Familial hyperkalemia and hypertension: pathogenetic insights based on lithium clearance

Gordon's syndrome in pregnancy

Gordon's syndrome, also known as pseudohypoaldosteronism type II and familial hyperkalaemic hypertension, is a rare inherited condition characterised by familial hyperkalaemia, normal anion gap hyperchloraemic metabolic acidosis, low renin with normal glomerular filtration rate and hypertension. The outcome of 11 pregnancies in 3 women with Gordon's syndrome is presented and combined with 13 pregnancies in 7 women previously described. Pregnancy in women with Gordon's syndrome appears to be associated with a significant risk of adverse pregnancy outcomes, particularly where there is maternal hypertension preconception. No pregnancy registry exists for Gordon's syndrome. The available data is limited to case reports and small case series and may be affected by bias. A pregnancy registry would be valuable to assist in preconception counselling and management during pregnancy. The goal of this study was to summarise the available cases describing pregnancy outcomes with maternal Gordon's syndrome.

A young child with pseudohypoaldosteronism type II by a mutation of Cullin 3

BACKGROUND

Pseudohypoaldosteronism type II (PHA II), also referred to as Gordon syndrome, is a rare renal tubular disease that is inherited in an autosomal manner. Though mutations in WNK1 and WNK4 partially account for this disorder, in 2012, 2 research groups showed that KLHL3 and CUL3 were the causative genes for PHA II. Here, we firstly report on the Japanese child of PHA II caused by a mutation of CUL 3.

CASE PRESENTATION

The patient was a 3-year-old Japanese girl having healthy unrelated parents. She was initially observed to have hyperkalemia, hyperchloremia, metabolic acidosis, and hypertension. A close investigation led to the diagnosis of PHA II, upon which abnormal findings of laboratory examinations and hypertension were immediately normalized by administering thiazides. Genetic analysis of WNK1 and WNK4 revealed no mutations. However, analysis of the CUL3 gene of the patient showed abnormal splicing caused by the modification of exon 9. The patient is currently 17 years old and does not exhibit hypertension or any abnormal findings on laboratory examination.

CONCLUSIONS

In this patient, CUL3 was found to play a fundamental role in the regulation of blood pressure, potassium levels, and acid-base balance.

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

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

Cyclosporine metabolic side effects: association with the WNK4 system

BACKGROUND

Cyclosporine is used for treatment of transplanted patients and for immune-mediated diseases. Cyclosporine is known to cause a combination of metabolic side effects including hypertension, hyperkalemia, hypercalciuria and hypomagnesemia. These side effects except for hypomagnesemia are the cardinal features of familial hyperkalemia and hypertension (FHHt), also called pseudohypoaldosteronism type II (PHA II). FHHt is caused by mutations in the kinases WNK1 and WNK4 resulting in an increase in renal Na-Cl cotransporter (NCC) apical distribution and function. Therefore, we studied whether cyclosporine's metabolic side effects are mediated by WNK4 and NCC.

DESIGN

Sprague-Dawley (SD) rats were treated by cyclosporine 25 mg kg(-1) subcutaneously for 14 days. Blood pressure, blood chemistry values and kidney WNK4 protein were determined. In addition, mDCT cells were exposed to cyclosporine, and their WNK4 mRNA and protein content, and their NCC protein content and phosphorylation were determined.

RESULTS

The rats developed an FHHt-like syndrome including hypertension, hyperkalemia and salt-sensitive hypercalciuria. A significant increase in their kidney WNK4 protein content (0·13 ± 0·01 vs. 0·67 ± 0·16 WNK4/GAPDH in controls, P = 0·0183) was found. In mDCT cells, cyclosporine caused a rise in WNK4 mRNA levels and also a threefold rise in WNK4 protein content. This rise was followed by a rise in NCC protein content and pSer71 phosphorylation.

CONCLUSIONS

These observations may explain in part the mechanism of cyclosporine-induced hypertension, hyperkalemia and hypercalciuria.

Familial or genetic primary aldosteronism and Gordon syndrome

Salt-sensitive forms of hypertension have received considerable renewed attention in recent years. This article focuses on 2 main forms of salt-sensitive hypertension (familial or genetic primary aldosteronism [PA] and Gordon syndrome) and the current state of knowledge regarding their genetic bases. The glucocorticoid-remediable form of familial PA (familial hyperaldosteronism type I) is dealt with only briefly because it is covered in depth elsewhere.

Mechanisms for hypercalciuria in pseudohypoaldosteronism type II-causing WNK4 knock-in mice

The mechanisms underlying hypercalciuria in pseudohypoaldosteronism type II (PHAII) caused by WNK4 mutations remain unclear. In this study, we used Wnk4(D561A/+) knock-in mice as a model of human PHAII for investigating the pathogenesis of hypercalciuria in PHAII. Serum and urine biochemistries were obtained from Wnk4(+/+) and Wnk4(D561A/+) littermates. Expression of the epithelial Ca(2+) channels [transient receptor potential channel vanilloid subtype 5 (TRPV5) and TRPV6] and calbindin-D28k (CBP-D28k) in the distal nephron and two upstream Na(+) transporters, Na(+)/H(+) exchanger 3 and Na(+)-K(+)-2Cl(-) cotransporter 2 involved in paracellular Ca(2+) reabsorption, were examined by real-time PCR, immunofluorescent staining, and immunoblotting. Compared with Wnk4(+/+) littermate controls, Wnk4(D561A/+) mice manifested hypercalciuria despite no significant differences in serum creatinine, ionized Ca(2+), PTH, and 1,25 hydroxylvitamin D(3) levels. There was no significant difference in TRPV5 expression, but a significant increase in TRPV6 and CBP-D28k was observed in Wnk4(D561A/+) mice. Despite no significant change in Na(+)/H(+) exchanger 3 expression, Na(+)-K(+)-2Cl(-) cotransporter 2 expression was significantly attenuated and urine Ca(2+) excretion rate in response to furosemide was blunted in Wnk4(D561A/+) mice. Decreased Ca(2+) reabsorption in the upstream nephron, especially in the thick ascending loops of Henle, with a secondary adaptive increase in TRPV6 and CBP-D28k expression in the distal tubules might be involved in the hypercalciuria of PHAII.