Familial dominant pseudohypoaldosteronism

Renin-aldosterone system evaluation over four decades in an extended family with autosomal dominant pseudohypoaldosteronism due to a deletion in the NR3C2 gene

Renal pseudohypoaldosteronism (PHA1) is a mild form of an aldosterone-resistance syndrome caused by mutations in the NR3C2 gene that codes for the mineralocorticoid receptor (MR). The disease is inherited as an autosomal dominant trait characterized by signs and symptoms of salt-losing in infancy. Disease manifestations could be severe in infancy but improve after the age of 1-3 years. Some affected members are asymptomatic and remain so life-long. In this study, we report the identification of a large deletion in the NR3C2 gene (c.1897+1_1898-1)_(c.*2955+?)del in renal PHA1 patients from an extended family spanning four generations. We prospectively evaluated the plasma renin activity and serum aldosterone profiles over four decades in symptomatic and asymptomatic affected family members. The benefits of early diagnosis on the clinical outcome were assessed as well. The long-term follow-up showed an age-dependent decrease in both plasma renin activity and serum aldosterone levels over the years. However, aldosterone levels remain high life-long. Thus, levels of aldosterone are a reliable marker to detect asymptomatic family members. The diagnosis of the proposita led to early diagnosis and therapy in other affected family members, significantly mitigating the clinical course. Despite the extremely elevated serum aldosterone levels during pregnancy, affected pregnant women did not experience any ill effects. However, this should be verified by observations in other adult patients.

Clinical and Molecular Perspectives of Monogenic Hypertension

Advances in molecular research techniques have enabled a new frontier in discerning the mechanisms responsible for monogenic diseases. In this review, we discuss the current research on the molecular pathways governing blood pressure disorders with a Mendelian inheritance pattern, each presenting with a unique pathophysiology. Glucocorticoid Remediable Aldosteronism (GRA) and Apparent Mineralocorticoid Excess (AME) are caused by mutations in regulatory enzymes that induce increased production of mineralocorticoids or inhibit degradation of glucocorticoids, respectively. Geller syndrome is due to a point mutation in the hormone responsive element of the promotor for the mineralocorticoid receptor, rendering the receptor susceptible to activation by progesterone, leading to hypertension during pregnancy. Pseudohypoaldosteronism type II (PHA-II), also known as Gordon's syndrome or familial hyperkalemic hypertension, is a more variable disorder typically characterized by hypertension, high plasma potassium and metabolic acidosis. Mutations in a variety of intracellular enzymes that lead to enhanced sodium reabsorption have been identified. In contrast, hypertension in Liddle's syndrome, which results from mutations in the Epithelial sodium Channel (ENaC), is associated with low plasma potassium and metabolic alkalosis. In Liddle's syndrome, truncation of one the ENaC protein subunits removes a binding site necessary protein for ubiquitination and degradation, thereby promoting accumulation along the apical membrane and enhanced sodium reabsorption. The myriad effects due to mutation in phosphodiesterase 3A (PDE3A) lead to severe hypertension underlying sodium-independent autosomal dominant hypertension with brachydactyly. How mutations in PDE3A result in the phenotypic features of this disorder are discussed. Understanding the pathologies of these monogenic hypertensive disorders may provide insight into the causes of the more prevalent essential hypertension and new avenues to unravel the complexities of blood pressure regulation.

Erythrocyte Na+,K+-ATPase and nasal potential in pseudohypoaldosteronism

OBJECTIVES

Pseudohypoaldosteronism type 1 (PHA1) is a rare inherited disorder characterized by salt-wasting due to target organ unresponsiveness to mineralocorticoids. PHA1 comprises two clinically and genetically distinct entities; isolated renal and systemic forms.

DESIGN

The aim of this study was to investigate red blood cell (RBC) Na+,K+-ATPase activity and nasal potential difference (PD) in two pairs of unrelated dyzygous twins; one with the systemic form of the disease (PHA1-S) and the second with the isolated renal form (PHA1-R). Total and ouabain-sensitive ATPase activities were measured spectrophotometrically by a method that couples ATP hydrolysis with NADH oxidation. Maximal PD and response to amiloride perfusion were evaluated by a standard technique.

RESULTS

In the twins with PHA1-S, persistently low activity of RBC Na+,K+-ATPase was found during a 6-year follow-up. Normalization of plasma renin activity (PRA) and plasma aldosterone was observed at the end of the first year of life. Maximal nasal PD was low and there was no significant response to amiloride. In the twins with PHA1-R, RBC Na+,K+-ATPase activity was very low at the time of diagnosis and normalized at the age of 6-8 months. PRA reverted gradually to normal values, whereas aldosterone levels remained high during the 6 years of follow-up. Maximal nasal PD and response to amiloride were normal.

CONCLUSIONS

The observed differences in RBC Na+,K+-ATPase activity and nasal PD response to amiloride between the two pairs of twins support the contention of different basic pathogenic mechanisms in the two forms of PHA1.

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.

Syndromes of glucocorticoid and mineralocorticoid resistance

Glucocorticoid resistance results from incomplete but apparently generalized inability of glucocorticoids to exert their effects on their target tissues. The condition is associated with compensatory elevation of circulating ACTH and cortisol, with the former causing excess secretion of both adrenal androgens and adrenal steroid biosynthesis intermediates with salt-retaining activity. The manifestations of glucocorticoid resistance vary from asymptomatic to different degrees of hypertension and/or hypokalemic alkalosis and/or hyperandrogenism, caused by elevation cortisol and other salt-retaining steroids, and of adrenal androgens, respectively. In women, hyperandrogenism can result in acne, hirsutism, male type baldness, menstrual irregularities, oligoanovulation, and infertility; in men, it may lead to infertility; and in children to precocious puberty. Different molecular defects, such as point mutations or microdeletions of the highly conserved glucocorticoid receptor gene, alter the functional characteristics or concentrations of the intracellular receptor and cause glucocorticoid resistance. The extreme variability in the clinical manifestations of glucocorticoid resistance and its mimicry of many common diseases can be explained by different degrees of glucocorticoid resistance, differing sensitivity of target tissues to mineralocorticoids and/or androgens or both, and perhaps different biochemical defects of the glucocorticoid receptor. Mineralocorticoid resistance results from the inability of aldosterone to exert its effect on target tissues. The syndrome is associated with salt loss, hypotension, and hyperkalemic acidosis. We have cloned and sequenced the cDNA of five unrelated patients with this syndrome and have not found any mutations of pathophysiological significance that would explain the resistance of these patients to aldosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Opitz C syndrome and pseudohypoaldosteronism

The C syndrome of multiple congenital anomalies is described in a male infant with pseudohypoaldosteronism. The association of these 2 rare autosomal recessive conditions is discussed.

Inheritance of mineralocorticoid effector abnormalities of human mononuclear leucocytes in families with pseudohypoaldosteronism

In-vitro effects of aldosterone on intracellular sodium and potassium concentrations have been described for normal human mononuclear leucocytes (HML). After incubation for 1 h at 37 degrees C, intracellular sodium and potassium in HML are significantly higher in the presence of 1.4 nM aldosterone than after incubation without aldosterone. As published earlier, these effects were absent in patients with pseudohypoaldosteronism. In the present paper, the families of seven patients with pseudohypoaldosteronism (index cases) were studied. In the first family, two siblings were affected by the disease and had a reduced number of mineralocorticoid (MC) receptors on HML. Intracellular sodium and potassium in HML from these patients did not show a response to 1.4 nM aldosterone. The parents, who were first cousins, had no history of disease and normal receptor data, but in the mother, the response of HML electrolytes to aldosterone was abnormal. In the second family, the mother of a child with pseudohypoaldosteronism, the mother's sister, and her son, had low numbers of MC receptors. Only the aunt of the index case had an uncertain history of the disease. The MC effector mechanism was abnormal in both children and both mothers studied. In a third family, the effector defect was present only in HML of the father. In three further families the abnormality of the effector mechanism was detected in HML of the patient's mother. These data suggest an autosomal dominant inheritance of pseudohypoaldosteronism with variable expression of the gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal tubular hyperkalaemia in childhood

Potassium output from the body is regulated by renal excretion, which takes place predominantly in the late distal and cortical collecting tubules. The accepted model for potassium secretion implies the accumulation of potassium into the cell by the activity of basolateral Na-K-ATPase and its exit through voltage-dependent conductive channels. The factors regulating renal potassium secretion are potassium intake, distal urinary flow, systemic acid-base equilibrium, aldosterone, antidiuretic hormone and, probably, epinephrine. Renal handling of potassium is best studied by the response to the acute administration of furosemide. This loop diuretic not only increases sodium and chloride excretion but also enhances potassium and hydrogen ion excretion and stimulates the renin-aldosterone axis. The term "renal tubular hyperkalaemia" refers to a tubular dysfunction where the hyperkalaemia is disproportionate to any reduction in glomerular filtration rate (GFR) and not due primarily or solely to aldosterone deficiency or to drugs impairing either mineralocorticoid action or tubular transport. The syndromes of renal tubular hyperkalaemia mainly observed in childhood are "chloride shunt" syndrome, hyporeninaemic hypoaldosteronism and primary or secondary pseudohypoaldosteronism. Differential diagnosis between these conditions is easily made if attention is paid to the level of GFR, presence of sodium wasting, activity of the renin-aldosterone axis and renal response to acute administration of furosemide.

Familial pseudohypoaldosteronism

The clinical course of two siblings with a severe form of pseudohypoaldosteronism was followed over a period of seven and five years respectively. Both children persistently had a high sodium-potassium excretion ratio in the urine, sweat, saliva, and stools as well as high serum concentrations of aldosterone and renin and an increased urinary excretion of tetrahydroaldosterone. Despite sustained treatment with sodium chloride (10-40 mmol/kg/d) and cation exchange resin (sodium polystyrole sulfonate 0.5-2 g/kg/d) they repeatedly developed episodes of salt wasting and hyperkalemia which occurred mainly during uncomplicated respiratory tract infections. Aldosterone receptor characteristics were studied in the cytosol of the rectal mucosa at ages 2.5 years and 6 months respectively. Compared to age matched controls there was a decreased affinity for aldosterone at the low affinity binding site. Among the members of the family, the father and one of his sisters had high concentrations of sodium in the sweat and an increased urinary excretion of tetrahydroaldosterone.

Pseudohypoaldosteronism in a female infant and her family: diversity of clinical expression and mode of inheritance

Pseudohypoaldosteronism was diagnosed in an infant that clinically presented severe failure to thrive and vomiting. Evaluation of her extended family revealed many other affected family members with a vast range of clinical expression. The mode of inheritance is most likely autosomal dominant. Salt supplementation during infancy was effective in restoring normal growth, weight gain and serum electrolytes.

Pseudohypoaldosteronism in a child with Down syndrome. Long-term management of salt loss by ion exchange resin administration

At 4 weeks of age, an infant with Down syndrome developed severe dehydration and salt loss with the typical features of pseudohypoaldosteronism (PHA). Plasma renin activity, 11-deoxycorticosterone, corticosterone and aldosterone levels were all increased several-fold over the normal range for age, thus excluding an adrenal biosynthetic defect. Clinical condition, hyponatraemia and hyperkalaemia could be rapidly normalised by the ion exchange resin Resonium A administered first as enema and later orally (3 g/day). At that time, no further salt supplementation was necessary. At 18 months of age, Resonium A could be completely withdrawn with neither clinical deterioration nor electrolyte abnormalities. However at 3 1/2 years of age, plasma renin activity and aldosterone were still markedly elevated while precursor steroids were normal and the clinical condition satisfactory. No side effects were observed with the Resonium A therapy. The combination of trisomy 21 and PHA is very unusual. Similarly, the successful treatment of severe renal salt loss during infancy by sodium supplementation and concomitant potassium withdrawal via an oral ion exchange resin has not yet been described and warrants further therapeutic trials.

The syndromes of primary hormone resistance

The clinical features, genetics, pathophysiology, and management of endocrine diseases in which primary hormone resistance is the fundamental defect have been reviewed. Primary hormone resistance has been documented for nearly all hormones--vasopressin, parathyroid hormone, growth hormone, adrenocroticotropin, thyrotropin, gonadotropins, insulin, androgens, cortisol, aldosterone, progesterone, thyroid hormones, and vitamin D. A striking exception is estradiol, a steroid that may be vital for early embryonic development. Most of the hormone unresponsiveness syndromes represent only partial defects, and it is likely that most such patients go unrecognized. Therefore, hormone resistance should be suspected not only when a patient presents with hypofunction of particular endocrine system combined with high endogenous hormone levels but also whenever apparently normal function of an endocrine system is associated with inappropriately elevated levels of the corresponding hormone. The value of these defects in hormone responsiveness as a natural laboratory for the study of the normal mechanisms of hormone action is discussed.