Autosomal-dominant pseudohypoaldosteronism type 1 in a Turkish family is associated with a novel nonsense mutation in the human mineralocorticoid receptor gene

Pseudohypoaldosteronism types I and II: little more than a name in common

Pseudohypoaldosteronism (PHA) comprises a diverse group of rare diseases characterized by sodium and potassium imbalances incorrectly attributed to a defect in aldosterone production. Two different forms of PHA have been described, type I (PHAI) and type II (PHAII). PHAI has been subclassified into renal and systemic. Given the rarity and heterogeneity of this group of disorders we report three patients who carry PHA and a brief revision of current literature focused on the comparative analysis of PHAI and PHAII. Cases 1 and 2 presented with hyponatremia, hyperkalemia, metabolic acidosis and elevated plasma aldosterone and plasma renin activity in the neonatal period. Sequence analysis of the NRC2 gene demonstrated a novel heterozygous c.403C>T mutation in case 1 and a complete deletion in case 2, confirming the diagnosis of renal PHAI. Case 3 was a 4-year-old with hypertension, hyperkalemia, metabolic acidosis, normal plasma aldosterone and decreased plasma renin activity. Sequence analysis of the CUL3 gene demonstrated a previously unreported heterozygous c.1377+2T>3 mutation, confirming the diagnosis of PHAII-E. We highlight the importance of the determination of plasma aldosterone and plasma renin activity in the context of persistent sodium and potassium imbalances in children.

A novel frameshift mutation in NR3C2 leads to decreased expression of mineralocorticoid receptor: a family with renal pseudohypoaldosteronism type 1

Pseudohypoaldosteronism type 1 (PHA1) is a rare genetic disease characterized by resistance to aldosterone, and the renal form of PHA1 is associated with heterozygous inactivating mutations in NR3C2, which encodes mineralocorticoid receptor (MR). Here we report a case of renal PHA1 due to a novel frameshift mutation in NR3C2. A 10-day-old Japanese male infant, born at 39 weeks gestation (birth weight, 2,946 g), was admitted to our hospital because of lethargy and vomiting, with a 6.7% weight loss since birth. Laboratory test results were: Na⁺, 132 mEq/L; K⁺, 6.6 mEq/L; Cl⁺, 93 mEq/L. Both plasma aldosterone level and plasma renin activity were markedly elevated at diagnosis, 2,940 ng/dL (normal range: 26.9-75.8 ng/dL) and 560 ng/mL/h (normal range 3.66-12.05 ng/mL/h), respectively. Direct sequence analysis of NR3C2 revealed a novel heterozygous mutation (c.3252delC) in the patient and his father. The mutation causes a frameshift starting at amino acid I 963 within the C terminal ligand-binding domain of MR and results in a putative abnormal stop codon at amino acid 994, with an extension of 10 amino acids compared to normal MR. We performed cell culture experiments to determine the levels of mutant NR3C2 mRNA and MR, and evaluate the effects of the mutation on MR response to aldosterone. The mutation decreased the expression of MR, but not NR3C2 mRNA, and led to decreased MR function, with no dominant negative effect. These results provide important information about MR function and NR3C2 mutation in PHA1.

Linking genetic variants of the mineralocorticoid receptor and negative memory bias: interaction with prior life adversity

Substantial research has been conducted investigating the association between life adversity and genetic vulnerability for depression, but clear mechanistic links are rarely identified and investigation often focused on single genetic variants. Complex phenotypes like depression, however, are likely determined by multiple variants in interaction with environmental factors. As variations in the mineralocorticoid receptor gene (NR3C2) have been related to a higher risk for depression, we investigated whether NR3C2 variance is related to negative memory bias, an established endophenotype for depression, in healthy participants. Furthermore, we explored the influence of life adversity on this association. We used a set-based analysis to simultaneously test all measured variation in NR3C2 for an association with negative memory bias in 483 participants and an interaction with life adversity. To further specify this interaction, we split the sample into low and high live adversity groups and repeated the analyses in both groups separately. NR3C2 variance was associated with negative memory bias, especially in the high life adversity group. Additionally, we identified a functional polymorphism (rs5534) related to negative memory bias and demonstrating a gene×life adversity interaction. Variations in NR3C2 are associated with negative memory bias and this relationship appears to be influenced by life adversity. As negative memory bias is implicated in the susceptibility to depression, our findings provide mechanistic support for the notion that variations in NR3C2 - which could compromise the proper function of this receptor - are a risk factor for the development of mood disorders.

Clinical and molecular analysis of six Japanese patients with a renal form of pseudohypoaldosteronism type 1

Pseudohypoaldosteronism type 1 (PHA1) is a rare condition characterized by neonatal salt loss with elevated plasma aldosterone and renin levels. Two types of PHA1 have been described: an autosomal recessive systemic form and an autosomal dominant renal form, in which the target organ defect is confined to the renal tubules. The dominant renal form of PHA1 is caused by heterozygous mutations in the NR3C2 gene, which encodes the mineralocorticoid receptor (MR). We determined clinical and biochemical parameters in two familial and four sporadic Japanese patient and analyzed the status of the NR3C2 gene. Failure to thrive was noted in five of the six patients. In one of the familial cases, the mother had an episode of failure to thrive when she was a toddler, but received no medical treatment. NaCl supplementation was discontinued in four of the six patients after they reached one year of age and they have grown normally thereafter. However, in one patient, 9 g/day of salt has been required to maintain serum Na concentration after 1 year of age. Analysis of NR3C2 identified three novel mutations [c. C1951T (p.R651X), c.304_305delGC (p.A102fsX103), c.del 603A (p.T201fsX34)] and one previously reported mutation [c.A2839G (p.947X)]. p.R651X was identified in one familial case and one unrelated sporadic patient. The patient who has been supplemented with large amount of salt was heterozygous for c.del 603A in exon 2. In conclusion, our study expands the spectrum of phenotypes, and characterized mutations of NR3C2 in the renal form of PHA1.

Syndromes of impaired ion handling in the distal nephron: pseudohypoaldosteronism and familial hyperkalemic hypertension

The distal nephron, which is the site of the micro-regulation of water absorption and ion handling in the kidneys, is under the control of aldosterone. Impairment of the mineralocorticoid signal transduction pathway results in resistance to the action of aldosterone and of mineralocorticoids in general. Herein, we review two syndromes in which ion handling in the distal nephron is impaired: pseudohypoaldosteronism (PHA) and familial hyperkalemic hypertension (FHH). PHA is a rare inherited syndrome characterized by mineralocorticoid resistance, which leads to salt loss, hypotension, hyperkalemia and metabolic acidosis. There are two types of this syndrome: a renal (autosomal dominant) type due to mutations of the mineralocorticoid receptor (MR), and a systemic (autosomal recessive) type due to mutations of the epithelial sodium channel (ENaC). There is also a transient form of PHA, which may be due to urinary tract infections, obstructive uropathy or several medications. FHH is a rare autosomal dominant syndrome, characterized by salt retention, hypertension, hyperkalemia and metabolic acidosis. In FHH, mutations of WNK (with-no-lysine kinase) 4 and 1 alter the activity of several ion transportation systems in the distal nephron. The study of the pathophysiology of PHA and FHH greatly elucidated our understanding of the renin-angiotensin-aldosterone system function and ion handling in the distal nephron. The physiological role of the distal nephron and the pathophysiology of diseases in which the renal tubule is implicated may hence be better understood and, based on this understanding, new drugs can be developed.

Mineralocorticoid receptor mutations differentially affect individual gene expression profiles in pseudohypoaldosteronism type 1

CONTEXT

Type 1 pseudohypoaldosteronism (PHA1), a primary form of mineralocorticoid resistance, is due to inactivating mutations of the NR3C2 gene, coding for the mineralocorticoid receptor (MR).

OBJECTIVE

The objective of the study was to assess whether different NR3C2 mutations have distinct effects on the pattern of MR-dependent transcriptional regulation of aldosterone-regulated genes.

DESIGN AND METHODS

Four MR mutations affecting residues in the ligand binding domain, identified in families with PHA1, were tested. MR proteins generated by site-directed mutagenesis were analyzed for their binding to aldosterone and were transiently transfected into renal cells to explore the functional effects on the transcriptional activity of the receptors by cis-trans-cotransactivation assays and by measuring the induction of endogenous gene transcription.

RESULTS

Binding assays showed very low or absent aldosterone binding for mutants MR(877Pro), MR(848Pro), and MR(947stop) and decreased affinity for aldosterone of MR(843Pro). Compared with wild-type MR, the mutations p.Leu843Pro and p.Leu877Pro displayed half-maximal aldosterone-dependent transactivation of reporter genes driven by mouse mammary tumor virus or glucocorticoid response element-2 dependent promoters, whereas MR(848Pro) and MR(947stop) nearly or completely lost transcriptional activity. Although MR(848Pro) and MR(947stop) were also incapable of inducing aldosterone-dependent gene expression of endogenous sgk1, GILZ, NDRG2, and SCNN1A, MR(843Pro) retained complete transcriptional activity on sgk1 and GILZ gene expression, and MR(877Pro) negatively affected the expression of sgk1, NDRG2, and SCNN1A.

CONCLUSIONS

Our data demonstrate that MR mutations differentially affect individual gene expression in a promoter-dependent manner. Investigation of differential gene expression profiles in PHA1 may allow a better understanding of the molecular substrate of phenotypic variability and to elucidate pathogenic mechanisms underlying the disease.

Structural chromosome disruption of the NR3C2 gene causing pseudohypoaldosteronism type 1 presenting in infancy

Type I pseudohypoaldosteronism (PHA1) is a rare form of mineralocorticoid resistance presenting in infancy with renal salt wasting and failure to thrive. Here, we present the case of a 6-week-old baby girl who presented with mild hyponatraemia and dehydration with a background of severe failure to thrive. At presentation, urinary sodium was not measurably increased, but plasma aldosterone and renin were increased, and continued to rise during the subsequent week. Despite high calorie feeds the infant weight gain and hyponatraemia did not improve until salt supplements were commenced. Subsequently, the karyotype was reported as 46,XX,inv (4)(q31.2q35). A search of the OMIM database for related genes at or near the inversion breakpoints, showed that the mineralocorticoid receptor gene (NR3C2) at 4q31.23 was a likely candidate. Further FISH analysis showed findings consistent with disruption of the NR3C2 gene by the proximal breakpoint (4q31.23) of the inversion. There was no evidence of deletion or duplication at or near the breakpoint. This is the first report of a structural chromosome disruption of the NR3C2 gene giving rise to the classical clinical manifestations of pseudohypoaldosteronism type 1 in an infant.

Autosomal dominant pseudohypoaldosteronism type 1 with a novel splice site mutation in MR gene

Background

Autosomal dominant pseudohypoaldosteronism type 1 (PHA1) is a rare inherited condition that is characterized by renal resistance to aldosterone as well as salt wasting, hyperkalemia, and metabolic acidosis. Renal PHA1 is caused by mutations of the human mineralcorticoid receptor gene (MR), but it is a matter of debate whether MR mutations cause mineralcorticoid resistance via haploinsufficiency or dominant negative mechanism. It was previously reported that in a case with nonsense mutation the mutant mRNA was absent in lymphocytes because of nonsense mediated mRNA decay (NMD) and therefore postulated that haploinsufficiency alone can give rise to the PHA1 phenotype in patients with truncated mutations.

Methods and Results

We conducted genomic DNA analysis and mRNA analysis for familial PHA1 patients extracted from lymphocytes and urinary sediments and could detect one novel splice site mutation which leads to exon skipping and frame shift result in premature termination at the transcript level. The mRNA analysis showed evidence of wild type and exon-skipped RT-PCR products.

Conclusion

mRNA analysis have been rarely conducted for PHA1 because kidney tissues are unavailable for this disease. However, we conducted RT-PCR analysis using mRNA extracted from urinary sediments. We could demonstrate that NMD does not fully function in kidney cells and that haploinsufficiency due to NMD with premature termination is not sufficient to give rise to the PHA1 phenotype at least in this mutation of our patient. Additional studies including mRNA analysis will be needed to identify the exact mechanism of the phenotype of PHA.

Association of a mineralocorticoid receptor gene polymorphism with hypertension in a Spanish population

BACKGROUND

To assess the association of polymorphisms and haplotypes of the mineralocorticoid receptor (MR) (NR3C2) gene to the risk of essential hypertension (HTN) in a Spanish population.

METHODS

This is a population-based study which included 1,502 subjects (748 women) >18 years old. Twenty-four polymorphisms of NR3C2 gene were analyzed by using SNPlex (Genotyping System based on OLA/PCR technology).

RESULTS

Alleles of the single-nucleotide polymorphism (SNP) rs5522 were significantly associated with the risk of HTN, both in the recessive and codominant models adjusted by age, gender, and body mass index (BMI). Genotype GG of the rs5522 showed to be protective against HTN odds ratio (OR) 0.10 (0.02-0.56), P < 0.01. One haplotype, which included the G allele of the rs5522, was also associated with reduced risk of HTN and four haplotypes which included the A allele were associated with increased risk of HTN. When the 24-h urinary sodium excretion and the estimated glomerular filtration rate (eGFR) were added, they did not reduce the significance level. Interaction between genotypes of the rs5522 and quartiles of 24-h sodium excretion has been observed. In subjects with the AA genotype, those with higher urinary sodium excretion had the lowest risk to be hypertensive.

CONCLUSION

A functional polymorphism of the NR3C2 gene was associated with risk of HTN. The data provided in this study seems to give credit to the hypothesis of the participation of MR gene in the development of HTN, although further studies are necessary to better assess its real impact.

A novel nonsense mutation of the mineralocorticoid receptor gene in the renal form of pseudohypoaldosteronism type 1

Pseudohypoaldosteronism type 1 (PHA1) is a rare congenital disease characterized by salt loss resistant to mineralocorticoids. Most patients are identified by failure to thrive or poor weight gain in early infancy. Plasma renin activity and aldosterone are markedly elevated. PHA1 is caused by mutations in genes encoding either subunits of the amiloride-sensitive epithelial sodium channel (ENaC) or mineralocorticoid receptor (MR) inherited in an autosomal recessive or dominant form, respectively. Patients with the autosomal dominant form of PHA1 show gradual clinical improvement with advancing age; however, the reason for this remains unclear. We report the renal form of PHA1 in a Japanese family. Polymerase chain reaction and direct sequencing revealed a heterozygous nonsense mutation changing codon 861 Arg (CGA) to stop (TGA) in the index patient. Segregation analysis revealed an identical mutation in the patient's father and older sister. Inheritance in this case is assumed to be of the autosomal dominant type.

Molecular pathogenesis of renal pseudohypoaldosteronism type 1

Pseudohypoaldosteronism is a rare heterogeneous syndrome of mineralocorticoid resistance resulting in insufficient potassium and hydrogen secretion. Pseudohypoaldosteronism type 1 is characterized by mineralocorticoid resistance leading to neonatal salt loss, dehydration and failure to thrive. At least two different forms of pseudohypoaldosteronism type 1 can be distinguished, showing either a systemic or renal form of mineralocorticoid resistance. This review offers an overview on transepithelial sodium reabsorption and pseudohypoaldosteronism in general, and focuses on the underlying molecular pathology of the renal-restricted pseudohypoaldosteronism type 1 form caused by heterozygous mutations in the mineralocorticoid receptor-coding gene NR3C2. The investigation of several NR3C2 mutants in vitro has resulted in important progress in the understanding of the physiology of the mineralocorticoid receptor. However, there are still some families or individuals suffering from renal pseudohypoaldosteronism type 1 in whom no genetic defect was found in the NR3C2 or other genes such as SCNN1A, SCNN1B, SCNN1G, NEDD4 or SGK1 that are involved in the epithelial salt transport machinery. Further research in these cases may enable the identification of other pathologies leading to renal pseudohypoaldosteronism type 1 and permit deeper insights into the epithelial sodium reabsorption process.

[Mineralocorticoid resistance: pseudohypoaldosteronism type 1]

Pseudohypoaldosteronism type 1 (PHA1) is a rare genetic disease characterized by neonatal renal salt wasting, vomiting, dehydration and failure to thrive. Affected patients present hyponatremia, hyperkalemia, associated with high levels of plasma renin and aldosterone resulting from a renal or systemic resistance to aldosterone. The systemic form of PHA1 results in a severe phenotype, and high doses of salt supplementation are necessary. The symptoms are life-long recurrent. This form is associated with autosomal recessive transmission. Homozygous or compound heterozygous loss of function mutations in the genes coding for the epithelial sodium channel (ENaC) subunities are responsible for this disease. The renal form of PHA1 results in a mild phenotype. Low doses of salt supplementation are required and usually the symptoms remit at the end of the first year of life. Heterozygous loss-of-function mutations in the mineralocorticoid receptor (MR) gene are associated with the renal form of PHA1 in the majority of the affected families but sporadic cases have been reported. In this review the mechanisms of aldosterone action and its effects are discussed. Additionally, clinical and molecular findings of a Brazilian family with the renal form of PHA1 caused by a nonsense mutation (R947X) in the MR gene are presented.

Mineralocorticoid receptor mutations are the principal cause of renal type 1 pseudohypoaldosteronism

Aldosterone plays a key role in electrolyte balance and blood pressure regulation. Type 1 pseudohypoaldosteronism (PHA1) is a primary form of mineralocorticoid resistance characterized in the newborn by salt wasting, hyperkalemia, and failure to thrive. Inactivating mutations of the mineralocorticoid receptor (MR; NR3C2) are responsible for autosomal dominant and some sporadic cases of PHA1. The question as to whether other genes may be involved in the disease is of major importance because of the potential life-threatening character of the disease, the potential cardiovascular effects of compensatory aldosterone excess, and the role of the mineralocorticoid system in human hypertension. We present the first comprehensive study seeking nucleotide substitutions in coding regions, intron-exon junctions, and untranslated exons, as well as for large deletions. A total of 22 MR gene abnormalities were found in 33 patients. We demonstrate that MR mutations are extremely frequent in PHA1 patients classified according to aldosterone and potassium levels and give indications for accurate clinical and biological investigation. In our study the possibility of a genocopy exists in three PHA1 kindreds. The other patients without MR mutations might have different diseases resembling to PHA1 in the neonatal period, which could be identified by extensive clinical and functional exploration.

Recurrence of the R947X mutation in unrelated families with autosomal dominant pseudohypoaldosteronism type 1: evidence for a mutational hot spot in the mineralocorticoid receptor gene

BACKGROUND

The renal form of pseudohypoaldosteronism type 1 (PHA1) is a rare disease characterized by congenital mineralocorticoid resistance of the kidney. Twenty-two different loss-of-function mutations in the mineralocorticoid receptor gene have been described in families with PHA1. These mutations were not recurrent and resulted in a large phenotypic variability.

OBJECTIVE

The objective of this study is to analyze the recurrence of an inactivating mutation in the mineralocorticoid receptor gene in unrelated families with autosomal dominant PHA1.

PATIENTS

Seventeen members from three unrelated families with autosomal dominant PHA1 were studied, including 11 affected patients with variable clinical manifestations. Fifty healthy subjects were used as controls.

METHODS

Genomic DNA was extracted, and the entire coding region of the mineralocorticoid receptor gene was submitted to automatic sequencing. Four dinucleotide microsatellite markers spanning a region of 3.2 cM in the human mineralocorticoid receptor gene locus, and two intragenic polymorphisms were used for haplotype analysis.

RESULTS

A heterozygous point mutation at codon 947 (c.2839C>T) changing arginine to stop codon (R947X) was found in the three families. Different haplotypes segregated with the R947X mutation in each family, demonstrating the absence of a founder effect for this mutation.

CONCLUSION

Codon 947 of the mineralocorticoid receptor is the first mutational hot spot for autosomal dominant PHA1.

A Novel Missense Mutation, F826Y, in the Mineralocorticoid Receptor Gene in Japanese Hypertensives: Its Implications for Clinical Phenotypes

A gain-of-function mutation resulting in the S810L amino acid substitution in the hormone-binding domain of the mineralocorticoid receptor (MR, locus symbol NR3C2) is responsible for early-onset hypertension that is exacerbated in pregnancy. The objective of this study was to test whether other types of missense mutations in the hormone-binding domain could be implicated in hypertension in Japanese. Here, we screened 942 Japanese patients with hypertension for the S810L mutation in exon 6 in the MR. We did not identify the S810L mutation in our hypertensive population, indicating that S810L does not play a major role in the etiology of essential hypertension in Japanese. However, we identified a novel missense mutation, F826Y, in three patients in a heterozygous state, in addition to four single nucleotide polymorphisms, including one synonymous mutation (L809L). The F826Y mutation is present in the MR hormone-binding domain and might affect the ligand affinity. The F826Y mutation was also identified in 13 individuals (5 hypertensives and 8 normotensives) in a Japanese general population (n=3,655). The allele frequency was 0.00178. The frequencies of the F826Y mutation in the hypertensive population (3/942) and in the hypertensive group (5/ 1,480) and the normotensive group (8/2,175) in the general population were not significantly different, suggesting that this mutation does not greatly affect hypertension. Although it is unclear at present whether or not the F826Y mutation makes a substantial contribution to the mineralocorticoid receptor activity, this missense mutation may contribute, to some extent, to clinical phenotypes through its effects on MR.

Genetic heterogeneity in autosomal dominant pseudohypoaldosteronism type I: exclusion of claudin-8 as a candidate gene

BACKGROUND/AIMS

Pseudohypoaldosteronism type I (PHAI) is an inherited disorder characterized by renal salt wasting, hyperkalemic metabolic acidosis, and hyperaldosteronism. Its known causes are mutations in the mineralocorticoid receptor and the epithelial sodium channel (ENaC), but there are reports of genetic heterogeneity. Claudin-8 is a tight junction protein that acts as a paracellular cation barrier in the distal nephron. The aim of this study was to test the hypothesis that mutations in claudin-8, which would be expected to induce a distal tubule cation leak, can be a cause of PHAI.

METHODS

We identified 10 patients with autosomal dominant PHAI in whom mutations in the mineralocorticoid receptor and ENaC had been excluded. The claudin-8 gene and upstream region was sequenced in all patients.

RESULTS

No disease-associated claudin-8 mutations were identified. A novel polymorphic allele in the 3'-untranslated region was identified in 2 patients, but was also found in 15% of individuals in a panel of normal controls.

CONCLUSION

We present further evidence for locus heterogeneity in PHAI. Mutations in claudin-8 are unlikely to be a cause of PHAI. Further studies of other claudins in this disease are warranted.