Electrocardiogram with prolonged QT interval in Gitelman disease

Cardiovascular and arrhythmic manifestations of Bartter's and Gitelman's syndromes: do not forget the heart. A narrative literature review

Bartter's and Gitelman's syndromes (BS/GS) are genetically determined kidney tubulopathies leading to electrolyte and neurohormonal abnormalities. Although considered benign entities, major adverse cardiovascular events may complicate both syndromes, in form of ventricular arrhythmias leading to palpitations, syncope or sudden cardiac death, microvascular cardiac dysfunction and exercise-induced myocardial contractile deficit. The mechanisms leading to cardiovascular complications are not only driven by chronic electrolyte abnormalities, i.e. chronic hypokalemia and hypomagnesemia, but also by neurohormonal alterations that can impair vascular tone and myocardial contractility. In presence of triggering factors, BS/GS patients may experience a spectrum of cardiac arrhythmias necessitating prompt diagnosis and treatment. The aim of this review is to explore the pathophysiological mechanisms of BS and GS, highlighting those responsible for cardiovascular involvement, and to analyze the spectrum of associated cardiovascular complications. This highlights the importance of an integrated shared management of GS/BS patients between Nephrologist and Cardiologist.

Heart's Dangerous Symphony: Torsade De Pointes Unleashed by Gitelman Syndrome-Induced Hypomagnesemia

Gitelman syndrome (GS) is a rare autosomal recessive salt-losing renal tubular disorder associated with a mutation of SLC12A3 or CLCNKB genes which encodes the thiazide-sensitive sodium-chloride co-transporter (NCCT) in the distal renal tubule. It is inherited as an autosomal recessive disorder. Hypokalemia, metabolic alkalosis, hypomagnesemia, hypocalciuria, and renin-angiotensin-aldosterone system (RAAS) activation are characteristics of GS. GS is often misdiagnosed or underdiagnosed owing to its low incidence and lack of awareness. Its prevalence is estimated to be around 1-10 per 40,000 people. We report a case of cardiac arrest secondary to torsade de pointes (TdP) because of GS-induced hypomagnesemia. Our case highlights the importance of clinicians being aware of the potential electrolyte abnormalities and complications associated with GS, as it can lead to catastrophic consequences if not identified and corrected earlier.

Sudden cardiac arrest in a child with Gitelman syndrome: a case report and literature review

Salt-losing tubulopathies are well-recognised diseases predisposing to metabolic disturbances in affected patients. One of the most severe complications can be life-threatening arrhythmias causing sudden cardiac arrest. We present here the first case of a pediatric patient with Gitelman syndrome associated sudden cardiac arrest without precipitating event. A 10-year-old boy collapsed due to ventricular fibrillation in the Prague tram. Lay cardiopulmonary resuscitation was initiated and external defibrillation restored sinus rhythm within minutes. Initial laboratory examination revealed severe hypokalemia requiring large amounts of electrolyte supplementation. Genetic testing focused to tubulopathies was performed and the diagnosis of Gitelman syndrome was made following the identification of two pathogenic variants in SLC12A3 gene (c.2633 + 1G>A and c.2221G>A). Implantable cardioverter-defibrillator was implanted to prevent sudden cardiac death. The patient was in a good clinical condition with satisfactory electrolyte serum levels at the last follow-up. Causes of electrolyte abnormalities in children should be identified early to prevent the development of rare but potentially fatal complications.

Anesthetic Considerations for Cesarean Delivery in a Parturient With Severe Gitelman Syndrome

Gitelman syndrome is an autosomal recessive inherited disorder that impairs the function of thiazide-sensitive sodium-chloride cotransporters in the distal convoluted tubule of the nephron. During labor and delivery, avoidance of sympathetic overactivity, meticulous hemodynamic monitoring, and expedited repletion of potassium and magnesium are required to avoid adverse outcomes. We present a parturient with severe Gitelman syndrome, requiring continuous electrolyte and fluid infusions, who underwent successful cesarean delivery. Potential severe morbidity was avoided with multidisciplinary planning and management.

Magnesium and Hypertension: Decoding Novel Anti-hypertensives

Hypertension (HTN) is a complex multifactorial disease that is one of the most prevalent disorders in our modern world. It can lead to fatal complications like coronary artery disease (CAD) and congestive heart failure (CHF) in high-risk individuals. The silent nature of HTN also contributes to its immense caseload and, today, with a number of combinations and various antihypertensive agents, patient compliance is becoming increasingly difficult. This article has reviewed the role and mechanisms of magnesium (Mg) in reducing HTN in the human body so as to provide more information that may help include it as a mainstream antihypertensive regimen. This review has also shed light on the cardioprotective nature of Mg against pathologies like CHF with special mention to patient groups who are at high risk for low Mg levels. Many studies included in this article solidify the former link, but some also provide contradicting data.

Examination of the predicted prevalence of Gitelman syndrome by ethnicity based on genome databases

Gitelman syndrome is an autosomal recessive inherited salt-losing tubulopathy. It has a prevalence of around 1 in 40,000 people, and heterozygous carriers are estimated at approximately 1%, although the exact prevalence is unknown. We estimated the predicted prevalence of Gitelman syndrome based on multiple genome databases, HGVD and jMorp for the Japanese population and gnomAD for other ethnicities, and included all 274 pathogenic missense or nonsense variants registered in HGMD Professional. The frequencies of all these alleles were summed to calculate the total variant allele frequency in SLC12A3. The carrier frequency and the disease prevalence were assumed to be twice and the square of the total allele frequency, respectively, according to the Hardy–Weinberg principle. In the Japanese population, the total carrier frequencies were 0.0948 (9.5%) and 0.0868 (8.7%) and the calculated prevalence was 0.00225 (2.3 in 1000 people) and 0.00188 (1.9 in 1000 people) in HGVD and jMorp, respectively. Other ethnicities showed a prevalence varying from 0.000012 to 0.00083. These findings indicate that the prevalence of Gitelman syndrome in the Japanese population is higher than expected and that some other ethnicities also have a higher prevalence than has previously been considered.

Long-term Clinical Course after Living Kidney Donation by a Patient with Gitelman Syndrome Harboring a Compound Heterozygous Mutation of the SLC12A3 Gene

The eligibility for kidney donation and long-term post-donation renal prognosis of patients with Gitelman syndrome (GS) are unknown. We herein report a 44-year-old woman with GS who donated her kidney for transplant. A gene sequence analysis revealed compound heterozygous mutations of T180K and L858H in the SLC12A3 gene. Since transplantation, the renal function and serum potassium and magnesium levels of the donor and recipient have remained stable for seven years with careful monitoring and supplementation. Patients with asymptomatic GS who have no complications can be considered eligible to donate their kidney for transplant with proper monitoring after transplantation.

Review and Analysis of Two Gitelman Syndrome Pedigrees Complicated with Proteinuria or Hashimoto's Thyroiditis Caused by Compound Heterozygous SLC12A3 Mutations

Gitelman syndrome (GS) is an autosomal recessive inherited salt-losing renal tubular disease, which is caused by a pathogenic mutation of SLC12A3 encoding thiazide-sensitive Na-Cl cotransporter, which leads to disturbance of sodium and chlorine reabsorption in renal distal convoluted tubules, resulting in phenotypes such as hypovolemia, renin angiotensin aldosterone system (RAAS) activation, hypokalemia, and metabolic alkalosis. In this study, two GS families with proteinuria or Hashimoto's thyroiditis were analyzed for genetic-phenotypic association. Sanger sequencing revealed that two probands carried SLC12A3 compound heterozygous mutations, and proband A carried two pathogenic mutations: missense mutation Arg83Gln, splicing mutation, or frameshift mutation NC_000016.10:g.56872655_56872667 (gcggacatttttg>accgaaaatttt) in exon 8. Proband B carries two missense mutations: novel Asp839Val and Arg904Gln. Both probands manifested hypokalemia, hypomagnesemia, hypocalcinuria, metabolic alkalosis, and RAAS activation; in addition, the proband A exhibited decreased urinary chloride, phosphorus, and increased magnesium ions excretion, complicated with Hashimoto's Thyroiditis, while the proband B exhibited enhanced urine sodium excretion and proteinuria. The older sister of proband B with GS also had Hashimoto's thyroiditis. Electron microscopy revealed swelling and vacuolar degeneration of glomerular epithelial cells, diffuse proliferation of mesangial cells and matrix, accompanied by a small amount of low-density electron-dense deposition, and segmental fusion of epithelial cell foot processes in proband B. Light microscopy showed mild mesangial hyperplasia in the focal segment of the glomerulus, hyperplasia, and hypertrophy of juxtaglomerular apparatus cells, mild renal tubulointerstitial lesions, and one glomerular sclerosis. So, long-term hypokalemia of GS can cause kidney damage and may also be susceptible to thyroid disease.

Are the Clinical Presentations (Phenotypes) of Gitelman's and Bartter's Syndromes Gene Mutations Driven by Their Effects on Intracellular pH, Their "pH" Enotype?

Gitelman's syndrome (GS) and Bartter's syndrome (BS) are rare inherited salt-losing tubulopathies whose variations in genotype do not correlate well with either clinical course or electrolyte requirements. Using GS/BS patients as nature's experiments, we found them to be a human model of endogenous Ang II antagonism with activated Renin-Angiotensin System (RAS), resulting in high Ang II levels with blunted cardiovascular effects. These patients are also characterized by increased and directly correlated levels of both Angiotensin Converting Enzyme 2 (ACE2) and Ang 1-7. Understanding the myriad of distinctive and frequently overlapping clinical presentations of GS/BS arises remains challenging. Efforts to find a treatment for COVID-19 has fueled a recent surge in interest in chloroquine/hydroxychloroquine and its effects. Of specific interest are chloroquine/hydroxychloroquine's ability to inhibit SARS-CoV infection by impairing ACE2, the SARS-CoV2 entry point, through terminal glycosylation via effects on TGN/post-Golgi pH homeostasis. Several different studies with a GS or a BS phenotype, along with a nonsyndromic form of X-linked intellectual disability linked to a mutated SLC9A7, provide additional evidence that specific gene defects can act via misregulation of TGN/post-Golgi pH homeostasis, which leads to a common mechanistic basis resulting in overlapping phenotypes. We suggest that linkage between the specific gene defects identified in GS and BS and the myriad of distinctive and frequently overlapping clinical findings may be the result of aberrant glycosylation of ACE2 driven by altered TGN/endosome system acidification caused by the metabolic alkalosis brought about by these salt-losing tubulopathies in addition to their altered intracellular calcium signaling due to a blunted second messenger induced intracellular calcium release that is, in turn, amplified by the RAS system.

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+.

Inherited salt-losing tubulopathy: An old condition but a new category of tubulopathy

Bartter syndrome (BS) and Gitelman syndrome (GS) are syndromes associated with congenital tubular dysfunction, characterized by hypokalemia and metabolic alkalosis. Clinically, BS is classified into two types: the severe antenatal/neonatal type, which develops during the fetal period with polyhydramnios and preterm delivery; and the relatively mild classic type, which is usually found during infancy with failure to thrive. GS can be clinically differentiated from BS by its age at onset, usually after school age, or laboratory findings of hypomagnesemia and hypocalciuria. Recent advances in molecular biology have shown that these diseases can be genetically classified into type 1 to 5 BS and GS. As a result, it has become clear that the clinical classification of antenatal/neonatal BS, classic BS, and GS does not always correspond to the clinical symptoms associated with the genotypes in a one-to-one manner; and there is clinically no clear differential border between type 3 BS and GS. This has caused confusion among clinicians in the diagnosis of these diseases. It has been proposed that the disease name "inherited salt-losing tubulopathy" can be used for cases of tubulopathies accompanied by hypokalemia and metabolic alkalosis. It is reasonable to use this term prior to genetic typing into type 1-5 BS or GS, to avoid confusion in a clinical setting. In this article, we review causative genes and phenotypic correlations, diagnosis, and treatment strategies for salt-losing tubulopathy as well as the clinical characteristics of pseudo-BS/GS, which can also be called a "salt-losing disorder".

The challenges of diagnosis and management of Gitelman syndrome

Gitelman syndrome is an inherited tubulopathy characterized by renal salt wasting from the distal convoluted tubule. Defects in the sodium chloride cotransporter (encoded by SLC12A3) underlie this autosomal recessive condition. This article focuses on the specific challenges of diagnosing and treating Gitelman syndrome, with use of an illustrative case report. Symptoms relate to decreased serum potassium and magnesium levels, which include muscle weakness, tetany, fatigue and palpitations. Sudden cardiac deaths have been reported. Making a diagnosis may be difficult given its rarity but is important. A knowledge of the serum and urine biochemical picture is vital to distinguish it from a broad differential diagnosis, and application of genetic testing can resolve difficult cases. There is a group of Gitelman syndrome heterozygous carriers that experience symptoms and electrolyte disturbance and these patients should be managed in a similar way, though here genetic investigations become key in securing a difficult diagnosis. Potassium and magnesium replacement is the cornerstone of treatment, though practically this can be hard for patients to manage and often does not fully relieve symptoms even when serum levels are normalized. Challenges arise due to the lack of randomized controlled trials focussing on treatment of this rare disease; hence, clinicians endorse strategies in line with correction of the underlying pathophysiology such as sodium loading or pharmacological treatments, which seem to help some patients. Focussed dietary advice and knowing the best tolerated preparations of potassium and magnesium medications are useful tools for the physician, as well as an awareness of the specific burdens that this patient group face in order to signpost appropriate support.

Learning Physiology From Inherited Kidney Disorders

The identification of genes causing inherited kidney diseases yielded crucial insights in the molecular basis of disease and improved our understanding of physiological processes that operate in the kidney. Monogenic kidney disorders are caused by mutations in genes coding for a large variety of proteins including receptors, channels and transporters, enzymes, transcription factors, and structural components, operating in specialized cell types that perform highly regulated homeostatic functions. Common variants in some of these genes are also associated with complex traits, as evidenced by genome-wide association studies in the general population. In this review, we discuss how the molecular genetics of inherited disorders affecting different tubular segments of the nephron improved our understanding of various transport processes and of their involvement in homeostasis, while providing novel therapeutic targets. These include inherited disorders causing a dysfunction of the proximal tubule (renal Fanconi syndrome), with emphasis on epithelial differentiation and receptor-mediated endocytosis, or affecting the reabsorption of glucose, the handling of uric acid, and the reabsorption of sodium, calcium, and magnesium along the kidney tubule.

Persistent QT Prolongation in a Child with Gitelman Syndrome and SCN5A H558R Polymorphism

Gitelman syndrome (GS) is an inherited renal tubular disorder characterized by hypokalemic metabolic alkalosis, hypomagnesemia, and low urinary calcium excretion. While it is considered a benign disease, severe ventricular arrhythmia and sudden cardiac death related to the prolongation of the QT interval have been reported in rare cases. Herein we report a 13-year-old girl with GS who presented with persistent prolongation of the QT interval, even after being treated for hypokalemia and hypomagnesemia. Genetic analysis identified SCN5A H558R polymorphism, which modulates the function of myocardial sodium channel, and SLC12A3 A588V mutation, which causes GS. The SCN5A polymorphism and GS-related electrolyte disturbance might have contributed to the persistent QT prolongation in this patient. Although no ventricular arrhythmias were recorded in this case, careful cardiac surveillance should be applied for avoiding life-threatening cardiac events.

Clinical and Genetic Characteristics in Patients With Gitelman Syndrome

Introduction

Gitelman syndrome (GS) is a tubulopathy exhibited by salt loss. GS cases are most often diagnosed by chance blood test. Aside from that, some cases are also diagnosed from tetanic symptoms associated with hypokalemia and/or hypomagnesemia or short stature. As for complications, thyroid dysfunction and short stature are known, but the incidence rates for these complications have not yet been elucidated. In addition, no genotype–phenotype correlation has been identified in GS.

Methods

We examined the clinical characteristics and genotype–phenotype correlation in genetically proven GS cases with homozygous or compound heterozygous variants in SLC12A3 (n = 185).

Results

In our cohort, diagnostic opportunities were by chance blood tests (54.7%), tetany (32.6%), or short stature (7.2%). Regarding complications, 16.3% had short stature, 13.7% had experienced febrile convulsion, 4.3% had thyroid dysfunction, and 2.5% were diagnosed with epilepsy. In one case, QT prolongation was detected. Among 29 cases with short stature, 10 were diagnosed with growth hormone (GH) deficiency and GH replacement therapy started. Interestingly, there was a strong correlation in serum magnesium levels between cases with p.Arg642Cys and/or p.Leu858His and cases without these variants, which are mutational hotspots in the Japanese population (1.76 mg/dl vs. 1.43 mg/dl, P < 0.001).

Conclusion

This study has revealed, for the first time, clinical characteristics in genetically proven GS cases in the Japanese population, including prevalence of complications. Patients with hypokalemia detected by chance blood test should have gene tests performed. Patients with GS need attention for developing extrarenal complications, such as short stature, febrile convulsion, thyroid dysfunction, epilepsy, or QT prolongation. It was also revealed for the first time that hypomagnesemia was not severe in some variants in SLC12A3.

Magnesium and Cardiovascular Disease

Magnesium is the most abundant intracellular divalent cation and essential for maintaining normal cellular physiology and metabolism, acting as a cofactor of numerous enzymes, regulating ion channels and energy generation. In the heart, magnesium plays a key role in modulating neuronal excitation, intracardiac conduction, and myocardial contraction by regulating a number of ion transporters, including potassium and calcium channels. Magnesium also has a role in regulating vascular tone, atherogenesis and thrombosis, vascular calcification, and proliferation and migration of endothelial and vascular smooth muscle cells. As such, magnesium potentially has a major influence on the pathogenesis of cardiovascular disease. As the kidney is a major regulator of magnesium homeostasis, kidney disorders can potentially lead to both magnesium depletion and overload, and as such increase the risk of cardiovascular disease. Observational data have shown an association between low serum magnesium concentrations or magnesium intake and increased atherosclerosis, coronary artery disease, arrhythmias, and heart failure. However, major trials of supplementation with magnesium have reported inconsistent benefits and also raised potential adverse effects of magnesium overload. As such, there is currently no firm recommendation for routine magnesium supplementation except when hypomagnesemia has been proven or suspected as a cause for cardiac arrhythmias.

Coexistence of Gitelman Syndrome and Hypertrophic Cardiomyopathy in a Pregnant Woman

Gitelman syndrome (GS) is transmitted as an autosomal recessive trait and characterized by hypokalemic metabolic alkalosis in combination with significant hypomagnesemia and low urinary calcium excretion. The symptoms and severity of the disease can vary greatly from one person to another and can range from mild to severe. Sudden cardiac arrest has been reported occasionally as well. Here, for the first time, we reported a 34-year-old pregnant GS woman who was diagnosed to have hypertrophic obstructive cardiomyopathy during her cardiac examination for the complaints of palpitation and presyncope.

Gitelman syndrome: consensus and guidance from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference

Gitelman syndrome (GS) is a rare, salt-losing tubulopathy characterized by hypokalemic metabolic alkalosis with hypomagnesemia and hypocalciuria. The disease is recessively inherited, caused by inactivating mutations in the SLC12A3 gene that encodes the thiazide-sensitive sodium-chloride cotransporter (NCC). GS is usually detected during adolescence or adulthood, either fortuitously or in association with mild or nonspecific symptoms or both. The disease is characterized by high phenotypic variability and a significant reduction in the quality of life, and it may be associated with severe manifestations. GS is usually managed by a liberal salt intake together with oral magnesium and potassium supplements. A general problem in rare diseases is the lack of high quality evidence to inform diagnosis, prognosis, and management. We report here on the current state of knowledge related to the diagnostic evaluation, follow-up, management, and treatment of GS; identify knowledge gaps; and propose a research agenda to substantiate a number of issues related to GS. This expert consensus statement aims to establish an initial framework to enable clinical auditing and thus improve quality control of care.

Cryptic exon activation in SLC12A3 in Gitelman syndrome

Gitelman syndrome (GS) is an autosomal recessive renal tubulopathy characterized by hypokalemic metabolic alkalosis with hypocalciuria and hypomagnesemia. GS clinical symptoms range from mild weakness to muscular cramps, paralysis or even sudden death as a result of cardiac arrhythmia. GS is caused by loss-of-function mutations in the solute carrier family 12 member 3 (SLC12A3) gene, but molecular mechanisms underlying such a wide range of symptoms are poorly understood. Here we report cryptic exon activation in SLC12A3 intron 12 in a clinically asymptomatic GS, resulting from an intronic mutation c.1669+297 T>G that created a new acceptor splice site. The cryptic exon was sandwiched between the L3 transposon upstream and a mammalian interspersed repeat downstream, possibly contributing to inclusion of the cryptic exon in mature transcripts. The mutation was identified by targeted next-generation sequencing of candidate genes in GS patients with missing pathogenic SLC12A3 alleles. Taken together, this work illustrates the power of next-generation sequencing to identify causal mutations in intronic regions in asymptomatic individuals at risk of developing potentially fatal disease complications, improving clinical management of these cases.

Understanding the mechanisms of angiotensin II signaling involved in hypertension and its long-term sequelae: insights from Bartter's and Gitelman's syndromes, human models of endogenous angiotensin II signaling antagonism

Angiotensin II (Ang II) plays a key role in hypertension, renal and cardiovascular pathophysiology via intracellular pathways that involve the activation of a multiplicity of signaling mechanisms. Although experimental and genetic animal models have been developed and used to explore Ang II signaling's role in hypertension, a complete understanding of the processes mediating Ang II signaling in hypertension in humans remains elusive. One impediment is that these animal models do not exhibit all the traits of human hypertension, making it impossible to extrapolate from them to humans. To overcome this issue, we have used patients with Bartter's and Gitelman's syndromes, a human model of endogenously blunted and blocked Ang II signaling that presents a constellation of clinical findings which manifest themselves as the opposite of hypertension. This article reviews the aspects of the pathophysiology of human hypertension and its short and long term sequelae, and uses the results of our studies in Bartter's and Gitelman's syndromes along with those of others to gain better insight and understanding of the role of Ang II signaling in these processes.

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.

Angiotensin II and Cardiovascular-Renal Remodelling in Hypertension: Insights from a Human Model Opposite to Hypertension

Insights into the Angiotensin II (Ang II) signalling pathways have been provided by extensive studies using Bartter's/Gitelman's syndromes patients. These syndromes are characterized by activation of the renin-angiotensin-aldosterone system but do not develop hypertension and cardiovascular remodelling, therefore represent a mirror image of hypertension and clinically manifest themselves as the opposite of hypertension. The short and the long-term signalling of Ang II remain an important matter of investigation to shed light on mechanisms responsible for the pathophysiology of hypertension and its long-term complications, such as cardiovascular remodelling and atherogenesis. In particular the long-term signalling of Ang II is involved in the pathophysiology of cardiovascular-renal remodelling, inflammatory and hypertrophic responses in which the relationship between RhoA/Rho kinase pathway and NO system plays a crucial role. This review reports the results of our studies in Bartter's and Gitelman's syndromes to get better insight these processes and the role of Ang II signaling. The information obtained from the studies in Bartter's/Gitelman's patients can, in fact, clarify, confirm or be used to gather more general data on the biochemical mechanisms responsible for the pathophysiology of hypertension and its long-term complications and could contribute to identify additional potential significant targets of therapy.

Miscellaneous non-inflammatory musculoskeletal conditions. Bartter's and Gitelman's diseases

Bartter's and Gitelman's syndromes are two different genetic renal diseases, but are both characterised by hypokalaemia and metabolic alkalosis. Bartter's syndrome is characterised by multiple gene mutations (Na-K-2Cl cotransporter; K(+) channels renal outer medullary potassium channel (ROMK); Cl channels, chloride channel Kb (ClCNKb); regulatory protein Barttin; and Ca(2+) -sensing receptor, CaSR) at the thick ascending limb of Henle's loop, while Gitelman's syndrome is caused by a mutation in the gene encoding the renal thiazide sensitive Na(+)-Cl(-) cotransporter, located in the apical membrane of the distal convoluted tubule. The co-existence of hypokalaemia with hypomagnesaemia and hypocalciuria represents the biochemical hallmark of Gitelman's syndrome that distinguishes it from Bartter's syndrome. Calcium pyrophosphate deposition (CPPD) including chondrocalcinosis has been frequently reported in association with Bartter's syndrome. Some authors postulate that these cases were probably due to Gitelman's syndrome and not due to Bartter's syndrome as all patients had hypomagnesaemia. This electrolyte disorder seems to induce CCP crystal deposition. To date, no cases of CPPD have been reported in patients who had Bartter's syndrome without hypomagnesaemia. CPPD may be found in other conditions associated with hypomagnesaemia, such as short bowel syndrome or tacrolimus therapy in liver transplantation patients. As acute CPP crystal arthropathy or pseudogout can be the onset presentation of Gitelman's syndrome, CPPD should be considered a major feature of this disease. Rheumatologists should be aware of the association between Gitelman's syndrome and CPPD, and should consider this metabolic disorder when CPPD occurs in younger patients.

Localization of tubular adaptation to renal sodium loss in Gitelman syndrome

BACKGROUND AND OBJECTIVES

Gitelman syndrome (GS) is a salt-wasting tubulopathy that results from the inactivation of the human thiazide-sensitive sodium chloride cotransporter located in the distal convoluted tubule. Tubular adaptation to renal sodium loss has been described and localized in the distal tubule in experimental models of GS but not in humans with GS.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The tubular adaptation to renal sodium loss is described. Osmole-free water clearance and endogenous lithium clearance with furosemide infusion are used to compare 7 patients with genetically confirmed GS and 13 control participants.

RESULTS

Neither endogenous lithium clearance nor osmole-free water clearance disclosed enhanced proximal fluid reabsorption in patients with GS. These patients displayed significantly lower osmole-free water clearance factored by inulin clearance (7.1 ± 1.9 versus 10.1 ± 2.2; P<0.01) and significantly lower fractional sodium reabsorption in the diluting nephron (73.2% ± 7.1% versus 86.1% ± 4.7%; P<0.005), consistent with the inactivation of the thiazide-sensitive sodium chloride cotransporter. The furosemide-induced reduction rate of fractional sodium reabsorption in the diluting segment was higher in patients with GS (75.6% ± 6.1% versus 69.9% ± 3.2%; P<0.039), suggesting that sodium reabsorption would be enhanced in the cortical part of the thick ascending limb of the loop of Henle in patients with GS.

CONCLUSIONS

These findings suggest that tubular adaptation to renal sodium loss in GS would be devoted to the cortical part of the thick ascending limb of the loop of Henle in humans.

Eplerenone improved hypokalemia in a patient with Gitelman's syndrome

A 47-year-old woman presented with hypokalemia (2.4 mmol/L). She also had hypomagnesemia, hypocalciuria, and hyperreninemic hyperaldosteronism. Sequence analysis revealed a compound heterozygous mutation, R655C and R955Q, in the SLC12A3 gene. These findings were compatible with Gitelman's syndrome (GS). Eplerenone, a selective aldosterone blocker, in combination with oral potassium chloride improved serum potassium level (3.6 mmol/L) with no apparent adverse effect. Although eplerenone has an advantage over spironolactone for its selective affinity for the aldosterone receptor, the efficacy and safety of eplerenone for GS is little understood. Our observation suggests that eplerenone is a useful treatment option for GS.

Cardiac arrhythmias and rhabdomyolysis in Bartter-Gitelman patients

Recent data demonstrate that patients affected with hypokalemic salt-losing tubulopathies are prone to acute cardiac arrhythmias and rhabdomyolysis. The tendency to these potentially fatal complications is especially high if chronic hypokalemia is severe, in patients with diarrhea, vomiting or a prolonged QT interval on standard electrocardiography, in patients on drug management with compounds prolonging the electrocardiographic QT interval (including antiarrhythmic agents, some antihistamines, macrolides, antifungals, psychotropics, beta2-adrenergic agonists or cisapride), following acute alcohol abuse and during exercise. Cardiac arrhythmias and rhabdomyolysis occur with sufficient frequency in hypokalemic salt-losing tubulopathies to merit wider awareness of their presence and the preparation of specific prevention and management recommendations.

Gitelman syndrome: pathophysiological and clinical aspects

Giltelman syndrome (GS) is a recessive salt-losing tubulopathy of children or young adults caused by a mutation of genes encoding the human sodium chloride cotransporters and magnesium channels in the thiazide-sensitive segments of the distal convoluted tubule. The plasma biochemical picture is characterized by hypokalemia, hypomagnesemia, hypocalciuria, metabolic alkalosis and hypereninemic hyperaldosteronism. However, patients with GS present some clinical and biochemical alterations resembling that observed in thiazide diuretics abuse. On the pathophysiological point of view, GS represents a useful and interesting human model to better understand the clinical consequences of plasma hydro-electrolytes and acid-base derangements, associated with multiple hormonal alterations. The impact of this complex disorder involves cardiovascular, muscle-skeletal and some other physiological functions, adversely affecting the patient's quality of life. This review tries to summarize and better explain the linkage between the electrolytes, neurohormonal derangements and clinical picture. Moreover, the differential diagnosis between other similar electrolyte-induced clinical disorders and GS is also discussed.

An unusual presentation of primary renal hypokalemia-hypomagnesemia (Gitelman's syndrome)

Gitelman's syndrome, or congenital hypokalemic hypomagnesemic hypocalciuria with metabolic alkalosis, is widely described as a benign or milder variant of Bartter's syndrome and most commonly presents with transient periods of weakness and fatigue, presyncope, vertigo, ataxia, and blurred vision, though aborted sudden cardiac death has also been rarely reported. Despite this there are limited data in the literature regarding the formal cardiac evaluation of patients with Gitelman's syndrome. We present the case of a gentleman with Gitelman's syndrome who initially presented to his primary physician with symptoms suggestive of an upper respiratory tract infection and subsequently survived a ventricular fibrillation (VF) cardiac arrest in the community. We review the literature regarding possible life-threatening cardiac complications in these patients.

Gitelman syndrome in Gypsy paediatric patients carrying the same intron 9 + 1 G>T mutation. Clinical features and impact on quality of life

BACKGROUND

Gitelman syndrome is a primary tubular disorder causing hypokalaemic metabolic alkalosis with hypocalciuria. Its prevalence is high in Gypsies, who harbour an identical mutation, intron 9 + 1 G>T, in the SLC12A3 gene.

METHODS

To better define the Gitelman syndrome in Gypsies, the clinical and biochemical features of 34 Spanish paediatric Gypsy patients were analysed. At diagnosis, symptoms, height and weight as well as serum and urinary biochemical data were collected. During a follow-up of 4.5 ± 2.4 years [X ± standard deviation (SD)], therapy, treatment compliance, symptoms, frequency of hospital admissions and, at the last visit, growth and biochemical work-up of 29 patients followed for at least 6 months were analysed. Quality of life items were also assessed by a questionnaire.

RESULTS

Muscle cramps (41%) and asthenia (35%) were the most frequent presenting symptoms. Biochemical data at diagnosis were serum K 2.76 ± 0.46 mEq/L, serum Mg 1.32 ± 0.28 mg/dL, blood pH 7.45 ± 0.06, serum bicarbonate 28.2 ± 2.9 mEq/L, urinary calcium/creatinine ratio 0.03 ± 0.04 mg/mg, fractional K excretion 24.4 ± 17.1% and fractional Mg excretion 8.9 ± 8.3%. During follow-up, Mg and K supplements were prescribed to 79 and 86% of patients, respectively; compliance with treatment was good in 35%. Hospital admission rate was 0.03/patient/month. Muscle cramps were the symptom most often referred by the patients (45%) during the follow-up, and 71% of patients considered their health status as excellent or good. Twenty-one patients stated that their disease did not adversely interfere with their mood or social relationships. Height and weight of patients at diagnosis were -0.60 ± 1.17 and -0.49 ± 1.32 SD, respectively, and improved to -0.44 ± 1.28 (P < 0.05) and 0.18 ± 1.79 SD (P < 0.01) at the last visit.

CONCLUSIONS

Gypsy children with Gitelman syndrome mostly exhibit muscle symptoms and asthenia although the disease is not particularly severe in this ethnic group. Body growth improves with treatment and close follow-up.

Electrocardiography as an early cardiac screening test in children with mitochondrial disease

Purpose

To evaluate myocardial conductivity to understand cardiac involvement in patients with mitochondrial disease.

Methods

We performed retrospective study on fifty-seven nonspecific mitochondrial encephalopathy patients with no clinical cardiac manifestations. The patients were diagnosed with mitochondrial respiratory chain complex defects through biochemical enzyme assays of muscle tissue. We performed standard 12-lead electrocardiography (ECG) on all patients.

Results

ECG abnormalities were observed in 30 patients (52.6%). Prolongation of the QTc interval (>440 ms) was seen in 19 patients (33.3%), widening of the corrected QRS interval in 15 (26.3%), and bundle branch block in four (7.0%). Atrioventricular block, premature atrial contraction and premature ventricular contraction were seen in two patients each (3.5%) and Wolff-Parkinson-White syndrome in one patient (1.8%).

Conclusion

Given this finding, we recommend active screening with ECG in patients with mitochondrial disease even in patients without obvious cardiac manifestation.

Myocardial perfusion defects in Bartter and Gitelman syndromes

BACKGROUND

Normotensive hypokalaemic tubulopathies (Bartter and Gitelman syndromes (BS/GS)) are genetic diseases that are considered benign. However, QT prolongation, left ventricular dysfunction and reduction of cardiac index upon exercise leading to arrhythmias and sudden cardiac death have been reported in these patients. Hence, we aimed to verifying whether an isometric exercise could represent a useful tool for the identification of patients at risk for future cardiac events.

PATIENTS AND METHODS

Myocardial function (MF) and perfusion, evaluated as myocardial blood flow (MBF) of 10 BS/GS patients and 10 healthy controls, were investigated at rest and during isometric exercise. MF and MBF were evaluated using quantitative two-dimensional and myocardial contrast echocardiography.

RESULTS

BS/GS patients had normal baseline MF and MBF. During exercise in BS/GS patients, corrected QT (QTc) was prolonged to peak value of 494 +/- 9.1 ms (P < 0.001). In controls, MF increased from resting to peak exercise (left ventricular ejection fraction: 65 +/- 4% to 78 +/- 5%, P < 0.003) while in seven BS/GS patients (Group 1) it declined (64 +/- 5% to 43 +/- 9%, P < 0.001). Myocardial perfusion increased upon exercise in controls as shown by changes of its markers: beta (a measure of myocardial flow velocity; 0.89 +/- 0.12 vs. 0.99 +/- 0.12, P < 0.001) and myocardial blood volume (14.4 +/- 2 vs. 20.2 +/- 0.25, P < 0.001), while in Group 1 BS/GS it decreased (0.87 +/- 0.15 vs. 0.67 +/- 0.15, P < 0.001; and 14.5 +/- 1.9 vs. 8.3 +/- 0.22, P < 0.001, respectively).

CONCLUSIONS

Our results document for the first time that exercise induce coronary microvascular and myocardial defects in BS/GS patients. Therefore, this may challenge the idea that BS/GS are benign diseases. In addition, the diagnostic approach to these syndromes should include an in-depth cardiac assessment in order to identify patients at higher risk.

Loss of consciousness and hypokalemia in an elderly man with a mutation of the thiazide-sensitive Na-Cl cotransporter gene

An 80-year-old man was referred to our department for evaluation of repetitive loss of consciousness and faintness with hypokalemia. He had relatively low blood pressure, hypomagnesemia, hypocalciuria and chondrocalcinosis in the knee, clinically suggesting Gitelman's syndrome. A renal clearance study could not be carried out due to the patient's age and complications of the heart. Sequence analysis of the gene of thiazide-sensitive Na-Cl cotransporter (TSC) showed a heterozygous missense mutation from C to T at 1712 base pairs from the translation start site, with resultant changes in codon 569 from alanine to valine (A569V). Treatment with oral administration of potassium chloride improved all the symptoms. Although Gitelman's syndrome has been considered to be autosomal recessive, cases of only heterozygous mutation detected have recently been reported. Therefore, the mutation found in this patient may be responsible for Gitelman's syndrome.

Inherited Renal Tubulopathies Associated With Metabolic Alkalosis: Effects on Blood Pressure

Inherited tubular disorders associated with metabolic alkalosis are caused by several gene mutations encoding different tubular transporters responsible for NaCl renal handling. Body volume and renin-angiotensin-aldosterone system status are determined by NaCl reabsorption in the distal nephron. Two common hallmarks in affected individuals: hypokalemia and normal / high blood pressure, support the differential diagnosis. Bartter's syndrome, characterized by hypokalemia and normal blood pressure, is a heterogenic disease caused by the loss of function of SLC12A1 (type 1), KCNJ1 (type 2), CLCNKB (type 3), or BSND genes (type 4). As a result, patients present with renal salt wasting and hypercalciuria. Gitelman's syndrome is caused by the loss of funcion of the SLC12A3 gene and may resemble Bartter's syndrome, though is associated with the very low urinary calcium. Liddle's syndrome, also with similar phenotype but with hypertension, is produced by the gain of function of the SNCC1B or SNCC1G genes, and must be distinguished from other entities of inherited hypertension such as Apparently Mineralocorticoid Excess, of glucocorticoid remediable hypertension.

Sclerochoroidal calcification associated with Gitelman syndrome and calcium pyrophosphate dihydrate deposition

Sclerochoroidal calcification is an uncommon condition. Metabolic evaluation and clinical examination are important to exclude associated systemic conditions such as the Bartter and Gitelman syndromes. It has been suggested that the lesions seen in sclerochoroidal calcification are calcium pyrophosphate dihydrate crystals. This report describes the first documented case in the UK of sclerochoroidal calcification associated with Gitelman syndrome and calcium pyrophosphate dihydrate deposition.

Severe syncope and sudden death in children with inborn salt-losing hypokalaemic tubulopathies

BACKGROUND

Potassium deficiency may cause cardiac arrhythmias culminating in syncope or sudden death.

METHODS

An inquiry performed among physicians caring for a total of 249 patients with inborn salt-losing tubulopathies revealed that acute cardiac complications occurred in seven children.

RESULTS

Four patients died suddenly and three had severe syncope. These episodes occurred in the context of severe chronic hypokalaemia (< or =2.5 mmol/l) or were precipitated by acute diseases, which exacerbated hypokalaemia (< or =2.0 mmol/l).

CONCLUSIONS

In conclusion, severe chronic or acute hypokalaemia is hazardous in inborn salt-losing tubulopathies.