[Regulation of kidney on potassium balance and its clinical significance].

Virtually all of the dietary potassium intake is absorbed in the intestine, over 90% of which is excreted by the kidneys regarded as the most important organ of potassium excretion in the body. The renal excretion of potassium results primarily from the secretion of potassium by the principal cells in the aldosterone-sensitive distal nephron (ASDN), which is coupled to the reabsorption of Na+ by the epithelial Na+ channel (ENaC) located at the apical membrane of principal cells. When Na+ is transferred from the lumen into the cell by ENaC, the negativity in the lumen is relatively increased. K+ efflux, H+ efflux, and Cl- influx are the 3 pathways that respond to Na+ influx, that is, all these 3 pathways are coupled to Na+ influx. In general, Na+ influx is equal to the sum of K+ efflux, H+ efflux, and Cl- influx. Therefore, any alteration in Na+ influx, H+ efflux, or Cl- influx can affect K+ efflux, thereby affecting the renal K+ excretion. Firstly, Na+ influx is affected by the expression level of ENaC, which is mainly regulated by the aldosterone-mineralocorticoid receptor (MR) pathway. ENaC gain-of-function mutations (Liddle syndrome, also known as pseudohyperaldosteronism), MR gain-of-function mutations (Geller syndrome), increased aldosterone levels (primary/secondary hyperaldosteronism), and increased cortisol (Cushing syndrome) or deoxycorticosterone (hypercortisolism) which also activate MR, can lead to up-regulation of ENaC expression, and increased Na+ reabsorption, K+ excretion, as well as H+ excretion, clinically manifested as hypertension, hypokalemia and alkalosis. Conversely, ENaC inactivating mutations (pseudohypoaldosteronism type 1b), MR inactivating mutations (pseudohypoaldosteronism type 1a), or decreased aldosterone levels (hypoaldosteronism) can cause decreased reabsorption of Na+ and decreased excretion of both K+ and H+, clinically manifested as hypotension, hyperkalemia, and acidosis. The ENaC inhibitors amiloride and Triamterene can cause manifestations resembling pseudohypoaldosteronism type 1b; MR antagonist spironolactone causes manifestations similar to pseudohypoaldosteronism type 1a. Secondly, Na+ influx is regulated by the distal delivery of water and sodium. Therefore, when loss-of-function mutations in Na+-K+-2Cl- cotransporter (NKCC) expressed in the thick ascending limb of the loop and in Na+-Cl- cotransporter (NCC) expressed in the distal convoluted tubule (Bartter syndrome and Gitelman syndrome, respectively) occur, the distal delivery of water and sodium increases, followed by an increase in the reabsorption of Na+ by ENaC at the collecting duct, as well as increased excretion of K+ and H+, clinically manifested as hypokalemia and alkalosis. Loop diuretics acting as NKCC inhibitors and thiazide diuretics acting as NCC inhibitors can cause manifestations resembling Bartter syndrome and Gitelman syndrome, respectively. Conversely, when the distal delivery of water and sodium is reduced (e.g., Gordon syndrome, also known as pseudohypoaldosteronism type 2), it is manifested as hypertension, hyperkalemia, and acidosis. Finally, when the distal delivery of non-chloride anions increases (e.g., proximal renal tubular acidosis and congenital chloride-losing diarrhea), the influx of Cl- in the collecting duct decreases; or when the excretion of hydrogen ions by collecting duct intercalated cells is impaired (e.g., distal renal tubular acidosis), the efflux of H+ decreases. Both above conditions can lead to increased K+ secretion and hypokalemia. In this review, we focus on the regulatory mechanisms of renal potassium excretion and the corresponding diseases arising from dysregulation.

Regulation of kidney on potassium balance and its clinical significance / 生理学报

Virtually all of the dietary potassium intake is absorbed in the intestine, over 90% of which is excreted by the kidneys regarded as the most important organ of potassium excretion in the body. The renal excretion of potassium results primarily from the secretion of potassium by the principal cells in the aldosterone-sensitive distal nephron (ASDN), which is coupled to the reabsorption of Na+ by the epithelial Na+ channel (ENaC) located at the apical membrane of principal cells. When Na+ is transferred from the lumen into the cell by ENaC, the negativity in the lumen is relatively increased. K+ efflux, H+ efflux, and Cl- influx are the 3 pathways that respond to Na+ influx, that is, all these 3 pathways are coupled to Na+ influx. In general, Na+ influx is equal to the sum of K+ efflux, H+ efflux, and Cl- influx. Therefore, any alteration in Na+ influx, H+ efflux, or Cl- influx can affect K+ efflux, thereby affecting the renal K+ excretion. Firstly, Na+ influx is affected by the expression level of ENaC, which is mainly regulated by the aldosterone-mineralocorticoid receptor (MR) pathway. ENaC gain-of-function mutations (Liddle syndrome, also known as pseudohyperaldosteronism), MR gain-of-function mutations (Geller syndrome), increased aldosterone levels (primary/secondary hyperaldosteronism), and increased cortisol (Cushing syndrome) or deoxycorticosterone (hypercortisolism) which also activate MR, can lead to up-regulation of ENaC expression, and increased Na+ reabsorption, K+ excretion, as well as H+ excretion, clinically manifested as hypertension, hypokalemia and alkalosis. Conversely, ENaC inactivating mutations (pseudohypoaldosteronism type 1b), MR inactivating mutations (pseudohypoaldosteronism type 1a), or decreased aldosterone levels (hypoaldosteronism) can cause decreased reabsorption of Na+ and decreased excretion of both K+ and H+, clinically manifested as hypotension, hyperkalemia, and acidosis. The ENaC inhibitors amiloride and Triamterene can cause manifestations resembling pseudohypoaldosteronism type 1b; MR antagonist spironolactone causes manifestations similar to pseudohypoaldosteronism type 1a. Secondly, Na+ influx is regulated by the distal delivery of water and sodium. Therefore, when loss-of-function mutations in Na+-K+-2Cl- cotransporter (NKCC) expressed in the thick ascending limb of the loop and in Na+-Cl- cotransporter (NCC) expressed in the distal convoluted tubule (Bartter syndrome and Gitelman syndrome, respectively) occur, the distal delivery of water and sodium increases, followed by an increase in the reabsorption of Na+ by ENaC at the collecting duct, as well as increased excretion of K+ and H+, clinically manifested as hypokalemia and alkalosis. Loop diuretics acting as NKCC inhibitors and thiazide diuretics acting as NCC inhibitors can cause manifestations resembling Bartter syndrome and Gitelman syndrome, respectively. Conversely, when the distal delivery of water and sodium is reduced (e.g., Gordon syndrome, also known as pseudohypoaldosteronism type 2), it is manifested as hypertension, hyperkalemia, and acidosis. Finally, when the distal delivery of non-chloride anions increases (e.g., proximal renal tubular acidosis and congenital chloride-losing diarrhea), the influx of Cl- in the collecting duct decreases; or when the excretion of hydrogen ions by collecting duct intercalated cells is impaired (e.g., distal renal tubular acidosis), the efflux of H+ decreases. Both above conditions can lead to increased K+ secretion and hypokalemia. In this review, we focus on the regulatory mechanisms of renal potassium excretion and the corresponding diseases arising from dysregulation.

R158Q and G212S, novel pathogenic compound heterozygous variants in SLC12A3 of Gitelman syndrome.

The dysfunction of Na+-Cl- cotransporter (NCC) caused by mutations in solute carrier family12, member 3 gene (SLC12A3) primarily causes Gitelman syndrome (GS). In identifying the pathogenicity of R158Q and G212S variants of SLC12A3, we evaluated the pathogenicity by bioinformatic, expression, and localization analysis of two variants from a patient in our cohort. The prediction of mutant protein showed that p.R158Q and p.G212S could alter protein's three-dimensional structure. Western blot showed a decrease of mutant Ncc. Immunofluorescence of the two mutations revealed a diffuse positive staining below the plasma membrane. Meanwhile, we conducted a compound heterozygous model-Ncc R156Q/G210S mice corresponding to human NCC R158Q/G212S. NccR156Q/G210S mice clearly exhibited typical GS features, including hypokalemia, hypomagnesemia, and increased fractional excretion of K+ and Mg2+ with a normal blood pressure level, which made NccR156Q/G210S mice an optimal mouse model for further study of GS. A dramatic decrease and abnormal localization of the mutant Ncc in distal convoluted tubules contributed to the phenotype. The hydrochlorothiazide test showed a loss of function of mutant Ncc in NccR156Q/G210S mice. These findings indicated that R158Q and G212S variants of SLC12A3 were pathogenic variants of GS.

Gitelman's and Bartter's Syndromes: From Genetics to the Molecular Basis of Hypertension and More.

BACKGROUND: Gitelman's and Bartter's syndromes (GS/BS) are rare genetic tubulopathies characterized by electrolyte imbalance and activation of the renin-angiotensin-aldosterone system (RAAS). These syndromes have intriguing biochemical and hormonal abnormalities that lead them to be protected from hypertension and cardiovascular and renal remodeling. SUMMARY: In this review, we explore the biochemical/molecular mechanisms induced by the activation of the RAAS and its counterregulatory arm which is particularly activated in GS/BS patients, in the context of blood pressure regulation. In addition, we report our findings in the context of the COVID-19 pandemic where we observed GS/BS subjects being protected from infection. KEY MESSAGES: The intracellular pathways induced by Ang II, starting from induction of oxidative stress and vasoconstriction, are crucial for the progression toward cardiovascular-renal remodeling and might be useful targets in order to reduce/halt the progression of Ang II/oxidative stress-induced cardiovascular-renal morbidity in several diseases.

Different roles of the RAAS affect bone metabolism in patients with primary aldosteronism, Gitelman syndrome and Bartter syndrome.

BACKGROUND: Components of the RAAS may influence bone metabolism. Different roles of the RAAS are found in patients with primary aldosteronism (PA), Gitelman syndrome (GS) and Bartter syndrome (BS). We collected inpatient medical records including 20 patients with Gitelman syndrome (GS group), 17 patients with Bartter syndrome (BS group) and 20 age-matched patients with primary aldosteronism (PA group). We found the following results. (1) PA patients had significantly higher serum magnesium, potassium, plasma aldosterone, serum parathyroid hormone, urinary calcium and BMI (p<0.05) while significantly lower serum calcium and phosphorus (P < 0.05) than GS and BS patients. (2) Total hip and femoral neck bone mineral density (BMD) in PA patients were significantly lower than those in GS and BS patients (P<0.05). (3) GS patients had lower serum magnesium and urinary calcium than BS patients (P < 0.05). (4) Compared with BS patients, the vertebral BMD in GS patients were significantly higher (P < 0.05). So we believe higher aldosterone and PTH levels may be the reason that PA patients have lower hip BMD. Lower urinary calcium and inactivation of the NCC gene (Na-Cl cotransporter) in GS patients may have protective effects on vertebral bone mineral density. CONCLUSIONS: With persistence disordered RAAS, PA patients have lower BMD, especially hip BMD as compared with GS and BS patients. We presumed the lower renin and higher aldosterone level may be the reason. With the same level of renin and aldosterone, BS patients have lower vertebrate BMD than GS patients. Decreased urinary calcium excretion may be the reason.

Gitelman-Like Syndrome Caused by Pathogenic Variants in mtDNA.

BACKGROUND: Gitelman syndrome is the most frequent hereditary salt-losing tubulopathy characterized by hypokalemic alkalosis and hypomagnesemia. Gitelman syndrome is caused by biallelic pathogenic variants in SLC12A3, encoding the Na+-Cl- cotransporter (NCC) expressed in the distal convoluted tubule. Pathogenic variants of CLCNKB, HNF1B, FXYD2, or KCNJ10 may result in the same renal phenotype of Gitelman syndrome, as they can lead to reduced NCC activity. For approximately 10 percent of patients with a Gitelman syndrome phenotype, the genotype is unknown. METHODS: We identified mitochondrial DNA (mtDNA) variants in three families with Gitelman-like electrolyte abnormalities, then investigated 156 families for variants in MT-TI and MT-TF, which encode the transfer RNAs for phenylalanine and isoleucine. Mitochondrial respiratory chain function was assessed in patient fibroblasts. Mitochondrial dysfunction was induced in NCC-expressing HEK293 cells to assess the effect on thiazide-sensitive 22Na+ transport. RESULTS: Genetic investigations revealed four mtDNA variants in 13 families: m.591C>T (n=7), m.616T>C (n=1), m.643A>G (n=1) (all in MT-TF), and m.4291T>C (n=4, in MT-TI). Variants were near homoplasmic in affected individuals. All variants were classified as pathogenic, except for m.643A>G, which was classified as a variant of uncertain significance. Importantly, affected members of six families with an MT-TF variant additionally suffered from progressive chronic kidney disease. Dysfunction of oxidative phosphorylation complex IV and reduced maximal mitochondrial respiratory capacity were found in patient fibroblasts. In vitro pharmacological inhibition of complex IV, mimicking the effect of the mtDNA variants, inhibited NCC phosphorylation and NCC-mediated sodium uptake. CONCLUSION: Pathogenic mtDNA variants in MT-TF and MT-TI can cause a Gitelman-like syndrome. Genetic investigation of mtDNA should be considered in patients with unexplained Gitelman syndrome-like tubulopathies.

A novel homozygous mutation (p.N958K) of SLC12A3 in Gitelman syndrome is associated with endoplasmic reticulum stress.

PURPOSE: Gitelman syndrome (GS) is an autosomal recessive renal tubular disease that arises as a consequence of mutations in the SLC12A3 gene, which codes for an Na-Cl cotransporter (NCC) in distal renal tubules. This study was designed to explore the mutations associated with GS in an effort to more fully understand the molecular mechanisms governing GS. METHODS: We analyzed SLC12A3 mutations in a pedigree including a 42-year-old male with GS as well as four related family members over three generations using Sanger and next generation sequencing approaches. We additionally explored the functional ramifications of identified mutations using both Xenopus oocytes and the HEK293T cell line. RESULTS: We found that the subject with GS exhibited characteristic symptoms including sporadic thirst, fatigue, excess urination, and substantial hypokalemia and hypocalciuria, although magnesium levels were normal. Other analyzed subjects in this pedigree had normal laboratory findings and did not exhibit clear signs of GS. Sequencing analyses revealed that the GS subject exhibited a homozygous missense mutation (c.2874C > G, p.N958K) in exon 24 of SLC12A3. Both parents of this GS subject, as well as his older brother and daughter all exhibited heterozygous mutations at this same site. Functional analyses in Xenopus oocytes indicated that this mutated SLC12A3 gene encodes a protein which fails to mediate normal sodium transport, and when this mutant gene was expressed in HEK293T cells, we observed significant increases in endoplasmic reticulum (ER)-stress pathway activation. CONCLUSION: The p.N958K mutation in exon 24 of SLC12A3 can trigger GS at least in part via enhancing ER stress responses.

Abnormal FDG Biodistribution in a Patient With Gitelman Syndrome.

ABSTRACT: Gitelman syndrome is an autosomal recessive renal tubulopathy. A 38-year-old woman was diagnosed with Gitelman syndrome. Eight years later, 18F-FDG PET/CT was performed to evaluate recurrence of endometrial cancer. FDG PET images showed an extremely abnormal FDG biodistribution. They showed decreased brain uptake, increased cardiac muscle uptake, and diffuse increased muscle and adipose tissue uptake. This pattern is similar to high insulin state; however, her glucose level was normal, and insulin level was very low.

NaCl cotransporter activity and Mg2+ handling by the distal convoluted tubule.

The genetic disease Gitelman syndrome, knockout mice, and pharmacological blockade with thiazide diuretics have revealed that reduced activity of the NaCl cotransporter (NCC) promotes renal Mg2+ wasting. NCC is expressed along the distal convoluted tubule (DCT), and its activity determines Mg2+ entry into DCT cells through transient receptor potential channel subfamily M member 6 (TRPM6). Several other genetic forms of hypomagnesemia lower the drive for Mg2+ entry by inhibiting activity of basolateral Na+-K+-ATPase, and reduced NCC activity may do the same. Lower intracellular Mg2+ may promote further Mg2+ loss by directly decreasing activity of Na+-K+-ATPase. Lower intracellular Mg2+ may also lower Na+-K+-ATPase indirectly by downregulating NCC. Lower NCC activity also induces atrophy of DCT cells, decreasing the available number of TRPM6 channels. Conversely, a mouse model with increased NCC activity was recently shown to display normal Mg2+ handling. Moreover, recent studies have identified calcineurin and uromodulin (UMOD) as regulators of both NCC and Mg2+ handling by the DCT. Calcineurin inhibitors paradoxically cause hypomagnesemia in a state of NCC activation, but this may be related to direct effects on TRPM6 gene expression. In Umod-/- mice, the cause of hypomagnesemia may be partly due to both decreased NCC expression and lower TRPM6 expression on the cell surface. This mini-review discusses these new findings and the possible role of altered Na+ flux through NCC and ultimately Na+-K+-ATPase in Mg2+ reabsorption by the DCT.

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.

Identification of compound mutations of SLC12A3 gene in a Chinese pedigree with Gitelman syndrome exhibiting Bartter syndrome-liked phenotypes.

BACKGROUND: Gitelman syndrome is a rare salt-losing renal tubular disorder associated with mutation of SLC12A3 gene, which encodes the Na-Cl co-transporter (NCCT). Gitelman syndrome is characterized by hypokalemia, metabolic alkalosis, hypomagnesemia, hypocalciuria, and renin-angiotensin-aldosterone system (RAAS) activation. Different SLC12A3 variants may lead to phenotypic variability and severity. METHODS: In this study, we reported the clinical features and genetic analysis of a Chinese pedigree diagnosed with Gitelman syndrome. RESULTS: The proband exhibited hypokalaemia, hypomagnesemia, metabolic alkalosis, but hypercalciuria and kidney stone formation. The increased urinary calcium excretion made it confused to Bartter syndrome. The persistent renal potassium wasting resulted in renal tubular lesions, and might affect urinary calcium reabsorption and excretion. Genetic analysis revealed mutations of SLC12A3 gene with c.433C > T (p.Arg145Cys), c.1077C > G (p.Asn359Lys), and c.1666C > T (p.Pro556Ser). Potential alterations of structure and function of NCCT protein due to those genetic variations of SLC12A3 are predicted. Interestingly, one sibling of the proband carried the same mutant sites and exhibited similar clinical features with milder phenotypes of hypokalemia and hypomagnesemia, but hypocalciuria rather than hypercalciuria. Family members with at least one wild type copy of SLC12A3 had normal biochemistry. With administration of spironolactone, potassium chloride and magnesium supplement, the serum potassium and magnesium were maintained within normal ranges. CONCLUSIONS: In this study, we identified compound mutations of SLC12A3 associated with varieties of clinical features. Further efforts are needed to investigate the diversity in clinical manifestations of Gitelman syndrome and its correlation with specific SLC12A3 mutations.

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+.

[Gitelman syndrome]. / Síndrome de Gitelman.

Gitelman syndrome is one of the salt losing tubulopathies. Hypokalemia and hypomagnesemia appear in the setting of the partial blockade of salt absorption in the distal tubule. We conducted a descriptive study of a case series of five patients with Gitelman syndrome (4 women, from 28 to 85 years) in our institution, between the years 2004 and 2015. The most frequent form of diagnosis in our series was by laboratory finding. The only acknowledged clinical symptom was malaise. Regarding laboratory findings, the mean potassemia was of 2.5 ± 0.5 mmol/l, with a minimum value of 2.1 mmol/l. Additionally, the serum magnesium value was of 1.3 ± 0.3 mg/dl. In conclusion, we observed that the forms of presentation consist of biochemical alterations with or without nonspecific manifestations, which currently represents the greatest diagnostic difficulty and reinforces the importance to achieve a timely diagnosis, especially in young patients with critical serum potassium values.

El síndrome de Gitelman forma parte de las denominadas tubulopatías perdedoras de sal. El bloqueo parcial de la reabsorción de sodio en el túbulo contorneado distal determina la aparición de hipokalemia e hipomagnesemia. Se realizó un estudio descriptivo de una serie de cinco casos de síndrome de Gitelman (4 mujeres, de 28 a 85 años de edad) atendidos en nuestra institución entre los años 2004 y 2015. La forma de diagnóstico más frecuente en nuestra serie fue por hallazgo de laboratorio. El único síntoma clínico manifestado en forma espontánea fue astenia. En cuanto a los valores de laboratorio, la potasemia fue 2.5 ± 0.5 mmol/l, con un valor mínimo de 2.1. Adicionalmente, el valor de magnesio en sangre fue 1.3 ± 0.3 mg/dl. Como conclusión, observamos que las formas de presentación consisten en alteraciones bioquímicas con o sin manifestaciones inespecíficas, lo que representa actualmente la mayor dificultad diagnóstica y refuerza la importancia de lograr un diagnóstico oportuno, en especial en pacientes jóvenes y con valores críticos de potasio sérico.

Síndrome de Gitelman / Gitelman syndrome

El síndrome de Gitelman forma parte de las denominadas tubulopatías perdedoras de sal. El bloqueo parcial de la reabsorción de sodio en el túbulo contorneado distal determina la aparición de hipokalemia e hipomagnesemia. Se realizó un estudio descriptivo de una serie de cinco casos de síndrome de Gitelman (4 mujeres, de 28 a 85 años de edad) atendidos en nuestra institución entre los años 2004 y 2015. La forma de diagnóstico más frecuente en nuestra serie fue por hallazgo de laboratorio. El único síntoma clínico manifestado en forma espontánea fue astenia. En cuanto a los valores de laboratorio, la potasemia fue 2.5 ± 0.5 mmol/l, con un valor mínimo de 2.1. Adicionalmente, el valor de magnesio en sangre fue 1.3 ± 0.3 mg/dl. Como conclusión, observamos que las formas de presentación consisten en alteraciones bioquímicas con o sin manifestaciones inespecíficas, lo que representa actualmente la mayor dificultad diagnóstica y refuerza la importancia de lograr un diagnóstico oportuno, en especial en pacientes jóvenes y con valores críticos de potasio sérico.

Gitelman syndrome is one of the salt losing tubulopathies. Hypokalemia and hypomagnesemia appear in the setting of the partial blockade of salt absorption in the distal tubule. We conducted a descriptive study of a case series of five patients with Gitelman syndrome (4 women, from 28 to 85 years) in our institution, between the years 2004 and 2015. The most frequent form of diagnosis in our series was by laboratory finding. The only acknowledged clinical symptom was malaise. Regarding laboratory findings, the mean potassemia was of 2.5 ± 0.5 mmol/l, with a minimum value of 2.1 mmol/l. Additionally, the serum magnesium value was of 1.3 ± 0.3 mg/dl. In conclusion, we observed that the forms of presentation consist of biochemical alterations with or without nonspecific manifestations, which currently represents the greatest diagnostic difficulty and reinforces the importance to achieve a timely diagnosis, especially in young patients with critical serum potassium values.

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.

Loss of sodium chloride co-transporter impairs the outgrowth of the renal distal convoluted tubule during renal development.

BACKGROUND: Loss-of-function mutations in the sodium chloride (NaCl) co-transporter (NCC) of the renal distal convoluted tubule (DCT) cause Gitelman syndrome with hypokalemic alkalosis, hypomagnesemia and hypocalciuria. Since Gitelman patients are usually diagnosed around adolescence, we tested the idea that a progressive regression of the DCT explains the late clinical onset of the syndrome. METHODS: NCC wild-type and knockout (ko) mice were studied at Days 1, 4 and 10 and 6 weeks after birth using blood plasma analysis and morphological and biochemical methods. RESULTS: Plasma aldosterone levels and renal renin messenger RNA expression were elevated in NCC ko mice during the first days of life. In contrast, plasma ion levels did not differ between genotypes at age 10 days, but a significant hypomagnesemia was observed in NCC ko mice at 6 weeks. Immunofluorescent detection of parvalbumin (an early DCT marker) revealed that the fractional cortical volume of the early DCT is similar for mice of both genotypes at Day 4, but is significantly lower at Day 10 and is almost zero at 6 weeks in NCC ko mice. The DCT atrophy correlates with a marked reduction in the abundance of the DCT-specific Mg2+ channel TRPM6 (transient receptor potential cation channel subfamily M member 6) and an increased proteolytic activation of the epithelial Na+ channel (ENaC). CONCLUSION: After an initial outgrowth, DCT development lags behind in NCC ko mice. The impaired DCT development associates at Day 1 and Day 10 with elevated renal renin and plasma aldosterone levels and activation of ENaC, respectively, suggesting that Gitelman syndrome might be present much earlier in life than is usually expected. Despite an early downregulation of TRPM6, hypomagnesemia is a rather late symptom.

Genetic Analysis of SLC12A3 Gene in Chinese Patients with Gitelman Syndrome.

BACKGROUND The incidence of Gitelman syndrome (GS) has been increasing in our hospital. The aim of this study was to explore the diagnostic accuracy and features of SLC12A3 gene in Chinese patients with GS. MATERIAL AND METHODS We searched the literature about Chinese patients with GS in the PubMed database up to July 2018 and also included 8 GS Chinese patients from our hospital in our analysis that explored the features of SLC12A3 gene. We divided all the patients into 3 groups according to diagnostic consensus. Complete compliance was defined to mean containing 2 allelic mutations, partial compliance to mean one allelic mutation, and clinical compliance to mean no mutations. RESULTS Totally, 137 patients were enrolled in this study and 90 mutations were counted. Missense mutations accounted for over 72% in Chinese GS patients and the most common one was Thr60Met. According to the consensus, there were 102 patients (74.5%) in the complete compliance group, 31 patients (22.6%) in the partial compliance group, and only 4 patients (2.9%) in the clinical compliance group. CONCLUSIONS The SLC12A3 gene analysis in Chinese GS patients revealed that the most common mutation was Thr60Met, one of the missense mutations. Most of the patients were in the complete compliance group (i.e., 2 allelic mutations); the other cases might be explained by gene rearrangement.

Rapid Aldosterone-Mediated Signaling in the DCT Increases Activity of the Thiazide-Sensitive NaCl Cotransporter.

BACKGROUND: The NaCl cotransporter NCC in the kidney distal convoluted tubule (DCT) regulates urinary NaCl excretion and BP. Aldosterone increases NaCl reabsorption via NCC over the long-term by altering gene expression. But the acute effects of aldosterone in the DCT are less well understood. METHODS: Proteomics, bioinformatics, and cell biology approaches were combined with animal models and gene-targeted mice. RESULTS: Aldosterone significantly increases NCC activity within minutes in vivo or ex vivo. These effects were independent of transcription and translation, but were absent in the presence of high potassium. In vitro, aldosterone rapidly increased intracellular cAMP and inositol phosphate accumulation, and altered phosphorylation of various kinases/kinase substrates within the MAPK/ERK, PI3K/AKT, and cAMP/PKA pathways. Inhibiting GPR30, a membrane-associated receptor, limited aldosterone's effects on NCC activity ex vivo, and NCC phosphorylation was reduced in GPR30 knockout mice. Phosphoproteomics, network analysis, and in vitro studies determined that aldosterone activates EGFR-dependent signaling. The EGFR immunolocalized to the DCT and EGFR tyrosine kinase inhibition decreased NCC activity ex vivo and in vivo. CONCLUSIONS: Aldosterone acutely activates NCC to modulate renal NaCl excretion.

Digenetic inheritance of SLC12A3 and CLCNKB genes in a Chinese girl with Gitelman syndrome.

BACKGROUND: Gitelman syndrome (GS) is an autosomal recessive disorder and mild variant of classic Bartter syndrome. The latter is caused by defects in the genes CLCNKB and/or CLCNKA (chloride voltage-gated channel Ka and Kb). Patients with GS usually have loss-of-function mutations in SLC12A3. No patient has been reported with compound heterozygous mutations in these genes. We report a girl with GS with a paternally inherited heterozygous mutation in SLC12A3, and maternally inherited heterozygous variants in both CLCNKB and CLCNKA. CASE PRESENTATION: In this report, we reported a female patient (8 y and 10 mo) who had growth retardation (111.8 cm, - 1.62 standard deviation height for age) and normal blood pressure, with persistent hypokalemia, hypomagnesemia, hypocalciuria, hypochloremic alkalosis, and elevated levels of plasma renin and aldosterone. Her younger brother, father, and paternal grandmother all had histories of mild low levels of plasma potassium (3.0-3.5 mmol/L), which were rectified by potassium-rich foods. The genomic DNA of the patient, younger brother, parents, and grandparents were screened for gene variations and pedigree analysis using trio whole exome sequencing (WES). The candidate variants were validated by Sanger sequencing. Protein-protein interaction analysis utilized the following databases: Biogrid, MINT, HPRD, STRING, IntAct, iRefIndex, and ppiTrim. The trio WES screening showed that the patient has paternally inherited SLC12A3 p.N359K, and maternally inherited CLCNKB p.L94I. The paternal grandmother and younger brother are both carriers of SLC12A3 p.N359K. According to the STRING database, SLC12A3 and CLCNKB proteins may interact or coexpress with proteins associated with GS. CONCLUSIONS: Based on clinical phenotypes, genetic evidence of the pedigree, and previous reported studies, this case of GS indicates a digenetic inheritance of SLC12A3 and CLCNKB that resulted in renal tubular dysfunction perhaps, due to a genetic double-hit mechanism. The putative pathogenicity of the CLCNKB p.L94I variant requires confirmation.