Type 2 diabetes mellitus caused by Gitelman syndrome-related hypokalemia: A case report

INTRODUCTION

Gitelman syndrome (GS) is an autosomal-recessive disease caused by SLC12A3 gene mutations. It is characterized by hypokalemic metabolic alkalosis in combination with hypomagnesemia and hypocalciuria. Recently, patients with GS are found at an increased risk for developing type 2 diabetes mellitus (T2DM). However, diagnosis of hyperglycemia in GS patients has not been thoroughly investigated, and family studies on SLC12A3 mutations and glucose metabolism are rare. Whether treatment including potassium and magnesium supplements, and spironolactone can ameliorate impaired glucose tolerance in GS patients, also needs to be investigated.

PATIENT CONCERNS

We examined a 55-year-old Chinese male with intermittent fatigue and persistent hypokalemia for 17 years.

DIAGNOSES

Based on the results of the clinical data, including electrolytes, oral glucose tolerance test (OGTT), and genetic analysis of the SLC12A3 gene, GS and T2DM were newly diagnosed in the patient. Two mutations of the SLC12A3 gene were found in the patient, one was a missense mutation p.N359K in exon 8, and the other was a novel insert mutation p.I262delinsIIGVVSV in exon 6. SLC12A3 genetic analysis and OGTT of 9 other family members within 3 generations were also performed. Older brother, youngest sister, and son of the patient carried the p.N359K mutation in exon 8. The older brother and the youngest sister were diagnosed with T2DM and impaired glucose tolerance by OGTT, respectively.

INTERVENTIONS

The patient was prescribed potassium and magnesium (potassium magnesium aspartate, potassium chloride) oral supplements and spironolactone. The patient was also suggested to maintain a high potassium diet. Acarbose was used to maintain the blood glucose levels.

OUTCOMES

The electrolyte imbalance including hypokalemia and hypomagnesemia, and hyperglycemia were improved with a remission of the clinical manifestations.

CONCLUSION

GS is one of the causes for manifestation of hypokalemia. SLC12A3 genetic analysis plays an important role in diagnosis of GS. Chinese male GS patients characterized with heterozygous SLC12A3 mutation should be careful toward occurrence of T2DM. Moreover, the patients with only 1 SLC12A3 mutant allele should pay regular attention to blood potassium and glucose levels. GS treatment with potassium and magnesium supplements, and spironolactone can improve impaired glucose metabolism.

Markers of potassium homeostasis in salt losing tubulopathies- associations with hyperaldosteronism and hypomagnesemia

BACKGROUND

Renal loss of potassium (K+) and magnesium (Mg2+) in salt losing tubulopathies (SLT) leads to significantly reduced Quality of Life (QoL) and higher risks of cardiac arrhythmia. The normalization of K+ is currently the most widely accepted treatment target, however in even excellently designed RCTs the increase of K+ was only mild and rarely normalized. These findings question the role of K+ as the ideal marker of potassium homeostasis in SLT. Aim of this hypothesis-generating study was to define surrogate endpoints for future treatment trials in SLT in terms of their usefulness to determine QoL and important clinical outcomes.

METHODS

Within this prospective cross-sectional study including 11 patients with SLTs we assessed the biochemical, clinical and cardiological parameters and their relationship with QoL (RAND SF-36). The primary hypothesis was that QoL would be more dependent of higher aldosterone concentration, assessed by the transtubular-potassium-gradient (TTKG). Correlations were evaluated using Pearson's correlation coefficient.

RESULTS

Included patients were mainly female (82%, mean age 34 ± 12 years). Serum K+ and Mg2+ was 3.3 ± 0.6 mmol/l and 0.7 ± 0.1 mmol/l (mean ± SD). TTKG was 9.5/3.4-20.2 (median/range). While dimensions of mental health mostly correlated with serum Mg2+ (r = 0.68, p = 0.04) and K+ (r = 0.55, p = 0.08), better physical health was associated with lower aldosterone levels (r = -0.61, p = 0.06). TTKG was neither associated with aldosterone levels nor with QoL parameters. No relevant abnormalities were observed in neither 24 h-ECG nor echocardiography.

CONCLUSIONS

Hyperaldosteronism, K+ and Mg2+ were the most important parameters of QoL. TTKG was no suitable marker for hyperaldosteronism or QoL. Future confirmatory studies in SLT should assess QoL as well as aldosterone, K+ and Mg2+.

Sheehan syndrome with Gitelman syndrome, Tackling Additive Morbidity

Sheehan syndrome (SS) is postpartum hypopituitarism resulting from pituitary gland necrosis caused by severe hypotension due to massive intra or post-partum hemorrhage. Defective NaCl transport in the distal convoluted tubule, due to mutations affecting the thiazide sensitive Na-Cl-cotransporter results in the autosomal recessive salt-losing renal tubulopathy, Gitelman syndrome (GS). These two have been rarely described together. We report the case of a middle-aged woman with both these conditions, resulting in management issues. Physicians encountering unexplained hypokalemia refractory to standard management must consider the possibility of renal tubular disorders.

Gαq/p63RhoGEF interaction in RhoA/Rho kinase signaling: investigation in Gitelman's syndrome and implications with hypertension

PURPOSE

Gitelman's syndrome (GS) presents normo-hypotension and absence of cardiovascular-renal remodeling despite high angiotensin II (Ang II), activation of renin-angiotensin-aldosterone system and is a human model of endogenous antagonism of Ang II signaling, opposite to hypertension. GS's clinical presentation leads to questions regarding what features might be responsible. One area of investigation involves Ang II signaling. In hypertensive patients, RhoA/Rho kinase (RhoA/ROCK) pathway activation by Ang II is involved in hypertension development/maintenance and induction of long-term consequences (cardiovascular-renal remodeling), while GS has reduced p63RhoGEF gene and protein levels and ROCK activity. Ang II signaling is mediated by Gαq, which interacts with p63RhoGEF via the α6-αN linker connecting p63RhoGEF's DH and PH domains acting as a conformational switch to activate RhoA/ROCK signaling.

METHODS

We have investigated in GS patients, the presence of mutations in either p63RhoGEF's α6-αN linker domain and in Gαq's Ala253, Trp263, and Tyr356 residues, crucial for p63RhoGEF-Gαq interplay.

RESULTS

No mutations have been found in specific aminoacids of p63RhoGEF α6-αN linker and Gαq, key for p63RhoGEF/Gαq interplay.

CONCLUSIONS

Gitelman's syndrome normo/hypotension and lack of cardiovascular-renal remodeling are not due to mutations of p63RhoGEF α6-αN linker and Gαq interactions. This opens the way for investigations on different coding and no-coding regions (p63RhoGEF and Gαq promoters) and on altered transcriptional/post-transcriptional regulation. Clarification of how these biochemical/molecular mechanisms work/interact would provide insights into mechanisms involved in the GS's Ang II signaling fine tuning, in human physiology/pathophysiology in general and could also identify significant targets for intervention in the treatments of hypertension.

Salt-Losing Tubulopathies in Children: What's New, What's Controversial?

Renal tubulopathies provide insights into the inner workings of the kidney, yet also pose therapeutic challenges. Because of the central nature of sodium in tubular transport physiology, disorders of sodium handling may affect virtually all aspects of the homeostatic functions of the kidney. Yet, owing to the rarity of these disorders, little clinical evidence regarding treatment exists. Consequently, treatment can vary widely between individual physicians and centers and is based mainly on understanding of renal physiology, reported clinical observations, and individual experiences. Salt-losing tubulopathies can affect all tubular segments, from the proximal tubule to the collecting duct. But the more frequently observed disorders are Bartter and Gitelman syndrome, which affect salt transport in the thick ascending limb of Henle's loop and/or the distal convoluted tubule, and these disorders generate the greatest controversies regarding management. Here, we review clinical and molecular aspects of salt-losing tubulopathies and discuss novel insights provided mainly by genetic investigations and retrospective clinical reviews. Additionally, we discuss controversial topics in the management of these disorders to highlight areas of importance for future clinical trials. International collaboration will be required to perform clinical studies to inform the treatment of these rare disorders.

Bartter/Gitelman syndromes as a model to study systemic oxidative stress in humans

Reactive oxygen species (ROS) are intermediates in reduction-oxidation reactions that begin with the addition of one electron to molecular oxygen, generating the primary ROS superoxide, which in turn interacts with other molecules to produce secondary ROS, such as hydrogen peroxide, hydroxyl radical, and peroxynitrite. ROS are continuously produced during metabolic processes and are deemed to play an important role in cardiovascular diseases, namely, myocardial hypertrophy and fibrosis and atherosclerosis, via oxidative damage of lipids, proteins, and deoxyribonucleic acid. Angiotensin II (Ang II) is a potent vasoactive agent that also exerts mitogenic, proinflammatory, and profibrotic effects through several signaling pathways, in part involving ROS, particularly superoxide and hydrogen peroxide. Moreover, Ang II stimulates NADPH oxidases, leading to higher ROS generation and oxidative stress. Bartter/Gitelman syndrome patients, despite elevated plasma renin activity, Ang II, and aldosterone levels, exhibit reduced peripheral resistance, normal/low blood pressure, and blunted pressor effect of vasoconstrictors. In addition, notwithstanding the activation of the renin-angiotensin system and the increased plasma levels of Ang II, these patients display decreased production of ROS, reduced oxidative stress, and increased antioxidant defenses. In fact, Bartter/Gitelman syndrome patients are characterized by reduced levels of p22(phox) gene expression and undetectable plasma peroxynitrite levels, while showing increased plasma antioxidant power and expression of antioxidant enzymes, such as heme oxygenase-1. In conclusion, multifarious data suggest that Bartter and Gitelman syndrome patients are a model of low oxidative stress and high antioxidant defenses. The contribution offered by the study of these syndromes in elucidating the molecular mechanisms underlying this favorable status could offer chances for new therapeutic targets in disease characterized by high levels of reactive oxygen species.

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.

Systems biology of diuretic resistance

Diuretics are commonly used to treat hypertension and extracellular fluid volume expansion. However, the development of compensatory responses in the kidney limits the benefit of this class of drugs. In this issue of the JCI, Grimm and colleagues use a systems biology approach in mice lacking the kinase SPAK and unravel a complex mechanism that explains thiazide diuretic resistance. The overall process involves interactions among six different cell types in the kidney.

Integrated compensatory network is activated in the absence of NCC phosphorylation

Thiazide diuretics are used to treat hypertension; however, compensatory processes in the kidney can limit antihypertensive responses to this class of drugs. Here, we evaluated compensatory pathways in SPAK kinase-deficient mice, which are unable to activate the thiazide-sensitive sodium chloride cotransporter NCC (encoded by Slc12a3). Global transcriptional profiling, combined with biochemical, cell biological, and physiological phenotyping, identified the gene expression signature of the response and revealed how it establishes an adaptive physiology. Salt reabsorption pathways were created by the coordinate induction of a multigene transport system, involving solute carriers (encoded by Slc26a4, Slc4a8, and Slc4a9), carbonic anhydrase isoforms, and V-type H⁺-ATPase subunits in pendrin-positive intercalated cells (PP-ICs) and ENaC subunits in principal cells (PCs). A distal nephron remodeling process and induction of jagged 1/NOTCH signaling, which expands the cortical connecting tubule with PCs and replaces acid-secreting α-ICs with PP-ICs, were partly responsible for the compensation. Salt reabsorption was also activated by induction of an α-ketoglutarate (α-KG) paracrine signaling system. Coordinate regulation of a multigene α-KG synthesis and transport pathway resulted in α-KG secretion into pro-urine, as the α-KG-activated GPCR (Oxgr1) increased on the PP-IC apical surface, allowing paracrine delivery of α-KG to stimulate salt transport. Identification of the integrated compensatory NaCl reabsorption mechanisms provides insight into thiazide diuretic efficacy.

A pedigree analysis of two homozygous mutant Gitelman syndrome cases

Gitelman syndrome (GS) is a salt-wasting tubulointerstitial disease of autosomal recessive inheritance (OMIM613395) caused by genic mutation of SLC12A3, which codes thiazide-sensitive Na-Cl cotransporter (NCCT) gene. The gene mutation of the majority of GS patients is compound heterozygous. This study analyzes two cases of GS gene mutation and the clinical phenotype. Twenty patients of two GS pedigrees underwent direct sequence alignment of 26 exons of SLC12A3 to spot and locate mutant site. Proband A of Pedigree I had three mutant sites: Arg928Cys, a homozygote, missense mutation, and two homozygous silent mutations, Ala122Ala and Thr465Thr, and 8 members of Pedigree I carried Arg928Cy heterozygous mutation. Proband B of Pedigree II had a homozygote, Ser710X, and a termination codon was spotted, which would inevitably be translated into abridged and defective protein, and 7 members had Ser710X heterozygous mutation. The heterozygous mutation carriers of the two pedigrees often have stimulus-controlled hypokalemia after strenuous exercise. The parents of Proband A are cousins, a case of intermarriage. Both probands show hypokalemia, hypochloraemia, hypocalcinuria, hyperreninemia, and hyperaldosteronemia; Proband A has normal serum magnesium and increased urinary sodium excretion, while Proband B has hypomagnesemia and increased urinary magnesium ion excretion. Both probands have normal or lower blood pressure, weakness and numbness of lower extremities, muscular soreness, and occasional palpitations and chest discomfort. Proband A wearies easily and Proband B has occasional joint numbness and pain. These two homozygous mutations are responsible for the morbidity of two GS families and they show heterogenicity of clinical phenotype.

[Structural functional and pathological aspects of the NaCl contransporter thiazide sensitive]

NCC cotransporter is the mayor pathway for sodium chloride reabsorption in the distal nephron and the target of thiazide diuretics which, given their clinical utility in the management of arterial hypertension, are amongst the top sold drugs in the world. NCC protein is of great physiological importance given its role in the maintenance of water and salt homeostasis on the organism. Inactivating mutations in the gene that codes for NCC cause Gitelman's syndrome: an autosomal recessive disease associated with arterial hypotension, metabolic alkalosis, hipokalemia and hypocalciuria. This syndrome represents strong evidence of the relevance of the role of NCC in blood pressure regulation, electrolyte and acid base balance. In this work we review the up to date knowledge regarding this cotransporter with special attention to the molecular aspects of the protein that determine is physiological function and pathological roles.

Gitelman's syndrome: a pathophysiological and clinical update

Gitelman's syndrome (GS), also known as familial hypokalemic hypomagnesemia, is a rare autosomal recessive hereditary salt-losing tubulopathy, characterized by hypokalemic metabolic alkalosis, hypomagnesemia, and hypocalciuria, which is usually caused by mutations in the SLC12A3 gene encoding the thiazide-sensitive sodium chloride contrasporter. Because 18-40% of suspected GS patients carry only one SLC12A3 mutant allele, large genomic rearrangements must account for unidentified mutations. The clinical manifestations of GS are highly variable in terms of age at presentation, severity of symptoms, and biochemical abnormalities. Molecular analysis in our sibling's patients revealed compound heterozygous mutations in the coding region of SLC12A3 as underlying their disease. Such compound heterozygosity can result in disease phenotype for such loss of function mutations in the absence of homozygosis through consanguineous inheritance of mutant alleles, identical by descent. Missense mutations account for approximately 70% of the mutations in GS, and there is a predisposition to large rearrangements caused by the presence of repeated sequences within the SLC12A3. We report two adult male siblings of Jewish origin with late onset GS, who presented in their fifth decade of life with muscle weakness, hypokalemia, hypomagnesaemia, and metabolic alkalosis. Rapid clinical and biochemical improvement was achieved by replacement therapy with potassium and magnesium.

A novel compound heterozygous mutation of Gitelman's syndrome in Japan, as diagnosed by an extraordinary response of the fractional excretion rate of chloride in the trichlormethiazide loading test

Gitelman's syndrome (GS), an inherited disorder due to loss of function of ion channels and transporters such as Na-Cl co-transporter (NCCT) in distal convoluted tubules, is characterized by hypokalemia, hypomagnesemia, hypocalciuria, metabolic alkalosis and hyperreninemic-hyperaldosteronism. A 39-year-old man was admitted to our hospital because of muscle weakness with such intractable disorders. We performed a thiazide-loading test, which revealed a poor response of the fractional excretion rate of chloride compared to healthy subjects. Based on these data, the clinical diagnosis of GS was made. Gene-sequencing analysis revealed compound heterozygous mutations of c.539C > A and c.1844C > T in SLC12A3, which is newly reported in Japanese GS.

Does hypokalaemia cause nephropathy? An observational study of renal function in patients with Bartter or Gitelman syndrome

BACKGROUND

Hypokalaemic nephropathy has been described in patients with chronic potassium depletion; it is a condition in which proximal tubular vacuolization and interstitial fibrosis occur, resulting in a decline in glomerular filtration rate (GFR) and, in some cases, renal failure. It has been described in patients with chronic diarrhoea, eating disorders, laxative abuse and primary hyperaldosteronism; also occasionally in Bartter syndrome (BS), in which severe hypokalaemia accompanies significant renal sodium and water losses, though rarely in Gitelman syndrome (GS), in which there is equally severe hypokalaemia, but only modest sodium losses.

AIM

We hypothesized that hypokalaemic nephropathy may not be due to potassium depletion per se, but persistently elevated circulating levels of aldosterone, possibly with superimposed episodes of renal hypoperfusion.

DESIGN AND METHODS

We searched UK and European data sets to retrospectively compare serum and urinary parameters in patients with GS and BS.

RESULTS

The patients with GS often had lower serum potassium concentrations than patients with BS, but the BS patients had significantly higher serum creatinine concentrations and lower estimated GFRs (eGFR). BS patients had significantly higher fractional excretions of sodium compared with GS patients, as well as higher plasma renin activities and serum aldosterone levels.

CONCLUSION

These findings show that in genetically confirmed cases of BS and GS, the degree of hypokalaemia (as an index of chronic potassium depletion) does not correlate with GFR, and that on-going sodium and water losses, and consequent secondary hyperaldosteronism, may play a more important role in the aetiology of hypokalaemic nephropathy.

The pharmacological characteristics of molecular-based inherited salt-losing tubulopathies

CONTEXT

Our understanding of inherited salt-losing tubulopathies has improved with recent advances in molecular genetics. However, the terminology of Bartter syndrome and Gitelman syndrome does not always accurately reflect their pathophysiological basis or clinical presentation, and some patients are difficult to diagnose from their clinical presentations.

OBJECTIVE

In the present study, we conducted molecular analysis and diuretic tests for patients with inherited salt-losing tubulopathies to clarify the pharmacological characteristics of these disorders.

PATIENTS

We detected mutations and subsequently conducted diuretic tests using furosemide and thiazide for 16 patients with salt-losing tubulopathies (two with SLC12A1; two with KCNJ1; nine with CLCNKB; and three with SLC12A3).

RESULTS

Patients with SLC12A1 mutations showed no response to furosemide, whereas those with SLC12A3 mutations showed no response to thiazide. However, patients with CLCNKB mutations showed no response to thiazide and a normal response to furosemide, and those with KCNJ1 mutations showed a good response to both diuretics. This study revealed the following characteristics of these disorders: 1) subjects with CLCNKB mutations showed one or more biochemical features of Gitelman syndrome (including hypomagnesemia, hypocalciuria, and fractional chloride excretion insensitivity to thiazide administration); and 2) subjects with KCNJ1 mutations appeared to show normal fractional chloride excretion sensitivity to furosemide and thiazide administration.

CONCLUSIONS

These results indicate that these disorders are difficult to distinguish in some patients, even when using diuretic challenge. This clinical report provides important findings that can improve our understanding of inherited salt-losing tubulopathies and renal tubular physiology.

ACE2 and angiotensin 1-7 are increased in a human model of cardiovascular hyporeactivity: pathophysiological implications

BACKGROUND

ACE and ACE2 produce angiotensin II (Ang II), a vasopressor that induces cardiovascular remodeling, and Ang 1-7, a vasodilator with an antiremodeling effect. While Ang 1-7 has antiarrhythmic properties, at higher concentration it may induce ventricular tachycardia and sudden death. ACE2, therefore, may play an essential role in blood pressure homeostasis, in the long-term complications of hypertension (cardiovascular remodeling), and in the induction of cardiac electric abnormalities. This study evaluated the levels of ACE2 and Ang 1-7 in Bartter's/Gitelman's patients (BS/GS) who have elevated Ang II and endogenous blockade of Ang II type 1 receptor signaling compared with healthy subjects (C) and essential hypertensives (EH). BS/ GS patients were also considered because of their predisposition to cardiac arrhythmias, which has yet to be completely clarified.

METHODS

Mononuclear cell ACE2 and Ang 1-7 were evaluated using western blot.

RESULTS

One-way ANOVA showed that ACE2 and Ang 1-7 levels were significantly different between the three groups (p=0.0074 and p=0.0001, respectively). Post-hoc analysis (Tukey's HSD) showed that both ACE2 (1.59+/-0.63) and Ang1-7 (2.26+/-1.18) were significantly elevated in BS/GS compared with either C (0.98+/-0.45; p=0.008; 1.12+/-0.48, p=0.002, respectively) or EH (1.06+/-0.24; p=0.043; 0.72+/-0.28; p=0.0001, respectively). ACE2 and Ang 1-7 directly correlated only in BS/GS (r=0.91, p<0.0003).

CONCLUSIONS

The elevated ACE2 and Ang 1-7 in BS/ GS patients mirror those in hypertensives and are in line with the clinical, hemodynamic and pathophysiological characteristics of BS/GS, likely contributing to them. In consideration of the clinical picture of these syndromes, the opposite of hypertension, the results of this study further strengthen the importance of the ACE2/Ang 1-7 system in the regulation of vascular tone and cardiovascular biology.

New roles for renal potassium channels

The role of the kidney in controlling and maintaining plasma potassium levels in the normal range requires the presence and activity of renal potassium channels, and their importance has been highlighted in patients with Bartter syndrome harboring mutations in the ROMK (Kir1.1, KCJN1) channel and hyperkalemia. However, the kidney expresses far more potassium channels than ROMK. Their functions are slowly emerging from studies in animal models and human rare inherited disorders that allow a better understanding of the plethora of functions that potassium channels fulfill in the kidney. Three recent studies shed light on the function of 2 members of the family of voltage-gated potassium channels. The group of René Bindels demonstrates that patients with isolated hypomagnesemia and inappropriately normal magnesuria carry mutations in the Kv1.1 (KCNA) potassium channel (Glaudemans B, et al. J Clin Invest. 2009;119:936-942). Two other studies elucidate a rather complex syndrome involving seizures, ataxia, deafness and renal salt loss, and show that mutations in the Kir4.1 (KCNJ10) potassium channel are responsible (Scholl UI, et al. Proc Natl Acad Sci U S A. 2009;106:5842-5847; Bockenhauer D, et al. N Engl J Med. 2009;360:1960-1970). This human disease is recapitulated by a mouse model deficient for the Kir4.1 channel presenting with similar symptoms. These studies together show that potassium channels in the kidney serve purposes far beyond controlling systemic potassium homeostasis, and are involved in various essential functions of the kidney. Moreover, defects of 2 different potassium channels expressed on opposing membrane domains of the same cells cause distinct symptoms.

High angiotensin II state without cardiac remodeling (Bartter's and Gitelman's syndromes): are angiotensin II type 2 receptors involved?

BACKGROUND/AIMS

While Angiotensin II (Ang II) is a major factor in the development of cardiomyocyte hypertrophy and a pivotal role for Ang II signals via ERK1/2 has been identified, mechanism(s) responsible are still unclear. As Bartter's and Gitelman's syndrome patients (BS/GS) have increased Ang II, and yet normo/hypotension, hyporesponsiveness to pressors and blunted Ang II signaling via type 1 receptors (AT1R), this study assesses BS/GS's left ventricular (LV) mass and structure as well as Ang II induced ERK1/2 phosphorylation compared with essential hypertensive patients (EH) and normotensive healthy subjects (C) to gain insight into Ang II mediated processes.

METHODS

Indices of cardiac hypertrophy were determined by M-mode, two-dimensional echo Doppler and ERK phosphorylation by Western blot.

RESULTS

None of BS/GS exhibited LV remodelling; LV mass, LV end-diastolic volume and mass/volume ratio were unchanged vs C (60+/-14 g/m2 vs 64+/-12, 64+/-12 ml/m2 vs 60+/-8 and 0.95+/-0.2 vs 1.0+/-0.2, respectively) and reduced vs EH (119+/-15, p<0.001, 78+/-9, p<0.05 and 1.52+/-0.15, p<0.01). Despite BS/GS's higher plasma renin activity and aldosterone and unchanged level of AT1R, Ang II induced ERK1/2 phosphorylation was reduced vs both C and EH: 0.64 d.u.+/-0.08 vs 0.90+/-0.06 in C, p<0.006, and vs 1.45+/-0.07 in EH, p<0.001.

CONCLUSION

The data point to a direct cardioremodeling role for Ang II and support a role of Ang II type 2 receptor (AT2R) signaling as involved in the lack of cardiovascular remodeling in BS/GS. However, further studies using more direct approaches to demonstrate the effects of AT2R signaling must be pursued.

Coexistence of normotensive primary aldosteronism in two patients with Gitelman's syndrome and novel thiazide-sensitive Na-Cl cotransporter mutations

BACKGROUND

Primary aldosteronism (PA) is the most common form of secondary hypertension, while Gitelman's syndrome (GS) is the most common inherited renal tubular disease. However, coexistence of these two diseases has never been previously reported. AIM AND SUBJECTS: The aim of our study was to describe the association of GS and PA in two unrelated patients and compare their clinical presentation with a group of patients with GS.

METHODS

Ten subjects suspected to have only GS were assigned to the control group. Saline infusion test was used to confirm the diagnosis of PA. GS was confirmed by sequencing of the causal genes (SLC12A3 and CLCNKB) and functional analyses in Xenopus laevis oocytes.

RESULTS

Confirmatory tests, gene analysis, and functional studies demonstrated the coexistence of GS and PA in both patients. In total, nine novel SLC12A3 gene variants, including seven missense mutations, one splice mutation, and one frameshift deletion, were found in 12 subjects. Four mutations (p.T60M, p.T304M, p.T465P, and p.N611T) harbored by the two patients with both PA and GS were revealed to be loss-of-function variants. Although both patients were normotensive, neither of them had normal nocturnal dip.

CONCLUSIONS

Two rare diseases GS and PA may occasionally coexist in one subject. In these patients, salt depletion and volume constriction might explain the absence of hypertension normally seen in PA patients. However, the protective mechanism against hypertension via down-regulation of renal sodium handling was probably not sufficient in those patients, since their normal circadian rhythm of blood pressure was disrupted.

Novel mutations in theSLC12A3gene causing Gitelman's syndrome in Swedes

PURPOSE

Gitelman's syndrome (GS) is an inherited autosomal recessive disorder due to loss of function mutations in the SLC12A3 gene encoding the Na-Cl co-transporter (NCCT), the target of thiazide diuretics. The defective function of the NCCT, which normally is expressed in the apical membrane of the distal convolute tubule in the kidney, leads to mild hypotension, hypokalemia, hyperreninemic hyperaldosteronism, mild metabolic alkalosis, hypomagnesemia and hypocalciuria. Up to now, more than 100 mutations of the SLC12A3 gene have been described in GS patients.

METHODS

We have collected 30 patients from Sweden with a clinical diagnosis of GS and undertaken a mutation screening by SSCP and successive sequencing of the 26 exons and intronic boundaries. Both mutations were identified in most (n = 28, 93%) and at least one mutation was identified in all patients.

RESULTS

We found 22 different mutations evenly distributed throughout the gene, 11 of which have not been described previously. The new variants include 8 missense mutations (Glu68Lys, His69Asn, Argl45His, Vall53Met, Gly230Asp, Gly342Ala, Val677Leu and Gly867Ser), 1 insertion (c.834_835insG on exon 6) and 2 splice-site mutations (c.2667 + lT>G substitution in splicing donor site after exon 22, c.1569-1G>A substitution in the splicing acceptor site before exon 13).

CONCLUSION

In Swedish patients with the clinical features of GS, disease-causing mutations in the SLC12A3 gene were identified in most patients. The spectrum of GS mutations is wide making full mutation screening of the SLC12A3 gene necessary to confirm the diagnosis.

Hypocalciuria in patients with Gitelman syndrome: role of blood volume

BACKGROUND

Hypocalciuria is common in patients with Gitelman syndrome (GS), and its cause primarily is enhanced renal reabsorption of calcium in the proximal tubule in response to hypovolemia, judged by recent studies in animals.

STUDY DESIGN

Uncontrolled trial in cases and controls to evaluate the effect of acute reexpansion of extracellular fluid volume (ECFV) on urine calcium excretion in patients with GS.

SETTING & PARTICIPANTS

8 patients with GS and 8 sex- and age-matched healthy control subjects (CSs) were enrolled in an academic medical center.

PREDICTOR

ECFV expansion with isotonic saline at 1 L/h for 3 hours.

OUTCOMES & MEASUREMENTS

Urinary calcium excretion was measured hourly for 6 hours, and subsequent 18-hour urine was analyzed as a single collection; hormones and electrolytes were measured.

RESULTS

Patients with GS had hypokalemia, metabolic alkalosis, hypomagnesemia, severe hypocalciuria (urine calcium-creatinine ratio, 0.006 +/- 0.002 versus 0.08 +/- 0.02 mg/mg [0.02 +/- 0.01 versus 0.22 +/- 0.05 mmol/mmol]; P < 0.005), and a mild degree of ECFV contraction. Sodium excretion and creatinine clearance rates were similar to those in CSs. In patients with GS, saline infusion increased ECFV, which caused a significantly greater sodium excretion rate, but there was only a small increase in calcium excretion rate, in both the first 6 hours (0.04 +/- 0.02 mg/min [1.0 +/- 0.6 micromol/min]) and subsequent 18-hour period (0.02 +/- 0.01 mg/min [0.4 +/- 0.2 micromol/min]), as in CSs. Notwithstanding, their calcium excretion rate was still much less than that in CSs before volume repletion (0.13 +/- 0.04 mg/min [3.2 +/- 1.0 micromol/min]).

LIMITATION

Patients with GS did not become euvolemic on a long-term sodium chloride supplementation because they excreted sodium chloride so rapidly.

CONCLUSION

Hypovolemia is not the sole cause of hypocalciuria in patients with GS.

Autonomic nervous system function in chronic hypotension associated with Bartter and Gitelman syndromes

Autonomic nervous system dysfunction has a major role in the blood pressure (BP) decrease associated with orthostatic hypotension and syncope. The clinical picture of Bartter and Gitelman syndromes includes reduced extracellular fluid volume and normotension or hypotension, but no study has explored autonomic nervous system status in patients with hypotensive episodes associated with these diseases. We tested sympathetic and parasympathetic nervous system function in 4 patients with Bartter and Gitelman syndromes with chronic hypotension. Each patient underwent a battery of autonomic reflex tests, including BP and heart rate response to orthostatism, Valsalva maneuver, cold-pressor test, hand-grip test, and deep breathing. Plasma catecholamines also were measured. BP was monitored during tests by means of continuous noninvasive finger BP recording. Orthostatic hypotension was observed in 1 patient who experienced syncope episodes. Valsalva ratio ranged from 1.21 to 1.61. During the cold-pressor test, the range of systolic and diastolic BP increases were 8 to 31 and 6 to 24 mm Hg, respectively. During the hand-grip test, systolic and diastolic BP increases ranged from 10 to 39 and 8 to 32 mm Hg, respectively. During hyperventilation, the difference between the highest and lowest heart rates was 12 or more beats/min in all patients. Patients' plasma norepinephrine concentrations increased during standing. Our preliminary results suggest that chronic hypotension in patients with Bartter and Gitelman syndromes is not associated with sympathetic and parasympathetic nervous system dysfunction, even when orthostatic hypotension is present. This normal autonomic function suggests that other pathophysiological mechanisms, such as the characteristic vasoconstrictor abnormal cell signaling, may account for hypotension in patients with Bartter and Gitelman syndromes.

C1q nephropathy in association with Gitelman syndrome: a case report

There have been rare reports of glomerulopathies developing in patients with Bartter syndrome (BS) and its milder variant, Gitelman syndrome (GS). We present the first case of C1q nephropathy (C1qN) in an African American child with GS. This child was diagnosed with GS at 9 years of age and subsequently developed nephrotic range proteinuria 3 years later. Renal biopsy revealed mesangial hypercellularity and focal segmental glomerulosclerosis (FSGS). The segmental lesions were generally located at the vascular pole. Dominant C1q (2+) staining along with IgG (1-2+) was demonstrated in the mesangium, which correlated with scattered electron dense mesangial deposits demonstrated by electron microscopy. Treatment with an angiotensin-converting enzyme inhibitor led to an improvement in proteinuria to near-normal values (urine protein/creatinine ratio down to 0.5), but the creatinine clearance declined to approximately 58 ml/min/1.73 m(2). This case highlights the possible association between the milder hypokalemic tubulopathy, GS, and glomerular disease, including C1qN. Prompt evaluation of proteinuria with renal biopsy in these patients is recommended to detect significant glomerular pathology. Further research is needed to define risk factors for this complication.