Three-point linkage analysis using multiple DNA polymorphic markers in families with X-linked nephrogenic diabetes insipidus

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

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

CONCLUSION

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

WHAT IS KNOWN

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

Nephrogenic diabetes insipidus

In nephrogenic diabetes insipidus, the kidney is unable to concentrate urine despite normal or elevated concentrations of the antidiuretic hormone arginine vasopressin (AVP). In congenital nephrogenic diabetes insipidus (NDI), the obvious clinical manifestations of the disease, that is polyuria and polydipsia, are present at birth and need to be immediately recognized to avoid severe episodes of dehydration. Most (>90%) congenital NDI patients have mutations in the AVPR2 gene, the Xq28 gene coding for the vasopressin V2 (antidiuretic) receptor. In <10% of the families studied, congenital NDI has an autosomal recessive inheritance and mutations of the aquaporin-2 gene (AQP2), ie, the vasopressin-sensitive water channel, have been identified. When studied in vitro, most AVPR2 mutations lead to receptors that are trapped intracellularly and are unable to reach the plasma membrane. A minority of the mutant receptors reach the cell surface but are unable to bind AVP or to trigger an intracellular cyclic adenosine-monophosphate (cAMP) signal. Similarly AQP2 mutant proteins are trapped intracellularly and cannot be expressed at the luminal membrane. The acquired form of NDI is much more common than the congenital form, is almost always less severe, and is associated with downregulation of AQP2. The advances described here are examples of "bedside physiology" and provide diagnostic tools for physicians caring for these patients.

Vasopressin type-2 receptor and aquaporin-2 water channel mutants in nephrogenic diabetes insipidus

The regulation of water excretion by the kidney is one of the few physiologic processes that are prominent in everyday life. This process predominantly occurs in renal collecting duct cells, where transcellular water reabsorption is induced after binding of the pituitary hormone arginine-vasopressin to its vasopressin type-2 receptor and the subsequent insertion of aquaporin-2 (AQP2) water channels in the apical membrane of these cells. Removal of the hormone triggers endocytosis of AQP2 and restores the water-impermeable state of the collecting duct cells. Nephrogenic diabetes insipidus is characterized by the inability of the kidney to concentrate urine in response to vasopressin; the vasopressin type-2 receptor and the AQP2 water channel have both been shown to be involved in this disease. This article focuses on mutations in the vasopressin V2 receptor and aquaporin-2 water channel identified in nephrogenic diabetes insipidus patients, and on the effects of these mutations on the transport and function of these proteins upon expression in cell systems.

Diabetes insipidus

The advances in our understanding of the pathophysiology of defects in the antidiuretic hormone, the V2 receptor and the water channel, owing to mutations in the prepro-AVP-NPII, AVPR2 and AQP2 genes respectively, is providing insight into inherited diabetes insipidus as well as the more numerous sporadic cases. Further structure-function analyses of these mutated genes will increase our understanding of normal vasopressin-regulated water transport across the kidney epithelium at the molecular level.

Molecular characterization of nephrogenic diabetes insipidus

Nephrogenic diabetes insipidus (NDI) is characterized by insensitivity of the distal renal nephron to the antidiuretic effect of the neurohypophyseal hormone arginine vasopressin. In the last 2 years, two different genetic defects causing the NDI phenotype have been identified. The genes involved encode proteins that reside at both ends of the cellular vasopressin signaling cascade, namely the vasopressin V(2) receptor and the aquaporin-2 water channel. Analysis of naturally occurring mutations in the V(2) receptor and the aquaporin-2 water channel will facilitate the study of structure-function correlates of both proteins, which will lead to substantial progress in elucidating the cellular mechanisms involved in the antidiuretic effect of vasopressin.

Inheritance of mutations in the V2 receptor gene in thirteen families with nephrogenic diabetes insipidus

Congenital nephrogenic diabetes insipidus (NDI) is an X-linked recessive disease characterized by insensitivity of the distal nephron to the antidiuretic effect of arginine vasopressin. The hypothesis that the defect underlying NDI might be a dysfunctional renal vasopressin V2 receptor has recently been proven by the identification of mutations in the V2 receptor gene in NDI patients. We examined thirteen unrelated Dutch NDI families and identified thirteen distinct and unique mutations. These included nine missense mutations, two nonsense mutations and two small deletions and were found in the extracellular domains II, III and IV, the intracellular domains II and IV and in the transmembrane loops I, II, IV and V of the vasopressin type 2 receptor. In the families with multiple NDI patients the mutated gene cosegregated with the disease. Our data suggest a higher mutation frequency in male than in female gametes. No discrepancies between carrier detection by means of DNA analysis with closely linked polymorphic markers and the definite diagnosis based on sequencing data were found.

Nephrogenic diabetes insipidus: identification of the genetic defect

Congenital nephrogenic diabetes insipidus (NDI) is an X-linked inherited disorder characterized by renal resistance to the antidiuretic hormonal action of arginine vasopressin. The disease gene has been assigned to the subtelomeric region of the X chromosome long arm by demonstrating close linkage between NDI and several X-chromosomal DNA markers. The finding of closely linked genetic markers is useful in the diagnosis of NDI. Receptor studies in patients have indicated that NDI might be due to the absence or an abnormality of the adenylate cyclase-bound vasopressin type 2 receptor. This assumption was supported by the discovery of functional vasopressin V2 receptor activity in somatic cell hybrid cell lines that carried at least the distal part of the human X chromosome long arm. Definite evidence for a V2 receptor defect being the cause of NDI was found in a recent study demonstrating point mutations in the V2 receptor gene from affected individuals. Direct mutation analysis is now applicable for accurate carrier detection and early (prenatal) diagnosis.

X-linked nephrogenic diabetes insipidus mutations in North America and the Hopewell hypothesis

In X-linked nephrogenic diabetes insipidus (NDI) the urine of male patients is not concentrated after the administration of the antidiuretic hormone arginine-vasopressin. This disease is due to mutations in the V2 receptor gene that maps to chromosome region Xq28. In 1969, Bode and Crawford suggested that most NDI patients in North America shared common ancestors of Ulster Scot immigrants who arrived in Halifax in 1761 on the ship Hopewell. A link between this family and a large Utah kindred was also suggested. DNA was obtained from 17 affected male patients from the "Hopewell" kindred and from four additional families from Nova Scotia and New Brunswick who shared the same Xq28 NDI haplotype. The Utah kindred and two families (Q2, Q3) from Quebec were also studied. The "Hopewell" mutation, W71X, is a single base substitution (G-->A) that changes codon 71 from TGG (tryptophan) to TGA (stop). The W71X mutation was found in affected members of the Hopewell and of the four satellite families. The W71X mutation is the cause of X-linked NDI for the largest number of related male patients living in North America. Other families (Utah, Q2 and Q3) that are historically and ethnically unrelated bear other mutations in the V2 receptor gene.

Mutations in the vasopressin type 2 receptor gene (AVPR2) associated with nephrogenic diabetes insipidus

Nephrogenic diabetes insipidus (DIR) is an X-linked disorder characterized by insensitivity of the distal nephron for the pituitary hormone, vasopressin. The genetic map location of the DIR gene on chromosome Xq28 coincides with the physical map location of the functional vasopressin renal V2-type receptor. Recently, the human and rat cDNAs for the vasopressin V2 receptor (AVPR2) have been identified. We show here that the structural AVPR2 gene is localized between DXS52 and G6PD, which is within the genetic map location of DIR. We also tested eight X-linked DIR probands and their families for mutations in one of the most conserved extracellular regions of AVPR2: in three of them, we have identified point mutations resulting in non-conservative amino acid substitutions which cosegregated with DIR in all families.

Nephrogenic diabetes insipidus: clinical symptoms, pathogenesis, genetics and treatment

This review summarizes various aspects of the inherited kidney disorder nephrogenic diabetes insipidus (NDI). The clinical manifestations of the disease are presented. The important role of the genetic localization of the NDI gene to the X-chromosome long arm, in region Xq28, for carrier detection and early (prenatal) diagnosis of the disorder is emphasized. Following an overview of the cellular physiology involved in the antidiuretic action of vasopressin, possible mechanisms in the pathogenesis of NDI are discussed. We hypothesize that NDI is most probably due to the absence or abnormality of the renal V2 receptor. This assumption is strengthened by recent findings in receptor studies, which indicate a general V2 receptor defect in NDI, and in experiments with somatic cell hybrid cell lines, which are consistent with a co-localization of the genes for NDI and for the V2 receptor in the Xq28 region. Finally, the efficacy of the combination amiloride-hydrochlorothiazide, compared with the indomethacin-hydrochlorothiazide regimen, in the treatment of NDI is presented and the advantages of the former combination are discussed.

Colocalization of the gene for nephrogenic diabetes insipidus (DIR) and the vasopressin type 2 receptor gene (AVPR2) in the Xq28 region

The gene for nephrogenic diabetes insipidus (DIR) and the vasopressin type 2 receptor gene (AVPR2) have both been localized in the Xqter region by genetic mapping and functional expression studies, respectively. In this paper genetic evidence that the DIR locus is localized distal to the DXS305 locus and that the functional gene for the V2 receptor is localized between the markers DXS269 and F8 is presented. These further refinements in the localization of both genes strengthen the assumption that both genes are identical and provide a rationale for cloning the gene by reversed genetics strategies.

Platelet vasopressin receptors in patients with congenital nephrogenic diabetes insipidus

Arginine-vasopressin (AVP), interacts with at least two types of receptors: V1 receptors which mediate the aggregating effects of AVP on human blood platelets and other AVP actions on vascular smooth muscle and hepatocytes; and V2 receptors which mediate the antidiuretic effects on renal tubules. Congenital nephrogenic diabetes insipidus (CNDI) is a rare X-linked disorder in humans with abnormal renal and extrarenal V2-receptor responses. However, the V1 receptor responses are apparently normal, since in these patients blood pressure increases in response to AVP. To assess V1 receptor responses, binding studies (3H-AVP) were done on intact platelets obtained from 6 male patients with CNDI, 10 normal subjects and 4 patients with autosomal dominant central diabetes insipidus (ADCDI). The affinity constant (0.68 +/- 0.04 vs. 0.59 +/- 0.06 nM) and the number of specific binding sites per platelet (101 +/- 6 vs. 86 +/- 12) were similar in the normal subjects and the patients with CNDI. However, the number of binding sites per platelet was increased in the patients with ADCDI (189 +/- 12). Platelet aggregation induced by AVP was equivalent in the three groups. Platelet-fraction AVP was elevated in patients with CNDI and undetectable in patients with ADCDI. These results suggest that the structure and the function of V1 platelet receptor-effector pathway are normal in patients with CNDI.

Autosomal recessive inheritance of vasopressin-resistant diabetes insipidus

We report on 2 intellectually normal sisters with vasopressin-resistant (nephrogenic) diabetes insipidus (NDI). The sex of the patients, the history of parental consanguinity, and the fact that both parents formed normally concentrated urine suggested that the NDI in the 2 sisters was the result of inheritance of an autosomal recessive mutation affecting renal tubular water reabsorption. The results of DNA analysis of the DXS52 locus with the use of St14 as probe, shown by Knoers et al. [1988] to be tightly linked to the NDI locus on the X-chromosome, showed that each girl inherited different Xq28 regions of the maternal X chromosomes, ruling out a diagnosis of classical X-linked NDI.