Temporal delays and individual variation in antidiuretic response to desmopressin.

This study aimed to estimate the relationship between pharmacokinetics and the antidiuretic effect of desmopressin. In the investigator-blind, randomized, parallel group study, 5 dose groups and 1 placebo group, each consisting of 12 healthy, overhydrated, nonsmoking male subjects 18-55 yr of age were infused intravenously over 2 h with placebo or 30, 60, 125, 250, and 500 ng desmopressin in 50 ml of normal saline. Plasma desmopressin and urine osmolality rose by variable amounts during the infusions of 60, 125, 250, and 500 ng desmopressin. Plotting mean urine osmolality against the concurrent mean plasma desmopressin yielded a temporal delay between pharmacokinetic (PK) and -dynamic (PD) responses in all dose groups. Using simulation from the indirect-response model, assuming a constant (4 ng/ml) desmopressin concentration, this delay between PK and PD was estimated at 4 h (10th-90th percentile: 1.8-8.1). Within each group, however, there were large individual variations (2- to 10-fold) in the magnitude and duration of the antidiuretic effect. The antidiuretic effect of intravenous desmopressin in water-loaded healthy adults varies considerably due largely to factors other than individual differences in pharmacokinetics. The antidiuretic effect is time as well as dose dependent and may be self-amplifying. The most likely explanation for these findings is that the time required for a given level of plasma desmopressin to exert its maximum antidiuretic effect varies markedly from person to person due to individual differences in the kinetics of one or more of the intracellular mechanisms that promote the reabsorption of solute-free water by principal cells in renal collecting tubules.

A Novel Form of Familial Vasopressin Deficient Diabetes Insipidus Transmitted in an X-linked Recessive Manner.

CONTEXT: Familial pituitary diabetes insipidus has been described only in an autosomal dominant or recessive mode of inheritance. OBJECTIVE: This work aims to determine the cause of a novel form of familial diabetes insipidus (DI) that is controlled by desmopressin therapy but segregates in an X-linked recessive manner. METHODS: Thirteen members from 3 generations of the kindred with familial DI were studied. Water intake, urine volume, urine osmolality, plasma osmolality, and plasma vasopressin were measured under basal conditions, during fluid deprivation, 3% saline infusion, and water loading. Magnetic resonance images of the posterior pituitary also were obtained. In affected males, the effects of desmopressin therapy and linkage of the DI to markers for chromosome Xq28 were determined. In addition, the genes encoding vasopressin, aquaporin-2, the AVPR2 receptor, and its flanking regions were sequenced. RESULTS: This study showed that 4 males from 3 generations of the kindred have DI that is due to a deficiency of vasopressin, is corrected by standard doses of desmopressin, and segregates with markers for the AVPR2 gene in Xq28. However, no mutations were found in AVPR2 or its highly conserved flanking regions. Exome sequencing confirmed these findings and also revealed no deleterious variants in the provasopressin and aquaporin-2 genes. The 4 obligate female carriers osmo-regulated vasopressin in the low normal range. CONCLUSION: X-linked recessive transmission of DI can be due to a defect in either the secretion or the action of vasopressin. Other criteria are necessary to differentiate and manage the 2 disorders correctly.

Differential diagnosis of familial diabetes insipidus.

Diabetes insipidus (DI) is a syndrome characterized by the persistent excretion of abnormally large volumes of dilute urine. It can be caused by any of four fundamentally different abnormalities: deficient production of the antidiuretic hormone, arginine vasopressin (AVP) by magnocellular neurons that form the posterior pituitary (hypothalamic DI); impaired renal effects of AVP (nephrogenic DI); reduced AVP secretion due to excessive water intake (primary polydipsia); or degradation of AVP by placental vasopressinase (gestational DI). Each type of DI can be caused or potentiated by other disorders. Hypothalamic and nephrogenic DI can also be caused by mutation of the gene that encodes the AVP prohormone, the AVP-2 receptors in the kidney, or the aquaporin-2 water channels that mediate antidiuresis. Familial hypothalamic DI is usually transmitted in an autosomal dominant mode, but autosomal recessive or X-linked recessive forms also exist. Familial nephrogenic DI is usually transmitted in an X-linked recessive mode but can also be autosomal recessive or dominant. Hence the mode of inheritance does not always indicate the type of DI. Indirect methods of differential diagnosis are also unreliable and the pituitary MRI signal is diminished in both types of familial DI. Thus the determination of plasma AVP and/or the response to desmopressin therapy plus gene sequencing provides the best basis for effective management and family counseling.

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: Differential diagnosis and management.

Diabetes insipidus (DI) is a syndrome characterized by the excretion of abnormally large volumes of dilute urine. It can be caused by any of 4 fundamentally different defects that must be distinguished for safe and effective management. They are: (1) pituitary DI, due to inadequate production and secretion of antidiuretic hormone, arginine-vasopressin (AVP); (2) gestational DI due to degradation of AVP by an enzyme made in placenta; (3) primary polydipsia, due to suppression of AVP secretion by excessive fluid intake; and (4) nephrogenic DI due to renal insensitivity to the antidiuretic effect of AVP. This review describes several methods of differential diagnosis, indicates the advantages and disadvantages of each and presents a new approach that is simpler and less costly but just as reliable as the best of the older methods. The various treatments for the different types of DI and recent findings on the genetic basis of the familial forms of DI are also discussed with emphasis on their contributions to improved diagnosis and management.

Exposures of preschool children to chlorpyrifos and its degradation product 3,5,6-trichloro-2-pyridinol in their everyday environments.

As part of the Children's Total Exposure to Persistent Pesticides and Other Persistent Organic Pollutants (CTEPP) study, we investigated the exposures of preschool children to chlorpyrifos and its degradation product 3,5,6-trichloro-2-pyridinol (TCP) in their everyday environments. During this study, the participants were still able to purchase and apply chlorpyrifos at their homes or day care centers. Participants were recruited randomly from 129 homes and 13 day care centers in six North Carolina counties. Monitoring was performed over a 48-h period at the children's homes and/or day care centers. Samples that were collected included duplicate plate, indoor and outdoor air, urine, indoor floor dust, play area soil, transferable residues (PUF roller), and surface wipes (hand, food preparation, and hard floor). The samples were extracted and analyzed by gas chromatography/mass spectrometry. Chlorpyrifos was detected in 100% of the indoor air and indoor floor dust samples from homes and day care centers. TCP was detected at homes and day care centers in 100% of the indoor floor dust and hard floor surface wipe, in >97% of the solid food, and in >95% of the indoor air samples. Generally, median levels of chlorpyrifos were higher than those of TCP in all media, except for solid food samples. For these samples, the median TCP concentrations were 12 and 29 times higher than the chlorpyrifos concentrations at homes and day care centers, respectively. The median urinary TCP concentration for the preschool children was 5.3 ng/ml and the maximum value was 104 ng/ml. The median potential aggregate absorbed dose (ng/kg/day) of chlorpyrifos for these preschool children was estimated to be 3 ng/kg/day. The primary route of exposure to chlorpyrifos was through dietary intake, followed by inhalation. The median potential aggregate absorbed dose of TCP for these children was estimated to be 38 ng/kg/day, and dietary intake was the primary route of exposure. The median excreted amount of urinary TCP for these children was estimated to be 117 ng/kg/day. A full regression model of the relationships among chlorpyrifos and TCP for the children in the home group explained 23% of the variability of the urinary TCP concentrations by the three routes of exposure (inhalation, ingestion, dermal absorption) to chlorpyrifos and TCP. However, a final reduced model via step-wise regression retained only chlorpyrifos through the inhalation route and explained 22% of the variability of TCP in the children's urine. The estimated potential aggregate absorbed doses of chlorpyrifos through the inhalation route were low (median value, 0.8 ng/kg/day) and could not explain most of the excreted amounts of urinary TCP. This suggested that there were other possible sources and pathways of exposure that contributed to the estimated potential aggregate absorbed doses of these children to chlorpyrifos and TCP. One possible pathway of exposure that was not accounted for fully is through the children's potential contacts with contaminated surfaces at homes and day care centers. In addition, other pesticides such as chlorpyrifos-methyl may have also contributed to the levels of TCP in the urine. Future studies should include additional surface measurements in their estimation of potential absorbed doses of preschool children to environmental pollutants. In conclusion, the results showed that the preschool children were exposed to chlorpyrifos and TCP from several sources, through several pathways and routes. .

Autosomal dominant neurohypophyseal diabetes insipidus due to substitution of histidine for tyrosine(2) in the vasopressin moiety of the hormone precursor.

The autosomal dominant form of familial neurohypophyseal diabetes insipidus (adFNDI) has been linked to 40 different mutations of the gene encoding the vasopressin-neurophysin II (AVP-NPII) precursor. All of these mutations have been located in either the signal peptide or neurophysin II moiety. We now report a three-generation Turkish kindred in which severe adFNDI cosegregates with a novel missense mutation in the part of the AVP-NPII gene encoding the AVP moiety. This mutation (T-->C at position 285 in the genomic sequence) was found in only one allele and predicts a substitution of histidine for tyrosine at position 2 in AVP. Like other adFNDI mutations, this substitution is expected to impair folding and processing of the precursor, in this case by interfering with normal binding of the AVP and NPII moieties. It is associated clinically with inability to concentrate urine during fluid deprivation, a greater than 80% deficiency of AVP secretion, and absence of the posterior pituitary bright spot on magnetic resonance imaging. These findings are consistent with the hypothesis that mutations in the AVP-NPII gene cause adFNDI by directing the production of a folding incompetent precursor that prevents the expression of the normal allele via a cytotoxic effect on the magnocellular neurons.

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.

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.

Clinical and molecular analysis of three families with autosomal dominant neurohypophyseal diabetes insipidus associated with a novel and recurrent mutations in the vasopressin-neurophysin II gene.

OBJECTIVE: To test further the hypothesis that autosomal dominant neurohypophyseal diabetes insipidus (adFNDI) is caused by heterozygous mutations in the vasopressin-neurophysin II (AVP-NPII) gene that exert a dominant negative effect by producing a precursor that misfolds, accumulates and eventually destroys the neurosecretory neurons. METHODS: Antidiuretic function, magnetic resonance imaging (MRI) of the posterior pituitary and AVP-NPII gene analysis were performed in 10 affected members of three unreported families with adFNDI. RESULTS: As in previously studied patients, adFNDI apparently manifested after birth, was due to a partial or severe deficiency of AVP, and was associated with absence or diminution of the hyperintense MRI signal normally emitted by the posterior pituitary, and with a heterozygous mutation in the AVP-NPII gene. In family A, a transition 275G-->A, which predicts replacement of cysteine 92 by tyrosine (C92Y), was found in the index patient, but not in either parent, indicating that it arose de novo. The six affected members of family B had a transversion 160G-->C, which predicts replacement of glycine 54 by arginine (G54R). It appeared de novo in the oldest affected member, and was transmitted in a dominant manner. In family C, six of 15 living affected members were tested and all had a novel transition, 313T-->C, which predicts replacement of cysteine 105 by arginine (C105R). It, too, was transmitted in a dominant manner. As in other patients with adFNDI, the amino acids replaced by the mutations in these three families are known to be particularly important for correct and efficient folding of the precursor. CONCLUSIONS: These findings are consistent with the malfolding/toxicity hypothesis underlying the pathogenesis of adFNDI. Moreover, they illustrate the value of genetic analysis in all patients who develop idiopathic diabetes insipidus in childhood, even if no other family members are affected.

Clinical review: Treatment of neurohypophyseal diabetes insipidus.

CONTEXT: In recent years, there have been several improvements in the treatment of neurohypophyseal diabetes insipidus (DI). They include new formulations of the vasopressin analog, desmopressin; a better understanding of the effect of fluid intake on dosing; and more information about treatments of infants, children, and pregnant women who present special challenges. This review aims to summarize past and current information relative to the safety and efficacy of treatments for the types of DI caused by a primary deficiency of vasopressin. EVIDENCE ACQUISITION: The review is based on publications identified primarily by a PubMed search of the international literature without limitations of date. EVIDENCE SYNTHESIS: In acute settings where fluid intake is determined by factors other than thirst, desmopressin should be given iv in doses that have a short duration of action and can be adjusted quickly in accordance with changes in hydration as indicated by plasma sodium. In ambulatory patients, the oral formulations (tablet or melt) are preferred for their convenience. If fluid intake is regulated normally by the thirst mechanism, the tablets or melt can be taken safely 1 to 3 times a day in doses sufficient to completely eliminate the polyuria. However, if fluid intake consistently exceeds replacement needs as evidenced by the development of hyponatremia, the dose should be reduced to allow higher than normal rates of urine output or intermittent breakthrough diuresis. This regimen is often indicated in infants or children because their rate of fluid intake tends to be greater than in adults. In all cases, the appropriate dose should be determined by titration, owing to considerable interindividual differences in bioavailability and antidiuretic effect. CONCLUSIONS: Desmopressin can provide effective and safe therapy for all patients with neurohypophyseal or gestational DI if given in doses and by a route that takes into account the determinants of fluid intake.

Vaptans for the treatment of hyponatremia.

The vaptans constitute a new class of pharmaceuticals developed for the treatment of the hypervolemic and euvolemic forms of hyponatremia. These agents are nonpeptide vasopressin antagonists that interfere with the antidiuretic effect of the hormone by competitively binding to V(2) receptors in the kidney. This blockade results in water diuresis (aquaresis) that, if not offset by increased fluid intake, reduces body water content and raises plasma sodium levels. Probably as a result of this rise in plasma sodium, thirst and plasma vasopressin concentration increase, potentionally limiting the effects of the vasopressin antagonists. Nonetheless, vaptans are particularly useful to treat hypervolemic hyponatremia associated with severe congestive heart failure or chronic liver failure, as the only other treatments currently available, such as fluid restriction and diuretics, are slow-acting and minimally effective. Vaptans are also useful for treating euvolemic hyponatremia associated with the syndrome of inappropriate antidiuretic hormone (SIADH), at least when it is chronic and/or minimally symptomatic. However, because their effects vary unpredictably from patient to patient, vaptans are less useful than hypertonic saline infusion in cases of acute, severe and symptomatic hyponatremia. Vaptan therapy is absolutely contraindicated in hypovolemic hyponatremia (in which total body water is reduced) and is ineffective in the vasopressin-independent form of inappropriate antidiuresis caused by constitutive activating mutations of V(2) receptors.

Familial forms of diabetes insipidus: clinical and molecular characteristics.

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

Semivolatile organic compounds in residential air along the Arizona-Mexico border.

Concerns about indoor air quality and the potential effects on people living in these environments are increasing as more reports about the toxicities and the potential indoor air exposure levels of household-use chemicals and chemicals from housing and fumishing manufacture in air are being assessed. Gas chromatography/mass spectromery was used to confirm numerous airborne contaminants obtained from the analysis of semipermeable membrane devices deployed inside of 52 homes situated along the border between Arizona and Mexico. We also describe nontarget analytes in the organochlorine pesticide fractions of 12 of these homes; this fraction is also the most likely to contain the broadest scope of bioconcentratable chemicals accumulated from the indoor air. Approximately 400 individual components were identified, ranging from pesticides to a wide array of hydrocarbons, fragrances such as the musk xylenes, flavors relating to spices, aldehydes, alcohols, esters and phthalate esters, and other miscellaneous types of chemicals. The results presented in this study demonstrate unequivocally that the mixture of airborne chemicals present indoors is far more complex than previously demonstrated.

Regulation of arginine vasopressin in the syndrome of inappropriate antidiuresis.

The syndrome of inappropriate antidiuresis (SIAD) is a disorder of sodium and water balance characterized by hypotonic hyponatremia and impaired water excretion in the absence of renal insufficiency, adrenal insufficiency, or any recognized stimulus for the antidiuretic hormone arginine vasopressin (AVP). Hyponatremia is primarily a result of excessive water retention caused by a combination of excessive intake and inappropriate antidiuresis. It is sometimes aggravated by a sodium deficiency caused by decreased intake and/or a secondary natriuresis triggered by and largely corrective of the increase in extracellular volume. Hence, there is neither edema nor signs of hypovolemia. Inappropriate antidiuresis is usually due to administration or endogenous production of AVP or another vasopressin receptor agonist such as desmopressin. Endogenous production can be either ectopic (from a tumor) or eutopic (from the neurohypophysis). The latter apparently is induced by a wide variety of diseases, drugs, or injuries and is divisible into 3 different types of abnormal AVP release during hypertonic saline infusion: high, erratic fluctuations unrelated to increases in plasma sodium (type A); a slow constant "leak" that is also unaffected by increases in plasma sodium (type B); and rapid progressive increases in plasma AVP that correlate closely with plasma sodium as it rises toward the normal range (type C or "reset osmostat"). In 5% to 10% of patients, there is no demonstrable abnormality in the osmoregulation of AVP (type D) and the cause of inappropriate antidiuresis is unclear. In some children it appears to be due to an activating mutation of the V2 receptor (V2R). In other patients, it may be due to abnormal control of aquaporin-2 water channels in renal collecting tubules or production of an antidiuretic principle other than AVP. These different types of osmoregulatory dysfunction underlying SIAD may result in marked differences in clinical presentation or response to therapy with fluid restriction, hypertonic saline infusion, or vasopressin antagonists.

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.

Impaired trafficking of mutated AVP prohormone in cells expressing rare disease genes causing autosomal dominant familial neurohypophyseal diabetes insipidus.

OBJECTIVE AND STUDY DESIGN: Two different mutations in the arginine vasopressin (AVP) gene associated with autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI) predict Y21H (AVP2) and V67A (NP36) amino acid substitutions of the AVP prohormone. They are unique in that they change, respectively, the AVP moiety and a region of the neurophysin II domain not so far affected by any mutations. To test whether they affect the cellular handling of the AVP prohormone in a similar manner to previously investigated mutations, they were examined by heterologous expression in cell lines. RESULTS: Both mutations resulted in significantly reduced amounts of immunoreactive AVP in the cell culture medium as determined by radioimmunoassay analysis. Metabolic labelling combined with immunoprecipitation demonstrated that processing and secretion of the mutant prohormones was reduced but not prevented. Finally, confocal laser scanning microscopy showed that normal AVP prohormone and/or its processed products were localized in the tips of the cellular processes, whereas both mutant prohormones were accumulated in the endoplasmic reticulum (ER) and in the case of the V67A prohormone, also in perinuclear structures outside the ER. CONCLUSION: Both mutations result in reduced AVP prohormone processing and secretion probably due to retention in the ER. This supports, at least partly, the hypothesis that the mutations lead to the production of a mutant hormone precursor that fails to fold and/or dimerize properly and, as a consequence, is retained by the ER protein quality control machinery. Perinuclear accumulation of the V67A prohormone outside the ER indicates that additional mechanisms could be involved.

Report of 33 novel AVPR2 mutations and analysis of 117 families with X-linked nephrogenic diabetes insipidus.

X-linked nephrogenic diabetes insipidus (NDI) is a rare disease caused by mutations in the arginine vasopressin receptor 2 gene (AVPR2). Thirty-three novel AVPR2 mutations were identified in 62 families that were not included in our previous studies. This study describes the diversity of mutations observed in a total of 117 families, the number of affected people at the time of diagnosis, skewed X chromosome inactivation in severely affected females, the inferred parental origin of de novo mutations, and it provides estimates of incidence. Among 117 families, there were 82 different putative disease-causing mutations. Based on haplotype analysis, it can be inferred that when the same AVPR2 mutation is identified in different families that were not known to be related, the mutations most likely arose independently. More than half of the families had only one affected male; two families presented with a severely affected female and no family history of NDI. A de novo mutation arose during oogenesis in the mother in 20% of isolated cases. The estimate of about 8.8 per million male live births of the incidence of X-linked NDI in the province of Quebec, Canada may be representative of the general population except in Nova Scotia and New Brunswick, where the incidence is more than six times higher. Documentation of the diversity of mutations will assist in revealing the full spectrum of clinical variation. Discussion of genetic and population genetic aspects of X-linked NDI may contribute to early diagnosis and treatment.