Genetic Markers Regulating Blood Pressure in Extreme Discordant Sib Pairs.

Genome-wide scans performed in affected sib pairs have revealed small and often inconsistent clues to the loci responsible for the inherited components of hypertension. Since blood pressure is a quantitative trait regulated by many loci, two siblings at opposite extremes of the blood pressure distribution are more likely to have inherited different alleles at any given locus. Hence, we investigated an extreme discordant sib pair strategy to analyse markers from two previous loci of interest: (1) the Gordons syndrome locus that includes the WNK4 gene and (2) the ROMK locus identified in our first genome-wide scan. For this study, 24 sib pairs with strong family histories of essential hypertension were selected from the top and bottom 10% of the blood pressure distribution and genotyped for highly polymorphic microsatellite markers on chromosomes 11 and 17. The mean age of the population was 39.8 ± 7.8 years. A significant inverse correlation was found between the squared difference in pulse pressure and the number of alleles shared by IBD between the siblings for the DS11925 marker (r = -0.44, p = 0.031), systolic pressure and chromosome 17 markers (D17S250: r = -0.42, p = 0.040; D17S799 (r = -0.51, p = 0.011), and this relationship persisted after correcting for age and gender. Markers on chromosome 17 (D17S250, D17S928 and D17S1301) and 11 (D11S1999) also correlated with diastolic pressure. These results illustrate the successful use of discordant sib pair analysis to detect linkage within relatively small numbers of pedigrees with hypertension. Further analysis of this cohort may be valuable in complementing findings from the large genome wide scans in affected sib pairs.

Nonadherence to antihypertensive medications amongst patients with uncontrolled hypertension: A retrospective study.

ABSTRACT: Medication nonadherence represents a modifiable risk factor for patients with hypertension. Identification of nonadherent patients could have significant clinical and economic implications in the management of uncontrolled hypertension.We analysed the results of 174 urinary adherence screens from patients referred to Addenbrooke's Hospital, Cambridge, for uncontrolled hypertension. Cases were identified for evaluation by results of liquid chromatography-tandem mass spectrometry of urine samples (males: 91; females: 83; age range: 17-87). We performed a binary logistic regression analysis for nonadherence using age, sex, and number of medications prescribed (both antihypertensives and non-antihypertensives separately) as independent predictors. Rates of nonadherence for individual antihypertensive drugs were calculated if prescribed to ≥10 patients.The overall rate of nonadherence to one or more prescribed antihypertensive medications was 40.3%. 14.4% of all patients were nonadherent to all prescribed antihypertensive medications (complete nonadherence), whereas 25.9% of all patients were nonadherent to at least 1, (but not all) prescribed antihypertensive medications (partial nonadherence). 72% of patients were prescribed ≥3 antihypertensives And for every increase in the number of antihypertensive medications prescribed, nonadherence increased with adjusted odds ratios of 2.9 (P < .001). Logistic regression showed that women were 3.3 times more likely to be nonadherent (P = .004). Polypharmacy (≥6 medications prescribed for hypertension and/or concomitant comorbidities) was prevalent in 52%. Bendroflumethiazide and chlortalidone demonstrated the highest and lowest nonadherences respectively (45.5% and 11.8%).Rate of nonadherence in patients with hypertension was significantly impacted by sex and number of antihypertensive medications prescribed. Understanding these factors is crucial in identifying and managing nonadherence.

Modified HEK cells simulate DCT cells in their sensitivity and response to changes in extracellular K.

A potassium (K+ ) rich diet is known to have an antihypertensive effect that has been embodied by the NHLBI in the DASH diet. However, the molecular basis for this blood pressure-lowering effect has been unclear, until a recent study proposed a model in which the DCT cells of the kidney regulate their salt transport in response to variations in intracellular chloride ([Cl- ]i ), which are directly regulated by serum K+ . With the knowledge that WNK proteins are Cl- sensors, and are a part of the WNK/SPAK/NCC signaling cascade which regulates the NCC, the main salt transporter in the distal nephron, we examined the effect of serum K+ on the ([Cl- ]i ) and, in turn its effect on the WNK4 signaling pathway in a "modified HEK 293T" cell line. Using a fluorescence-based approach in this cell line, we have shown that the membrane potential of the cell membrane is sensitive to the small changes in external KCl within the physiological range (2-5 mM), thus functioning as a K+ electrode. When the extracellular K+ was progressively increased (2-5 mM), the membrane depolarization lead to a subsequent increase in [Cl- ]i measured by fluorescence quenching of an intracellular chloride sensor. Increase in extracellular [K] resulted in a decrease in the phosphorylation of the WNK4 protein and its downstream targets, SPAK and NCC. This confirms that small changes in serum K can affect WNK4/SPAK/NCC signaling and transcellular Na+ flux through the DCT and provide a possible mechanism by which a K-rich DASH diet could reduce blood pressure.

ß1-Adrenoreceptor Polymorphisms and Blood Pressure: 49S Variant Increases Plasma Renin But Not Blood Pressure in Hypertensive Patients.

BACKGROUND: Activation of beta-1 adrenoreceptor (ß1-AR) in the kidney releases renin that plays a major role in the maintenance of blood pressure. Genetic variation in ß1-AR could therefore alter the physiological and clinical effects of this hormone. We tested this hypothesis in patients from a primary care cohort being screened for primary hyperaldosteronism (n = 467). METHODS: Demographic and hemodynamic data were measured and plasma renin was determined by a standard immunoassay. Subjects were genotyped for the 2 common single-nucleotide polymorphisms Arg389Gly (rs1801253) and Ser49Gly (rs1801252), and thus the 4 possible haplotypes in ß1-AR gene. RESULTS: In patients being screened for hyperaldosteronism, plasma renin was significantly elevated in Ser49 homozygotes (49SS) compared with Gly49 (49G) allele carriers (0.307 ± 0.03 vs. 0.164 ± 0.05; P = 0.01). However, this did not translate into differences in either blood pressure or heart rate. On the other hand, the Arg389Gly polymorphism did not affect either plasma renin or blood pressure in this group. There was also no evidence that the 2 loci were linked in this group of patients. CONCLUSION: These data suggest that in this cohort the Ser49 variant of the Ser49Gly ß1-AR gene polymorphism associates with higher renin levels. However, these common ß1-AR gene polymorphisms do not affect blood pressure in the same cohort.

The matrix proteins aggrecan and fibulin-1 play a key role in determining aortic stiffness.

Stiffening of the aorta is an important independent risk factor for myocardial infarction and stroke. Yet its genetics is complex and little is known about its molecular drivers. We have identified for the first time, tagSNPs in the genes for extracellular matrix proteins, aggrecan and fibulin-1, that modulate stiffness in young healthy adults. We confirmed SNP associations with ex vivo stiffness measurements and expression studies in human donor aortic tissues. Both aggrecan and fibulin-1 were found in the aortic wall, but with marked differences in the distribution and glycosylation of aggrecan reflecting loss of chondroitin-sulphate binding domains. These differences were age-dependent but the striking finding was the acceleration of this process in stiff versus elastic young aortas. These findings suggest that aggrecan and fibulin-1 have critical roles in determining the biomechanics of the aorta and their modification with age could underpin age-related aortic stiffening.

Targeted disruption of the Kcnj5 gene in the female mouse lowers aldosterone levels.

Aldosterone is released from adrenal zona glomerulosa (ZG) cells and plays an important role in Na and K homoeostasis. Mutations in the human inwardly rectifying K channel CNJ type (KCNJ) 5 (KCNJ5) gene encoding the G-coupled inwardly rectifying K channel 4 (GIRK4) cause abnormal aldosterone secretion and hypertension. To better understand the role of wild-type (WT) GIRK4 in regulating aldosterone release, we have looked at aldosterone secretion in a Kcnj5 knockout (KO) mouse. We found that female but not male KO mice have reduced aldosterone levels compared with WT female controls, but higher levels of aldosterone after angiotensin II (Ang-II) stimulation. These differences could not be explained by sex differences in aldosterone synthase (Cyp11B2) gene expression in the mouse adrenal. Using RNAseq analysis to compare WT and KO adrenals, we showed that females also have a much larger set of differentially expressed adrenal genes than males (395 compared with 7). Ingenuity Pathway Analysis (IPA) of this gene set suggested that peroxisome proliferator activated receptor (PPAR) nuclear receptors regulated aldosterone production and altered signalling in the female KO mouse, which could explain the reduced aldosterone secretion. We tested this hypothesis in H295R adrenal cells and showed that the selective PPARα agonist fenofibrate can stimulate aldosterone production and induce Cyp11b2. Dosing mice in vivo produced similar results. Together our data show that Kcnj5 is important for baseline aldosterone secretion, but its importance is sex-limited at least in the mouse. It also highlights a novel regulatory pathway for aldosterone secretion through PPARα that may have translational potential in human hyperaldosteronism.

Phenotypic and pharmacogenetic evaluation of patients with thiazide-induced hyponatremia.

Thiazide diuretics are among the most widely used treatments for hypertension, but thiazide-induced hyponatremia (TIH), a clinically significant adverse effect, is poorly understood. Here, we have studied the phenotypic and genetic characteristics of patients hospitalized with TIH. In a cohort of 109 TIH patients, those with severe TIH displayed an extended phenotype of intravascular volume expansion, increased free water reabsorption, urinary prostaglandin E2 excretion, and reduced excretion of serum chloride, magnesium, zinc, and antidiuretic hormone. GWAS in a separate cohort of 48 TIH patients and 2,922 controls from the 1958 British birth cohort identified an additional 14 regions associated with TIH. We identified a suggestive association with a variant in SLCO2A1, which encodes a prostaglandin transporter in the distal nephron. Resequencing of SLCO2A1 revealed a nonsynonymous variant, rs34550074 (p.A396T), and association with this SNP was replicated in a second cohort of TIH cases. TIH patients with the p.A396T variant demonstrated increased urinary excretion of prostaglandin E2 and metabolites. Moreover, the SLCO2A1 phospho-mimic p.A396E showed loss of transporter function in vitro. These findings indicate that the phenotype of TIH involves a more extensive metabolic derangement than previously recognized. We propose one mechanism underlying TIH development in a subgroup of patients in which SLCO2A1 regulation is altered.

WNK signalling pathways in blood pressure regulation.

Hypertension (high blood pressure) is a major public health problem affecting more than a billion people worldwide with complications, including stroke, heart failure and kidney failure. The regulation of blood pressure is multifactorial reflecting genetic susceptibility, in utero environment and external factors such as obesity and salt intake. In keeping with Arthur Guyton's hypothesis, the kidney plays a key role in blood pressure control and data from clinical studies; physiology and genetics have shown that hypertension is driven a failure of the kidney to excrete excess salt at normal levels of blood pressure. There is a number of rare Mendelian blood pressure syndromes, which have shed light on the molecular mechanisms involved in dysregulated ion transport in the distal kidney. One in particular is Familial hyperkalemic hypertension (FHHt), an autosomal dominant monogenic form of hypertension characterised by high blood pressure, hyperkalemia, hyperchloremic metabolic acidosis, and hypercalciuria. The clinical signs of FHHt are treated by low doses of thiazide diuretic, and it mirrors Gitelman syndrome which features the inverse phenotype of hypotension, hypokalemic metabolic alkalosis, and hypocalciuria. Gitelman syndrome is caused by loss of function mutations in the thiazide-sensitive Na/Cl cotransporter (NCC); however, FHHt patients do not have mutations in the SCL12A3 locus encoding NCC. Instead, mutations have been identified in genes that have revealed a key signalling pathway that regulates NCC and several other key transporters and ion channels in the kidney that are critical for BP regulation. This is the WNK kinase signalling pathway that is the subject of this review.

A missense TGFB2 variant p.(Arg320Cys) causes a paradoxical and striking increase in aortic TGFB1/2 expression.

Loeys-Dietz syndrome (LDS) is an autosomal dominant connective tissue disorder with a range of cardiovascular, skeletal, craniofacial and cutaneous manifestations. LDS type 4 is caused by mutations in TGFß ligand 2 (TGFB2) and based on the family pedigrees described to date, appears to have a milder clinical phenotype, often presenting with isolated aortic disease. We sought to investigate its molecular basis in a new pedigree. We identified a missense variant p.(Arg320Cys) (NM_003238.3) in a highly evolutionary conserved region of TGFB2 in a new LDS type 4 pedigree with multiple cases of aortic aneurysms and dissections. There was striking upregulation of TGFB1 and TGFB2 expression on immunofluorescent staining, and western blotting of the aortic tissue from the index case confirming the functional importance of the variant. This case highlights the striking paradox of predicted loss-of-function mutations in TGFB2 causing enhanced TGFß signaling in this emerging familial aortopathy.

ROMK expression remains unaltered in a mouse model of familial hyperkalemic hypertension caused by the CUL3Δ403-459 mutation.

Familial hyperkalemic hypertension (FHHt) is a rare inherited form of salt-dependent hypertension caused by mutations in proteins that regulate the renal Na(+)-Cl(-) cotransporter NCC Mutations in four genes have been reported to cause FHHt including CUL3 (Cullin3) that encodes a component of a RING E3 ligase. Cullin-3 binds to WNK kinase-bound KLHL3 (the substrate recognition subunit of the ubiquitin ligase complex) to promote ubiquitination and proteasomal degradation of WNK kinases. Deletion of exon 9 from CUL3 (affecting residues 403-459, CUL3(Δ403-459)) causes a severe form of FHHt (PHA2E) that is recapitulated closely in a knock-in mouse model. The loss of functionality of CUL3(Δ403-459) and secondary accumulation of WNK kinases causes substantial NCC activation. This accounts for the hypertension in FHHt but the origin of the hyperkalemia is less clear. Hence, we explored the impact of CUL3(Δ403-459) on expression of the distal secretory K channel, ROMK, both in vitro and in vivo. We found that expressing wild-type but not the CUL3(Δ403-459) mutant form of CUL3 prevented the suppression of ROMK currents by WNK4 expressed in Xenopus oocytes. The mutant CUL3 protein was also unable to affect ROMK-EGFP protein expression at the surface of mouse M-1 cortical collecting duct (CCD) cells. The effects of CUL3 on ROMK expression in both oocytes and M-1 CCD cells was reduced by addition of the neddylation inhibitor, MLN4924. This confirms that neddylation is important for CUL3 activity. Nevertheless, in our knock-in mouse model expressing CUL3(Δ403-459) we could not show any alteration in ROMK expression by either western blotting whole kidney lysates or confocal microscopy of kidney sections. This suggests that the hyperkalemia in our knock-in mouse and human PHA2E subjects with the CUL3(Δ403-459) mutation is not caused by reduced ROMK expression in the distal nephron.

Novel Insertion Mutation in KCNJ5 Channel Produces Constitutive Aldosterone Release From H295R Cells.

Primary aldosteronism accounts for 5%-10% of hypertension and in a third of cases is caused by autonomous aldosterone production by adenomas (APA). Somatic mutations in the potassium channel encoded by KCNJ5 have been detected in surgically removed APAs. To better understand the role of these mutations, we resequenced the KCNJ5 channel in a large Australian primary aldosteronism cohort. KCNJ5 mutations were detected in 37 APAs (45% of the cohort), including previously reported E145Q (n = 3), G151R (n = 20), and L168R (n = 13) mutations. In addition, we found a novel 12-bp in-frame insertion mutation (c.414-425dupGCTTTCCTGTTC, A139_F142dup) that duplicates the AFLF sequence in the pore helix upstream of the selectivity filter. Expressed in Xenopus oocytes, the A139_F142dup mutation depolarized the oocytes and produced a G-protein-sensitive Na(+) current with altered K(+) selectivity and loss of inward rectification but retained Ba(2+) sensitivity. Transfected into H295R cells, A139_F142dup increased basal aldosterone release 2.3-fold over the wild type. This was not increased further by incubation with angiotensin II. Although the A139_F142dup mutant trafficked to the plasma membrane of H295R cells, it showed reduced tetramer stability and surface expression compared with the wild-type channel. This study confirms the frequency of somatic KCNJ5 mutations in APAs and the novel mutation identified (A139_F142dup) extend the phenotypic range of the known KCNJ5 APA mutations. Being located in the pore helix, it is upstream of the previously reported mutations and shares some features in common with selectivity filter mutants but additionally demonstrates insensitivity to angiotensin II and decreased channel stability.

Characterisation of the Cullin-3 mutation that causes a severe form of familial hypertension and hyperkalaemia.

Deletion of exon 9 from Cullin-3 (CUL3, residues 403-459: CUL3(Δ403-459)) causes pseudohypoaldosteronism type IIE (PHA2E), a severe form of familial hyperkalaemia and hypertension (FHHt). CUL3 binds the RING protein RBX1 and various substrate adaptors to form Cullin-RING-ubiquitin-ligase complexes. Bound to KLHL3, CUL3-RBX1 ubiquitylates WNK kinases, promoting their ubiquitin-mediated proteasomal degradation. Since WNK kinases activate Na/Cl co-transporters to promote salt retention, CUL3 regulates blood pressure. Mutations in both KLHL3 and WNK kinases cause PHA2 by disrupting Cullin-RING-ligase formation. We report here that the PHA2E mutant, CUL3(Δ403-459), is severely compromised in its ability to ubiquitylate WNKs, possibly due to altered structural flexibility. Instead, CUL3(Δ403-459) auto-ubiquitylates and loses interaction with two important Cullin regulators: the COP9-signalosome and CAND1. A novel knock-in mouse model of CUL3(WT) (/Δ403-459) closely recapitulates the human PHA2E phenotype. These mice also show changes in the arterial pulse waveform, suggesting a vascular contribution to their hypertension not reported in previous FHHt models. These findings may explain the severity of the FHHt phenotype caused by CUL3 mutations compared to those reported in KLHL3 or WNK kinases.

Critical role of the SPAK protein kinase CCT domain in controlling blood pressure.

The STE20/SPS1-related proline/alanine-rich kinase (SPAK) controls blood pressure (BP) by phosphorylating and stimulating the Na-Cl (NCC) and Na-K-2Cl (NKCC2) co-transporters, which regulate salt reabsorption in the kidney. SPAK possesses a conserved carboxy-terminal (CCT) domain, which recognises RFXV/I motifs present in its upstream activator [isoforms of the With-No-lysine (K) kinases (WNKs)] as well as its substrates (NCC and NKCC2). To define the physiological importance of the CCT domain, we generated knock-in mice in which the critical CCT domain Leu502 residue required for high affinity recognition of the RFXI/V motif was mutated to Alanine. The SPAK CCT domain defective knock-in animals are viable, and the Leu502Ala mutation abolished co-immunoprecipitation of SPAK with WNK1, NCC and NKCC2. The CCT domain defective animals displayed markedly reduced SPAK activity and phosphorylation of NCC and NKCC2 co-transporters at the residues phosphorylated by SPAK. This was also accompanied by a reduction in the expression of NCC and NKCC2 protein without changes in mRNA levels. The SPAK CCT domain knock-in mice showed typical features of Gitelman Syndrome with mild hypokalaemia, hypomagnesaemia, hypocalciuria and displayed salt wasting on switching to a low-Na diet. These observations establish that the CCT domain plays a crucial role in controlling SPAK activity and BP. Our results indicate that CCT domain inhibitors would be effective at reducing BP by lowering phosphorylation as well as expression of NCC and NKCC2.

A systematic review and meta-analysis of thiazide-induced hyponatraemia: time to reconsider electrolyte monitoring regimens after thiazide initiation?

AIMS: Hyponatraemia is one of the major adverse effects of thiazide and thiazide-like diuretics and the leading cause of drug-induced hyponatraemia requiring hospital admission. We sought to review and analyze all published cases of this important condition. METHODS: Ovid Medline, Embase, Web of Science and PubMed electronic databases were searched to identify all relevant articles published before October 2013. A proportions meta-analysis was undertaken. RESULTS: One hundred and two articles were identified of which 49 were single patient case reports. Meta-analysis showed that mean age was 75 (95% CI 73, 77) years, 79% were women (95% CI 74, 82) and mean body mass index was 25 (95% CI 20, 30) kg m(-2) . Presentation with thiazide-induced hyponatraemia occurred a mean of 19 (95% CI 8, 30) days after starting treatment, with mean trough serum sodium concentration of 116 (95% CI 113, 120) mm and serum potassium of 3.3 (95% CI 3.0, 3.5) mm. Mean urinary sodium concentration was 64 mm (95% CI 47, 81). The most frequently reported drugs were hydrochlorothiazide, indapamide and bendroflumethiazide. CONCLUSIONS: Patients with thiazide-induced hyponatraemia were characterized by advanced age, female gender, inappropriate saliuresis and mild hypokalaemia. Low BMI was not found to be a significant risk factor, despite previous suggestions. The time from thiazide initiation to presentation with hyponatraemia suggests that the recommended practice of performing a single investigation of serum biochemistry 7-14 days after thiazide initiation may be insufficient or suboptimal. Further larger and more systematic studies of thiazide-induced hyponatraemia are required.

Gordon Syndrome: a continuing story.

Gordon Syndrome (GS) is a rare familial hypertension syndrome with a characteristic hyperkalaemia which distinguishes it from other syndromic forms of hypertension that typically cause hypokalaemia. Patients with GS respond to aggressive salt-restriction or relatively small doses of thiazide diuretics, which suggests that activation of the thiazide-sensitive Na/Cl cotransporter (NCC) in the distal nephron is to blame. However, the mechanism has proved to be complex. In 2001, mutations in genes encoding two serine/threonine kinases, WNK1 and WNK4, were identified as causing GS. However, it took several years to appreciate that these kinases operated in a cascade with downstream serine/threonine kinases (SPAK and OSR1) actually phosphorylating and activating NCC and the closely related cotransporters NKCC1 and NKCC2. The hyperkalaemia in GS arises from an independent action of WNK1/WNK4 to reduce cell-surface expression of ROMK, the secretory K-channel in the collecting ducts. However, mutations in WNK1/4 are present in a small minority of GS families, and further genes have emerged (CUL3 and KLHL3) that code for Cullin-3 (a scaffold protein in an ubiquitin-E3 ligase) and an adaptor protein, Kelch3, respectively. These new players regulate the ubiquitination and proteasomal degradation of WNK kinases, thereby adding to the complex picture we now have of NCC regulation in the distal nephron.

Role for germline mutations and a rare coding single nucleotide polymorphism within the KCNJ5 potassium channel in a large cohort of sporadic cases of primary aldosteronism.

Primary aldosteronism (autonomous aldosterone production with suppressed renin) plays an important pathophysiological role in what has been previously labeled as essential hypertension. Besides the recently described germline mutations in the KCNJ5 potassium channel associated with familial primary aldosteronism, somatic mutations in the same channel have been identified within aldosterone-producing adenomas. In this study, we have resequenced the flanking and coding region of KCNJ5 in peripheral blood DNA from 251 white subjects with primary aldosteronism to look for rare variants that might be important for the pathophysiology of sporadic primary aldosteronism. We have identified 3 heterozygous missense mutations (R52H, E246K, and G247R) in the cohort and found that 12 (5% of the cohort) were carriers for the rare nonsynonymous single nucleotide polymorphism rs7102584 causing E282Q substitution of KCNJ5. By expressing the channels in Xenopus oocytes and human adrenal H295R cells, we have shown that the R52H, E246K, and E282Q substitutions are functional, but the G247R mutation is indistinguishable from wild type. Although the functional substitutions are remote from the selectivity filter, they affect the inward-rectification, the ability of the KCNJ5 channels to conduct Na(+) currents and ATII-induced aldosterone release from the H295R cell line. Together these data suggest that germline variation in the KCNJ5 gene has a role to play in the common sporadic form as well as the much rarer syndromic forms of primary aldosteronism.

Detection of mutations in KLHL3 and CUL3 in families with FHHt (familial hyperkalaemic hypertension or Gordon's syndrome).

The study of families with rare inherited forms of hypo- and hyper-tension has been one of the most successful strategies to probe the molecular pathophysiology of blood pressure control and has revealed dysregulation of distal nephron Na+ reabsorption to be a common mechanism. FHHt (familial hyperkalaemic hypertension; also known as Gordon's syndrome) is a salt-dependent form of hypertension caused by mutations in the regulators of the thiazide-sensitive Na+-Cl- co-transporter NCC [also known as SLC12A3 (solute carrier family 12 member 3)] and is effectively treated by thiazide diuretics and/or dietary salt restriction. Variation in at least four genes can cause FHHt, including WNK1 [With No lysine (=K) 1] and WNK4, KLHL3 (kelch-like family member 3), and CUL3 (cullin 3). In the present study we have identified novel disease-causing variants in CUL3 and KLHL3 segregating in 63% of the pedigrees with previously unexplained FHHt, confirming the importance of these recently described FHHt genes. We have demonstrated conclusively, in two unrelated affected individuals, that rare intronic variants in CUL3 cause the skipping of exon 9 as has been proposed previously. KLHL3 variants all occur in kelch-repeat domains and so probably disrupt WNK complex binding. We have found no evidence of any plausible disease-causing variants within SLC4A8 (an alternative thiazide-sensitive sodium transporter) in this population. The results of the present study support the existing evidence that the CUL3 and KLHL3 gene products are physiologically important regulators of thiazide-sensitive distal nephron NaCl reabsorption, and hence potentially interesting novel anti-hypertensive drug targets. As a third of our non-WNK FHHt families do not have plausible CUL3 or KLHL3 variants, there are probably additional, as yet undiscovered, regulators of the thiazide-sensitive pathways.

Extrarenal roles of the with-no-lysine[K] kinases (WNKs).

Identified over a decade ago, the with-no-lysine[K] kinases (WNKs) have been the subsequent focus of intense research into the renal handling of Na(+) , Cl(-) and K(+) and several rare monogenetic diseases. However, the potential extrarenal roles for WNKs have been less well explored. Thiazides and Gordon syndrome are known to have effects on bone mineral density, Ca(2+) and PO4 (3-) homeostasis, which were originally assumed to be an indirect effect through the kidney. However, current data suggest a complex and direct role for WNKs in the physiology of bone. The WNKs also modulate systemic blood pressure at several levels, including the vascular resistance vessels, where they cause vasoconstriction by altering the abundance of the transient receptor potential canonical channel 3 and/or phosphorylation of the Na(+) -K(+) -2Cl(-) cotransporter 1 in vascular smooth muscle cells. The WNKs and many of the cation-coupled Cl(-) cotransporters they regulate are highly expressed in the central nervous system and recent work suggests that WNK dysfunction may have a role in the development of autism, schizophrenia and hereditary sensory and autonomic neuropathy Type 2. Finally, the WNK-sterile 20 kinase signalling axis represents an evolutionarily ancient mechanism for maintaining osmotic homeostasis, but a rapidly expanding body of evidence also shows a role in immunity and cellular regulation.