Expression of three different mutations in the arginine vasopressin gene suggests genotype-phenotype correlation in familial neurohypophyseal diabetes insipidus kindreds

Familial neurohypophyseal diabetes insipidus: clinical, genetic and functional studies of novel mutations in the arginine vasopressin gene

PURPOSE

Familial neurohypophyseal diabetes insipidus (FNDI) is a rare disorder characterized by childhood-onset progressive polyuria and polydipsia due to mutations in the arginine vasopressin (AVP) gene. The aim of the study was to describe the clinical and molecular characteristics of families with neurohypophyseal diabetes insipidus.

METHODS

Five Portuguese families with autosomal dominant FNDI underwent sequencing of the AVP gene and the identified mutations were functionally characterized by in vitro studies.

RESULTS

Three novel and two recurrent heterozygous mutations were identified in the AVP gene. These consisted of one initiation codon mutation in the signal peptide coding region (c.2T > C, p.Met1?), three missense mutations in the neurophysin II (NPII) coding region (c.154T > C, p.Cys52Arg; c.289C > G, p.Arg97Gly; and c.293G > C, p.Cys98Ser), and one nonsense mutation in the NPII coding region (c.343G > T, p.Glu115Ter). In vitro transfection of neuronal cells with expression vectors containing each mutation showed that the mutations resulted in intracellular retention of the vasopressin prohormone. Patients showed progressive symptoms of polyuria and polydipsia, but with wide variability in severity and age at onset. No clear genotype-phenotype correlation was observed.

CONCLUSION

The intracellular accumulation of mutant vasopressin precursors supports the role of cellular toxicity of the mutant proteins in the etiology of the disorder and explains the progressive onset of the disorder. These findings further expand the AVP mutational spectrum in FNDI and contribute to the understanding of the molecular pathogenic mechanisms involved in FNDI.

Central Diabetes Insipidus Caused by Arginine Vasopressin Gene Mutation: Report of a Novel Mutation and Review of Literature

Familial neurohypophyseal diabetes insipidus (FNDI) is an autosomal dominant hereditary disorder characterized by severe polydipsia and polyuria that usually presents in early childhood. In this study, we describe a new arginine vasopressin (AVP) gene mutation in an ethnic German family with FNDI and provide an overview of disease-associated AVP-gene mutations that are already described in literature. Three members of a German family with neurohypophyseal diabetes insipidus were studied. Isolated DNA from peripheral blood samples was used for mutation analysis by sequencing the whole coding region of AVP-NPII gene. Furthermore, we searched the electronic databases MEDLINE (Pubmed) as well as HGMD, LOVD-ClinVar, db-SNP and genomAD in order to compare our cases to that of other patients with FNDI. Genetic analysis of the patients revealed a novel heterozygote missense mutation in exon 2 of the AVP gene (c.274T>G), which has not yet been described in literature. We identified reports of more than 90 disease-associated mutations in the AVP gene in literature. The novel mutation of the AVP gene seems to cause FNDI in the presented German family. Similar to our newly detected mutation, most mutations causing FNDI are found in exon 2 of the AVP gene coding for neurophysin II. Clinically, it is important to think of FNDI in young children presenting with polydipsia and polyuria.

Genetic forms of neurohypophyseal diabetes insipidus

In the majority of cases, hereditary neurohypophyseal diabetes insipidus (DI) is a monogenic disorder caused by mutations in the AVP gene. Dominant transmission is by far the most common form. In these patients, symptoms develop gradually at various ages during childhood, progressing with complete penetrance to polyuria and polydipsia that is usually severe. In autosomal dominant neurohypophyseal DI (ADNDI), the mutant prohormone is folding deficient and consequently retained in the ER, where it forms amyloid-like fibrillar aggregates. Degradation by proteasomes occurs, but their clearance capacity appears to be insufficient. Postmortem studies in affected individuals suggest a neurodegenerative process confined to vasopressinergic neurons. Other forms of genetic neurohypophyseal DI include the very rare autosomal recessive type, also caused by mutations in the AVP gene, and complex multiorgan disorders, such as Wolfram syndrome. In all individuals where a congenital form of DI is suspected, including nephrogenic types, genetic analysis should be performed.

Protein Misfolding Diseases and Therapeutic Approaches

Protein folding is the process by which a polypeptide chain acquires its functional, native 3D structure. Protein misfolding, on the other hand, is a process in which protein fails to fold into its native functional conformation. This misfolding of proteins may lead to precipitation of a number of serious diseases such as Cystic Fibrosis (CF), Alzheimer's Disease (AD), Parkinson's Disease (PD), and Amyotrophic Lateral Sclerosis (ALS) etc. Protein Quality-control (PQC) systems, consisting of molecular chaperones, proteases and regulatory factors, help in protein folding and prevent its aggregation. At the same time, PQC systems also do sorting and removal of improperly folded polypeptides. Among the major types of PQC systems involved in protein homeostasis are cytosolic, Endoplasmic Reticulum (ER) and mitochondrial ones. The cytosol PQC system includes a large number of component chaperones, such as Nascent-polypeptide-associated Complex (NAC), Hsp40, Hsp70, prefoldin and T Complex Protein-1 (TCP-1) Ring Complex (TRiC). Protein misfolding diseases caused due to defective cytosolic PQC system include diseases involving keratin/collagen proteins, cardiomyopathies, phenylketonuria, PD and ALS. The components of PQC system of Endoplasmic Reticulum (ER) include Binding immunoglobulin Protein (BiP), Calnexin (CNX), Calreticulin (CRT), Glucose-regulated Protein GRP94, the thiol-disulphide oxidoreductases, Protein Disulphide Isomerase (PDI) and ERp57. ER-linked misfolding diseases include CF and Familial Neurohypophyseal Diabetes Insipidus (FNDI). The components of mitochondrial PQC system include mitochondrial chaperones such as the Hsp70, the Hsp60/Hsp10 and a set of proteases having AAA+ domains similar to the proteasome that are situated in the matrix or the inner membrane. Protein misfolding diseases caused due to defective mitochondrial PQC system include medium-chain acyl-CoA dehydrogenase (MCAD)/Short-chain Acyl-CoA Dehydrogenase (SCAD) deficiency diseases, hereditary spastic paraplegia. Among therapeutic approaches towards the treatment of various protein misfolding diseases, chaperones have been suggested as potential therapeutic molecules for target based treatment. Chaperones have been advantageous because of their efficient entry and distribution inside the cells, including specific cellular compartments, in therapeutic concentrations. Based on the chemical nature of the chaperones used for therapeutic purposes, molecular, chemical and pharmacological classes of chaperones have been discussed.

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.

Genetic forms of neurohypophyseal diabetes insipidus

Neurohypophyseal diabetes insipidus is characterized by polyuria and polydipsia owing to partial or complete deficiency of the antidiuretic hormone, arginine vasopressin (AVP). Although in most patients non-hereditary causes underlie the disorder, genetic forms have long been recognized and studied both in vivo and in vitro. In most affected families, the disease is transmitted in an autosomal dominant manner, whereas autosomal recessive forms are much less frequent. Both phenotypes can be caused by mutations in the vasopressin-neurophysin II (AVP) gene. In transfected cells expressing dominant mutations, the mutated hormone precursor is retained in the endoplasmic reticulum, where it forms fibrillar aggregates. Autopsy studies in humans and a murine knock-in model suggest that the dominant phenotype results from toxicity to vasopressinergic neurons, but the mechanisms leading to cell death remain unclear. Recessive transmission results from AVP with reduced biologic activity or the deletion of the locus. Genetic neurohypophyseal diabetes insipidus occurring in the context of diabetes mellitus, optic atrophy, and deafness is termed DIDMOAD or Wolfram syndrome, a genetically and phenotypically heterogeneous autosomal recessive disorder caused by mutations in the wolframin (WFS 1) gene.

A case of idiopathic diabetes insipidus presented with bilateral hydroureteronephrosis and neurogenic bladder: A pediatric case report and literature review

Diabetes insipidus (DI) is a condition with heterogeneous clinical symptoms characterized by polyuria (urine output >4 mL/kg/hr) and polydipsia (water intake >2 L/m (2)/d). In children, acquired nephrogenic DI (NDI) is more common than central DI (CDI). Diagnosis is based on the presence of high plasma osmolality and low urinary osmolality with significant water diuresis. A water deprivation test with vasopressin challenge, though has limitations, is done to differentiate NDI from CDI and diagnose their incomplete forms. Neonates and young infants are better managed with hydration therapy alone. Older children with CDI are treated with desmopressin (1-deamino-8-D-arginine vasopressin, dDAVP). Its oral form is safe, highly effective and has dosing flexibility. We report a case of an 8-year-old male patient with CDI with severe bilateral non-obstructive hydronephrosis and megaureter. Dramatic clinical and radiological responses to dDAVP treatment were achieved and therapy reduced urine volume and led to marked radiological improvement in hydronephrosis.

A novel variation in the AVP gene resulting in familial neurohypophyseal diabetes insipidus in a large Italian kindred

Familial neurohypophyseal diabetes insipidus (FNDI) is mostly an autosomal dominant inherited disorder presenting with severe polydipsia and polyuria typically in early childhood. To date, 69 different variations in the AVP gene encoding the AVP prohormone have been identified in autosomal dominant FNDI (adFNDI). In this study we present a family of seven generations, in which a novel variation in the AVP gene seems to cause adFNDI. Clinical assessment by 24 h urine collection, water deprivation test, desmopressin (dDAVP) challenge, and magnetic resonance imaging (MRI) of the posterior pituitary are presented. The diagnosis of adFNDI was confirmed by direct DNA sequence analysis of the AVP gene. Inheritance pattern and clinical history clearly pointed towards adFNDI. Inability of concentrating urine upon dehydration was demonstrated by a water deprivation test, and neurohypophyseal diabetes insipidus was strongly suspected after dDAVP administration, during which renal concentration ability quadrupled. MRI revealed a very weak pituitary "bright spot" in each of six subjects and a further reduction in the size of the neurohypophysis in a 7-year follow-up MRI scan in one subject. DNA sequence analysis revealed heterozygousity for a novel g.1785T > C gene variation predicting a p.Leu63Pro substitution in four affected subjects. Genetic testing in the diagnostic evaluation of families in which diabetes insipidus segregates is highly recommended in that interpretation of clinical assessments can be difficult. Furthermore, presymptomatic diagnosis can ease the parental concern of the carrier status of their offspring, and also avoid unnecessary surveillance of those being unaffected.

A missense mutation in the arginine-vasopressin neurophysin-II gene causes autosomal dominant neurohypophyseal diabetes insipidus in a Chinese family

BACKGROUND

Familial neurohypophyseal diabetes insipidus, an autosomal dominant disorder, is mostly caused by mutations in the genes that encode AVP or its intracellular binding protein, neurophysin-II. The mutations lead to aberrant preprohormone processing and progressive destruction of AVP-secreting cells, which gradually manifests a progressive polyuria and polydipsia during early childhood, and a disorder of water homeostasis.

OBJECTIVE

We characterized the clinical and biochemical features, and sequenced the AVP neurophysin-II(AVP-NPII) gene of the affected individuals with autosomal dominant neurohypophyseal diabetes insipidus(ADNDI)to determine whether this disease was genetically determined.

PATIENTS AND METHODS

We obtained the histories of eight affected and four unaffected family individuals. The diagnosis of ADNDI was established using a water deprivation test and exogenous AVP administration. For molecular analysis, genomic DNA was extracted and the AVP-NPII gene was amplified using polymerase chain reaction and sequenced.

RESULTS

The eight affected individuals showed different spectra of age of onsets (7-15 years) and urine volumes (132-253 ml/kg/24 h). All affected individuals responded to vasopressin administration, with a resolution of symptoms and an increase in urine osmolality by more than 50%. The characteristic hyperintense signal in the posterior pituitary on T1-weighted magnetic resonance imaging was absent in six family members and present in one. Sequencing analysis revealed a missense heterozygous mutation 1516G > T (Gly17Val) in exon 2 of the AVP-NPII gene among the ADNDI individuals.

CONCLUSIONS

We identified a missense mutation in the AVP-NPII gene and the same mutation showed different spectra of age of onsets and urine volumes in a new Chinese family with ADNDI. The mutation may provide a molecular basis for understanding the characteristics of NPII and add to our knowledge of the pathogenesis of ADNDI, which would allow the presymptomatic diagnosis of asymptomatic subjects.

Late-onset familial neurohypophyseal diabetes insipidus due to a novel mutation in the AVP gene

OBJECTIVE

Familial neurohypophyseal diabetes insipidus (FNDI) is mainly an autosomal dominant inherited disorder presenting with severe polydipsia and polyuria in early childhood. In this study, we aimed to determine the molecular genetics and clinical characteristics of a large Swedish-Norwegian family presenting with very late-onset autosomal dominant FNDI.

PATIENTS

Six probands with a history of developing polyuria and polydipsia during adolescence were studied.

MEASUREMENTS

Information on family demography was collected by personal interview with family members. The genetic cause of FNDI was identified by DNA sequencing analysis of the coding regions of the AVP gene. The clinical characteristics were determined by the measurement of basal urine production and osmolality as well as by measurements of concurrent levels of plasma AVP, plasma osmolality, and urine osmolality during fluid deprivation and bolus injection of DDAVP. The integrity of the neurohypophysis was evaluated by magnetic resonance imaging.

RESULTS

The mean age of encountering the first clinical symptoms in the family was 14·8 years (range 3-30 years) (n = 17). All six affected subjects investigated were heterozygous for a novel mutation in the AVP gene (g.1848C>T) predicting a p.Pro84Leu substitution in the AVP precursor protein. We found partial deficiency in evoked AVP secretion during fluid deprivation in one subject and complete deficiency in another. The pituitary bright spot was absent in all six affected subjects studied.

CONCLUSION

A novel mutation in the AVP gene predicted to cause a neurophysin II dimerization defect is causing surprisingly late onset of FNDI in a large, six generation, Swedish-Norwegian family. The mutation is associated with both complete and partial deficiency in evoked AVP secretion during fluid deprivation in patients who have suffered from FNDI for decades.

Management of diabetes insipidus in children

Diabetes Insipidus (DI) is a heterogeneous clinical syndrome of disturbance in water balance, characterized by polyuria (urine output > 4 ml/kg/hr), polydypsia (water intake > 2 L/m(2)/d) and failure to thrive. In children, Nephrogenic DI (NDI) is more common than Central DI (CDI), and is often acquired. The signs and symptoms vary with etiology, age at presentation and mode of onset. Neonates and infants with NDI are severely affected and difficult to treat. Diagnosis is based on the presence of high plasma osmolality and low urinary osmolality with significant water diuresis. Water deprivation test with vasopressin challenge, though has limitations, is done to differentiate NDI and CDI and diagnose their partial forms. Measurement of urinary aquaporin 2 and serum copeptin levels are being studied and show promising diagnostic potential. Magnetic Resonance Imaging (MRI) pituitary helps in the etiological diagnosis of CDI, absence of posterior pituitary bright signal being the pathognomic sign. If pituitary stalk thickening of < 2 mm is present, these children need to be monitored for evolving lesion. Neonates and young infants are better managed with fluids alone. Older children with CDI are treated with desmopressin. The oral form is safe, highly effective, with more flexibility of dosing and has largely replaced the intranasal form. In NDI besides treatment of the underlying cause, use of high calorie low solute diet and drugs to ameliorate water excretion (thiazide, amelioride, indomethacin) are useful. Children with NDI however well treated, remain short and have mental retardation on follow up.

Clinical features and molecular analysis of arginine-vasopressin neurophysin II gene in long-term follow-up patients with idiopathic central diabetes insipidus

INTRODUCTION: Central diabetes insipidus (DI) characterized by polyuria, polydipsia and inability to concentrate urine, has different etiologies including genetic, autoimmune, post-traumatic, among other causes. Autosomal dominant central DI presents the clinical feature of a progressive decline of arginine-vasopressin (AVP) secretion. OBJECTIVE: In this study, we characterized the clinical features and sequenced the AVP-NPII gene of seven long-term follow-up patients with idiopathic central DI in an attempt to determine whether a genetic cause would be involved. METHODS: The diagnosis of central DI was established by fluid deprivation test and hyper-tonic saline infusion. For molecular analysis, genomic DNA was extracted and the AVP-NPII gene was amplified by polymerase chain reaction and sequenced. RESULTS: Sequencing analysis revealed a homozygous guanine insertion in the intron 2 (IVS2 +28 InsG) of the AVP-NPII gene in four patients, which represents an alternative gene assembly. No mutation in the code region of the AVP-NPII gene was found. CONCLUSIONS: The homozygous guanine insertion in intron 2 (IVS2 +28 InsG) is unlikely to contribute to the AVP-NPII gene modulation in DI. In addition, the etiology of idiopathic central DI in children may not be apparent even after long-term follow-up, and requires continuous etiological surveillance.

Further genetic evidence implicates the vasopressin system in childhood-onset mood disorders

Studies in both animals and humans advocate a role for the vasopressin (AVP) system in the aetiology of depressive symptoms. Attention has particularly focused on the role of AVP in the overactivation of the hypothalamic-pituitary-adrenal (HPA)-axis in mood disorders. Elevated AVP plasma levels have been found in mood disorder patients, which are often positively correlated with the severity of symptoms. We recently reported an association between childhood-onset mood disorders (COMD) and polymorphisms in the receptor responsible for the AVP-mediated activation of the HPA-axis (AVPR1B). As genetic variation in the vasopressinergic system could provide a mechanism to explain the endocrine alterations observed in mood disorders, we investigated other genes in this system. The gene encoding AVP is the strongest candidate, particularly as genetic variation in this gene in rodents is associated with anxiety-related behaviours. Six single-nucleotide polymorphisms (SNPs) were genotyped across the AVP gene in a sample comprised of 586 Hungarian nuclear families ascertained through affected probands with a diagnosis of COMD. In addition, AVP coding and putative regulatory regions were screened for mutations using denaturing high-performance liquid chromatography. One SNP, 3' to the AVP, gene reached significance (P = 0.03), as did the overtransmission of a five-marker haplotype with a frequency of 22% (P = 0.0001). The subsequent mutation screen failed to identify any putative functional polymorphisms. The outcome of this study, combined with our previous association between COMD and AVPR1B, implicates genetic variation in vasopressinergic genes in mediating vulnerability to COMD.

Akt induces apoptosis in neuroblastoma cells expressing a C98X vasopressin mutant following autophagy suppression

Mutations in the arginine vasopressin (AVP)-neurophysin II (NP-II) gene that affect the folding and transport of the prohormone result in loss of secretion of the anti-diuretic hormone AVP from pituitary nerve terminals and cause autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI). One such mutation consists of the replacement of a Cys residue at position 98 with a stop codon (C98X) in the AVP precursor (corresponding to C67X in NP domain). In neuroblastoma cells over-expressing this truncated AVP precursor autophagy, a macromolecular degradation process, was shown to be essential for assuring cell survival. In the present study, we investigated the role of the Akt pro-survival signalling in the regulation of autophagy and of apoptosis linked with the handling of C98X AVP. Impairing autophagy-lysosomal sequestration or cathepsin D (CD)-mediated proteolysis triggered the activation of the intrinsic death pathway of apoptosis in C98X-expressing cells, but not in the wild-type -AVP-expressing cells. This was shown by the expression of a Vps34 dominant negative, which down-regulates the PI3k class III-dependent signalling needed for autophagosome (APH) formation, by genetic silencing as a result of RNA interference (RNAi) of Lamp2, a protein indispensable for the fusion of APHs with lysosomes, and by RNAi silencing of the lysosomal protease CD. Ectopic expression of either the wild-type or the mutated C98X AVP altered neither the expression nor the phosphorylation of the pro-survival signalling molecule Akt. Strikingly, the ectopic adenoviral-directed expression of a constitutively active Akt, instead of preserving cell survival, resulted in the suppression of autophagy, and precipitated Bax-mediated cell death. The present data demonstrate the need for autophagy-mediated degradation of mutated C98X peptides, which otherwise become toxic to the cell, and suggest that, in the presence of mis-folded proteins, the stimulation of the Akt signalling counteracts the beneficial effects of autophagy and precipitates cell death. It follows that growth factors impinging on the Akt pathway may have deleterious effect in neurones expressing mutant neuropeptides. This can provide an explanation for the late onset and progressive neuronal cell loss observed in hypothalamic magnocellular neurones of adFNDI patients.

Partial nephrogenic diabetes insipidus caused by a novel mutation in the AVPR2 gene

OBJECTIVE

To identify the molecular basis and clinical characteristics of X-linked congenital nephrogenic diabetes insipidus (CNDI) presenting with an unusual phenotype characterized by partial resistance to AVP.

SUBJECTS

The proband was admitted at the age of 4 years with a history of polydipsia and polyuria since infancy. Initial clinical testing confirmed a diagnosis of diabetes insipidus (DI). Urine osmolarity rose during fluid deprivation and after 20 microg of intranasal desmopressin [1-deamino-8-D-arginine-vasopressin (dDAVP)]. A similar DI phenotype was found in his brother.

METHODS

The coding regions of the AVP gene and the AVP receptor 2 (AVPR2) genes were sequenced in two affected and three unaffected family members. Clinical studies included a fluid deprivation test, intranasal dDAVP challenge, infusion of graded doses of dDAVP and AVP, and measurements of 24-h urine output before and at the end of a 7-day therapeutic trial of intranasal dDAVP.

RESULTS

A novel missense mutation (1454C > A) in exon 3 of the AVPR2 gene predicting a Ser329Arg substitution was identified in the X-chromosome of the two affected brothers and in one of the X-chromosomes in the mother. The AVPR2 gene was normal in two unaffected siblings. Under basal conditions, the 24-h urine volumes of the two affected boys were 5.5 l (229 ml/kg) and 3.5 l (192 ml/kg), the urine osmolalities were 78 and 90 mosm/kg, and plasma AVP 13.5 and 19.0 pg/ml. Urine osmolalities increased to 573 and 720 mosm/kg while plasma AVP levels were practically unchanged, 13.6 and 8.8 pg/ml, during fluid deprivation. Infusion of AVP resulted in urine osmolalities of 523 and 623 mosm/kg at plasma AVP levels of 58 and 42 pg/ml. Infusion of dDAVP had a similar effect, while treatment with standard doses of intranasal dDAVP had no effect on urine output.

DISCUSSION

The affected members of this Belgian kindred have CNDI with partial resistance to AVP caused by a mutation in the AVPR2 gene that differs from any of the six mutations reported previously to produce this phenotype. Because the resistance to AVP is partial, this form of CNDI can be difficult to distinguish by indirect diagnostic tests from partial pituitary and dipsogenic DI.

Diabetes insipidus

Water balance is precisely regulated by vasopressin, thirst and the kidneys; plasma osmolality is maintained within a narrow range, despite large variations in normal water intake and loss. Disruption of these finely balanced mechanisms is common, however, and can be precipitated by various disease states. Diabetes insipidus is a disease process with several underlying pathogenic mechanisms--all ultimately resulting in excretion of large volumes of dilute urine. This review will discuss the pathophysiology, diagnosis and treatment of diabetes insipidus, with emphasis on disorders of osmoregulation following neurosurgery of the pituitary and hypothalamus.

Familial neurohypophyseal diabetes insipidus--an update

Although molecular research has contributed significantly to our knowledge of familial neurohypophyseal diabetes insipidus (FNDI) for more than a decade, the genetic background and the pathogenesis still is not understood fully. Here we provide a review of the genetic basis of FNDI, present recent progress in the understanding of the molecular mechanisms underlying its development, and survey diagnostic and treatment aspects. FNDI is, in 87 of 89 kindreds known, caused by mutations in the arginine vasopressin (AVP) gene, the pattern of which seems to be largely revealed as only few novel mutations have been identified in recent years. The mutation pattern, together with evidence from clinical, cellular, and animal studies, points toward a pathogenic cascade of events, initiated by protein misfolding, involving intracellular protein accumulation, and ending with degeneration of the AVP producing magnocellular neurons. Molecular research has also provided an important tool in the occasionally difficult differential diagnosis of DI and the opportunity to perform presymptomatic diagnosis. Although FNDI is treated readily with exogenous administration of deamino-D-arginine vasopressin (dDAVP), other treatment options such as gene therapy and enhancement of the endoplasmic reticulum protein quality control could become future treatment modalities.

Protein Misfolding and Human Disease

Protein misfolding is a common event in living cells. In young and healthy cells, the misfolded protein load is disposed of by protein quality control (PQC) systems. In aging cells and in cells from certain individuals with genetic diseases, the load may overwhelm the PQC capacity, resulting in accumulation of misfolded proteins. Dependent on the properties of the protein and the efficiency of the PQC systems, the accumulated protein may be degraded or assembled into toxic oligomers and aggregates. To illustrate this concept, we discuss a number of very different protein misfolding diseases including phenylketonuria, Parkinson's disease, alpha-1-antitrypsin deficiency, familial neurohypophyseal diabetes insipidus, and short-chain acyl-CoA dehydrogenase deficiency. Despite the differences, an emerging paradigm suggests that the cellular effects of protein misfolding provide a common framework that may contribute to the elucidation of the cell pathology and guide intervention and treatment strategies of many genetic and age-dependent diseases.