Short stature, hyperkalemia and acidosis: A defect in renal transport of potassium

Transient early-childhood hyperkalaemia without salt wasting, pathophysiological approach of three cases

Two types of early childhood hyperkalemia had been recognized, according to the presence or absence of urinary salt wasting. This condition was attributed to a maturation disorder of aldosterone receptors and is characterized by sustained hyperkalemia, hyperchloremic metabolic acidosis (MA) due to reduced ammonium urinary excretion and bicarbonate loss, and normal creatinine with growth delay. We present 3 patients of the type without salt wasting, which we will call transient early-childhood hyperkalemia (TECHH) without salt wasting, and discuss its physiopathology according to new insights into sodium and potassium handling by the aldosterone in distal nephron. In 3 children from 30 to 120-day-old admitted with bronchiolitis and growth delay hyperkalemia was found in routine laboratory. Further studies revealed a normal creatinine with inappropriately normal or low fractional excretion (FE) of potassium, accompanied by inadequately normal serum aldosterone and plasma renin activity for their higher plasma potassium levels, but without urine salt wasting. They also presented hyperchloremic MA with FE of bicarbonate 0.58%-2.2%, positive urinary anion gap during MA and normal ability to acidify the urine. Based on these findings a diagnosis of TECHH without salt wasting was made and they were treated sodium bicarbonate and hydrochlorothiazide with favorable response. The condition was transient in all cases leading to treatment discontinuation. Given that TECCH without salt wasting is a tubular disorder of transient nature with mild symptoms; it must be keep in mind in the differential diagnosis of hyperkalemia in young children.

Transient early-childhood hyperkalemia without salt wasting, physiopathological approach of three cases

Two types of early-childhood hyperkalemia had been recognized, according to the presence or absence of urinary salt wasting. This condition was attributed to a maturation disorder of aldosterone receptors and is characterized by sustained hyperkalemia, hyperchloremic metabolic acidosis due to reduced ammonium urinary excretion and bicarbonate loss, and normal creatinine with growth delay. We present three patients of the type without salt wasting, which we will call transient early-childhood hyperkalemia without salt wasting, and discuss its physiopathology according to new insights into sodium and potassium handling by the aldosterone in distal nephron. In three children from 30 to 120-day-old admitted with bronchiolitis and growth delay hyperkalemia was found in routine laboratory. Further studies revealed a normal creatinine with inappropriately normal or low fractional excretion of potassium, accompanied by inadequately normal serum aldosterone and plasma renin activity for their higher plasma potassium levels, but without urine salt wasting. They also presented hyperchloremic metabolic acidosis with fractional excretion of bicarbonate 0.58-2.2%, positive urinary anion gap during metabolic acidosis and normal ability to acidify the urine. Based on these findings a diagnosis of transient early-childhood hyperkalemia without salt wasting was made and they were treated sodium bicarbonate and hydrochlorothiazide with favorable response. The condition was transient in all cases leading to treatment discontinuation. Given that transient early-childhood hyperkalemia without salt wasting is a tubular disorder of transient nature with mild symptoms; it must be keep in mind in the differential diagnosis of hyperkalemia in young children.

Mutation affecting the conserved acidic WNK1 motif causes inherited hyperkalemic hyperchloremic acidosis

Gain-of-function mutations in with no lysine (K) 1 (WNK1) and WNK4 genes are responsible for familial hyperkalemic hypertension (FHHt), a rare, inherited disorder characterized by arterial hypertension and hyperkalemia with metabolic acidosis. More recently, FHHt-causing mutations in the Kelch-like 3-Cullin 3 (KLHL3-CUL3) E3 ubiquitin ligase complex have shed light on the importance of WNK's cellular degradation on renal ion transport. Using full exome sequencing for a 4-generation family and then targeted sequencing in other suspected cases, we have identified new missense variants in the WNK1 gene clustering in the short conserved acidic motif known to interact with the KLHL3-CUL3 ubiquitin complex. Affected subjects had an early onset of a hyperkalemic hyperchloremic phenotype, but normal blood pressure values"Functional experiments in Xenopus laevis oocytes and HEK293T cells demonstrated that these mutations strongly decrease the ubiquitination of the kidney-specific isoform KS-WNK1 by the KLHL3-CUL3 complex rather than the long ubiquitous catalytically active L-WNK1 isoform. A corresponding CRISPR/Cas9 engineered mouse model recapitulated both the clinical and biological phenotypes. Renal investigations showed increased activation of the Ste20 proline alanine-rich kinase-Na+-Cl- cotransporter (SPAK-NCC) phosphorylation cascade, associated with impaired ROMK apical expression in the distal part of the renal tubule. Together, these new WNK1 genetic variants highlight the importance of the KS-WNK1 isoform abundance on potassium homeostasis.

A patient with pseudohypoaldosteronism type II complicated by congenital hypopituitarism carrying a KLHL3 mutation

Pseudohypoaldosteronism type II (PHA II) is a renal tubular disease that causes hyperkalemia, hypertension, and metabolic acidosis. Mutations in four genes (WNK4, WNK1, KLHL3, and CUL3) are known to cause PHA II. We report a patient with PHA II carrying a KLHL3 mutation, who also had congenital hypopituitarism. The patient, a 3-yr-old boy, experienced loss of consciousness at age 10 mo. He exhibited growth failure, hypertension, hyperkalemia, and metabolic acidosis. We diagnosed him as having PHA II because he had low plasma renin activity with normal plasma aldosterone level and a low transtubular potassium gradient. Further investigations revealed defective secretion of GH and gonadotropins and anterior pituitary gland hypoplasia. Genetic analyses revealed a previously known heterozygous KLHL3 mutation (p.Leu387Pro), but no mutation was detected in 27 genes associated with congenital hypopituitarism. He was treated with sodium restriction and recombinant human GH, which normalized growth velocity. This is the first report of a molecularly confirmed patient with PHA II complicated by congenital hypopituitarism. We speculate that both GH deficiency and metabolic acidosis contributed to growth failure. Endocrinological investigations will help to individualize the treatment of patients with PHA II presenting with growth failure.

Monogenic forms of hypertension

Arterial hypertension in childhood is less frequent as compared to adulthood but is more likely to be secondary to an underlying disorder. After ruling out more obvious causes, some patients still present with strongly suspected secondary hypertension of yet unknown etiology. A number of these children have hypertension due to single gene mutations inherited in an autosomal dominant or recessive fashion. The finding of abnormal potassium levels (low or high) in the presence of suppressed renin secretion, and metabolic alkalosis or acidosis should prompt consideration of these familial diseases. However, mild hypertension and the absence of electrolyte abnormalities do not exclude hereditary conditions. In monogenic hypertensive disorders, three distinct mechanisms leading to the common final pathway of increased sodium reabsorption, volume expansion, and low plasma renin activity are documented. The first mechanism relates to gain-of-function mutations with a subsequent hyperactivity of renal sodium and chloride reabsorption leading to plasma volume expansion (e.g., Liddle's syndrome, Gordon's syndrome). The second mechanism involves deficiencies of enzymes that regulate adrenal steroid hormone synthesis and deactivation (e.g., subtypes of congenital adrenal hyperplasia, apparent mineralocorticoid excess (AME)). The third mechanism is characterized by excessive aldosterone synthesis that escapes normal regulatory mechanisms and leading to volume-dependent hypertension in the presence of suppressed renin release (glucocorticoid remediable aldosteronism). Hormonal studies coupled with genetic testing can help in the early diagnosis of these disorders.

Inherited forms of mineralocorticoid hypertension

PURPOSE OF REVIEW

Inherited forms of mineralocorticoid hypertension are a group of monogenic disorders that, although rare, have enlightened our understanding of normal physiology, and subsequent processes implicated in the pathogenesis of 'essential' hypertension. They often present in early life and can be a cause of major morbidity and mortality that can be effectively treated with simple but targeted pharmacological therapy. Interestingly, all the conditions centre on the regulation of sodium transport through its epithelial channel, either directly or through mediators that act via the mineralocorticoid receptor.

RECENT FINDINGS

In recent years, molecular mechanisms of these conditions and their functional consequences have been elucidated. Diagnosis has been facilitated by plasma and urinary biomarkers.

SUMMARY

We provide an overview and diagnostic approach to apparent mineralocorticoid excess, glucocorticoid remediable aldosteronism, familial hyperaldosteronism type 2, Liddle's syndrome, Gordon's syndrome, activating mutations of the mineralocorticoid receptor, generalized glucocorticoid resistance and hypertensive forms of congenital adrenal hyperplasia.

Heritable forms of hypertension

Among the causes of secondary hypertension are a group of disorders with a Mendelian inheritance pattern. Recent advances in molecular biology have unveiled the pathogenesis of hypertension in many of these conditions. Remarkably, the mechanism in every case has proved to be upregulation of sodium (Na) reabsorption in the distal nephron, with accompanying expansion of extracellular volume. In one group, the mutations involve the Na-transport machinery in distal tubule cells themselves: the distal convoluted tubule (DCT) cell and the principal cell of the collecting duct. Examples include Liddle's syndrome, with an activating mutation of epithelial Na channel (ENaC); two types of Gordon's syndrome, with mutations in two regulatory kinases [with no lysine (K) serine/threonine protein kinases (WNK)1 or WNK4]; and apparent mineralocorticoid excess (AME), with an inactivating mutation in the glucocorticoid-metabolizing 11beta-hydroxysteroid dehydrogenase type 2 enzyme (11HD2). In another group, abnormal adrenal steroid production leads to inappropriate stimulation of the mineralocorticoid receptor (MR) in the distal nephron. The pathophysiology may involve inappropriate production of aldosterone [in glucocorticoid-remediable aldosteronism (GRA) and familial hyperaldosteronism type II (FH II)], of cortisol (in familial glucocorticoid resistance), or of other steroid metabolites (in congenital adrenal hyperplasia and GRA). In contrast to earlier beliefs, hypertension in many of the inherited disorders may be mild, and electrolyte and acid-base abnormalities are often not present. Monogenic hypertension should therefore enter the differential diagnosis of any child or adolescent with hypertension. Plasma renin activity (PRA) is the appropriate screening tool for all types of inherited hypertension.

A young female with Spitzer-Weinstein syndrome diagnosed by thiazide test

Spitzer-Weinstein syndrome is a rare disorder characterized by thiazide responsive hyperkalemia and normal anion gap metabolic acidosis, similar to Gordon syndrome. The hyperfunction of thiazide-sensitive Na+-Cl- cotransporter (TSC) is the main pathophysiological mechanism. We presented a 19-year-old female with short stature, normal blood pressure, persistently elevated serum potassium, and metabolic acidosis. The diagnosis of Spitzer-Weinstein Syndrome was made by clinical pictures and thiazide test. After taking 4 mg hydrochlorothiazide, her daily urine potassium excretion increased from 18.1 mmol to 41.8 mmol, urine pH decreased from 7.32 to 6.50, and urinary net charge decreased from 65.7 to 54.4. This patient then took hydrochlorothiazide 4 mg daily. The persistent hyperkalemia and metabolic acidosis were corrected. Thiazide, a powerful inhibitor of TSC, proved to be a useful tool for the diagnosis and treatment of Spitzer-Weinstein syndrome.

Molecular Physiology and Pathophysiology of Electroneutral Cation-Chloride Cotransporters

Electroneutral cation-Cl−cotransporters compose a family of solute carriers in which cation (Na+or K+) movement through the plasma membrane is always accompanied by Cl−in a 1:1 stoichiometry. Seven well-characterized members include one gene encoding the thiazide-sensitive Na+−Cl−cotransporter, two genes encoding loop diuretic-sensitive Na+−K+−2Cl−cotransporters, and four genes encoding K+−Cl−cotransporters. These membrane proteins are involved in several physiological activities including transepithelial ion absorption and secretion, cell volume regulation, and setting intracellular Cl−concentration below or above its electrochemical potential equilibrium. In addition, members of this family play an important role in cardiovascular and neuronal pharmacology and pathophysiology. Some of these cotransporters serve as targets for loop diuretics and thiazide-type diuretics, which are among the most commonly prescribed drugs in the world, and inactivating mutations of three members of the family cause inherited diseases such as Bartter's, Gitelman's, and Anderman's diseases. Major advances have been made in the past decade as consequences of molecular identification of all members in this family. This work is a comprehensive review of the knowledge that has evolved in this area and includes molecular biology of each gene, functional properties of identified cotransporters, structure-function relationships, and physiological and pathophysiological roles of each cotransporter.

Role of WNK kinases in regulating tubular salt and potassium transport and in the development of hypertension

A recently discovered family of protein kinases is responsible for an autosomal-dominant disease known as Gordon's syndrome or pseudohypoaldosteronism type II (PHA-II) that features hyperkalemia and hyperchloremic metabolic acidosis, accompanied by hypertension and hypercalciuria. Four genes have been described in this kinase family, which has been named WNK, due to the absence of a key lysine in kinase subdomain II (with no K kinases). Two of these genes, WNK1 and WNK4 located in human chromosomes 12 and 17, respectively, are responsible for PHA-II. Immunohystochemical analysis revealed that WNK1 and WNK4 are predominantly expressed in the distal convoluted tubule and collecting duct. The physiological studies have shown that WNK4 downregulates the activity of ion transport pathways expressed in these nephron segments, such as the apical thiazide-sensitive Na+-Cl−cotransporter and apical secretory K+channel ROMK, as well as upregulates paracellular chloride transport and phosphorylation of tight junction proteins such as claudins. In addition, WNK4 downregulates other Cl−influx pathways such as the basolateral Na+-K+-2Cl−cotransporter and Cl−/HCO3−exchanger. WNK4 mutations behave as a loss of function for the Na+-Cl−cotransporter and a gain of function when it comes to ROMK and claudins. These dual effects of WNK4 mutations fit with proposed mechanisms for developing electrolyte abnormalities and hypertension in PHA-II and point to WNK4 as a multifunctional regulator of diverse ion transporters.

Hereditary disorders of potassium homeostasis

There has been a dramatic recent increase in the understanding of the renal epithelial transport systems with the identification, cloning and characterization of a large number of membrane transport proteins. The aim of this chapter is to integrate this body of knowledge with the understanding of the clinical disorders that accompany gain, loss or dysregulation of function of these transport systems. The specific focus is on the best-defined human clinical syndromes in which there are derangements in potassium (K(+)) homeostasis. The focus is on inherited syndromes, rather than on acquired syndromes due to tubular transport defects, and the therapeutic approaches address chronic derangements of K(+) homeostasis rather than acute interventions directed at life-threatening hyperkalaemia.

Renal genetic disorders related to K+ and Mg2+

The recent knowledge of the renal epithelial transport systems has exploded with the identification, cloning, and characterization of a large number of membrane transport proteins. The fundamental aspects of these transporters are beginning to emerge at the molecular level and are summarized in the accompanying contributions in this volume of the Annual Review of Physiology. The aim of my review is to integrate this body of knowledge with the understanding of the clinical disorders of human mineral homeostasis that accompany gain, loss, or dysregulation of function of these transport systems. The specific focus is on the best defined human clinical syndromes in which there are derangements in K(+) and Mg(2+) homeostasis.

Phenotypic and genetic heterogeneity of familial hyperkalaemic hypertension (Gordon syndrome)

1. Familial hyperkalaemic hypertension (FHH), also called pseudohypoaldosteronism type II (PHA2) or Gordon syndrome, is a rare Mendelian-form of low-renin hypertension. The first cases of FHH were reported approximately 30 years ago and they described the peculiar biochemical abnormalities (i.e. hyperkalaemia and hyperchloraemic acidosis despite a normal glomerular filtration rate). 2. Since then, more than 90 single cases and families have been reported in the literature. These various reports show marked differences in phenotype. 3. Our group has now collected 14 unrelated pedigrees originating from different parts of France and Europe. We confirm the large variations in the age of discovery and in the severity of the biochemical abnormalities from one individual to another and from one family to another one. 4. Blood pressure levels have no significant relationship with hyperkalaemia or hyperchloraemia, but there is a positive relationship with age, as in the normal population. 5. Analyses of clinical features and Mendelian segregation in our families demonstrate autosomal-dominant inheritance, as expected from the literature. 6. Efforts have been made in the past years to unravel the gene responsible for the disease. Until now, a primary responsibility of the gene encoding the thiazide-sensitive Na-Cl cotransporter (SLC12A3) has been excluded in PHA2 families. Three loci have been identified on chromosomes 1 (PHA2A), 17 (PHA2B) and 12 (PHA2C). 7. More recently, analysis of three additional pedigrees, including 10 affected subjects, with over 25 members allowed us to demonstrate further genetic heterogeneity and the existence of at least a fourth locus. 8. The genetic heterogeneity of this syndrome, and thus the variety of molecular defects, suggests the role of either several new components of the same pathway, multiple aldosterone- regulated effectors or direct or indirect partners of the Na-Cl cotransporter.

Neonatal presentation of Gordon syndrome

Gordon syndrome, the association of hypertension with hyperkalemic acidosis, has been described in older children and adults. We report an affected family in which two of the members had exhibited the metabolic manifestations of the disease since infancy. Both patients responded well to thiazides. To our knowledge, these are the youngest patients with documented cases of Gordon syndrome.

Hormone-nuclear receptor interactions in health and disease. Mineralocorticoid resistance

Mineralocorticoid resistance, or pseudohypoaldosteronism (PHA), is a rare cause of salt wasting in young children. It may be inherited as an autosomal dominant or recessive trait, it may occur sporadically or, rarely, it may develop secondary to other conditions. It is characterized by episodes of dehydration and hyponatraemia in the face of high aldosterone levels. In most cases, after a short period of salt supplementation no further ill effects are experienced. The condition is of great interest because it provides insights into both the mechanisms by which salt and water balance are controlled and the actions of aldosterone. This article reviews the normal physiology of aldosterone, with particular reference to its biosynthesis and its actions in specific target tissues. Current knowledge regarding the molecular mechanisms involved in aldosterone action is discussed in some detail. The clinical features of PHA are reviewed and diagnostic issues and clinical management considered. Finally, current views regarding the pathophysiology of the condition are presented. Here, considerable uncertainty remains. Whilst in many cases of PHA there is greatly reduced binding of aldosterone to its receptor, the underlying abnormality is yet to be identified; in particular, in spite of strong reasons for suspecting a defect or defects in the mineralocorticoid receptor, there is so far no direct evidence to support this hypothesis. The article concludes with a discussion of other possible explanations for the underlying abnormality in PHA.

"Chloride-shunt" syndrome: an overlooked cause of renal hypercalciuria

The case of a 7-year-old boy with the normotensive form of "chloride-shunt" syndrome is described. An unusual feature was the clinical presentation with lithiasis, caused by marked hypercalciuria of renal origin. The present studies were carried out to investigate the nature of the renal tubular defect. Indices for proximal and distal sodium chloride reabsorption were increased during hypotonic saline diuresis. Baseline sodium chloride excretion was low but increased above the range of control values after acute furosemide administration. Baseline potassium excretion was low, was not modified by the infusion of sodium chloride and increased significantly during infusions of sodium sulphate or sodium bicarbonate. Calcium excretion remained unchanged during sodium chloride, sodium sulphate or sodium bicarbonate infusions, but increased after furosemide administration. Nasal insufflation of 1-desamino-8-D-arginine-vasopressin induced both an increase in potassium excretion and a decrease in calcium and magnesium excretion. Plasma atrial natriuretic peptide was increased and was not significantly modified by infusion of hypertonic saline or acute administration of furosemide. These findings indicate that the primary renal abnormality appears to be an enhanced tubular reabsorption of sodium chloride, apparently present in the proximal tubule and the ascending loop of Henle. The associated presence of hypercalciuria also suggests a transport defect in the distal tubule. Decreased potassium excretion probably depends on a voltage-shunting defect in the cortical collecting tubule, which can be reversed by increasing the delivery of non-reabsorbable anions or by enhancing the conductance of the luminal membrane.(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.

The syndrome of hypertension and hyperkalaemia with normal glomerular function (Gordon's syndrome). A pathophysiological study

A 14-year-old boy with the syndrome of hypertension and hyperkalaemia with normal glomerular filtration rate (Gordon's syndrome) is described. The patient's clinical symptoms consisted of periodic paralysis, slight metabolic acidosis of the proximal type and hypercalciuria. Prostaglandin excretion was normal. Infusion of atrial natriuretic peptide had no effect on electrolyte excretion or glomerular function although a normal increase in cyclic guanosine monophosphate was demonstrated in plasma and urine. This lack of sensitivity to atrial natriuretic peptide offers a new pathophysiological concept in this syndrome. Treatment with hydrochlorothiazide was successful in this case.

Mineralocorticoid-induced kaliuresis in type-II pseudohypoaldosteronism

Type II pseudohypoaldosteronism is an uncommonly reported disorder. The authors recently evaluated a patient who in many respects appeared to have this syndrome. He had hyperkalemia, a normal glomerular filtration rate, "normal" serum and urinary aldosterone levels, and low plasma renin activity. In addition, he had a hyperchloremic metabolic acidosis and hypertension. Fractional excretion of potassium was reduced in response to sodium chloride loading. However, renal potassium excretion in response to administration of sodium sulfate was normal. Thiazide diuretic restored the serum potassium, the low bicarbonate, and blood pressure to normal. He developed marked natriuresis and kaliuresis in response to high-dose exogenous mineralocorticoid. The magnitude of the kaliuretic response achieved to exogenous mineralocorticoid has been reported only once previously.

Treatment of mineralocorticoid-resistant renal hyperkalemia with hypertension (type II pseudohypoaldosteronism)

A 16 year old girl with the rare syndrome characterised by hypertension, hyperkalemia, and acidosis was treated with a range of drugs, including thiazides, frusemide, and beta-adrenoceptor antagonists. None of the agents normalised the hypertension and biochemical abnormalities. Best results were obtained with methyclothiazide in full dosage, which normalised the blood pressure, serum potassium level, and bicarbonate level in the face of increased plasma renin activity. Empirical treatment with thiazides is the most satisfactory method for long term management.

The Spitzer-Weinstein syndrome: one form of type IV renal tubular acidosis and its response to hydrochlorothiazide

A twelve-year-old girl with persistent hyperkalemia, metabolic acidosis, normal blood pressure and glomerular filtration rate, and short stature (first percentile for height) was studied using metabolic balance techniques. Prior to therapy with hydrochlorothiazide (HCTZ), urinary potassium and acid excretion were low and urine pH was inappropriately high at 5.8. HCTZ (25 mg orally per day) (1 mg/kg) was then started and rapidly corrected her serum electrolytes. The therapy with HCTZ was associated with a diuresis, a decrease in urine pH to 4.8, and concomitant increases in potassium, titratable acid (TA) and ammonium excretion. The increase in TA excretion was explicable, in part, to the decrease in urine pH and, in part, to the considerable increase in phosphate excretion (from 56 to 81 mmol/d). Plasma renin activity and plasma aldosterone increased markedly following HCTZ but urinary prostaglandin E (PGE) excretion was unchanged. These observations suggest that administration of HCTZ in this setting increases hydrogen ion secretion. It is unclear whether this effect is a direct consequence of HCTZ at the level of the tubule or is secondary to some other action of HCTZ. However, it is clear that this effect is not related to an alteration in PGE excretion.

[Primary hypoaldosteronism, pseudo-hypoaldosteronism and distal tubular acidosis]

Aldosterone deficiency is caused by various defects of aldosterone biosynthesis in the adrenal gland or hyporeninism. The most important symptoms are hyponatremia and hyperkalemia. These electrolyte disturbances are also found in pseudohypoaldosteronism. Pseudohypoaldosteronism type I is characterized by insensitivity of the distal nephron for aldosterone. Hyperabsorption of chloride in the distal nephron leads to pseudohypoaldosteronism type II, which is linked with hypertension, whereas blood pressure in the other mentioned disorders is decreased. Renal tubular acidosis, mainly type 4, with impaired production of ammonia due to hyperkalemia, is frequently observed in hypoaldosteronism and both types of pseudohypoaldosteronism as well. The therapeutic regimen is different: low doses of fludrocortisone in hypoaldosteronism, potassium restriction, sodium bicarbonate and loop diuretics in type I of pseudohypoaldosteronism, and sodium restriction and chloruretic diuretics (thiazide) in type II of pseudohypoaldosteronism. In some cases hyperkalemia requires the use of potassium-binding resins.

[Primary hypoaldosteronism and secondary pseudo-hypoaldosteronism]

We observed a 23-year-old man with pronounced hyperkalemia (max. 6.8 mmol/l) and hyponatremia (min. 112 mmol/l), which had been existent for 3 years without complaint except a transitory psychorganic syndrome due to hyponatremia. Physical examination showed no abnormality except hypotension (blood pressure 100/70 mmHg). Renal function tests were normal. Fractional clearance of sodium was significantly increased (0.8%), whereas that of potassium was decreased (2.4%). Plasma renin activity was tripled and rose after furosemide. Plasma aldosterone was lowered and showed no rise after furosemide. Suppression of plasma renin and aldosterone by saline infusion was normal. Pressor dose of angiotensin II was increased (17,9 ng AT II/kg/min). Urinary excretion of aldosterone and its conjugates was below normal, and aldosterone precursors were within normal range. The findings were interpreted as selective primary hypoaldosteronism caused by corticosterone methyl oxidase defect type II. However, neither fludrocortisone (0.5 mg/day) nor sodium chloride (200 mmol/day) led to a normalization of sodium and potassium in plasma. Additional pseudohypoaldosteronism was thus assumed. Aldosterone infusion (3 mg in 1 h) decreased renal excretion of sodium; potassium excretion failed, however, to increase in contrast to its pattern in normal man. These findings resemble additional pseudohypo-aldosteronism of type II. After 8 weeks' application of additional 80 mmol sodium (as sodium bicarbonate) plasma sodium and potassium showed normal values under combined treatment with fludrocortisone (0.1 mg/day) and sodium bicarbonate (80 mmol/day). It is to be assumed that the patient suffers from a reduced aldosterone biosynthesis in the presence of an additional transitory secondary pseudohypoaldosteronism.

Isolated adrenal mineralocorticoid deficiency due to amyloidosis associated with familial Mediterranean fever

A patient with familial Mediterranean fever (FMF) associated with renal amyloidosis, presented with hyperkalemia and acidosis which were excessive to his moderate degree of azotemia. The cause of this abnormality was isolated hypoaldosteronism with otherwise normal adrenal function and tubular capacity to transport potassium. This selective involvement of the zona glomerulosa stands in marked contrast to the usual sparing of the glomerulosa seen in post mortem studies of patients with FMF and amyloidosis reported from this country.

Renal tubular acidosis

In the past decade major advances in our understanding of renal tubular hydrogen ion secretion and bicarbonate reabsorption have provided new insight into the pathophysiology of renal tubular acidosis. Thus "fragment to fragment clings" and the number of disorders categorized within the syndrome grows, until we have come to know and name four types, with many subtypes. We hope this new perspective provides a basis for the physician to recognize renal tubular acidosis in its several forms so that an informed decision may be arrived at in choosing the best therapy. The physician may also be prepared to reasonably project the prognosis for each patient. We also hope that our detailed examination of renal acidification will provide a reference for delineation of new clinical expressions of acid-base disorders and kidney malfunction certain to be described in the years ahead.

Distal renal tubular acidosis: pathogenesis and classification

Distal renal tubular acidosis results from ineffective addition of hydrogen ions to the lumen of the distal nephron. The syndrome is manifested by hyperchloremic metabolic acidosis often associated with hypokalemia. More recently, it has been recognized that hyperkalemia rather than hypokalemia can be a dominant feature of some cases of distal renal tubular acidosis. It has been generally accepted that all cases of this syndrome ultimately resulted from a similar mechanism. The prevailing view was that the abnormality underlying distal renal tubular acidosis was that of inability to either generate or maintain a steep pH gradient across the distal nephron. Recent advances in our understanding of the process of distal acidification have provided evidence that different mechanisms can alter distal hydrogen ion secretion. In this article, the significance of the various indices of urinary acidification and their use in the characterization of the mechanism underlying distal renal tubular acidosis are revised. A classification of distal renal tubular acidosis on the basis of mechanism is presented. The importance of plasma potassium and renal potassium excretion in the evaluation of patients with distal renal tubular acidosis is emphasized.

Diagnostic strategies in disorders of fluid, electrolyte and acid-base homeostasis

Our understanding of the physiology and biochemistry of acid-base and fluid-electrolyte regulations has greatly expanded in recent years. Key physiologic principles have emerged that now permit rational diagnosis and therapy of clinical disorders of serum electrolyte concentration. This paper describes diagnostic strategies based upon these principles. The etiology of the myriad factors in hyponatremia is best derived by first measuring serum tonicity and then assessing extracellular fluid volume. The hyper-, iso- and hypotonic hyponatremia are defined, and the hypotonic group is subclassified into hypo-, iso- and hyper volemic forms. The hypernatremias are best categorized by their state of volume expansion. Classification into the hypo-, hyper- and isovolemic hypernatremias simplifies their diagnosis. Metabolic acidoses are classified in terms of the anion gap. Clinical and chemical aspects of increased and normal anion gap acidoses are described. Metabolic alkaloses require a source of new bicarbonate and its retention by the kidney. The means by which new alkali is synthesized and urinary loss prevented serve to effectively classify the alkaloses. Hypokalemic syndromes are defined in terms of associated changes in body potassium. The potassium-depleted states are further subclassified by whether normotension or hypertension is associated. Hyperkalemia is produced by redistribution of cellular and extracellular potassium or by increased body potassium. Defects in the renin-angiotensin-aldosterone-distal renal tubule effector arm usually underlie hyperkalemic states, which are than classified in terms of this regulatory hormonal cascade. Classifications for disordered serum concentrations of calcium, magnesium, phosphorus and uric acid are presented. Hormonal, metabolic and renal regulatory factors form the basis for an organized approach to these disorders.

Mineralocorticoid-resistant renal hyperkalemia without salt wasting (type II pseudohypoaldosteronism): role of increased renal chloride reabsorption

A rare syndrome has been described in which mineralocorticoid-resistant hyperkalemia of renal origin occurs in the absence of glomerular insufficiency and renal sodium wasting and in which hyperchloremic acidosis, hypertension, and hyporeninemia coexist. The primary abnormality has been postulated to be a defect of the potassium secretory mechanism of the distal nephron. The present studies were carried out to investigate the mechanism of impaired renal potassium secretion in a patient with this syndrome. When dietary intake of sodium chloride was normal, renal clearance of potassium was subnormal (CK/GFR = 3.6 +/- 0.2%; normal subjects, 9.0 +/- 0.9%, N = 4) despite high normal or supernormal levels of plasma and urinary aldosterone. The fractional clearance of potassium remained subnormal (CK/GFR = 5.1 +/- 0.2%) during superimposed chronic administration of superphysiologic doses of mineralocorticoid hormone. Little increase in renal potassium clearance occurred when the delivery of sodium to distal nephron segments was increased further by the i.v. infusion of sodium chloride, despite experimentally sustained hypermineralocorticoidism. But potassium clearance increased greatly when delivery of sodium to the distal nephron was increased by infusion of nonchloride anions: sulfate (sodium sulfate infusion, low sodium chloride diet; CK/GFR = 63.7 +/- 0.4%) or bicarbonate (sodium bicarbonate plus acetazolamide infusion; CK/GFR = 81.7 +/- 1.7%). These findings indicate that mineralocorticoid-resistant renal hyperkalemia in this patient cannot be attributed to the absence of a renal potassium secretory capability or to diminished delivery of sodium to distal nephron segments; instead it may be dependent on chloride delivery to the distal nephron. We suggest that the primary abnormality in this syndrome increases the reabsorptive avidity of the distal nephron for chloride, which (1) limits the sodium and mineralocorticoid-dependent voltage driving force for potassium and hydrogen ion secretion, resulting in hyperkalemia and acidosis and (2) augments distal sodium chloride reabsorption resulting in hyperchloremia, volume expansion, hyporeninemia, and hypertension.