Phenotypic diversity and correlation with the genotypes of pseudohypoaldosteronism type 1.

Background Type I pseudohypoaldosteronism (PHA1) is a rare condition characterised by profound salt wasting, hyperkalaemia and metabolic acidosis due to renal tubular resistance to aldosterone (PHA1a) or defective sodium epithelial channels (PHA1b or systemic PHA). Our aim was to review the clinical presentation related to the genotype in patients with PHA1. Methods A questionnaire-based cross-sectional survey was undertaken through the British Society of Paediatric Endocrinology and Diabetes (BSPED) examining the clinical presentation and management of patients with genetically confirmed PHA1. We also reviewed previously reported patients where genotypic and phenotypic information were reported. Results Genetic confirmation was made in 12 patients with PHA1; four had PHA1a, including one novel mutation in NR3C2; eight had PHA1b, including three with novel mutations in SCNN1A and one novel mutation in SCNN1B. It was impossible to differentiate between types of PHA1 from early clinical presentation or the biochemical and hormonal profile. Patients presenting with missense mutations of SCNN1A and SCNN1B had a less marked rise in serum aldosterone suggesting preservation in sodium epithelial channel function. Conclusions We advocate early genetic testing in patients with presumed PHA1, given the challenges in differentiating between patients with PHA1a and PHA1b. Clinical course differs between patients with NR3C2 and SCNN1A mutations with a poorer prognosis in those with multisystem PHA. There were no obvious genotype-phenotype correlations between mutations on the same gene in our cohort and others, although a lower serum aldosterone may suggest a missense mutation in SCNN1 in patients with PHA1b.

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.

Pseudohypoaldosteronisms, report on a 10-patient series.

BACKGROUND: Type 1 pseudohypoaldosteronism (PHA1) is a salt-wasting syndrome caused by mineralocorticoid resistance. Autosomal recessive and dominant hereditary forms are caused by Epithelial Na Channel and Mineralocorticoid Receptor mutation respectively, while secondary PHA1 is usually associated with urological problems. METHODS: Ten patients were studied in four French pediatric units in order to characterize PHA1 spectrum in infants. Patients were selected by chart review. Genetic, clinical and biochemistry data were collected and analyzed. RESULTS: Autosomal recessive PHA1 (n = 3) was diagnosed at 6 and 7 days of life in three patients presenting with severe hyperkalaemia and weight loss. After 8 months, 3 and 5 years on follow-up, neurological development and longitudinal growth was normal with high sodium supplementation. Autosomal dominant PHA1 (n = 4) was revealed at 15, 19, 22 and 30 days of life because of failure to thrive. At 8 months, 3 and 21 years of age, longitudinal growth was normal in three patients who were given salt supplementation; no significant catch-up growth was obtained in the last patient at 20 months of age. Secondary PHA1 (n = 3) was diagnosed at 11, 26 days and 5 months of life concomitantly with acute pyelonephritis in three children with either renal hypoplasia, urinary duplication or bilateral megaureter. The outcome was favourable and salt supplementation was discontinued after 3, 11 and 13 months. CONCLUSIONS: PHA1 should be suspected in case of severe hyperkalemia and weight loss in infants and need careful management. Pathogenesis of secondary PHA1 is still challenging and further studies are mandatory to highlight the link between infection, developing urinary tract and pseudohypoaldosteronism.

Pseudohypoaldosteronism type 1 and the genes encoding prostasin, alpha-spectrin, and Nedd4.

Pseudohypoaldosteronism type 1 (PHA1), a rare disorder of infancy, presents with potential life-threatening salt wasting and failure to thrive. Thus far, PHA1 has been attributed to mutations affecting the mineralocorticoid receptor or any of the three subunits assembling the amiloride-sensitive epithelial sodium channel (ENaC). However, a lot of patients with a phenotype resembling PHA1, show no defects in these proteins, making it likely that further genes are involved in the aetiology of this disease. Recent studies have elucidated additional participants (alpha-spectrin and members of the families of transmembrane serine proteases, ubiquitin-protein ligases, and serum- and glucocorticoid-regulated kinases, respectively) regulating and/or interacting in the complex pathway of sodium retention in the amiloride-sensitive distal nephron. This led us to investigate whether PHA1 can also be associated with mutations in some of these genes. Our data suggest that at least the prostasin gene might be excluded as a causative locus.

Mineralocorticoid resistance.

Mineralocorticoid resistance, also known as type I pseudohypoaldosteronism (PHA1), is a rare inherited disease characterized by salt wasting, dehydration and failure to thrive in the newborn. Two different forms of the disease, which present with either systemic or exclusively renal resistance to aldosterone, are associated with two different modes of inheritance. The generalized, recessive form of the disease is due to abnormalities in the epithelial sodium channel, and inactivating mutations of the mineralocorticoid receptor are responsible for the autosomal dominant form of PHA1 and some sporadic cases. Here, we review the role of aldosterone in the maintenance of normal sodium balance and discuss the different forms of mineralocorticoid resistance and the underlying genetic abnormalities. Although important progress has been made in the past years, there remain several families in whom the genetic defect has not been identified. Precise clinical diagnosis and establishment of intermediate phenotypes should be helpful for identifying other genes involved in PHA1 and gaining new insight into the regulation of sodium homeostasis.

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.

[Fetal pseudohypoaldosteronism: rare cause of hydramnios]. / Pseudoipoaldosteronismo fetale: rara causa di polidramnios.

PHA is a rare cause of hydramnios, characterized by increased amniotic fluid levels of aldosterone and sodium. Two distinct genetic entities (PHA type I and PHA type II) are included. Both are stemmed by a target organ defect with diminished renal tubular responsiveness to aldosterone. The AA present a case in which pregnancy resulted in a preterm infant with severe hydramnios, metabolic acidosis, hyponatriemia, hyperkaliemia. Salt and fluid replacement significantly improved clinical and metabolic condition. However a growth deficiency (-2 SDS) persists at follow-up.

Different inactivating mutations of the mineralocorticoid receptor in fourteen families affected by type I pseudohypoaldosteronism.

We have analyzed the human mineralocorticoid receptor (hMR) gene in 14 families with autosomal dominant or sporadic pseudohypoaldosteronism (PHA1), a rare form of mineralocorticoid resistance characterized by neonatal renal salt wasting and failure to thrive. Six heterozygous mutations were detected. Two frameshift mutations in exon 2 (insT1354, del8bp537) and one nonsense mutation in exon 4 (C2157A, Cys645stop) generate truncated proteins due to premature stop codons. Three missense mutations (G633R, Q776R, L979P) differently affect hMR function. The DNA binding domain mutant R633 exhibits reduced maximal transactivation, although its binding characteristics and ED(50) of transactivation are comparable with wild-type hMR. Ligand binding domain mutants R776 and P979 present reduced or absent aldosterone binding, respectively, which is associated with reduced or absent ligand-dependent transactivation capacity. Finally, P979 possesses a transdominant negative effect on wild-type hMR activity, whereas mutations G633R and Q776R probably result in haploinsufficiency in PHA1 patients. We conclude that hMR mutations are a common feature of autosomal dominant PHA1, being found in 70% of our familial cases. Their absence in some families underscores the importance of an extensive investigation of the hMR gene and the role of precise diagnostic procedures to allow for identification of other genes potentially involved in the disease.

Pseudohypoaldosteronism type II: marked sensitivity to thiazides, hypercalciuria, normomagnesemia, and low bone mineral density.

Mutations in WNK kinases cause pseudohypoaldosteronism type II (PHA II) and may represent a novel signaling pathway regulating blood pressure and K(+) and H(+) homeostasis. PHA II is an autosomal dominant disorder characterized by hypertension, hyperkalemia, and metabolic acidosis, with normal glomerular filtration rate. Thiazide diuretics correct all abnormalities. Inactivating mutations in the thiazide-sensitive NaCl cotransporter cause Gitelman syndrome, featuring hypotension, hypokalemia, and metabolic alkalosis plus hypocalciuria and hypomagnesemia. We investigated whether hypercalciuria and hypermagnesemia occurred in a large family with PHA II. Eight affected and eight unaffected members of a PHA II family with the Q565E WNK 4 mutation were studied. In affected members blood and urinary chemistry were measured on and off hydrochlorothiazide (HCTZ), and bone mineral density was determined. Marked sensitivity to HCTZ was found. A mean dose of 20 mg/d reduced mean blood pressure in the six hypertensive subjects by 54.3 (systolic) and 24.5 (diastolic) mm Hg. In affected subjects, HCTZ reduced mean serum K(+) by 1.12 mmol/liter, mean serum Cl(-) by 6.2 mmol/liter, and mean urinary calcium by 65% and elevated mean serum calcium by 0.11 mmol/liter and mean serum urate by 118 micromol/liter. Compared with the literature, this represents an increase of 6-7 in HCTZ potency. Affected members had normomagnesemia, hypercalciuria (336 +/- 113 vs. 155 +/- 39 mg/d in unaffected relatives, P = 0.0002), and decreased bone mineral density. In PHA II the observed marked sensitivity to thiazides and the hypercalciuria are consistent with increased NaCl cotransporter activity. PHA II may serve as a model to investigate thiazides' beneficial effects and side effects.

Genetic heterogeneity of familial hyperkalaemic hypertension.

BACKGROUND: Familial hyperkalaemic hypertension (FHH) is a Mendelian form of low-renin hypertension characterized by hyperkalaemia and hyperchloraemic acidosis despite a normal glomerular filtration rate. To date, three different loci have been identified, on chromosomes 1, 17 and 12. OBJECTIVE: To test for genetic linkage between the three FHH loci and three new affected kindreds. DESIGN AND METHODS: Clinical, biological and genetic analyses were made of three kindreds, including 11 affected individuals among 25 members. Genotyping was performed using four series of microsatellite markers spanning the chromosomes 1, 17 and 12 loci, and the thiazide-sensitive Na-Cl cotransporter (SLC12A3) gene. RESULTS: Segregation of the trait in each kindred was compatible with an autosomal transmission, the affected individuals displaying reasonably consistent biochemical abnormalities and the expected variability in arterial hypertension. Multipoint linkage analysis excluded linkage with the four candidate loci in kindreds 1 and 2, but not with the chromosome 1 locus in kindred 3. CONCLUSION: These results demonstrate further genetic heterogeneity and that a fourth gene is responsible for FHH in at least two unrelated kindreds. They suggest a variety of molecular defects leading to FHH.

Disorders of the epithelial Na(+) channel in Liddle's syndrome and autosomal recessive pseudohypoaldosteronism type 1.

The epithelial Na(+) channel (ENaC) is the key step in many Na(+)-absorptive epithelia, such as kidney and distal colon, that controls the overall rate of transepithelial Na(+) transport. ENaC is composed of three homologous subunits, alpha, beta, and gamma. The alpha subunit is the key subunit for the formation of a functional ion channel, while the beta and gamma subunits can greatly potentiate the level of expressed Na(+) currents. ENaCs belong to the recently identified DEG/ENaC supergene family, sharing the same basic structure with cytoplasmic amino and carboxy termini, two transmembrane regions, and a large extracellular loop. The human ENaC genes have been cloned, and using genetic linkage analysis the involvement of ENaC gene mutations in two distinct human diseases, Liddle's syndrome and autosomal recessive pseudohypoaldosteronism type 1 (PHA-1), has been demonstrated. In Liddle's syndrome, gain-of-function mutations in the beta or gamma ENaC subunits have been found; all identified mutations so far reside in the carboxy terminus of the protein, either deleting or modifying the functionally important PY motif. In PHA-1, loss-of-function mutations in the alpha, beta, or gamma subunits have been found; these mutations either truncate a significant portion of the structure or modify an amino acid that plays an important role in channel function. In this review, our current understanding about ENaC and the pathophysiology of Liddle's syndrome and PHA-1 caused by ENaC mutations will be discussed.

Pseudohypoaldosteronism: mineralocorticoid unresponsiveness syndrome.

We described a 10 day old boy who presented with hyponatremia, hyperkalemia, and metabolic acidosis. Therapeutic treatment with exogenous glucocorticoid and mineralocorticoid for 8 months failed to correct the electrolyte abnormalities. The elevated serum cortisol up to 44.34 micrograms/dl along with the absence of skin hyperpigmentation excluded defects in the glucocorticoid pathway. Pseudohypoaldosteronism was diagnosed on the basis of hyponatremia, severe urinary salt loss despite the markedly elevated serum aldosterone up to 6,500 pg/ml (normal range 50-800 pg/ml). The patient responded very well to oral salt supplementation and cation exchange resin therapy shown by normal physical growth and normal levels of serum electrolytes.

A patient with pseudohypoaldosteronism type 1 and respiratory distress syndrome.

We present a patient born at 36 weeks' gestation with respiratory distress, who required 6 days of mechanical ventilation, without a demonstrable infectious cause. He also developed hyponatremia, hypernatriuria, elevated serum aldosterone levels, and probable pseudohypoaldosteronism type 1 (PHA-1). This appears to be the first reported human case of both respiratory distress and a renal salt wasting process with elevated serum aldosterone. In animal models, abnormalities of subunits of the epithelial sodium channel produce respiratory distress and PHA-1. This patient's clinical presentation could be due to the same processes.

Sodium transporters in health and disease.

Our understanding of sodium transport defects has exploded in the past 18 months, and has provided unique insights into epithelial transport processes and unusual clinical syndromes resulting from mutations of specific transporters. These genetic disorders disturb sodium balance, with both sodium retaining and sodium wasting disorders as the consequence.

Mutations in subunits of the epithelial sodium channel cause salt wasting with hyperkalaemic acidosis, pseudohypoaldosteronism type 1.

Autosomal recessive pseudohypoaldosteronism type I is a rare life-threatening disease characterized by severe neonatal salt wasting, hyperkalaemia, metabolic acidosis, and unresponsiveness to mineralocorticoid hormones. Investigation of affected offspring of consanguineous union reveals mutations in either the alpha or beta subunits of the amiloride-sensitive epithelial sodium channel in five kindreds. These mutations are homozygous in affected subjects, co-segregate with the disease, and introduce frameshift, premature termination or missense mutations that result in loss of channel activity. These findings demonstrate the molecular basis and explain the pathophysiology of this disease.

Contribution to problems of pseudohypoaldosteronism type I in children.

Pseudohypoaldosteronism Type I may occur due to several different causes. The authors recommend distinguishing between effector and receptor disorders with regard to the diverse mode of inheritance and prognosis.