Clinical presentation and follow-up of 30 patients with congenital nephrogenic diabetes insipidus

Functional Rescue of a Nephrogenic Diabetes Insipidus Causing Mutation in the V2 Vasopressin Receptor by Specific Antagonist and Agonist Pharmacochaperones

The urine concentrating function of the kidney is essential to maintain the water homeostasis of the human body. It is mainly regulated by the arginine-vasopressin (AVP), which targets the type 2 vasopressin receptor (V2R) in the kidney. The inability of V2R to respond to AVP stimulation leads to decreased urine concentration and congenital nephrogenic diabetes insipidus (NDI). NDI is characterized by polyuria, polydipsia, and hyposthenuria. In this study, we identified a point mutation (S127F) in the AVPR2 gene of an NDI patient, and we characterized the impaired function of the V2R mutant in HEK293 cells. Based on our data, the S127F-V2R mutant is almost exclusively located intracellularly in the endoplasmic reticulum (ER), and very few receptors were detected at the cell surface, where the receptor can bind to AVP. The overexpressed S127F-V2R mutant receptor has negligible cAMP generation capability compared to the wild-type receptor in response to AVP stimulation. Since certain misfolded mutant proteins, that are retained in the ER, can be rescued by pharmacological chaperones, we examined the potential rescue effects of two pharmacochaperones on the S127F-V2R. We found that pretreatment with both tolvaptan (an established V2R inverse agonist) and MCF14 compound (a cell-permeable high-affinity agonist for the V2R) were capable of partially restoring the cAMP generating function of the receptor in response to vasopressin stimulation. According to our data, both cell permeant agonists and antagonists can function as pharmacochaperones, and serve as the starting compounds to develop medicines for patients carrying the S127F mutation.

Congenital nephrogenic diabetes insipidus presenting as osmotic demyelination syndrome in infancy: A case report

RATIONALE

Almost 90% of congenital nephrogenic diabetes insipidus (NDI) cases are caused by mutations in the arginine vasopressin receptor 2 gene, which has X-linked recessive inheritance. Although NDI is commonly diagnosed in early infancy based on its characteristic findings, clinical diagnosis can be delayed when no other family members have been diagnosed with NDI because several findings of NDI are nonspecific.

PATIENT CONCERNS

A 3-month-old boy diagnosed with NDI presenting with osmotic demyelination syndrome (ODS) was admitted for poor weight gain after birth and poor feeding during the week prior to admission.

DIAGNOSIS

On admission, the initial blood examination showed hypernatremia (158 mmol/L), and treatment with intravenous fluids over the next 2 days further elevated the serum sodium level (171 mmol/L). After admission, polyuria was recognized, and polyuria in his grandmother and mother since childhood without a diagnosis of NDI was found. Magnetic resonance imaging showed multifocal, symmetrical lesions, including the lateral pons, on diffusion- and T2-weighted imaging, which led to a diagnosis of ODS.

INTERVENTION

The infusion was stopped, and the patient was fed milk diluted 2-fold with water.

OUTCOMES

The serum sodium level gradually decreased to 148 mmol/L over the course of 1 week. Low-sodium milk was started at 4 months of age and maintained a serum sodium level of approximately 140 mmol/L, which was within the normal range. The developmental quotient was 94 at 4 years of age.

LESSONS

ODS is an encephalopathy resulting from extreme fluctuations in serum sodium concentration and plasma osmolality. ODS due to hypernatremia has been reported in several patients, although it usually occurs during rapid correction of hyponatremia. Consequences of the central nervous system are a critical complication of NDI that affects prognosis. These consequences can be avoided with treatment. Early blood examination or polyuria in the patient, mother, or another family member and hypernatremic dehydration with good urine output should lead to an early diagnosis and prevent central nervous system consequences.

Oral disintegrating desmopressin tablet is effective for partial congenital nephrogenic diabetes insipidus with AVPR2 mutation: a case report

Congenital nephrogenic diabetes insipidus (NDI) is a rare disease that causes polydipsia and polyuria, and there are currently no effective treatments for most cases, particularly severe ones. The present report describes the case of a 1-yr-5-mo-old male patient with partial congenital NDI who was successfully treated with oral disintegrating 1-deamino-8-D-arginine vasopressin (DDAVP). The patient presented with poor weight gain and polydipsia (fluid, 1.5 L/d) and received a diagnosis of NDI after genetic analysis revealed an AVPR2 mutation (c.383A>C, p.Y128S). His water-restricted urine osmolality increased from 360 mOsm/kg/H₂O to 667 mOsm/kg/H₂O after subcutaneous AVP injection, indicating that he had some urine concentrating ability. Oral disintegrating DDAVP therapy was started at 360 µg/d with hydrochlorothiazide and increased to 720 µg/d without any adverse effects. A 30% decrease in urine output and water intake was followed by an increase in body weight. The present study is the first to report the effectiveness and safety of oral disintegrating DDAVP in a patient with partial congenital NDI due to an AVPR2 gene mutation. The severity of NDI at which DDAVP therapy is the most effective remains to be determined.

Clinical and Functional Characterization of a Novel Mutation in AVPR2 Causing Nephrogenic Diabetes Insipidus in a Four-Generation Chinese Family

Background: Congenital nephrogenic diabetes insipidus (CNDI) is a rare inherited disease that is caused by mutations in arginine vasopressin receptor 2 (AVPR2) or aquaporin 2 (AQP2). Functional analysis of the mutated receptor is necessary to verify the impact of the mutation on receptor function and suggest some possible therapeutic strategies for specific functional defects. Methods: Family history and clinical information were collected. Whole-exome sequencing and sanger sequencing were performed to determine the potential genetic cause of diabetes insipidus. The identified variant was classified according to the American College of Medical Genetics (ACMG) criteria. Bioinformatic analysis was performed to predict the function of the identified variation. Moreover, wild-type and mutated AVPR2 vectors were constructed and transfection to HEK-293T cells. Immunofluorescence experiments were performed to investigate the expression and localization of the mutated protein and cAMP parameter assays were used to measure its activity in response to AVP. Results: The heights of the adult members affected with polyuria and polydipsia were normal, but all affected children had growth retardation. Next-generation sequencing identified a novel mutation in AVPR2 gene (c.530T > A) in this family. Bioinformatic analysis indicated that the mutation in AVPR2 changed the hydropathic characteristic of the protein and was probably deleterious. Although immunofluorescence showed that the mutated AVPR2 was normally expressed in the cell surface, the intracellular cAMP concentration stimulated by AVP was significantly lower in cells transfected with mutated AVPR2 than cells transfected with wild-type AVPR2. Based on the ACMG criteria, the novel c.530T > A variant of the AVPR2 gene was likely pathogenic and the affected family members were diagnosed as CNDI. After the confirmation of the diagnosis, the proband was treated with compound amiloride hydrochloride and rhGH, the symptoms of polyuria, polydipsia and growth retardation were all improved. Conclusion: These findings suggested that the novel mutation in AVPR2 (c.530T > A) was a true disease-causing variant with mild effects, which could be classified as a type III mutant receptor. Moreover, investigations of the function of growth hormone axis could be important for the pediatric CNDI patients with extreme short stature, and rhGH treatment might improve the final adult heights in these patients.

Recurrent Urinary Tract Infection in Craniopharyngioma: A Harbinger to a Sinister Diagnosis!

Craniopharyngiomas are benign tumors of neuroepithelial origin, believed to arise from remnants of Rathke’s pouch. Their proximity to vital structures of the visual pathway and hypothalamus leads to both neurological and endocrinological complications. Endocrinal complications are seen in 40%–87% of the affected and can develop at presentation or post-surgery and radiotherapy. Central diabetes insipidus (CDI) is a common endocrinopathy associated with craniopharyngioma, but rarely a presenting symptom before or after surgery. CDI most commonly presents with polyuria and polydipsia. Here, we report a postoperative child with craniopharyngioma where recurrent urinary tract infection and hydronephrosis were initial clues to diagnose CDI.

From infancy to adulthood: challenges in congenital nephrogenic diabetes insipidus

Objectives Congenital nephrogenic diabetes insipidus (NDI) is a rare hereditary disorder which is characterized by unresponsiveness to arginine vasopressin (AVP) in collecting ducts and leads to polyuria and polydipsia. The wide clinical spectrum of congenital NDI can cause difficulties in early diagnosis. We aimed to evaluate clinical prognosis of children with congenital NDI in long-term period. Methods Nineteen children with congenital NDI followed up in Pediatric Nephrology Department were enrolled to the study. This study is a single-center retrospective study, which reports clinical follow-up and genetic results of children with congenital NDI. Results Presenting symptoms of patients were mostly dehydration and fever due to polyuria and polydipsia. Four male patients had bilateral nonobstructive hydroureteronephrosis (HUN) and neurogenic bladder which requires clean intermittent catheterization (CIC). One patient had intracranial calcification which is a rarely seen complication in congenital NDI due to recurrent hypernatremic dehydration and severe brain dehydration. The causative mutations were identified in all patients. The identified mutations in six of them (31.6%) were hemizygous mutations in AVPR2 gene and homozygous mutations of AQP2 gene in the rest 13 cases (68.4%). More than that, four of these mutations (two in AVPR2 and two in AQP2) were novel mutations. Noncompliance with the treatments is associated with high risk of morbidity due to neurogenic bladder and chronic kidney disease (CKD). Conclusions The prognosis of congenital NDI is good when diagnosis can be made early and treatment is started immediately. Genetic counseling and prenatal testing for hereditary diseases are recommended especially in regions with relatively higher rates of consanguineous marriages.

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.

Hypertensive urgency in nephrogenic diabetes insipidus with concomitant Hinman syndrome

Diabetes insipidus is a syndrome characterised by the inability to conserve water or concentrate urine, leading to excessive excretion of urine. In congenital nephrogenic diabetes insipidus (CNDI), common presentations include failure to thrive, polydipsia, polyuria and dehydration. The long trajectory of the disease, coupled with psycho-behavioural changes as a child grows, can precipitate a period of non-adherence despite initial optimal control, especially in the adolescent age group. Social inconvenience of repeated voiding and nocturnal disturbances can lead to adapted urine holding behaviour, also known as non-neurogenic neurogenic bladder (Hinman syndrome). Anatomical changes in the urinary system, such as bladder trabeculation and hydroureteronephrosis, can subsequently give rise to functional renal impairment. We present a case of CNDI with concomitant Hinman syndrome, resulting in acute renal impairment and hypertensive emergency. We aim to raise awareness of the association between these two entities.

A novel AVPR2 missense mutation in an Asian family with inherited nephrogenic diabetes insipidus: A case report

RATIONALE

X-linked nephrogenic diabetes insipidus (NDI) is a rare inherited disease, and is characterized by renal resistance to arginine vasopressin (AVP). Its diagnosis can be clinically challenging. The application of molecular genetic analysis can provide a rapid and definitive diagnosis.

PATIENT CONCERNS

A 75-year-old woman presented with recurrent nausea and vomiting was admitted to the Department of Gastroenterology. The patient had a strong family history of polydipsia and polyuria. Sequencing analysis of the antidiuretic hormone arginine vasopressin receptor 2 (AVPR2) revealed the novel missense mutation p. Trp164Cys (c.492G>G/C) in exon 2. There was a heterozygous mutation in the patient's sister and niece, while there was a mutation in her sons, brother and nephews. The locus is located on the X chromosome Xq28, and its mutation can lead to X linked recessive NDI. The p. Trp164Cys mutation of AVPR2 gene has not been reported in literature before. The mutation was predicted to be probably damaging by several prediction methods, including SIFT and PolyPhen-2. There was no significant abnormal variation in other detection regions of the gene. And there was also no abnormal variation in AVP and AQP2 genes in this family.

DIAGNOSIS

X-linked NDI was diagnosed according to the patient's family history and DNA sequencing analysis.

INTERVENTIONS AND OUTCOMES

After treated with desmopressin, antiemetic drugs and massive infusion glucose transfusion, the patient's urine volume decreased and electrolyte disturbance was corrected, and the symptoms of nausea and vomiting gradually disappeared.

LESSONS

The patients with suspected congenital NDI should undergo genetic sequencing analysis of AVPR2, AVP and AQP2 genes. A definitive diagnosis can benefit patient and avoid unnecessary investigations.

Nephrogenic Diabetes Insipidus

Body fluid homeostasis is essential for normal life. In the maintenance of water balance, the most important factor and regulated process is the excretory function of the kidneys. The kidneys are capable to compensate not only the daily fluctuations of water intake but also the consequences of fluid loss (respiration, perspiration, sweating, hemorrhage). The final volume and osmolality of the excreted urine is set in the collecting duct via hormonal regulation. The hormone of water conservation is the vasopressin (AVP), and a large volume of urine is produced and excreted in the absence of AVP secretion or if AVP is ineffective in the kidneys. The aquaporin-2 water channel (AQP2) is expressed in the principal cells, and it plays an essential role in the reabsorption of water in the collecting ducts via type 2 vasopressin receptor (V2R)-mediated mechanism. If neural or hormonal regulation fails to operate the normal function of AVP-V2R-AQP2 system, it can result in various diseases such as diabetes insipidus (DI) or nephrogenic syndrome of inappropriate diuresis (NSIAD). The DI is characterized by excessive production of hyposmotic urine ("insipidus" means tasteless) due to the inability of the kidneys to concentrate urine. In this chapter, we focus and discuss the pathophysiology of nephrogenic DI (NDI) and the potential therapeutic interventions in the light of the current experimental data.

Diagnosis, Treatment, and Outcomes in Children With Congenital Nephrogenic Diabetes Insipidus: A Pediatric Nephrology Research Consortium Study

Background and Objectives: Congenital or primary nephrogenic diabetes insipidus (NDI) is a rare genetic disorder that severely impairs renal concentrating ability, resulting in massive polyuria. There is limited information about prognosis or evidence guiding the management of these patients, either in the high-risk period after diagnosis, or long-term. We describe the clinical presentation, genetic etiology, treatment and renal outcomes in a large group of children <21 years with NDI. Design: A multi-center retrospective chart review. Results: We report on 66 subjects from 16 centers. They were mainly male (89%) and white (67%). Median age at diagnosis was 4.2 months interquartile range (IQR 1.1, 9.8). A desmopressin acetate loading test was administered to 46% of children at a median age of 4.8 months (IQR 2.8, 7.6); only 15% had a water restriction test. Genetic testing or a known family history was present in 70% of the patients; out of those genetically tested, 89 and 11% had mutations in AVPR2 and AQP2, respectively. No positive family history or genetic testing was available for 30%. The most common treatments were thiazide diuretics (74%), potassium-sparing diuretics (67%) and non-steroidal anti-inflammatory drugs (42%). At the time of first treatment, 70 and 71% of children were below -2 standard deviations (SD) for weight and height, respectively. At last follow-up, median age was 72.3 months (IQR 40.9, 137.2) and the percentage below -2 SD improved to 29% and 38% for weight and height, respectively. Adverse outcomes included inpatient hospitalizations (61%), urologic complications (37%), and chronic kidney disease (CKD) stage 2 or higher in 23%. Conclusion: We found the majority of patients were treated with thiazides with either a potassium sparing diuretic and/or NSAIDs. Hospitalizations, urologic complications, short stature, and CKD were common. Prospective trials to evaluate different treatment strategies are needed to attempt to improve outcomes.

Four Japanese Patients with Congenital Nephrogenic Diabetes Insipidus due to the AVPR2 Mutations

Almost 90% of nephrogenic diabetes insipidus (NDI) is caused by mutations in the arginine vasopressin receptor 2 gene (AVPR2) on the X chromosome. Herein, we reported clinical and biochemical parameters in four cases of three unrelated Japanese families and analyzed the status of the AVPR2. Two of the four patients had poor weight gain. However, in the male and female sibling cases, neither had poor weight gain while toddlers, but in the male sibling, episodes of recurrent fever, polyuria, and polydipsia led to the diagnosis of NDI at 4 years of age. Analysis of AVPR2 identified two nonsense mutations (c.299_300insA; p.K100KfsX91 and c.296G > A; p.W99X) and one missense mutation (c.316C > T; p.R106C). These mutations were previously reported. The patient with c.316C > T; p.R106C had milder symptoms consistent with previous reports. Of the familial cases, the sister was diagnosed as having NDI, but a skewed X-inactivation pattern in her peripheral blood lymphocytes was not identified. In conclusion, our study expands the spectrum of phenotypes and characterized mutations in AVPR2 in NDI.

Long-term outcome in inherited nephrogenic diabetes insipidus

Background

Inherited nephrogenic diabetes insipidus (NDI) is a rare disorder characterized by impaired urinary concentrating ability. Little clinical data on long-term outcome exists.

Method

This was a single-centre retrospective medical record review of patients with a diagnosis of NDI followed between 1985 and 2017. We collected available data on growth, weight, school performance, complications and comorbidities.

Results

We identified 36 patients with available data and a clinical diagnosis of NDI, which was genetically confirmed in 33 of them. Patients presented at a median age of 0.6 years and median length of follow-up was 9.5 years. Chief symptoms at presentation were faltering growth, vomiting/feeding concerns, polyuria/polydipsia, febrile illness and hypernatraemic dehydration. Median weight standard deviation scores (SDS) improved from −2.1 at presentation to 0.2 at last follow-up. In contrast, height SDS remained essentially unchanged at −1.1 at presentation and −0.9 at last follow-up. Most patients were treated with prostaglandin synthesis inhibitors and thiazides, yet weaned off during school age without an obvious change in urine output. Median estimated glomerular filtration rate at last follow-up was 81 mL/min/1.73 m². Urological complications were noted in 15 patients, constipation in 11 and learning difficulties in 5. Median age at resolution of nocturnal enuresis was 11 years. Estimated median daily fluid intake at median age of 13 years was 3800 mL/m².

Conclusion

The overall prognosis in inherited NDI is favourable with regular treatment. As expected, most complications were related to polyuria. There is an apparent loss of efficacy of medications during school age. Our data inform the prognosis and management of patients with NDI.

Hereditary Nephrogenic Diabetes Insipidus: Pathophysiology and Possible Treatment. An Update

Under physiological conditions, excessive loss of water through the urine is prevented by the release of the antidiuretic hormone arginine-vasopressin (AVP) from the posterior pituitary. In the kidney, AVP elicits a number of cellular responses, which converge on increasing the osmotic reabsorption of water in the collecting duct. One of the key events triggered by the binding of AVP to its type-2 receptor (AVPR2) is the exocytosis of the water channel aquaporin 2 (AQP2) at the apical membrane the principal cells of the collecting duct. Mutations of either AVPR2 or AQP2 result in a genetic disease known as nephrogenic diabetes insipidus, which is characterized by the lack of responsiveness of the collecting duct to the antidiuretic action of AVP. The affected subject, being incapable of concentrating the urine, presents marked polyuria and compensatory polydipsia and is constantly at risk of severe dehydration. The molecular bases of the disease are fully uncovered, as well as the genetic or clinical tests for a prompt diagnosis of the disease in newborns. A real cure for nephrogenic diabetes insipidus (NDI) is still missing, and the main symptoms of the disease are handled with s continuous supply of water, a restrictive diet, and nonspecific drugs. Unfortunately, the current therapeutic options are limited and only partially beneficial. Further investigation in vitro or using the available animal models of the disease, combined with clinical trials, will eventually lead to the identification of one or more targeted strategies that will improve or replace the current conventional therapy and grant NDI patients a better quality of life. Here we provide an updated overview of the genetic defects causing NDI, the most recent strategies under investigation for rescuing the activity of mutated AVPR2 or AQP2, or for bypassing defective AVPR2 signaling and restoring AQP2 plasma membrane expression.

Novel de novo AVPR2 Variant in a Patient with Congenital Nephrogenic Diabetes Insipidus

Early diagnosis and treatment of congenital nephrogenic diabetes insipidus (CNDI) are essential due to the risk of intellectual disability caused by repeated episodes of dehydration and rapid rehydration. Timely genetic testing for disease-causing variants in the arginine vasopressin receptor 2 (AVPR2) gene is possible in at-risk newborns with a known family history of X-linked CNDI. In this study, a Swedish male with no family history was diagnosed with CNDI at 6 months of age during an episode of gastroenteritis. We analyzed the coding regions of AVPR2 by PCR and direct DNA sequencing and identified an 80-bp duplication in exon 2 (GenBank NM_000054.4; c.800_879dup) in the proband. This variant leads to a frameshift and introduces a stop codon four codons downstream (p.Ala294Profs*4). The variant gene product either succumbs to nonsense-mediated decay or is translated to a truncated nonfunctional vasopressin V2 receptor. This variant was absent in four unaffected family members, including his parents, as well as in 100 alleles from healthy controls, and is thus considered a novel de novo disease-causing variant. Identification of the disease-causing variant facilitated precise diagnosis of CNDI in the proband. Furthermore, it allows future genetic counseling in the family. This case study highlights the importance of genetic testing in sporadic infant cases with CNDI that can occur due to de novo variants in AVPR2 or several generations of female transmission of the disease-causing variant.

Genetics of Diabetes Insipidus

Diabetes insipidus is a disease characterized by polyuria and polydipsia due to inadequate release of arginine vasopressin from the posterior pituitary gland (neurohypophyseal diabetes insipidus) or due to arginine vasopressin insensitivity by the renal distal tubule, leading to a deficiency in tubular water reabsorption (nephrogenic diabetes insipidus). This article reviews the genetics of diabetes insipidus in the context of its diagnosis, clinical presentation, and therapy.

Two novel mutations in seven Czech and Slovak kindreds with familial neurohypophyseal diabetes insipidus-benefit of genetic testing

Familial neurohypophyseal diabetes insipidus (FNDI) is a rare hereditary disorder with unknown prevalence characterized by arginine-vasopressin hormone (AVP) deficiency resulting in polyuria and polydipsia from early childhood. We report the clinical manifestation and genetic test results in seven unrelated kindreds of Czech or Slovak origin with FNDI phenotype. The age of the sign outset ranged from 2 to 17 years with remarkable interfamilial and intrafamilial variability. Inconclusive result of the fluid deprivation test in three children aged 7 and 17 years old might cause misdiagnosis; however, the AVP gene analysis confirmed the FNDI. The seven families segregated together five different mutations, two of them were novel (c.164C > A, c.298G > C). In addition, DNA analysis proved mutation carrier status in one asymptomatic 1-year-old infant.

CONCLUSIONS

The present study together with previously published data identified 38 individuals with FNDI in the studied population of 16 million which predicts a disease prevalence of 1:450,000 for the Central European region. The paper underscores that diagnostic water deprivation test may be inconclusive in polyuric children with partial diabetes insipidus and points to the clinical importance and feasibility of molecular genetic testing for AVP gene mutations in the proband and her/his first degree relatives.

WHAT IS KNOWN

• At least 70 different mutations were reported to date in about 100 families with neurohypophyseal diabetes insipidus (FNDI), and new mutations appear sporadically. What is New: • Two novel mutations of the AVP gene are reported • The importance of molecular testing in children with polyuria and inconclusive water deprivation test is emphasized.

Polyuria due to vasopressin V2 receptor antagonism is not associated with increased ureter diameter in ADPKD patients

BACKGROUND

Tolvaptan, a vasopressin V2 receptor antagonist, has been shown to reduce the rates of growth in total kidney volume (TKV) and renal function loss in ADPKD patients, but also leads to polyuria because of its aquaretic effect. Prolonged polyuria can result in ureter dilatation with consequently renal function loss. Therefore, we aimed to investigate the effect of tolvaptan-induced polyuria on ureter diameter in ADPKD patients.

METHODS

70 ADPKD patients were included (51 were randomized to tolvaptan and 19 to placebo). At baseline and after 3 years of treatment renal function was measured (mGFR) and MRI was performed to measure TKV and ureter diameter at the levels of renal pelvis and fifth lumbar vertebral body (L5).

RESULTS

In these patients [65.7 % male, age 41 ± 9 years, mGFR 74 ± 27 mL/min/1.73 m² and TKV 1.92 (1.27-2.67) L], no differences were found between tolvaptan and placebo-treated patients in 24-h urine volume at baseline (2.5 vs. 2.5 L, p = 0.8), nor in ureter diameter at renal pelvis and L5 (4.0 vs. 4.2 mm, p = 0.4 and 3.0 vs. 3.1 mm, p = 0.3). After 3 years of treatment 24-h urine volume was higher in tolvaptan-treated patients when compared to placebo (4.7 vs. 2.3 L, p < 0.001), but no differences were found in ureter diameter between both groups (renal pelvis: 4.2 vs. 4.4 mm, p = 0.4 and L5: 3.1 vs. 3.3 mm, p = 0.4).

CONCLUSIONS

Tolvaptan-induced polyuria did not lead to an increase in ureter diameter, suggesting that tolvaptan is a safe therapy from a urological point of view.

Novel AVPR2 mutation causing partial nephrogenic diabetes insipidus in a Japanese family

BACKGROUND

X-linked recessive congenital nephrogenic diabetes insipidus (NDI) is caused by mutations of the arginine vasopressin type 2 receptor gene (AVPR2). More than 200 mutations of the AVPR2 gene with complete NDI have been reported although only 15 mutations with partial NDI has been reported to date.

METHODS

We herein report a Japanese kindred with partial NDI. The proband is an 8-year-old boy who was referred to our hospital for nocturnal enuresis. Water deprivation test and hypertonic saline test suggested partial renal antidiuretic hormone arginine vasopressin (AVP) resistance.

RESULTS

Analysis of genomic DNA revealed a novel missense mutation (p.L161P) in the patient. The patient's mother was heterozygous for the mutation. Three-dimensional (3-D) modeling study showed that L161P possibly destabilizes the transmembrane domain of the V2 receptor, resulting in its misfolding or mislocalization.

CONCLUSIONS

Distinguishing partial NDI from nocturnal enuresis is important. A clinical clue for diagnosis of partial NDI is an incompatibly high level of AVP despite normal serum osmolality.

Persistent severe polyuria after renal transplant

Polydipsia and polyuria are common symptoms in patients with diabetes insipidus (DI), which can be due to inadequate vasopressin production (cranial DI) or vasopressin insensitivity (nephrogenic DI). Clinical diagnosis of the subtypes of DI can be tricky. We present a 44-year-old man with a strong family history of DI who had been diagnosed with autosomal dominant nephrogenic DI from infancy. At the age of 40, he had progressed to end-stage renal failure. When he experienced unresolving severe polyuria after renal transplant, further investigations revealed that he was misdiagnosed and that he had a novel mutation causing autosomal dominant cranial DI.

Novel mutations associated with nephrogenic diabetes insipidus. A clinical-genetic study

Molecular diagnosis is a useful diagnostic tool in primary nephrogenic diabetes insipidus (NDI), an inherited disease characterized by renal inability to concentrate urine. The AVPR2 and AQP2 genes were screened for mutations in a cohort of 25 patients with clinical diagnosis of NDI. Patients presented with dehydration, polyuria-polydipsia, failure to thrive (mean ± SD; Z-height -1.9 ± 2.1 and Z-weight -2.4 ± 1.7), severe hypernatremia (mean ± SD; Na 150 ± 10 mEq/L), increased plasma osmolality (mean ± SD; 311 ± 18 mOsm/Kg), but normal glomerular filtration rate. Genetic diagnosis revealed that 24 male patients were hemizygous for 17 different putative disease-causing mutations in the AVPR2 gene (each one in a different family). Of those, nine had not been previously reported, and eight were recurrent. Moreover, we found those same AVPR2 changes in 12 relatives who were heterozygous carriers. Further, in one female patient, AVPR2 gene study turned out to be negative and she was found to be homozygous for the novel AQP2 p.Ala86Val alteration.

CONCLUSION

Genetic analysis presumably confirmed the diagnosis of nephrogenic diabetes insipidus in every patient of the studied cohort. We emphasize that we detected a high presence (50 %) of heterozygous females with clinical NDI symptoms.

WHAT IS KNOWN

• In most cases (90 %), inherited nephrogenic diabetes insipidus (NDI) is an X-linked disease, caused by mutations in the AVPR2 gene. • In rare occasions (10 %), it is caused by mutations in the AQP2 gene. What is new: • In this study, we report 10 novel mutations associated with NDI. • We have detected a high presence (50 %) of heterozygous carriers with clinical NDI symptoms.

A Rare Case of Congenital Diabetes Insipidus

Congenital nephrogenic diabetes insipidus (NDI) is a conformation disease resulting from protein misfolding. Ninety percent of mutations result from the inactivating mutations of the arginine vasopressin receptor 2 (AVPR2) gene transmitted in an X-linked fashion, blocking the response to vasopressin, resulting in the inability to concentrate urine. Clinical features include polyuria, polydispsia, dehydration, and hypernatremia. They are generally more severely in affected males but present variably in females due to skewed inactivation of the X chromosome. We describe a case of a 40-year-old woman with a history of Type 2 diabetes mellitus, hyperlipidemia, and obesity, who presents with debilitating polyuria since the age of 5 with no clear diagnosis. Interestingly, her son was diagnosed with NDI. Genetic testing revealed that she was heterozygous for the Val88Met mutation in the AVPR2 gene while her son was hemizygous for the same. The patient has since been successfully treated with diuretics and a low solute diet. We highlight that although X-linked NDI patients are mostly males, it should be considered in symptomatic females to prevent delays in the diagnosis. Conformational diseases such as NDI are presently the subject of research using pharmacological chaperones to restore proper receptor membrane localization and function.

Pathophysiology, diagnosis and management of nephrogenic diabetes insipidus

Healthy kidneys maintain fluid and electrolyte homoeostasis by adjusting urine volume and composition according to physiological needs. The final urine composition is determined in the last tubular segment: the collecting duct. Water permeability in the collecting duct is regulated by arginine vasopressin (AVP). Secretion of AVP from the neurohypophysis is regulated by a complex signalling network that involves osmosensors, barosensors and volume sensors. AVP facilitates aquaporin (AQP)-mediated water reabsorption via activation of the vasopressin V2 receptor (AVPR2) in the collecting duct, thus enabling concentration of urine. In nephrogenic diabetes insipidus (NDI), inability of the kidneys to respond to AVP results in functional AQP deficiency. Consequently, affected patients have constant diuresis, resulting in large volumes of dilute urine. Primary forms of NDI result from mutations in the genes that encode the key proteins AVPR2 and AQP2, whereas secondary forms are associated with biochemical abnormalities, obstructive uropathy or the use of certain medications, particularly lithium. Treatment of the disease is informed by identification of the underlying cause. Here we review the clinical aspects and diagnosis of NDI, the various aetiologies, current treatment options and potential future developments.

X-Linked Recessive form of Nephrogenic Diabetes Insipidus in a 7-Year-Old Boy

Nephrogenic diabetes insipidus (NDI) is caused by the inability of renal collecting duct cells to respond to arginine vasopressin (AVP)/antidiuretic hormone (ADH). We present the case of a 7-year-old boy with a history of excretion of large amounts of dilute urine and polydipsia since infancy. The boy had several vomiting episodes with mild dehydration during the first 3 years of life. There was no evidence of headaches, dizziness or visual problems. He drinks between 2 and 3 L/day and has 24-hour diuresis of 2 liters, now. He has prepubertal appearance with appropriate weight [+0.85 standard deviation score (SDS)] and height (+0.15 SDS) for his age. His intelligence was also normal. The water deprivation test showed low urine osmolality after 8 hours of dehydration. After desmopressin administration, urine osmolality remained low. Serum osmolality was in the normal range for sex and age before and after desmopressin administration. This indicated a nephrogenic form of diabetes insipidus. Molecular analyses revealed a P286L [p.Pro(CCC)286Leu(CTC)] mutation in the AVPR2 gene, that was inherited from his mother. This patient is the first case with genetically confirmed X-linked inherited form of NDI in the Republic of Macedonia. Molecular analysis confirmed the clinical diagnosis and enabled genetic advice for this family.

Urinary concentration: different ways to open and close the tap

Nephrogenic diabetes insipidus (NDI) provides an excellent model for the benefits and insights that can be gained from studying rare diseases. The discovery of underlying genes identified key molecules involved in urinary concentration, including the type 2 vasopressin receptor AVPR2 and the water channel AQP2, which constitute obvious pharmacologic targets. Subsequently developed drugs targeting AVPR2 not only provide potential benefit to some patients with NDI, but are now used for much more common clinical applications as diverse as nocturnal enuresis and heart failure. Yet, the story is still evolving: clinical observations and animal experiments continue to discover new ways to affect urinary concentration. These novel pathways can potentially be exploited for therapeutic gain. Here we review the (patho)physiology of water homoeostasis, the current status of clinical management, and potential new treatments.

Congenital nephrogenic diabetes insipidus with a novel mutation in the aquaporin 2 gene

gene has clinical significance, as early recognition of CNDI in infants that show only non-specific symptoms, can be facilitated. Thus, repeated episodes of dehydration, which may cause physical and mental retardation can be avoided.

Pre- and post-treatment urinary tract findings in children with nephrogenic diabetes insipidus

BACKGROUND

Nephrogenic diabetes insipidus (NDI) is characterized by the kidney's inability to concentrate urine, which causes intense polyuria that may lead to urinary tract dilation. We report the morphological findings of the urinary tract in ten boys with NDI specifically addressing the presence and changes of urinary tract dilation during treatment.

DIAGNOSIS/TREATMENT

Patients were diagnosed at a median age of 1.6 years (range, 0.16-6.33 years) and treated with a low osmotic diet, hydrochlorothiazide-amiloride and indomethacin, which decreased the diuresis from a median of 10.5 ml/kg/h to 4.4 ml/kg/h (p < 0.001). Three patients showed normal renal ultrasound before treatment until last control, while the remaining seven showed urinary tract dilation. In this second group, dilation was reduced with treatment in four patients and disappeared in the remaining three. Children without dilation or in whom the dilation disappeared were diagnosed and treated earlier than those with persistent dilation (median 1.66 versus 4.45 years, respectively). After a median of 10.4 (range, 2.3-20.3) years of follow-up, no patients showed urological complications.

CONCLUSIONS

Medical treatment of the disease improved the dilation in all cases, preventing its potential complications. Regardless of the good outcome of our patients, periodic urologic follow-up is recommended in NDI patients.

Nephrogenic diabetes insipidus: essential insights into the molecular background and potential therapies for treatment

The water channel aquaporin-2 (AQP2), expressed in the kidney collecting ducts, plays a pivotal role in maintaining body water balance. The channel is regulated by the peptide hormone arginine vasopressin (AVP), which exerts its effects through the type 2 vasopressin receptor (AVPR2). Disrupted function or regulation of AQP2 or the AVPR2 results in nephrogenic diabetes insipidus (NDI), a common clinical condition of renal origin characterized by polydipsia and polyuria. Over several years, major research efforts have advanced our understanding of NDI at the genetic, cellular, molecular, and biological levels. NDI is commonly characterized as hereditary (congenital) NDI, arising from genetic mutations in the AVPR2 or AQP2; or acquired NDI, due to for exmple medical treatment or electrolyte disturbances. In this article, we provide a comprehensive overview of the genetic, cell biological, and pathophysiological causes of NDI, with emphasis on the congenital forms and the acquired forms arising from lithium and other drug therapies, acute and chronic renal failure, and disturbed levels of calcium and potassium. Additionally, we provide an overview of the exciting new treatment strategies that have been recently proposed for alleviating the symptoms of some forms of the disease and for bypassing G protein-coupled receptor signaling.

The renal concentrating mechanism and the clinical consequences of its loss

The integrity of the renal concentrating mechanism is maintained by the anatomical and functional arrangements of the renal transport mechanisms for solute (sodium, potassium, urea, etc) and water and by the function of the regulatory hormone for renal concentration, vasopressin. The discovery of aquaporins (water channels) in the cell membranes of the renal tubular epithelial cells has elucidated the mechanisms of renal actions of vasopressin. Loss of the concentrating mechanism results in uncontrolled polyuria with low urine osmolality and, if the patient is unable to consume (appropriately) large volumes of water, hypernatremia with dire neurological consequences. Loss of concentrating mechanism can be the consequence of defective secretion of vasopressin from the posterior pituitary gland (congenital or acquired central diabetes insipidus) or poor response of the target organ to vasopressin (congenital or nephrogenic diabetes insipidus). The differentiation between the three major states producing polyuria with low urine osmolality (central diabetes insipidus, nephrogenic diabetes insipidus and primary polydipsia) is done by a standardized water deprivation test. Proper diagnosis is essential for the management, which differs between these three conditions.

Congenital nephrogenic diabetes insipidus: the current state of affairs

The anti-diuretic hormone arginine vasopressin (AVP) is released from the pituitary upon hypovolemia or hypernatremia, and regulates water reabsorption in the renal collecting duct principal cells. Binding of AVP to the arginine vasopressin receptor type 2 (AVPR2) in the basolateral membrane leads to translocation of aquaporin 2 (AQP2) water channels to the apical membrane of the collecting duct principal cells, inducing water permeability of the membrane. This results in water reabsorption from the pro-urine into the medullary interstitium following an osmotic gradient. Congenital nephrogenic diabetes insipidus (NDI) is a disorder associated with mutations in either the AVPR2 or AQP2 gene, causing the inability of patients to concentrate their pro-urine, which leads to a high risk of dehydration. This review focuses on the current knowledge regarding the cell biological aspects of congenital X-linked, autosomal-recessive and autosomal-dominant NDI while specifically addressing the latest developments in the field. Based on deepened mechanistic understanding, new therapeutic strategies are currently being explored, which we also discuss here.

Nonobstructive hydronephrosis due to social polydipsia: a case report

INTRODUCTION

Excessive fluid intake can lead to water intoxication, electrolyte abnormalities, exacerbation of heart failure and anatomical changes in the urinary tract that may present diagnostic and therapeutic challenges for patients and physicians. Although the development of nonobstructive hydronephrosis is recognized in patients with central and nephrogenic diabetes insipidus, pregnancy or psychiatric polydipsia, it is rarely a diagnostic consideration in healthy individuals with excessive fluid ingestion. We now present what we believe to be the first report of nonobstructive hydronephrosis associated with social polydipsia.

CASE PRESENTATION

A 53-year-old African-American woman with moderate back pain was found to have bilateral moderate hydronephrosis and hydroureter by abdominal computed tomography. She underwent ureteral stent placement followed by exploratory laparoscopy with lysis of adhesions and a right oophorectomy, without resolution of the nonobstructive hydronephrosis. A careful assessment revealed a social habit of consuming approximately 5.5L of fluid daily in an effort to remain hydrated in accordance with public health service announcements. It was recommended that the patient reduce her fluid intake. A repeat ultrasound after six weeks revealed complete resolution of the bilateral hydronephrosis and hydroureter.

CONCLUSION

Recognition of the nonobstructive nature of hydronephrosis caused by polydipsia in healthy individuals is important to prevent unnecessary interventions.

Identification and characterization of a novel X-linked AVPR2 mutation causing partial nephrogenic diabetes insipidus: a case report and review of the literature

X-linked nephrogenic diabetes insipidus (NDI) is a rare disease characterized by a malfunctioning renal response to the antidiuretic hormone arginine vasopressin (AVP) due to mutations in the AVPR2 gene. A limited number of mutations in the AVPR2 gene resulting in partial phenotype have been described so far. In this mini-review the retrospective analysis of 13 known AVPR2 mutations that have been previously shown in vitro to partially abolish AVPR2 function is described, along with a novel mutation diagnosed in a kindred with partial NDI. In the present study, a 14 year old male and his 73 year old maternal grandfather were diagnosed with partial NDI based on the clinical phenotype, the water deprivation test and the inadequate response to 1-desamino-8-d-arginine vasopressin (DDAVP) administration. Sequencing analysis of the AVPR2 gene revealed the novel missense mutation p.N317S (g.1417A > G) in both patients. This mutation was re-created by site directed mutagenesis in an AVPR2 cDNA expression vector and was functionally characterized, in terms of arginine vasopressin (AVP) and DDAVP response. AVPR2 activity of the p.N317S mutant receptor after the AVP and DDAVP administration, as assessed by cAMP production was reduced and impaired when compared to cells that expressed the wild type AVPR2 gene. In conclusion, the affected members of this family have X-linked NDI with partial resistance to AVP, due to a missense mutation in the AVPR2 gene.

Nonobstructive urinary tract dilatation in children with diabetes insipidus

We report 4 boys with diabetes insipidus associated with renal impairment and hydroureteronephrosis. The high flow states caused the bladder to become trabeculated in the absence of infravesical obstruction. Urodynamics have shown the bladder itself to be compliant, but drainage is poor leading to further renal impairment and overflow incontinence. All 4 boys have been managed with cystostomy button drainage and have done well on close follow-up.

A novel deletion partly removing the AVP gene causes autosomal recessive inheritance of early-onset neurohypophyseal diabetes insipidus

Familial neurohypophyseal diabetes insipidus (FNDI) typically presents with age-dependent penetrance and autosomal dominant inheritance caused by missense variations in one allele of the AVP gene encoding the arginine vasopressin (AVP) prohormone. We present the molecular genetic characteristics underlying an unusual form of FNDI occurring with very early onset and seemingly autosomal recessive inheritance. By DNA amplification and sequencing, we identified a novel variant allele of the AVP gene carrying a 10,396 base pair deletion involving the majority of the AVP gene as well as its regulatory sequences in the intergenic region between the AVP and the OXT gene, encoding the oxytocin prohormone. We found two chromosomes carrying the deletion in affected family members and one in unaffected family members suspected to transmit the deleted allele. Whole-genome array analysis confirmed the results and excluded the presence of any additional major pathogenic abnormalities. The deletion is predicted to abolish the transcription of the AVP gene, thus the fact that family members heterozygous for the deletion remain healthy argues, in general, against haploinsufficiency as the pathogenic mechanism FNDI. Accordingly, our data is strong support to the prevailing idea that dominant inheritance of FNDI is due to a dominant-negative effect exerted by variant AVP prohormone.

Pediatric disorders of water balance

Fluid homeostasis requires adequate water intake, regulated by an intact thirst mechanism and appropriate free water excretion by the kidneys, mediated by appropriate secretion of arginine vasopressin (AVP, also known as antidiuretic hormone). AVP exerts its antidiuretic action by binding to the X chromosome-encoded V2 vasopressin receptor (V2R), a G protein coupled receptor on the basolateral membrane of renal collecting duct epithelial cells. After V2R activation, increased intracellular cyclic adenosine monophosphate mediates shuttling of the water channel aquaporin 2 to the apical membrane of collecting duct cells, resulting in increased water permeability and antidiuresis. Clinical disorders of water balance are common, and abnormalities in many steps involving AVP secretion and responsiveness have been described. This article focuses on the principal disorders of water balance, diabetes insipidus, and the syndrome of inappropriate antidiuretic hormone secretion.

Familial forms of diabetes insipidus: clinical and molecular characteristics

Over the past two decades, the genetic and molecular basis of familial forms of diabetes insipidus has been elucidated. Diabetes insipidus is a clinical syndrome characterized by the excretion of abnormally large volumes of diluted urine (polyuria) and increased fluid intake (polydipsia). The most common type of diabetes insipidus is caused by lack of the antidiuretic hormone arginine vasopressin (vasopressin), which is produced in the hypothalamus and secreted by the neurohypophysis. This type of diabetes insipidus is referred to here as neurohypophyseal diabetes insipidus. The syndrome can also result from resistance to the antidiuretic effects of vasopressin on the kidney, either at the level of the vasopressin 2 receptor or the aquaporin 2 water channel (which mediates the re-absorption of water from urine), and is referred to as renal or nephrogenic diabetes insipidus. Differentiation between these two types of diabetes insipidus and primary polydipsia can be difficult owing to the existence of partial as well as complete forms of vasopressin deficiency or resistance. Seven different familial forms of diabetes insipidus are known to exist. The clinical presentation, genetic basis and cellular mechanisms responsible for them vary considerably. This information has led to improved methods of differential diagnosis and could provide the basis of new forms of therapy.

Childhood constipation; an overview of genetic studies and associated syndromes

Constipation is a common problem in children but little is known about its exact pathophysiology. Environmental, behavioural but also genetic factors are thought to play a role in the aetiology of childhood constipation. We provide an overview of genetic studies performed in constipation. Until now, linkage studies, association studies and direct gene sequencing have failed to identify mutations in specific genes associated with constipation. We show that along with functional constipation, there are numerous clinical syndromes associated with childhood constipation. These syndromic forms of constipation appear to be the result of mutations in genes affecting all aspects of the normal physiology of human defecation. We stress that syndromic causes of childhood constipation should be considered in the evaluation of a constipated child.

A novel AVPR2 missense mutation in a Chinese boy with severe inherited nephrogenic diabetes insipidus

Inherited nephrogenic diabetes insipidus (NDI) is characterized by renal resistance to arginine vasopressin (AVP). The most common cause is mutations in the AVP receptor 2 (AVPR2) gene at Xq28. Severe complications of NDI are rare but can occur after severe dehydration without treatment. A 7-year-old boy presented with short stature and severe intellectual disability other than polyuria and polydipsia. The karyotype was normal. Direct sequencing revealed a novel missense mutation c.506T > C (p.L169P) in AVPR2 in the patient. His mother was heterozygous for the mutation. The mutation was absent in 103 unrelated healthy males and predicted to be consistently pathogenic by several prediction methods, including Polyphen, SIFT, PMut, PhD-SNP, SNPs3D, PANTHER, and MEMPACK. Awareness of the primary signs of NDI, polyuria, and polydipsia would facilitate early diagnosis and treatment to prevent its severe complications. Also, molecular analysis will provide a rapid and definitive diagnosis and facilitate genetic counseling for family planning.

Angiotensin inhibition and longevity: a question of hydration

With the advancement of medical and investigative science, it is somewhat surprising that although it is possible to stabilise medical patients with hypertension and the associated kidney dysfunction, obesity, diabetes and even cancer, there is still no clear method of significantly reducing these chronic disease pathologies, and thus, extending life expectancy. There is one hormone common to these pathologies, the antagonism of which goes some way to clinical improvements, and this is angiotensin, which is released during hypovolaemia. Angiotensin antagonists are used to treat many of these pathologies, and it has been shown in the obesity literature that angiotensin antagonists decrease weight, but also increase the drinking of water. Increased cellular hydration, and hence, improved mitochondrial metabolism could be one of the mechanisms for the reduction in weight seen in these studies, as well as for reducing the other pathologies, all showing metabolic dysfunction. It appears that the application of straightforward physiological regulation might be an appropriate medical approach to the prevention of hypertension, kidney disease, obesity, diabetes and cancer, and thus, to an increased life expectancy.

A novel mutation in the AVPR2 gene (222delA) associated with X-linked nephrogenic diabetes insipidus in a boy with growth failure

OBJECTIVE

To study the case of a 2 10/12-year-old boy who had growth failure and delayed bone maturation.

METHODS

We reviewed the history, which revealed that he had had polyuria, polydipsia, lack of weight gain, and frequent vomiting since the age of 5 months. On physical examination, his height was 86 cm (-1.93 standard deviation [SD]), his weight 10.5 kg (-2.67 SD), and he had motor and mental retardation. His maternal great-grandfather also had polyuria and polydipsia (but not diabetes mellitus), suggesting X-linked nephrogenic diabetes insipidus as the underlying cause. The patient underwent a water deprivation-desmopressin test. The coding region of the AVPR2 gene was amplified by polymerase chain reaction and submitted to direct sequence analysis.

RESULTS

The water deprivation test confirmed the diagnosis of diabetes insipidus, and administration of desmopressin did not diminish his water secretion. Direct sequencing of the AVPR2 gene revealed a novel deletion of adenine at position 222 (222delA) in exon 2. This mutation is predicted to lead to a frameshift beginning at amino acid 75 and a premature stop codon at position 115 (FS75>115X). His height and weight, as well as his motor skills, improved after initiation of therapy with hydrochlorothiazide and amiloride.

CONCLUSION

Growth delay can be associated with diabetes insipidus. The X-linked nephrogenic diabetes insipidus in this boy is caused by a novel mutation in the AVPR2 gene that is predicted to truncate the receptor protein.

Pediatric disorders of water balance

Fluid homeostasis requires adequate water intake, regulated by an intact thirst mechanism and appropriate free water excretion by the kidneys, mediated by appropriate secretion of arginine vasopressin (AVP, also known as antidiuretic hormone). AVP exerts its antidiuretic action by binding to the X chromosome-encoded V2 vasopressin receptor (V2R), a G protein-coupled receptor on the basolateral membrane of renal collecting duct epithelial cells. After V2R activation, increased intracellular cyclic adenosine monophosphate mediates shuttling of the water channel aquaporin 2 to the apical membrane of collecting duct cells, resulting in increased water permeability and antidiuresis. Clinical disorders of water balance are common, and abnormalities in many steps involving AVP secretion and responsiveness have been described. This article focuses on the principal disorders of water balance, diabetes insipidus, and the syndrome of inappropriate antidiuretic hormone secretion.

Nephrogenic diabetes insipidus: treat with caution

Current therapy for congenital nephrogenic diabetes insipidus consists of appropriate water intake coupled with decreased urine output obtained by means of a low-sodium diet and a combination of thiazide diuretics with renal prostaglandins inhibitors or amiloride. We report a case of congenital nephrogenic diabetes insipidus that was complicated by paradoxical water intoxication secondary to liberal water intake and the initiation of hydrochlorothiazide and indomethacin combination therapy. This report emphasizes the importance of evaluating the water balance and of a quick response with strict protocols following the initiation of indomethacin and thiazide diuretics in nephrogenic diabetes insipidus.

A case for water in the treatment of polycystic kidney disease

Autosomal dominant polycystic disease (ADPKD) is an inherited disorder characterized by the development within renal tubules of innumerable cysts that progressively expand to cause renal insufficiency. Tubule cell proliferation and transepithelial fluid secretion combine to enlarge renal cysts, and 3'-5'-cyclic adenosine monophosphate (cAMP) stimulates that growth. The antidiuretic hormone, arginine vasopressin (AVP), operates continuously in ADPKD patients to stimulate the formation of cAMP, thereby contributing to cyst and kidney enlargement and renal dysfunction. Studies in animal models of ADPKD provide convincing evidence that blocking the action of AVP dramatically ameliorates the disease process. In the current analysis, the authors reason that increasing the amount of solute-free water drunk evenly throughout the day in patients with ADPKD and normal renal function will decrease plasma AVP concentrations and mitigate the action of cAMP on the renal cysts. Potential pitfalls of increasing fluid intake in ADPKD patients are considered, and suggestions for how physicians may prudently implement this therapy are offered.

Long-term growth of children with nephrogenic diabetes insipidus

Primary nephrogenic diabetes insipidus (NDI) is a genetic, chronic disease characterised by lack of distal renal tubule to antidiuretic hormone. The condition produces polyuria, polydipsia, and consequently, reduced caloric intake and growth failure. There is very scarce information on physical growth of affected children. The objective of the paper is to describe long-term growth of 14 patients from 11 families, studied retrospectively and followed for 3-16 years (median 11.6 years). Diagnosis was made on the basis of clinical and laboratory data and concentration test under pitressin. Patients were treated with indomethacin, thiazides, and amiloride. Weight and standing height was measured periodically at the Laboratory of Anthropometry, following standardised techniques. Information was obtained from clinical notes. The majority of children grew below the third centile of local standards, and many showed improvement of weight, height, and body mass index (BMI) over time. Mean height, weight, and BMI gain during follow-up was 1.72, 1.06, and 1.46 standard deviations (SDs), respectively. Three children who did not adhere to treatment showed growth delay. Height gain during the first 2 years of follow-up was inversely associated with height deficit at diagnosis. Further studies on growth at adolescence and in different mutations are recommended.