoring proteins (AKAPs). Dissociating the binding of AKAPs and PKA significantly increased PKA activity in the renal collecting ducts and activated AQP2 phosphorylation and trafficking. Remarkably, the AKAPs-PKA disruptor FMP-API-1 increased transcellular water permeability in isolated renal collecting ducts to the same extent as vasopressin. Moreover, derivatives of FMP-API-1 possessed much more high potency. FMP-API-1/27 is the first low-molecular-weight compound to be discovered that can phosphorylate AQP2 more effectively than preexisting drug candidates. CONCLUSION: AKAP-PKA disruptors are a promising therapeutic target for congenital NDI. In this article, we shall discuss the pathophysiological roles of PKA and novel strategies to activate PKA in renal collecting ducts.

Novel AVPR2 mutations and clinical characteristics in 28 Chinese families with congenital nephrogenic diabetes insipidus.

AIMS: To investigate genotype and phenotype of congenital nephrogenic diabetes insipidus caused by AVPR2 mutations, which is rare and limitedly studied in Chinese population. METHODS: 88 subjects from 28 families with NDI in a department (Beijing, PUMCH) were screened for AVPR2 mutations. Medical records were retrospectively reviewed and characterized. Genotype and phenotype analysis was performed. RESULTS: 23 AVPR2 mutations were identified, including six novel mutations (p.Y117D, p.W208R, p.L313R, p.S127del, p.V162Sfs*30 and p.G251Pfs*96). The onset-age ranged from 1 week to 3 years. Common presentations were polydipsia and polyuria (100%) and intermittent fever (57%). 21% and 14% of patients had short stature and mental impairment. Urine SG and osmolality were decreased, while serum osmolality and sodium were high. Urological ultrasonography results showed hydronephrosis of the kidney (52%), dilation of the ureter (48%), and thickened bladder wall or increased residual urine (32%), led to intermittent urethral catheterization (7%), cystostomy (11%) and binary nephrostomy (4%). Urological defects were developed in older patients. Genotype and phenotype analysis revealed patients with non-missense mutations had higher levels of serum sodium than missense mutations. CONCLUSION: In the first and largest case series of NDI caused by AVPR2 mutations in Chinese population, we established genetic profile and characterized clinical data, reporting six novel mutations. Further, we found genotype was associated with phenotype. This knowledge broadens genotype and phenotype spectrum of rare congenital NDI caused by AVPR2 mutations, and provides basis for studying molecular biology of AVPR2.

Functional characterization of a loss-of-function mutant I324M of arginine vasopressin receptor 2 in X-linked nephrogenic diabetes insipidus.

X-linked nephrogenic diabetes insipidus (X-linked NDI) is a rare inherited disease mainly caused by lost-of-function mutations in human AVPR2 gene encoding arginine vasopressin receptor 2 (V2R). Our focus of the current study is on exploration of the functional and biochemical properties of Ile324Met (I324M) mutation identified in a pedigree showing as typical recessive X-linked NDI. We demonstrated that I324M mutation interfered with the conformation of complex glycosylation of V2R. Moreover, almost all of the I324M-V2R failed to express on the cell surface due to being captured by the endoplasmic reticulum control system. We further examined the signaling activity of DDAVP-medicated cAMP and ERK1/2 pathways and the results revealed that the mutant receptor lost the ability in response to DDAVP stimulation contributed to the failure of accumulation of cAMP and phosphorylated ERK1/2. Based on the characteristics of molecular defects of I324M mutant, we selected two reagents (SR49059 and alvespimycin) to determine whether the functions of I324M-V2R can be restored and we found that both compounds can significantly "rescue" I324M mutation. Our findings may provide further insights for understanding the pathogenic mechanism of AVPR2 gene mutations and may offer some implications on development of promising treatments for patients with X-linked NDI.

Congenital nephrogenic diabetes insipidus accompanied with central nephrogenic diabetes secondary to pituitary surgery -a case report.

BACKGROUND: Diabetes insipidus (DI) can be a common cause of polydipsia and polyuria. Here, we present a case of congenital nephrogenic diabetes insipidus (CNDI) accompanied with central diabetes insipidus (CDI) secondary to pituitary surgery. CASE PRESENTATION: A 24-year-old Chinese woman came to our hospital with the complaints of polydipsia and polyuria for 6 months. Six months ago, she was detected with pituitary apoplexy, and thereby getting pituitary surgery. However, the water deprivation test demonstrated no significant changes in urine volume and urine gravity in response to fluid depression or AVP administration. In addition, the genetic results confirmed a heterozygous mutation in arginine vasopressin receptor type 2 (AVPR2) genes. CONCLUSIONS: She was considered with CNDI as well as acquired CDI secondary to pituitary surgery. She was given with hydrochlorothiazide (HCTZ) 25 mg twice a day as well as desmopressin (DDAVP, Minirin) 0.1 mg three times a day. There is no recurrence of polyuria or polydipsia observed for more than 6 months. It can be hard to consider AVPR2 mutation in female carriers, especially in those with subtle clinical presentation. Hence, direct detection of DNA sequencing with AVPR2 is a convenient and accurate method in CNDI diagnosis.