Identification of a novel mutation in the arginine vasopressin-neurophysin II gene in familial central diabetes insipidus

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.

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.

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.

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.

Autosomal dominant neurohypophyseal diabetes insipidus with linkage to chromosome 20p13 but without mutations in the AVP-NPII gene

CONTEXT

Autosomal dominant neurohypophyseal diabetes insipidus (ADNDI) has been known as a rare disorder transmitted as an autosomal dominant trait, characterized by polyuria and polydipsia, and caused by deficient neurosecretion of arginine vasopressin precursor (AVP-NPII). We reported an ADNDI family with linkage to chromosome 20p13 but without mutations in the AVP-NPII gene.

OBJECTIVE

The objective of this study was to identify the corresponding locus responsible for ADNDI in a family without AVP-NP II gene mutations.

SUBJECTS AND METHODS

Two families with ADNDI were diagnosed by water deprivation test. The AVP-NPII gene was amplified by PCR and sequenced. A genomewide scan was performed in one family using 400 microsatellite markers covering 22 autosomes.

RESULTS

A 3-bp deletion (1827-1829delAGG) of AVP-NPII gene was identified in the affected individuals in one family. Although no mutations could be detected in the coding, the promoter, and intronic regions of AVP-NPII gene in the other family, a maximum LOD score of 1.202999 (theta = 0.00) was obtained at marker D20S889 by genomewide scan, and a 7-cM interval on chromosome 20p13 was defined by fine mapping with markers D20S199-D20S849. Furthermore, the intragenic region that regulates AVP-NPII and oxytocin expression as an enhancer element and the UBCE7IP5 gene that participates in prohormone degradation were sequenced. No alterations could be detected either.

CONCLUSION

The corresponding locus responsible for ADNDI is possibly heterogeneous regarding the slightly different clinical features in these two families.

Novel mutant vasopressin-neurophysin II gene associated with familial neurohypophyseal diabetes insipidus

We describe a novel missense mutant of arginine vasopressin (AVP)-dependent neurohypophyseal diabetes insipidus in an autosomal dominant family. A 54-year-old woman was admitted to our hospital because of thyroidectomy for thyroid cancer. After thyroidectomy she was found to have hypernatremia and polyuria and polydipsia both of which had been present from childhood. She had no obstructive hydronephrosis. Her father, father's younger sister and her third son also had polyuria and polydipsia. Basal plasma AVP concentration at normal plasma osmolality was normal but did not respond to increased plasma osmolality despite hyperosmolality during infusion of hypertonic saline infusion, indicating that plasma AVP secretion was impaired. Sodium concentration in urine and urine osmolality were low and increased after nasal administration of DDAVP. There was a diminished but bright signal of pituitary posterior gland on magnetic resonance T1 weighted image. Molecular genetic analysis demonstrated that the patient and her son had a single heterozygous missense mutation (G-->A) at nucleotide 1829 in 1 AVP allele, yielding an abnormal AVP precursor with lacking Glu-47 in its neurophysin II moiety. The abnormal AVP precursor may be related to the impaired AVP secretion.

Degradation of wild-type vasopressin precursor and pathogenic mutants by the proteasome

Mutations in the gene encoding the antidiuretic hormone arginine vasopressin cause autosomal dominant neurogenic diabetes insipidus. Autoptic data in affected individuals suggest that the neurons expressing mutant vasopressin undergo selective degeneration. Expression studies have shown that the mutants are retained in the endoplasmic reticulum, but how this trafficking defect is linked to neurotoxicity is unknown. One possibility is that unsecreted mutant precursors, or degradation products thereof, are cytotoxic. We therefore investigated the fate of endoplasmic reticulum-retained pathogenic mutants. Our data show that the mutants are retrotranslocated to the cytosol and degraded by the proteasome. In the presence of proteasomal inhibitors, three distinct un- or deglycosylated cytosolic species of vasopressin precursors were stabilized: pre-pro-vasopressin, pro-vasopressin, and an N-terminally truncated form. In addition to the retrotranslocated forms, a fraction of the newly synthesized precursor was not translocated, but was synthesized into the cytosol due to inefficient function of the vasopressin signal peptide. As a result, cytosolic pre-pro-vasopressin and its degradation product were also recovered when wild-type vasopressin was expressed. Cytosolic forms of vasopressin might trigger cytotoxicity in vivo, as has been proposed in the case of prion protein, which also contains an inefficient N-terminal signal peptide.

A murine model of autosomal dominant neurohypophyseal diabetes insipidus reveals progressive loss of vasopressin-producing neurons

Familial neurohypophyseal diabetes insipidus (FNDI) is an autosomal dominant disorder caused by mutations in the arginine vasopressin (AVP) precursor. The pathogenesis of FNDI is proposed to involve mutant protein-induced loss of AVP-producing neurons. We established murine knock-in models of two different naturally occurring human mutations that cause FNDI. A mutation in the AVP signal sequence [A(-1)T] is associated with a relatively mild phenotype or delayed presentation in humans. This mutation caused no apparent phenotype in mice. In contrast, heterozygous mice expressing a mutation that truncates the AVP precursor (C67X) exhibited polyuria and polydipsia by 2 months of age and these features of DI progressively worsened with age. Studies of the paraventricular and supraoptic nuclei revealed induction of the chaperone protein BiP and progressive loss of AVP-producing neurons relative to oxytocin-producing neurons. In addition, Avp gene products were not detected in the neuronal projections, suggesting retention of WT and mutant AVP precursors within the cell bodies. In summary, this murine model of FNDI recapitulates many features of the human disorder and demonstrates that expression of the mutant AVP precursor leads to progressive neuronal cell loss.

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

Autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI) is caused by postnatal arginine vasopressin (AVP) deficiency resulting from mutations in the AVP gene encoding the AVP pre-prohormone. To advance the understanding of adFNDI further, we have searched for mutations in the AVP gene in 15 unrelated kindreds in which diabetes insipidus appeared to be segregating. In nine kindreds, seven different previously described mutations were identified. In each of the other six kindreds, unique novel mutations were identified. Two of these (225A>G and 227G>A) change a nucleotide in the translation initiation codon of the signal peptide, whereas the other four (1797T>C, 1884G>A, 1907T>G, and 2112C>G) predict amino-acid substitutions in the neurophysin II moiety of the AVP prohormone, namely V67A (NP36), G96D (NP65), C104G (NP73), and C116W (NP85). Among these, the mutation predicting the V67A (NP36) substitution is remarkable. It affects a region of the neurophysin II not affected by any other mutations, produces only a minor change, and its inheritance suggests an incomplete penetrance. Our findings both confirm and further extend the mutation pattern that has emerged in adFNDI, suggesting that the mutations affect amino-acid residues known or reasonably presumed to be important for the proper folding and/or dimerization of the neurophysin II moiety of the AVP prohormone.

Progressive decline of vasopressin secretion in familial autosomal dominant neurohypophyseal diabetes insipidus presenting a novel mutation in the vasopressin-neurophysin II gene

OBJECTIVE

Familial autosomal dominant neurohypophyseal diabetes insipidus (FNDI) is a rare form of central diabetes insipidus (DI), which is caused by mutations in the vasopressin-neurophysin II (AVP-NPII) gene. The present study evaluated the AVP secretion over time and analysed the structure of the AVP-NPII gene in a Brazilian family with FNDI.

SUBJECTS AND DESIGN

Four affected members and one nonaffected member from one Brazilian family with FNDI were studied. The diagnosis of central DI was established by fluid deprivation test and hypertonic saline infusion. Two affected members were assessed twice within a 6-year interval. For molecular analysis, genomic DNA was extracted and the AVP-NPII gene was amplified by polymerase chain reaction.

RESULTS

The functional assessment of patients with FNDI over time confirmed a progressive loss in AVP secretion. Two patients were first diagnosed as partial central DI and, several years later, they developed severe central DI. Sequencing analysis revealed a heterozygous new point mutation in the nucleotide 1892 in the coding sequence for neurophysin-II of the AVP-NPII gene (1892G>C) predicting an amino acid substitution (A68P) in all affected members.

CONCLUSION

Our data demonstrate a gradual vasopressinergic deficiency due to a novel mutation in the AVP-NPII gene in a Brazilian family with FNDI. The accumulation of A68P mutated precursor might have a cytotoxicity effect, leading to a gradual death of magnocellular neurones, and a progressive decline in AVP secretion.