Constitutively Active SPAK Causes Hyperkalemia by Activating NCC and Remodeling Distal Tubules.

Aberrant activation of with no lysine (WNK) kinases causes familial hyperkalemic hypertension (FHHt). Thiazide diuretics treat the disease, fostering the view that hyperactivation of the thiazide-sensitive sodium-chloride cotransporter (NCC) in the distal convoluted tubule (DCT) is solely responsible. However, aberrant signaling in the aldosterone-sensitive distal nephron (ASDN) and inhibition of the potassium-excretory renal outer medullary potassium (ROMK) channel have also been implicated. To test these ideas, we introduced kinase-activating mutations after Lox-P sites in the mouse Stk39 gene, which encodes the terminal kinase in the WNK signaling pathway, Ste20-related proline-alanine-rich kinase (SPAK). Renal expression of the constitutively active (CA)-SPAK mutant was specifically targeted to the early DCT using a DCT-driven Cre recombinase. CA-SPAK mice displayed thiazide-treatable hypertension and hyperkalemia, concurrent with NCC hyperphosphorylation. However, thiazide-mediated inhibition of NCC and consequent restoration of sodium excretion did not immediately restore urinary potassium excretion in CA-SPAK mice. Notably, CA-SPAK mice exhibited ASDN remodeling, involving a reduction in connecting tubule mass and attenuation of epithelial sodium channel (ENaC) and ROMK expression and apical localization. Blocking hyperactive NCC in the DCT gradually restored ASDN structure and ENaC and ROMK expression, concurrent with the restoration of urinary potassium excretion. These findings verify that NCC hyperactivity underlies FHHt but also reveal that NCC-dependent changes in the driving force for potassium secretion are not sufficient to explain hyperkalemia. Instead, a DCT-ASDN coupling process controls potassium balance in health and becomes aberrantly activated in FHHt.

Transient pseudohypoaldosteronism in infancy secondary to urinary tract infection.

AIM: Hyponatraemia with hyperkalaemia in infancy is a typical presentation of congenital adrenal hyperplasia. In the presence of pyelonephritis, the same biochemical picture can occur with transient type 1 pseudohypoaldosteronism (PHA-1) also termed type 4 renal tubular acidosis. Recognition of PHA-1 enables appropriate management thus avoiding unnecessary investigations and treatment. To improve awareness of this condition, we present a case series to highlight the clinical and biochemical features of PHA-1. METHODS: A retrospective chart review of patients diagnosed with transient PHA-1 at a tertiary children's hospital in Western Australia was conducted. RESULTS: Five male infants (32 days to 6 months) with transient PHA-1 were identified. Failure to thrive was the most common symptom with hyponatraemia on presentation. Two infants had antenatally diagnosed bilateral hydronephrosis and urinary tract infection (UTI) on admission. Two infants were treated for congenital adrenal hyperplasia and received hydrocortisone. All infants had UTI and required parenteral antibiotics. The condition was transient and hyponatraemia corrected by day 4 in all infants. There was no correlation between plasma sodium and aldosterone levels. The severity of PHA-1 was independent of the underlying renal anomaly. Four infants had hydronephrosis and vesicoureteric reflux. Surgical intervention was required in two infants. CONCLUSIONS: PHA-1 may be precipitated by UTI or urinary tract anomalies in early infancy. Urine analysis should be performed in infants with hyponatraemia. Diagnosis of PHA-1 facilitates appropriate renal investigations to reduce long-term morbidity.

Development of enzyme-linked immunosorbent assays for urinary thiazide-sensitive Na-Cl cotransporter measurement.

The Na-Cl cotransporter (NCC) in the distal convoluted tubules in kidney is known to be excreted in urine. However, its clinical significance has not been established because of the lack of quantitative data on urinary NCC. We developed highly sensitive enzyme-linked immunosorbent assays (ELISAs) for urinary total NCC (tNCC) and its active form, phosphorylated NCC (pNCC). We first measured the excretion of tNCC and pT55-NCC in urinary exosomes in pseudohypoaldosteronism type II (PHAII) patients since PHAII is caused by NCC activation. Highly increased excretion of tNCC and pNCC was observed in PHAII patients. In contrast, the levels of tNCC and pNCC in the urine of patients with Gitelman's syndrome were not detectable or very low, indicating that both assays could specifically detect the changes in urinary NCC excretion caused by the changes of NCC activity in the kidney. Then, to test whether these assays could be feasible for a more general patient population, we measured tNCC and pNCC in the urine of outpatients with different clinical backgrounds. Although urinary protein levels >30 mg/dl interfered with our ELISA, we could measure urinary pNCC in all patients without proteinuria. Thus we established highly sensitive and quantitative assays for urinary NCC, which could be valuable tools for estimating NCC activity in vivo.

Increased urinary Na-Cl cotransporter protein in familial hyperkalaemia and hypertension.

BACKGROUND: Familial hyperkalaemia and hypertension (FHH), also termed pseudohypoaldosteronism type II, is a rare monogenic form of hypertension caused by mutations in the WNK1 or WNK4 kinases. In vitro expression of WNK4 reduces surface abundance and activity of coexpressed NaCl cotransporter (NCCT). This effect is lost in disease-producing WNK4 mutants. In two mice models of FHH, one expressing two extra copies of mutant WNK4 (Q562E) and another in which a mutant (D561A) WNK4 replaced wild-type WNK4, renal distal tubule hyperplasia with overexpression of NCCT was found. Currently no FHH human renal tissue is available to test for increased distal tubule surface abundance of NCCT. The availability of a unique large family with FHH and the Q565E WNK4 mutation enabled us to investigate this issue in an indirect manner. METHODS: Assuming that shedding of NCCT to the urine reflects its abundance in the distal tubule epithelium, we measured urinary NCCT protein in eight subjects of the FHH family and in eight unrelated controls by western blotting. RESULTS: Urinary NCCT protein was about four times higher in FHH than in controls [111.1 +/- 40.5 versus 26.1 +/- 16.4 densitometry units (P < 0.0001)]. No significant difference in urinary sodium and potassium concentrations was seen between FHH and controls. CONCLUSIONS: The increased urinary NCCT in FHH most probably reflects increased NCCT abundance in the apical membrane of distal tubule cells in patients with FHH and the WNK4 mutation and points to the pathogenetic mechanism for the clinical phenotype of FHH and the WNK4 mutation, supporting results in transgenic mice with the same mutation and in knockin mice with another mutation.

Familial Hyperkalemia and Hypertension (FHHt) and KLHL3: Description of a Family with a New Recessive Mutation (S553L) Compared to a Family with a Dominant Mutation, Q309R, with Analysis of Urinary Sodium Chloride Cotransporter.

BACKGROUND: Familial hyperkalemia and hypertension (FHHt) is an inherited disorder manifested by hyperkalemia and hypertension. The following four causative genes were identified: WNK1, WNK4, CUL3, and KLHL3. For the first 3 genes, inheritance is autosomal dominant. For KLHL3, inheritance is mostly dominant. A few cases with autosomal recessive disease were described. The mechanism of these 2 modes of inheritance is not clear. In the recessive form, the phenotype of heterozygotes is not well described. METHODS: Clinical and genetic investigation of members of 2 families was performed, one with recessive FHHt, and the other, an expansion of a family with Q309R KLHL3 dominant mutation, previously reported by us. Urinary exosomal sodium chloride cotransporter (NCC) was measured. RESULTS: A family with recessive FHHt caused by a new KLHL3 mutation, S553L, is described. This consanguineous Jewish family of Yemenite extraction, included 2 homozygous and 7 heterozygous affected subjects. Increased urinary NCC was found in the affected members of the family with dominant Q309R KLHL3 mutation. In the recessive S553L family, homozygotes appeared to have increased urinary NCC abundance. Surprisingly, heterozygotes seemed to have also increased urinary NCC, though at an apparently lower degree. This was not accompanied by a clinical phenotype. CONCLUSIONS: A new recessive mutation in KLHL3 (S553L) was identified in FHHt. Increased urinary NCC was found in affected members (heterozygous) with dominant KLHL3 Q309R, and in affected members (homozygous) of the recessive form. Unexpectedly, in the recessive disease, heterozygotes seemed to have increased urinary NCC as well, apparently not sufficient quantitatively to produce a clinical phenotype.

Urinary steroid profile of a newborn suffering from pseudohypoaldosteronism.

A case is described of a newborn, admitted to hospital because of severe salt loss at the age of 1 month. Subsequent analysis of urinary steroid excretion, by gas chromatography and gas chromatography-mass spectrometry, revealed that the patient suffered from pseudohypoaldosteronism. However, it was difficult to interpret the results unambiguously, since the first urinary analysis appeared to suggest 21-hydroxylase- or 18-hydroxylase deficiency. The final diagnosis was possible only after detecting high urinary levels of aldosterone and tetrahydroaldosterone. It is concluded that neonatal urinary steroid profiles should be interpreted cautiously in order to arrive at the correct diagnosis.

Presumptive pseudohypoaldosteronism secondary to chronic urinary tract obstruction from sloughed urinary bladder mucosa and urinary tract infection in a cat.

OBJECTIVE: To describe a case of presumptive secondary pseudohypoaldosteronism (PHA) in a cat with urinary tract infection and chronic urethral obstruction. The obstruction was believed to have resulted from sloughed urinary bladder mucosa secondary to pressure necrosis. CASE SUMMARY: A 5-year-old, 4 kg, castrated male Siamese cat presented for vomiting and stranguria. Medical history included a perineal urethrostomy for urethral obstruction. Physical examination revealed a large, painful, nonexpressible urinary bladder. Point-of-care testing demonstrated electrolyte derangements consistent with a postrenal azotemia and metabolic acidosis. Results of urine culture was positive for bacterial growth. Diagnostic imaging revealed presence of retroperitoneal fluid, marked urinary bladder wall thickening, bilateral hydroureter, mild bilateral pyelectasia, and small nephroliths. The patient was treated for a urinary tract obstruction and infection. In the 3 weeks following initial discharge, the patient was evaluated on multiple occasions for lethargy, intermittent vomiting, inappropriate urination, and progressive polyuria and polydipsia. Although the urinary bladder was easily expressed during repeat examinations, it was persistently distended and subjectively thickened upon palpation. Repeat ultrasound of the urinary tract showed evidence of sloughed tissue in the bladder lumen, likely secondary to chronic urethral obstruction and pressure necrosis. A cystotomy was performed to remove the necrotic tissue, and a revised perineal urethrostomy was done due to a partial urethral stricture. Bladder biopsies were obtained at this time. Postoperatively, the cat was reported by the owners to be urinating normally but continued to be polyuric and polydipsic in the week following discharge. One week after surgery, the cat presented in hypovolemic shock with laboratory findings consistent with a presumptive diagnosis of secondary PHA. NEW OR UNIQUE INFORMATION PROVIDED: PHA has not been reported previously in a cat. This case report suggests that aldosterone resistance should be considered in cats with consistent laboratory findings and a history of documented obstructive uropathy and urinary tract infection.

Shakuyaku-kanzo-to induces pseudoaldosteronism characterized by hypokalemia, rhabdomyolysis, metabolic alkalosis with respiratory compensation, and increased urinary cortisol levels.

BACKGROUND: Licorice, the primary ingredient of the Japanese herbal medicine shakuyaku-kanzo-to, can cause pseudoaldosteronism. Thus, shakuyaku-kanzo-to can cause this condition. CASE DESCRIPTION: A 79-year-old woman was brought to the emergency room. She had been experiencing general fatigue, numbness in the hands, and weakness in the lower limbs and could not stand up without assistance. She presented with hypokalemia (potassium level, 1.7 mEq/L), increased urinary excretion of potassium (fractional excretion of K, 21.2%), abnormalities on an electrocardiogram (flat T waves in II, III, AVF, and V1-6), rhabdomyolysis (creatine kinase level, 28,376 U/L), myopathy, metabolic alkalosis with respiratory compensation (O(2) flow rate, 2 L/min; pH, 7.473; pco(2), 61.0 mm Hg; po(2), 78.0 mm Hg; HCO(3), 44.1 mmol/L), hypertension (174/93 mm Hg), hyperglycemia (blood glucose level, 200-300 mg/dL), frequent urination, suppressed plasma renin activity (0.1 ng/mL/hour), decreased aldosterone levels (2.6 ng/dL), and increased urinary cortisol levels (600.6 microg/day; reference range, 26.0-187.0 microg/day). CONCLUSIONS: In this case, the observed reduction in the urinary cortisol levels, from 600.6 to 37.8 microg/day, led to a definitive diagnosis of pseudoaldosteronism instead of the apparent mineralocorticoid excess syndrome. Discontinuing shakuyaku-kanzo-to treatment and administering spironolactone and potassium proved effective in improving the patient's condition. Medical practitioners prescribing shakuyaku-kanzo-to should take into account the association between licorice, which is its main ingredient, and pseudoaldosteronism.

Nephrocalcinosis in pseudohypoaldosteronism and the effect of indomethacin therapy.

We report four patients with pseudohypoaldosteronism, aged 5 months to 5 years. All patients had hypercalciuria and three had nephrocalcinosis. Two patients with nephrocalcinosis were treated with indomethacin. Polydipsia decreased and appetite and weight gain improved within 14 days of therapy. Hypercalciuria, polyuria, and creatinine clearance decreased 30% to 50% and urinary prostaglandin E2 levels decreased fourfold to eightfold.

Erythrocyte transmembrane Na and K fluxes in pseudohypoaldosteronism.

Pseudohypoaldosteronism (PHA) is a disease characterized by hyponatremia, hypotension, and dehydratation, despite the presence of hyperreninemic hyperaldosteronism. The membrane-bound Na,K ATPase activity and the transmembrane Na and K transport systems have been studied in vitro in red blood cells of two subjects, son and mother, affected by pseudohypoaldosteronism with different degrees of clinical involvement. Both parameters were significantly altered suggesting that the refractory response to mineralocorticoids is detectable, not only in kidneys and salivary and sweat glands, but also in red blood cells. Since pseudohypoaldosteronism, in its asymptomatic form, may be much more common than expected, we suggest the use of the tests described herein as a practical approach to the early diagnosis of pseudohypoaldosteronism in the investigation of sodium wasting syndromes.

Furosemide and dDAVP for the treatment of pseudohypoaldosteronism type II.

A 27-year-old Turkish male presented with fatigue, long lasting hypertension, hyperkalemia, hyperchloremic metabolic acidosis and normal glomerular filtration rate. His brother also showed hyperkalemia with no other features of the disease. Plasma renin levels were low and serum aldosterone levels were inappropriately low-normal to his hyperkalemia. Plasma cortisol levels were normal. Plasma renin aldosterone levels responded appropriately to postural changes, salt restriction and saline infusion. Fludrocortisone was ineffective in his hyperkalemia. The conditions were consistent with Type II pseudohypoaldosteronism (PHA). Furosemide and sodium bicarbonate were effective to control his hyperchloremia, metabolic acidosis and hypertension but partly effective for his hyperkalemia. dDAVP alone did not control the situation and hypertension and metabolic derangement reoccurred. Adding dDAVP to furosemide and sodium bicarbonate successfully controlled hyperkalemia, hyperchloremic acidosis and hypertension. The patient stayed normotensive with normal metabolic and biochemical parameters after 6 months with furosemide and dADVP although sodium bicarbonate had been discontinued after the first month of therapy. dDAVP is a useful adjunct to furosemide and non chloride anions which altogether successfully reverse the metabolic derangement in Type II PHA.

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.

Effect of hydrochlorothiazide in pseudohypoaldosteronism with hypercalciuria and severe hyperkalemia.

Severe hyperkalemia resistant to treatment with sodium chloride (NaCl) supplements plus cation exchange resins can be found in pseudohypoaldosteronism type I. In a patient with the multiple target organ variant of this condition, hyperkalemia persisted at dangerous levels (8.5 mmol/l) despite large doses of NaCl (50 mmol/kg per day) and cation exchange resins (6 g/kg per day). Hypercalciuria was also present. The total volume of fluids and supplements required was not tolerated orally. Indomethacin (2 mg/kg per day) and later hydrochlorothiazide (2 mg/kg per day) were tried to further correct imbalance. Plasma potassium (K) and Na levels, the urinary Na/K ratio, transtubular potassium gradient (TTKG), and urinary calcium/creatinine (Ca/Cr) ratio were used to evaluate the effect of hydrochlorothiazide. Under treatment, plasma Na was stable (137-144 mmol/l), K levels decreased from 8.5 to 5 mmol/l, urinary Na/K from 90 to 24, and TTKG increased from 0.3 to 1.8. Ca/Cr decreased from 3.5 to 1.5 mmol/mmol. The dosage of cation exchange resins was decreased, oral fluids were tolerated, and the patient's general condition improved. Hence: hydroclorothiazide can be useful in the treatment of severe hyperkalemia and hypercalciuria of pseudohypoaldosteronism type I.