Heterozygosity for a Pathogenic Variant in SLC12A3 That Causes Autosomal Recessive Gitelman Syndrome Is Associated with Lower Serum Potassium.

BACKGROUND: Potassium levels regulate multiple physiologic processes. The heritability of serum potassium level is moderate, with published estimates varying from 17% to 60%, suggesting genetic influences. However, the genetic determinants of potassium levels are not generally known. METHODS: A whole-exome sequencing association study of serum potassium levels in 5812 subjects of the Old Order Amish was performed. A dietary salt intervention in 533 Amish subjects estimated interaction between p.R642G and sodium intake. RESULTS: A cluster of variants, spanning approximately 537 kb on chromosome 16q13, was significantly associated with serum potassium levels. Among the associated variants, a known pathogenic variant of autosomal recessive Gitelman syndrome (p.R642G SLC12A3) was most likely causal; there were no homozygotes in our sample. Heterozygosity for p.R642G was also associated with lower chloride levels, but not with sodium levels. Notably, p.R642G showed a novel association with lower serum BUN levels. Heterozygotes for p.R642G had a two-fold higher rate of self-reported bone fractures and had higher resting heart rates on a low-salt diet compared with noncarriers. CONCLUSIONS: This study provides evidence that heterozygosity for a pathogenic variant in SLC12A3 causing Gitelman syndrome, a canonically recessive disorder, contributes to serum potassium concentration. The findings provide insights into SLC12A3 biology and the effects of heterozygosity on electrolyte homeostasis and related subclinical phenotypes that may have implications for personalized medicine and nutrition.

Adrenal adaptation in potassium-depleted men: role of progesterone?

BACKGROUND: In rodents, the stimulation of adrenal progesterone is necessary for renal adaptation under potassium depletion. Here, we sought to determine the role of progesterone in adrenal adaptation in potassium-depleted healthy human volunteers and compared our findings with data collected in patients with Gitelman syndrome (GS), a salt-losing tubulopathy. METHODS: Twelve healthy young men were given a potassium-depleted diet for 7 days at a tertiary referral medical centre (NCT02297048). We measured by liquid chromatography coupled to tandem mass spectroscopy plasma steroid concentrations at Days 0 and 7 before and 30 min after treatment with tetracosactide. We compared these data with data collected in 10 GS patients submitted to tetracosactide test. RESULTS: The potassium-depleted diet decreased plasma potassium in healthy subjects by 0.3 ± 0.1 mmol/L, decreased plasma aldosterone concentration by 50% (P = 0.0332) and increased plasma 17-hydroxypregnenolone concentration by 45% (P = 0.0232) without affecting other steroids. CYP17 activity, as assessed by 17-hydroxypregnenolone/pregnenolone ratio, increased by 60% (P = 0.0389). As compared with healthy subjects, GS patients had 3-fold higher plasma concentrations of aldosterone, 11-deoxycortisol (+30%) and delta 4-androstenedione (+14%). Their post-tetracosactide progesterone concentration was 2-fold higher than that of healthy subjects and better correlated to plasma potassium than to plasma renin. CONCLUSION: The increase in 17-hydroxypregnenolone concentration after mild potassium depletion in otherwise healthy human subjects suggests that 17 hydroxylation of pregnenolone prevents the increase in progesterone observed in potassium-depleted mice. The unexpected over-response of non-mineralocorticoid steroids to tetracosactide in GS subjects suggests that the adrenal system not only adapts to sodium depletion but may also respond to hypokalaemia.

A Case of Gitelman Syndrome that Was Difficult to Distinguish from Hypokalemic Periodic Paralysis Caused by Graves' Disease.

A 21-year-old man presented with hyperthyroidism and hypokalemia and was treated for thyrotoxic hypokalemic periodic paralysis caused by Graves' disease. Thyroid function soon normalized but hypokalemia persisted. Laboratory data revealed hyperreninemic hyperaldosteronism and metabolic alkalosis consistent with Gitelman Syndrome. The patient was found to have a previously unreported compound heterozygous mutation of T180K and L858H in the SLC12A3 gene, and Gitelman Syndrome was diagnosed. He was started on eplerenone to control serum potassium level. Alternative diagnoses should be considered when electrolyte imbalances persist after disease resolution.

Increased urinary prostaglandin E2 metabolite: A potential therapeutic target of Gitelman syndrome.

BACKGROUND: Gitelman syndrome (GS), an inherited autosomal recessive salt-losing renal tubulopathy caused by mutations in SLC12A3 gene, has been associated with normal prostaglandin E2 (PGE2) levels since 1995 by a study involving 11 clinically diagnosed patients. However, it is difficult to explain why cyclooxygenase-2 (COX2) inhibitors, which pharmacologically reduce PGE2 synthesis, are helpful to patients with GS, and few studies performed in the last 20 years have measured PGE2 levels. The relationships between the clinical manifestations and PGE2 levels were never thoroughly analyzed. METHODS: This study involved 39 GS patients diagnosed by SLC12A3 gene sequencing. Plasma and 24-h urine samples as well as the clinical data were collected at admission. PGE2 and PGEM levels were detected in plasma and urine samples by enzyme immunoassays. The in vivo function of the sodium-chloride co-transporter (NCC) in GS patients was evaluated using a modified thiazide test. The association among PGE2 levels, clinical manifestations and the function of NCC in GS patients were analyzed. RESULTS: Significantly higher levels of urinary and plasma PGEM were observed in GS patients than in the healthy volunteers. Higher urinary PGEM levels indicated more severe clinical manifestations and NCC dysfunction estimated by the increase of Cl- clearance. A higher PGEM level was found in male GS patients, who showed earlier onset age and more severe hypokalemia, hypochloremia and metabolic alkalosis than female GS patients. No relationship between renin angiotensin aldosterone system activation and PGEM level was observed. CONCLUSIONS: Higher urinary PGEM levels indicated more severe clinical manifestations and NCC dysfunction in GS patients. COX2 inhibition might be a potential therapeutic target in GS patients with elevated PGEM levels.

Acquired Gitelman Syndrome in an Anti-SSA Antibody-positive Patient with a SLC12A3 Heterozygous Mutation.

A 36-year-old woman developed hypokalemic metabolic alkalosis after anti SS-A antibody was found to be positive. Diuretic loading test results were compatible with Gitelman syndrome (GS). The patient had a heterozygous mutation in SLC12A3, which encodes for thiazide-sensitive NaCl cotransporter (NCCT). While the mutation may be responsible for a latent hypofunction of NCCTs, the underlying anti-SSA antibody-associated autoimmunity induced the manifestation of its hypofunction. To the best of our knowledge, this is the first report to demonstrate that anti SS-A antibody-associated autoimmunity may induce GS in a patient with a SLC12A3 heterozygous mutation.

Genotype/Phenotype Analysis in 67 Chinese Patients with Gitelman's Syndrome.

BACKGROUND: Gitelman's syndrome (GS) is an autosomal recessive renal tubular disorder, which is caused by the mutations in SLC12A3. This study was designed to analyze the characteristics of the genotype and phenotype, and follow-up in the largest group of Chinese patients with GS. METHODS: Sixty-seven patients with GS underwent SLCl2A3 analysis, and their clinical characteristics and biochemical findings as well as follow-up were reviewed, aiming to achieve a better description of GS. Additionally, the association of genotype and phenotype was explored. RESULTS: Forty-one different mutations were identified within these 67 GS patients, including 11 novel mutations and 5 recurrent ones. Typical hypocalciuria and hypomagnesemia were not found in 6 (9%) and 8 (11.9%) patients, respectively. Male patients and those harboring severe mutations in both alleles had significant higher urinary fractional excretion (FE) of potassium, magnesium and chlorine. In addition, there were 2 patients who had chronic kidney disease (estimated glomerular filtration rate <60 ml/min/1.73 m2) and 32 patients with abnormal glucose metabolism. CONCLUSIONS: We identified 41 mutations related to GS, containing 11 novel variants and 5 high-frequency ones, which should facilitate earlier and more accurate diagnosis of GS. FE of electrolytes in urine may be more sensitive in the phenotype evaluation and differential diagnosis than corresponding serum electrolytes. Hypokalemia and hypomagnesemia in GS were difficult to correct; however, spironolactone might be helpful for hypokalemia to some degree. Compared with normal people, patients with GS were at higher risk of developing type 2 diabetes.

Gitelman syndrome disclosed by calcium pyrophosphate deposition disease: early diagnosis by ultrasonographic study.

Gitelman's syndrome is a rare autosomal-recessive tubular disorder characterized by hypomagnesemia and hypocalciuria associated to hypokalemia. The clinical spectrum is wide and usually characterized by chronic fatigue, cramps, muscle weakness and paresthesiae. We describe a case of a 43 year-old male patient with early onset of knee arthritis and no other symptoms. Ultrasound revealed diffuse and confluent hyperechoic deposits in cartilage, fibrocartilage of the menisci and synovium and calcium pyrophosphate crystals were observed in the synovial fluid of the knee. The concomitant presence of hypomagnesemia, hypocalciuria and hypokalemia made clear the diagnosis of Gitelman's syndrome associated with chondrocalcinosis.

Management of a severe case of Gitelman syndrome with poor response to standard treatment.

Gitelman syndrome is an autosomal recessive distal renal tubular disorder caused by defective sodium chloride transporters. Biochemically, it presents with hypokalaemic metabolic alkalosis, hypomagnesaemia and hypocalciuria. It is usually managed with oral potassium supplements and potassium-sparing diuretics. We report a case of a 28-year-old woman whose condition worsened during pregnancy; she became resistant to standard management after delivery of her second child. She was managed in a specialist metabolic clinic through a comprehensive approach including perseverance with oral potassium supplement, weekly intravenous potassium and magnesium infusion, correction of vitamin D level and the offering of appropriate dietary advice; this controlled the patient's symptoms and prevented repeated hospital admissions. In this case report, we illustrate a patient's presentation and diagnosis with Gitelman syndrome, discuss triggers of exacerbation, review the relevant literature in terms of differential diagnoses and provide practical advice on the management of difficult cases in a specialist clinic.

A case report of Gitelman syndrome resulting from two novel mutations in SLC12A3 gene.

INTRODUCTION: Hypokalaemia is a common clinical problem. A potential but commonly overlooked cause of hypokalaemia is Gitelman syndrome. MATERIAL AND METHODS: A 26-year-old man was admitted to the hospital due to syncope with general and muscular weakness and muscle cramps. The patient's history revealed previous recurrent syncope events associated to hypokalaemia with the lowest serum potassium value being 2.6mmol/l. At admission, blood pressure was normal and no changes were found at physical examination. Laboratory tests showed mild hypokalaemia (3.0mmol/l), hypomagnesaemia (1.36mg/dl), hypocalciuria (< 40mg/24h), and metabolic alkalosis (HCO3(-) 29.7mmol/l, BE 5.3mmol/l). RESULTS: Further laboratory tests (FeK, TTKG) confirmed inappropriate kaliuresis. Conn's disease was excluded by hormonal and imaging assessments. Genetic testing was performed and two novel heterozygous mutations: c.35_36insA and c.1095+5G>A were found in transcript NM_000339.2 in SLC12A3 gene. CONCLUSION: The patient was diagnosed with Gitelman syndrome and was treated with supplements of potassium and magnesium.

NORMOMAGNESEMIC GITELMAN SYNDROME PATIENTS EXHIBIT A STRONGER REACTION TO THIAZIDE THAN HYPOMAGNESEMIC PATIENTS.

OBJECTIVE: In recent decades, the thiazide test has been introduced to aid the diagnosis of Gitelman syndrome (GS), but the effect of thiazide in normomagnesemic GS patients is currently unknown. This study was conducted to compare the thiazide test results of normomagnesemic and hypomagnesemic GS patients. METHODS: Seventeen GS patients with SLC12A3 gene mutations were enrolled, five of whom did not have a history of hypomagnesemia. The clinical data were documented, and SLC12A3 gene screening was performed. The thiazide test was performed in all of the patients and 20 healthy controls. A receiver operating characteristic curve was used to evaluate the sensitivity and specificity of the thiazide test in the diagnosis of GS. RESULTS: A 7-fold increase in sodium and chloride excretion was observed after thiazide application in healthy controls, and an approximately 2-fold increase was found in the 5 normomagnesemic GS patients; however, there was no change in the 12 hypomagnesemic GS patients. A weaker reaction to thiazide was observed in hypomagnesemic compared with normomagnesemic GS patients. The clearance of chloride in 1 patient was overestimated because of chronic renal function insufficiency (CRI). When a reasonable cutoff value for chloride fractional excretion was selected, the thiazide test was 95% sensitive and 94.1% specific for the diagnosis of GS. CONCLUSION: Hypomagnesemic GS patients exhibited greater sodium-chloride cotransporter dysfunction than normomagnesemic GS patients. When CRI occurs, the chloride and sodium clearance rates, rather than the fractional excretion, should be used in the evaluation of the thiazide test results.

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.

Clinical severity of Gitelman syndrome determined by serum magnesium.

BACKGROUND/AIMS: Normomagnesemia is considered atypical in Gitelman syndrome (GS). Here, we describe clinical, pathological and genetic characteristics in Chinese GS patients with or without hypomagnesemia in order to determine whether serum magnesium concentration indicates the severity of the disease. METHODS: 7 normomagnesemic and 25 hypomagnesemic GS patients who were confirmed by direct sequencing of SLC12A3 gene were included. Clinical manifestation and laboratory tests were documented. Supine and upright plasma renin activity, angiotensin II and aldosterone were determined by radioimmunoassay. Transient receptor potential channel melastatin subtype 6 (TRPM6) was detected by immunohistochemistry in paraffin-embedded renal biopsy sections of 12 GS patients. 14 patients with glomerular minor lesion served as controls. The distribution of the mutations on the predicted NCC protein was analyzed and compared between two subgroups. RESULTS: Clinical manifestations, electrolyte abnormalities, metabolic alkalosis and renin-angiotensin-aldosterone system activation were found to be milder in normomagnesemic compared with the hypomagnesemic group. Compared with glomerular minor lesion controls, the TRPM6-positive area was significantly decreased in hypomagnesemic patients (4.96 ± 1.88 vs. 8.63 ± 2.67%) while it was near normal (7.82 ± 5.23%) in 2 normomagnesemic GS patients. A higher percentage of intracellular mutations was observed in normomagnesemic patients than hypomagnesemic patients (92.31 vs. 56.52%, p = 0.02). CONCLUSIONS: Normomagnesemia is not rare in GS. Serum magnesium may indicate the severity of GS.

Plasma soluble (pro)renin receptor is independent of plasma renin, prorenin, and aldosterone concentrations but is affected by ethnicity.

A soluble (pro)renin receptor (sPRR) circulates in plasma and is able to bind renin and prorenin. It is not known whether plasma sPRR concentrations vary with the activity of the renin-angiotensin system. We measured plasma sPRR, renin, prorenin, and aldosterone concentrations in 121 white and 9 black healthy subjects, 40 patients with diabetes mellitus, 41 hypertensive patients with or without renin-angiotensin system blockers, 9 patients with primary aldosteronism, and 10 patients with Gitelman syndrome. Median physiological plasma sPRR concentration was 23.5 ng/mL (interquartile range, 20.9-26.5) under usual uncontrolled sodium diet. sPRR concentration in healthy subjects, unlike renin and prorenin, did not display circadian variation or dependence on age, sex, posture, or hormonal status. sPRR concentrations were ≈25% lower in black than in white subjects, whereas renin concentrations were ≈40% lower. Patients with diabetes mellitus (average renin-high prorenin levels) and with hypertension only (average renin-average prorenin levels) had sPRR concentrations similar to healthy subjects. Renin-angiotensin system blockade was associated with increase of sPRR concentration by ≈12%. sPRR in patients with primary aldosteronism (low renin-low prorenin) and Gitelman syndrome (high renin-high prorenin) were similar and ≈10% higher than in healthy subjects. There was no correlation between sPRR and renin or prorenin. In conclusion, our results show that plasma sPRR concentrations are dependent on ethnicity and independent of renin, prorenin, and aldosterone concentrations in healthy subjects and in patients with contrasted degrees of renin-angiotensin system activity.

Increased level of p63RhoGEF and RhoA/Rho kinase activity in hypertensive patients.

OBJECTIVE: p63RhoGEF, a guanine nucleotide exchange factor, has been reported 'in vitro' as key mediator of the angiotensin II-induced RhoA/Rho kinase activation leading to vasoconstriction and cardiovascular remodeling. We assessed p63RhoGEF gene and protein expression and RhoA/Rho kinase activity in essential hypertensive and Bartter's and Gitelman's syndrome patients, a human model opposite to hypertension; the latter have, in fact, increased plasma angiotensin II, activation of the renin-angiotensin system, yet normotension/hypotension, reduced peripheral resistance and lack of cardiovascular remodeling due to an endogenously blunted angiotensin II type 1 receptor signaling. METHODS: Mononuclear cell p63RhoGEF gene and protein expression and the phosphorylation status of the myosin phosphatase target protein-1 (MYPT-1), marker of Rho kinase activity, were assessed in essential hypertensive patients, Bartter's/Gitelman's patients and healthy individuals by quantitative real-time PCR and western blot. RESULTS: p63RhoGEF mRNA and protein level and MYPT-1 phosphorylation status were higher in hypertensive patients and lower in Bartter's/Gitelman's patients compared with healthy individuals: p63RhoGEF mRNA level: 0.59 ± 0.17 ΔΔCt vs. 0.37 ± 0.17 vs. 0.20 ± 0.19, analysis of variance (ANOVA): P <0.016; p63RhoGEF protein level 1.35 ± 0.14 vs. 1.09 ± 0.05 vs. 0.90 ± 0.09 densitometric units, ANOVA: P <0.0001; MYPT-1: 1.39 ± 0.34 vs. 1.01 ± 0.12 vs. 0.81 ± 0.06, ANOVA: P < 0.0001. p63RhoGEF mRNA was significantly correlated with both SBP and DBP in both hypertensive patients (R = 0.79, P < 0.02 and R = 0.78, P < 0.02) and in Bartter's syndrome/Gitelman's syndrome patients (R = 0.87, P < 0.001 and R = 0.86, P < 0.001), respectively. CONCLUSION: Increased p63RhoGEF mRNA and protein level and Rho kinase activity are shown for the first time in essential hypertensive patients, whereas the opposite was found in Bartter's/Gitelman's patients, a human model opposite to hypertension. These results combined with other 'in-vitro' studies strongly support the crucial importance of p63RhoGEF in Ang II-mediated signaling involved in the regulation of blood pressure and its long-term complications in humans.

Gitelman syndrome.

Hypokalaemia is a common clinical disorder, the cause of which can usually be determined by the patient's clinical history. Gitelman syndrome is an inherited tubulopathy that must be considered in some settings of hypokalaemia. We present the case of a 60-year-old male patient referred to our nephrology department for persistent hypokalaemia. Clinical history was positive for symptoms of orthostatic hypotension and polyuria. There was no history of drugs consumption other than potassium supplements. Complementary evaluation revealed hypokalaemia (2.15 mmol/l), hypomagnesaemia (0.29 mmol/l), metabolic alkalosis (pH 7.535, bicarbonate 34.1 mmol/l), hypereninaemia (281.7 U/ml), increased chloride (160 mmol/l) and sodium (126 mmol/l) urinary excretion and reduced urinary calcium excretion (0.73 mmol/l). Renal function, remainder serum and urinary ionogram, and renal ultrasound were normal. A diagnosis of Gitelman syndrome was established. We reinforced oral supplementation with potassium chloride and magnesium sulfate. Serum potassium stabilised around 3 mmol/l. The aim of our article is to remind Gitelman syndrome in the differential diagnosis of persistent hypokalaemia.

Outpatient management of Gitelman's syndrome in pregnancy.

Gitelman's syndrome is a congenital renal tubular defect which affects the apical membrane of the distal convoluted tubule of the renal system. The syndrome is characterised by hypokalaemia, hypomagnesaemia, metabolic alkalosis and hypocalcuria. There are only a few cases describing the impact of Gitelman's syndrome on pregnancy and the foetus. Although most pregnancies have favourable outcomes, fetal demise has been reported in the third trimester. We report the successful outcome of pregnancy in a patient with Gitelman's syndrome who continued on amiloride in pregnancy to optimise potassium and magnesium levels and review the literature for pregnancy outcomes of this condition.

The effects of serum potassium and magnesium levels in a patient with Gitelman's syndrome on the timing of ventricular wall motion and the pattern of ventricular strain and torsion.

Gitelman's syndrome is a primary renal tubular hypokalemic metabolic alkalosis. Hypokalemia and hypomagnesemia can cause cardiac tissue excitability and conduction. Global ventricular mechanical function is directly related to the contractile properties of cardiac myocytes, which are largely dependent on the flow of ions such as potassium and magnesium. Here, we show that increased levels of potassium, in addition to magnesium, in a patient with Gitelman's syndrome significantly impacts the timing of ventricular wall motion and the pattern of ventricular strain and torsion. Two-dimensional speckle tracking echocardiography was used for evaluation of the hypokalemic-hypomagnesemic period (first day) and third day after potassium chloride and magnesium replacement therapy. The transthoracic echocardiography showed that the percent ejection fraction was similar in hypokalemic-hypomagnesemic (63%) and normokalemic-normomagnesemic (after potassium and magnesium therapy, 67%) hearts. However, decreased left ventricular apical 4-chamber peak systolic longitudinal strain, left ventricle global peak systolic strain, and global torsion values increased after potassium chloride and magnesium replacement therapy.