Six novel mutations in the arginine vasopressin gene in 15 kindreds with autosomal dominant familial neurohypophyseal diabetes insipidus give further insight into the pathogenesis

Clinico-radiological features, molecular spectrum, and identification of prognostic factors in developmental and epileptic encephalopathy due to inosine triphosphate pyrophosphatase (ITPase) deficiency

Developmental and epileptic encephalopathy 35 (DEE 35) is a severe neurological condition caused by biallelic variants in ITPA, encoding inosine triphosphate pyrophosphatase, an essential enzyme in purine metabolism. We delineate the genotypic and phenotypic spectrum of DEE 35, analyzing possible predictors for adverse clinical outcomes. We investigated a cohort of 28 new patients and reviewed previously described cases, providing a comprehensive characterization of 40 subjects. Exome sequencing was performed to identify underlying ITPA pathogenic variants. Brain MRI (magnetic resonance imaging) scans were systematically analyzed to delineate the neuroradiological spectrum. Survival curves according to the Kaplan-Meier method and log-rank test were used to investigate outcome predictors in different subgroups of patients. We identified 18 distinct ITPA pathogenic variants, including 14 novel variants, and two deletions. All subjects showed profound developmental delay, microcephaly, and refractory epilepsy followed by neurodevelopmental regression. Brain MRI revision revealed a recurrent pattern of delayed myelination and restricted diffusion of early myelinating structures. Congenital microcephaly and cardiac involvement were statistically significant novel clinical predictors of adverse outcomes. We refined the molecular, clinical, and neuroradiological characterization of ITPase deficiency, and identified new clinical predictors which may have a potentially important impact on diagnosis, counseling, and follow-up of affected individuals.

Functional analyses of three different mutations in the AVP-NPII gene causing familial neurohypophyseal diabetes insipidus

PURPOSE

Familial neurohypophyseal diabetes insipidus (FNDI), a rare disorder, which is clinically characterized by polyuria and polydipsia, results from mutations in the arginine vasopressin-neurophysin II (AVP-NPII) gene. The aim of this study was to perform functional analyses of three different mutations (p.G45C, 207_209delGGC, and p.G88V) defined in the AVP-NPII gene of patients diagnosed with FNDI, which are not included in the literature.

METHODS

For functional analysis studies, the relevant mutations were created using PCR-based site-directed mutagenesis and restriction fragment replacement strategy and expressed in Neuro2A cells. AVP secretion into the cell culture medium was determined by radioimmunoassay (RIA) analysis. Fluorescence imaging studies were conducted to determine the differences in the intracellular trafficking of wild-type (WT) and mutant AVP-NPII precursors. Molecular dynamics (MD) simulations were performed to determine the changing of the conformational properties of domains for both WT and 207-209delGGC mutant structures and dynamics behavior of residues.

RESULTS

Reduced levels of AVP in the supernatant culture medium of p.G45C and p.G88V transfected cells compared to 207_209delGGC and WT cells were found. Fluorescence imaging studies showed that a substantial portion of the mutant p.G45C and p.G88V AVP-NPII precursors appeared to be located in the endoplasmic reticulum (ER), whereas 207_209delGGC and WT AVP-NPII precursors were distributed throughout the cytoplasm.

CONCLUSIONS

The mutations p.G45C and p.G88V cause a failure in the intracellular trafficking of mutant AVP-NPII precursors. However, 207_209delGGC mutation does not result in impaired cellular trafficking, probably due to not having any significant effect in processes such as the proper folding, gain of three-dimensional structure, or processing. These results will provide valuable information for understanding the influence of mutations on the function of the AVP precursor hormone and cellular trafficking. Therefore, this study will contribute to elucidate the mechanisms of the molecular pathology of AVP-NPII mutations.

Autosomal dominant familial neurohypophyseal diabetes insipidus caused by a novel missense mutation in AVP gene in a large Italian kindred

PURPOSE

Familial neurohypophysial diabetes insipidus (FNDI), commonly caused by autosomal dominant arginine vasopressin (AVP) mutations, is a rare condition in which vasopressin fails in regulating body's level of water with final polyuria and polydipsia. Genetic testing in familial cases of FNDI should be carry out to ensure adequate treatments and avoid disease manifestations especially in infants.

METHODS

In this study, we investigated three-generations of a large Italian family with clinical diagnosis of familial central diabetes insipidus for the presence of potential pathogenic mutations in the AVP gene.

RESULTS

We identified a heterozygous missense mutation (c.154 T > A; p.C52S) in AVP gene in all affected members studied of a large Italian family. In silico tools were used to investigate the pathogenic role of the mutation and three-dimensional protein structure predicted that the p.C52S impairs disulfide bridges formation resulting in misfolding of the protein.

CONCLUSIONS

This is the first study that identified a novel missense p.C52S mutation as causative of central diabetes insipidus in a large Italian pedigree.

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.

A Partial Phenotype of adFNDI Related to the Signal Peptide c.55G>A Variant of the AVP Gene

The autosomal dominant familial form of neurohypophyseal diabetes insipidus (adFNDI) is a rare inherited endocrine disorder characterized by hypotonic polyuria, severe thirst and polydipsia, which results from a deficient neurosecretion of the antidiuretic hormone, also known as arginine vasopressin (AVP). To date, adFNDI has been linked to more than 70 different heterozygous point mutations of the 2.5 kb AVP gene, encoding the composite precursor protein of AVP. A minority of disease-causing mutations, such as the common c.55G>A variant, are predicted to affect amino acid residues close to the signal peptide (SP) cleavage site, and result in abnormal post-translational processing and intracellular trafficking of AVP precursors exerting neurotoxic activity on vasopressinergic magnocellular neurons. Generally, SP variants cause a gradual decline in the neurohypophyseal secretion of AVP in small children, although a wide variability in clinical onset and severity of manifestations has been reported. For the first time, we describe a kindred from Calabria (Southern Italy) with adFNDI and document a partial clinical phenotype in one female young adult member of the family. Methods: A young adult woman was subjected to clinical, neuroradiological and genetic assessments for a mild, adolescent-onset, polyuric state at our Endocrinology Unit. Her family medical history revealed an early-onset (<12 years of age) occurrence of polyuria and polydipsia, which was successfully managed with high doses of oral desmopressin, and a typical adFNDI inheritance pattern that was seen over three generations. Results: In the index patient, the extensive hypertonic dehydration during fluid deprivation test elicited a prompt elevation of urine osmolality and diuresis contraction, indicative of a partial adFNDI phenotype. Diagnosis was confirmed by concordant hormonal tests and magnetic resonance imaging (MRI) evidence of a reduced hyperintense signal of the neurohypophysis, which was regarded as compatible with the depletion of the vasopressinergic magnocellular neurons. Direct DNA sequencing and restriction enzyme cleavage analysis revealed that a heterozygous c.55G>A transition, predicting a p.Ala19Thr replacement in the C-terminal region of SP, was the cause of adFNDI in the investigated kindred. Conclusions: The identification of the genetic cause of aFNDI in this Calabrian kindred provides further information and confirms the wide variability of disease onset and severity of manifestations related to SP variants of the AVP gene, supporting the need for genetic testing in all patients with familial occurrence of polyuria, regardless of their clinical and radiological phenotype. Even though sexual differences in the antidiuretic responses are documented, it is unclear whether female gender would attenuate clinical disease progression in the presence of a pathogenic c.55G>A mutation.

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.

Forty-One Individuals With Mutations in the AVP-NPII Gene Associated With Familial Neurohypophyseal Diabetes Insipidus

CONTEXT

Familial neurohypophyseal diabetes insipidus is a rare disease produced by a deficiency in the secretion of antidiuretic hormone and is caused by mutations in the arginine vasopressin gene.

OBJECTIVE

Clinical, biochemical, and genetic characterization of a group of patients clinically diagnosed with familial neurohypophyseal diabetes insipidus, 1 of the largest cohorts of patients with protein neurophysin II (AVP-NPII) gene alterations studied so far.

DESIGN

The AVP-NPII gene was screened for mutations by PCR followed by direct Sanger sequencing in 15 different unrelated families from Spain.

RESULTS

The 15 probands presented with polyuria and polydipsia as the most important symptoms at the time of diagnosis. In these patients, the disease was diagnosed at a median of 6 years of age. We observed 11 likely pathogenic variants. Importantly, 4 of the AVP-NPII variants were novel (p.(Tyr21Cys), p.(Gly45Ser), p.(Cys75Tyr), p.(Gly88Cys)).

CONCLUSIONS

Cytotoxicity seems to be due to consequences common to all the variants found in our cohort, which are not able to fold correctly and pass the quality control of the ER. In concordance, we found autosomal dominant familial neurohypophyseal diabetes insipidus in the 15 families studied.

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.

A novel AVP gene mutation in a Turkish family with neurohypophyseal diabetes insipidus

PURPOSE

Familial neurohypophyseal diabetes insipidus (FNDI) is a rare, autosomal dominant, inherited disorder which is characterized by severe polydipsia and polyuria generally presenting in early childhood. In the present study, we aimed to analyze the AVP gene in a Turkish family with FNDI.

METHODS

Four patients with neurohypophyseal diabetes insipidus and ten healthy members of the family were studied. Diabetes insipidus was diagnosed by the water deprivation test in affected family members. Mutation analysis was performed by sequencing the whole coding region of AVP-NPII gene using DNA isolated from peripheral blood samples.

RESULTS

Urine osmolality was low (<300 mOsm/kg) during water deprivation test, and an increase more than 50 % in urine osmolality and recovery of the symptoms were observed by the administration of desmopressin in all patients. Plasma copeptin levels were lower than expected according to plasma osmolality. Pituitary MRI revealed partial empty sella with a bright spot in index patient and a normal neurohypophysis in the other affected subjects. Genetic screening revealed a novel, heterozygous mutation designated as c.-3A>C in all patients.

CONCLUSION

c.-3A>C mutation in 5'UTR of AVP gene in this family might lead to the truncation of signal peptide, aggregation of AVP in the cytoplasm instead of targeting in the endoplasmic reticulum, thereby could disrupt AVP secretion without causing neuronal cytotoxicity, which might explain the presence of bright spot. The predicted effect of this mutation should be investigated by further in vitro molecular studies.

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.

Autosomal dominant familial neurohypophyseal diabetes insipidus caused by a mutation in the arginine-vasopressin II gene in four generations of a Korean family

Autosomal dominant neurohypophyseal diabetes insipidus is a rare form of central diabetes insipidus that is caused by mutations in the vasopressin-neurophysin II (AVP-NPII) gene. It is characterized by persistent polydipsia and polyuria induced by deficient or absent secretion of arginine vasopressin (AVP). Here we report a case of familial neurohypophyseal diabetes insipidus in four generations of a Korean family, caused by heterozygous missense mutation in exon 2 of the AVP-NPII gene (c.286G>T). This is the first report of such a case in Korea.

The contribution of the genomes of a termite and a locust to our understanding of insect neuropeptides and neurohormones

The genomes of the migratory locust Locusta migratoria and the termite Zootermopsis nevadensis were mined for the presence of genes encoding neuropeptides, neurohormones, and their G-protein coupled receptors (GPCRs). Both species have retained a larger number of neuropeptide and neuropeptide GPCRs than the better known holometabolous insect species, while other genes that in holometabolous species appear to have a single transcript produce two different precursors in the locust, the termite or both. Thus, the recently discovered CNMa neuropeptide gene has two transcripts predicted to produce two structurally different CNMa peptides in the termite, while the locust produces two different myosuppressin peptides in the same fashion. Both these species also have a calcitonin gene, which is different from the gene encoding the calcitonin-like insect diuretic hormone. This gene produces two types of calcitonins, calcitonins A and B. It is also present in Lepidoptera and Coleoptera and some Diptera, but absent from mosquitoes and Drosophila. However, in holometabolous insect species, only the B transcript is produced. Their putative receptors were also identified. In contrast, Locusta has a highly unusual gene that codes for a salivation stimulatory peptide. The Locusta genes for neuroparsin and vasopressin are particularly interesting. The neuroparsin gene produces five different transcripts, of which only one codes for the neurohormone identified from the corpora cardiaca. The other four transcripts code for neuroparsin-like proteins, which lack four amino acid residues, and that for that reason we called neoneuroparsins. The number of transcripts for the neoneuroparsins is about 200 times larger than the number of neuroparsin transcripts. The first exon and the putative promoter of the vasopressin genes, of which there are about seven copies in the genome, is very well-conserved, but the remainder of these genes is not. The relevance of these findings is discussed.

Disordered structural ensembles of vasopressin and oxytocin and their mutants

Vasopressin and oxytocin are intrinsically disordered cyclic nonapeptides belonging to a family of neurohypophysial hormones. Although unique in their functions, these peptides differ only by two residues and both feature a tocin ring formed by the disulfide bridge between first and sixth cysteine residues. This sequence and structural similarity are experimentally linked to oxytocin agonism at vasopressin receptors and vasopressin antagonism at oxytocin receptors. Yet single- or double-residue mutations in both peptides have been shown to have drastic impacts on their activities at either receptor, and possibly the ability to bind to their neurophysin carrier protein. In this study we perform molecular dynamics simulations of the unbound native and mutant sequences of the oxytocin and vasopressin hormones to characterize their structural ensembles. We classify the subpopulations of these structural ensembles on the basis of the distributions of radius of gyration and secondary structure and hydrogen-bonding features of the canonical tocin ring and disordered tail region. We then relate the structural changes observed in the unbound form of the different hormone sequences to experimental information about peptide receptor binding, and more indirectly, carrier protein binding affinity, receptor activity, and protease degradation. This study supports the hypothesis that the structural characteristics of the unbound form of an IDP can be used to predict structural or functional preferences of its functional bound form.

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.

A comparative protease stability study of synthetic macrocyclic peptides that mimic two endocrine hormones

Peptide therapeutics have traditionally faced many challenges including low bioavailability, poor proteolytic stability and difficult cellular uptake. Conformationally constraining the backbone of a peptide into a macrocyclic ring often ameliorates these problems and allows for the development of a variety of new drugs. Such peptide-based pharmaceuticals can enhance the multi-faceted functionality of peptide side chains, permitting the peptides to bind cellular targets and receptors necessary to impart their role, while protecting them from degrading cellular influences. In the work described here, we developed three cyclic peptides, VP mimic1, VP mimic2 and OT mimic1, which mimic endocrine hormones vasopressin and oxytocin. Making notable changes to the overall structure and composition of the parent hormones, we synthesized the mimics and tested their durability against treatment with three proteases chosen for their specificity: pepsin, alpha-chymotrypsin, and pronase. Vasopressin and oxytocin contain a disulfide linkage leaving them particularly vulnerable to deactivation from the reducing environment inside the cell. Thus, we increased the complexity of our assays by adding reducing agent glutathione to each mixture. Subsequently, we discovered each of our mimics withstood protease treatment with less degradation and/or a slower rate of degradation as compared to both parent hormones and a linear control peptide.

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.

The contributions of oxytocin and vasopressin pathway genes to human behavior

Arginine vasopressin (AVP) and oxytocin (OXT) are social hormones and mediate affiliative behaviors in mammals and as recently demonstrated, also in humans. There is intense interest in how these simple nonapeptides mediate normal and abnormal behavior, especially regarding disorders of the social brain such as autism that are characterized by deficits in social communication and social skills. The current review examines in detail the behavioral genetics of the first level of human AVP-OXT pathway genes including arginine vasopressin 1a receptor (AVPR1a), oxytocin receptor (OXTR), AVP (AVP-neurophysin II [NPII]) and OXT (OXT neurophysin I [NPI]), oxytocinase/vasopressinase (LNPEP), ADP-ribosyl cyclase (CD38) and arginine vasopressin 1b receptor (AVPR1b). Wherever possible we discuss evidence from a variety of research tracks including molecular genetics, imaging genomics, pharmacology and endocrinology that support the conclusions drawn from association studies of social phenotypes and detail how common polymorphisms in AVP-OXT pathway genes contribute to the behavioral hard wiring that enables individual Homo sapiens to interact successfully with conspecifics. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Misfolding of Mutated Vasopressin Causes ER-Retention and Activation of ER-Stress Markers in Neuro-2a Cells

Arginine-vasopressin (AVP) is a peptide hormone normally secreted from neuroendocrine cells via the regulated secretory pathway. In Familial Neurohypophyseal Diabetes Insipidus (FNDI), an autosomal dominant form of central diabetes insipidus, mutations of pro-vasopressin appear to accumulate in the endoplasmic reticulum (ER) causing a lack of biologically active AVP in the blood. To investigate the effect of pro-vasopressin mutations regarding intracellular functions of protein targeting and secretion, we created two FNDI-associated amino acid substitution mutants, e.g., G14R, and G17V in frame with green fluorescent protein (GFP) and pro-vasopressin (VP) in frame with red fluorescent protein (VP-RFP). Fluorescence microscopy of Neuro-2a cells expressing these constructs revealed co-localization of VP-GFP and VP-RFP to punctate granules along the length and accumulating at the tips of neurites, characteristic of regulated secretory granules. In contrast, the two FNDI-associated amino acid substitution mutants, e.g., G14R-GFP, and G17VGFP, were localized to a perinuclear region of the Neuro-2a cells characteristic of the endoplasmic reticulum. Co-expression of these mutants with VP-RFP showed VP-RFP was retained in the ER, co-localized with the mutants suggesting the formation of heterodimers as found in FNDI. Stimulated secretion experiments indicated that VP-GFP was secreted in an inducible manner whereas, G14R-GFP and G17V-GFP were retained to nearly 100% within the cells. Analysis by western blotting and semi-quantitative RT-PCR indicated an increased protein and mRNA expression for an ER resident molecular chaperone, BiP. Further analysis of ER-storage disease-associated proteins such as caspase 12 and CHOP showed an increase in these as well. The results suggest that G14R-GFP and G17V-GFP are retained in the ER of Neuro-2a cells, resulting in up-regulation of the molecular chaperone BiP, and activation of the ER-storage disease-associated caspase cascade system.

Utility of AVP gene testing in familial neurohypophyseal diabetes insipidus

CONTEXT

Familial neurohypophyseal diabetes insipidus (FNDI) is a rare disorder resulting from arginine vasopressin (AVP) gene mutations. A partial defect in AVP secretion occurs early in the course of FNDI and may not be detected by a water deprivation test (WDT). Testing for AVP gene mutations may confirm a diagnosis of FNDI when a WDT is inconclusive and may also predict individuals who will later develop FNDI.

OBJECTIVE

To test the utility of AVP gene analysis in confirming the diagnosis of FNDI.

PATIENTS

Five families (20 subjects, 14 symptomatic and six asymptomatic) with FNDI and nine children with idiopathic neurohypophyseal diabetes insipidus (INDI).

MEASUREMENTS

Genomic DNA was analysed for AVP gene mutations using polymerase chain reaction (PCR) amplification and sequencing.

RESULTS

Heterozygous AVP gene mutations were found in all subjects with FNDI but none of the ICDI patients. Each family had their own distinct mutation. We identified two novel mutations (C44W and C105S). One asymptomatic subject developed diabetes insipidus (DI) 4 months after detection of an AVP gene mutation. The WDT suggested partial DI in 4/6 but was normal in 2/6 children with FNDI.

CONCLUSION

AVP gene testing allowed diagnostic confirmation of FNDI when the WDT was inconclusive in symptomatic children, therefore obviating the need for a repeat WDT and enabling earlier initiation of appropriate treatment. AVP gene testing also has the potential to identify which asymptomatic children will later develop FNDI.

Genetic association and expression studies indicate a role of toll-like receptor 8 in pulmonary tuberculosis

Despite high rates of exposure, only 5-10% of people infected with Mycobacterium tuberculosis will develop active tuberculosis (TB) disease, suggesting a significant role for genetic variation in the human immune response to this infection. Here, we studied TB association and expression of 18 genes involved in the Toll-like receptor (TLR) pathways. Initially, we genotyped 149 sequence polymorphisms in 375 pulmonary TB patients and 387 controls from Indonesia. We found that four polymorphisms in the TLR8 gene on chromosome X showed evidence of association with TB susceptibility in males, including a non-synonymous polymorphism rs3764880 (Met1Val; P = 0.007, odds ratio (OR) = 1.8, 95% c.i. = 1.2-2.7). We genotyped these four TLR8 polymorphisms in an independent collection of 1,837 pulmonary TB patients and 1,779 controls from Russia and again found evidence of association in males (for rs3764880 P = 0.03, OR = 1.2, 95% c.i. = 1.02-1.48). Combined evidence for association is P = 1.2x10(-3)-6x10(-4). In addition, a quantitative PCR analysis indicated that TLR8 transcript levels are significantly up-regulated in patients during the acute phase of disease (P = 9.36x10(-5)), relative to baseline levels following successful chemotherapy. A marked increase in TLR8 protein expression was also observed directly in differentiated macrophages upon infection with M. bovis bacille Calmette-Guérin (BCG). Taken together, our results provide evidence, for the first time, of a role for the TLR8 gene in susceptibility to pulmonary TB across different populations.

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.

A novel initial codon mutation of the thiazide-sensitive Na-Cl cotransporter gene in a Japanese patient with Gitelman's syndrome

We here report a novel mutation of the thiazide-sensitive Na-Cl cotransporter (TSC) (SLC12A3) gene in a Japanese patient with Gitelman's syndrome (GS). GS is characterized by a renal disorder and is associated with hypokalemia, hypomagnesemia, metabolic alkalosis and hypocalciuria arising from the defective tubular reabsorption of magnesium and potassium. This disease is reportedly caused by mutations in the TSC gene. A 52-year-old man was referred to our hospital because of sleeplessness and tinnitus. He exhibited hypokalemia, hypomagnesemia, hypocalciuria, metabolic alkalosis and hyperreninemic hyperaldosteronism. A renal clearance study revealed that the administration of furosemide decreased chloride reabsorption; however, the ingestion of thiazide failed to decrease chloride reabsorption. A diagnosis of GS was made based on the clinical features, laboratory data and renal function test results. Sequencing of the patient's genomic DNA revealed an A to T transition at the initial codon of exon 1 of the TSC gene (c1A>T). Knowledge of this novel mutation may be helpful for understanding the pathophysiology of GS and the function of TSC as well as for providing genetic counseling.

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.

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

OBJECTIVE AND STUDY DESIGN

The autosomal dominant form of familial neurohypophyseal diabetes insipidus (adFNDI) is a rare disease characterized by a severe and progressive deficiency of AVP secondary to mutations in the gene encoding the AVP precursor. Whereas a number of studies have investigated the pathogenetic mechanisms behind the disease only few studies have included detailed clinical characterization of the affected patients, thereby making genotype-phenotype correlations difficult. The aims of the present study were to investigate the cellular effects of three different adFNDI mutations (A19T, L81P and C110X) by heterologous expression in a neurogenic cell line and to correlate these findings to the corresponding clinical phenotype as determined by extensive clinical tests.

RESULTS

The clinical studies showed a later age of onset in the family carrying the A19T mutation (3.4 years, range 2-9 years) compared with families with the L81P and C110X mutations [0.75 year, range 0.5-1 year and 1.0 year (n = 1), respectively]. No other differences could be demonstrated in the clinical phenotype between families. Expression studies showed that each of the three mutant genes caused significant reduction of the amount of immunoreactive AVP in the cell culture medium and severe impairment of the intracellular trafficking and processing of the AVP prohormone, supporting the disease causing nature of all three mutations. However, the A19T mutation was associated with some capacity for processing and trafficking consistent with the clinical observations. Immunoflourescence studies provided evidence of reticular accumulation of protein within the ER in the A19T and C110X mutants but a unique accumulation of much larger aggregates in the L81P, which were localized both within and immediately outside the ER.

CONCLUSION

The study suggests a genotype-phenotype correlation with regard to age of onset of diabetes insipidus symptoms and provides support by expression studies.

Novel variations in the signal peptide region of transforming growth factor beta1 gene in patients with hepatitis: a brief report from India

Genotypic status of the signal peptide region of transforming growth factor beta1 (TGF-beta1) showed a significant difference in C/C-genotype frequency at +29 position (codon 10) between a range of viral hepatitis patients and controls (P = 0.009, OR = 3.15, CI = 1.29-7.678), contributed by those who were infected with hepatitis B virus (HBV) alone or HBV + hepatitis delta virus (HDV) (P = 0.003, OR = 5.0, CI = 1.78-13.97).

Current perspective on the pathogenesis of central diabetes insipidus

Diabetes insipidus is a heterogeneous condition characterised by polyuria and polydipsia caused by a lack of secretion of vasopressin, its physiological suppression following excessive water intake, or kidney resistance to its action. The clinical and laboratory diagnosis is confirmed by standard tests, but recent advances in molecular biology and imaging techniques have shed new light on the pathophysiology of this disease. In many patients, central diabetes insipidus is caused by a germinoma or craniopharyngioma; Langerhans' cell histiocytosis and sarcoidosis of the central nervous system; local inflammatory, autoimmune or vascular diseases; trauma from surgery or accident; and, rarely, genetic defects in vasopressin biosynthesis inherited as autosomal dominant or X-linked recessive traits. Thirty to fifty percent of cases are considered idiopathic. Tumour-associated central diabetes insipidus is uncommon in children younger than 5 years old. Biopsy of enlarged pituitary stalk should be reserved for patients with hypothalamic-pituitary mass and progressive thickening of the pituitary stalk since spontaneous recovery may occur. Molecular biology in selected patients may identify those with apparently idiopathic diabetes insipidus carrying the vasopressin-neurophysin II gene mutation.

Autophagy‐dependent cell survival and cell death in an autosomal dominant familial neurohypophyseal diabetes insipidus in vitro model

Mutations in the human gene encoding the antidiuretic hormone vasopressin (VP) cause autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI), a rare inherited disorder that presents as polydipsia and polyuria as a consequence of a loss of secretion of VP from posterior pituitary nerve terminals. Work from our laboratories has shown that adFNDI, like other neurodegenerative diseases such as Alzheimer's, Parkinson's and Huntington's, is associated with autophagy. We have recently shown that the activation of autophagy in mouse neuroblastoma Neuro2a cells after adenoviral vector-mediated delivery of an adFNDI mutant VP transgene (Cys67stop) is a cell survival mechanism; its inhibition induces apoptosis. We now show that expression of Cys67stop sensitizes Neuro2a cells to the lethal effects of dopamine. This mode of cell death exhibits features typically associated with classical apoptosis. Yet inhibition of autophagy reversed these effects and rescued cell viability. We propose that autophagy-mediated cell death is a "two-hit" process: Following the cellular stress of the accumulation of a misfolded mutant protein, autophagy is prosurvival. However, a second insult triggers an autophagy-dependent apoptosis.

Differential cellular handling of defective arginine vasopressin (AVP) prohormones in cells expressing mutations of the AVP gene associated with autosomal dominant and recessive familial neurohypophyseal diabetes insipidus

An unusual mutation in the arginine vasopressin (AVP) gene, predicting a P26L amino acid substitution of the AVP prohormone, is associated with autosomal recessive familial neurohypophyseal diabetes insipidus (FNDI). To investigate whether the cellular handling of the P26L prohormone differed from that of the Y21H prohormone associated with autosomal dominant inheritance of FNDI, the mutations were examined by heterologous expression in cell lines. Immunoprecipitation demonstrated retarded processing and secretion of the Y21H prohormone, whereas the secretion of the P26L prohormone seemed to be unaffected. Confocal laser scanning microscopy showed accumulation of the Y21H prohormone in the endoplasmic reticulum, whereas the P26L prohormone and/or processed products were localized in secretory granules in the cellular processes. RIA analysis showed reduced amounts of immunoreactive Y21H-AVP and P26L-AVP in the cell culture medium. Thus, the recessive mutation does not seem to affect the intracellular trafficking but rather the final processing of the prohormone. Our results provide an important negative control in support of the hypothesis that autosomal dominant inheritance of FNDI is caused by mutations in the AVP gene that alter amino acid residues important for folding and/or dimerization of the neurophysin II moiety of the AVP prohormone and subsequent transport from the endoplasmic reticulum.