A novel compound heterozygous mutation of SLC12A3 gene in a Chinese pedigree with Gitelman syndrome

PURPOSE

Gitelman syndrome (GS) is an autosomal recessive renal tubular disorder characterized by salt wasting and hypokalemia resulting from loss-of-function mutations in the solute carrier family 12A3 (SLC12A3) gene encoding the thiazide-sensitive NaCl cotransporter (NCC). Here, we investigated the clinical manifestations and genetic features of a Chinese pedigree with GS.

METHODS

Next-generation sequencing and Sanger sequencing analysis were performed to define and confirm the SLC12A3 gene mutations of the patient (proband II:1) and this pedigree. Clinical manifestations and biochemical parameters were collected and analyzed.

RESULTS

Genetic analysis of the SLC12A3 gene identified two novel mutations in the proband, heterozygous (c.2842delT) and heterozygous (c.1569_1586del) mutation, respectively. Additionally, heterozygous (c.2842delT) mutation in SLC12A3 gene was found in his father and younger brother. The other heterozygous (c.1569_1586del) mutation in SLC12A3 gene was carried by his mother.

CONCLUSIONS

Two novel mutations may be related to the occurrence of the GS in the pedigree. However, additional studies are particularly required to explore the underlying molecular mechanisms.

Gitelman syndrome combined with growth hormone deficiency: Three cases report

RATIONALE

Gitelman syndrome (GS) is a rare autosomal recessive hereditary salt-losing tubulopathy caused by loss-of-function mutations in the SLC12A3 gene. It is usually characterized by hypokalemia, metabolic alkalosis, hypomagnesemia, and hypocalciuria. There are only a few reports on GS combined with growth hormone deficiency (GHD).

PATIENT CONCERNS

Three patients presented with weakness, spasm, and growth retardation, respectively.

DIAGNOSES

GS was diagnosed based on the clinical symptoms, laboratory test results, and genetic analysis. GH stimulation tests were performed when the magnesium level returned to normal under magnesium oxide (MgO) therapy.

INTERVENTIONS

Initially, all patients received oral replacement of MgO and potassium chloride, and 2 of them received simultaneous spironolactone therapy. Recombinant human growth hormone (rhGH) therapy was initiated after they were diagnosed with GHD.

OUTCOMES

All 3 patients exhibited satisfactory growth velocity and normal serum magnesium level, although the potassium level was still slightly lower than normal.

LESSONS

We suggest that all GS patients should undergo genetic evaluation, especially regarding SLC12A3 gene mutation. GHD should be considered if these patients have short stature. rhGH therapy is useful for stimulating the patients' growth, and it may increase the serum magnesium level.

Gitelman's syndrome with hyperphosphatemia, effectively responding to single oral magnesium oxide administration: A case report

RATIONALE

The Gitelman's syndrome (GS) is characterized by metabolic alkalosis, hypokalemia, hypomagnesemia, and hypocalciuria. However, the involvement of this deranged electrolyte balance in patients with GS in parathyroid hormone action has not been known.

PATIENT CONCERNS

We report a 34-year-old woman with muscle weakness and tetany/seizures caused by electrolyte imbalance. She had hyperphosphatemia and hypocalciuric hypocalcemia in addition to severe hypomagnesemia with low potassium in the absence of metabolic alkalosis. We identified 2 heterozygous mutations in the solute carrier family 12 member 3 gene in this case (c.1732G>A, p.Val578Met and c.2537_38delTT, p.846fs) by targeted sequence for all causative genes of salt-losing tubulopathies.

DIAGNOSES

A diagnosis of GS. Hypocalcemia and hyperphosphatemia were suggested to relate with the secondary obstruction of appropriate parathyroid hormone release following severe hypomagnesemia in GS.

INTERVENTIONS

She was treated with single oral magnesium oxide administration.

OUTCOMES

The electrolyte imbalance including hypocalcemia and hyperphosphatemia were resolved with a remission of clinical manifestations.

LESSONS

These observations, in this case, suggest that even severe hypomagnesemia caused by GS was associated with resistance to appropriate parathyroid hormone secretion. Through this case, we recognize that secondary hypoparathyroidism would be triggered by severe hypomagnesemia in GS.

Characteristics and Follow-Up of 13 pedigrees with Gitelman syndrome

CONTEXT

Gitelman syndrome (GS) is clinically heterogeneous. The genotype and phenotype correlation has not been well established. Though the long-term prognosis is considered to be favorable, hypokalemia is difficult to cure.

OBJECTIVE

To analyze the clinical and genetic characteristics and treatment of all members of 13 GS pedigrees.

METHODS

Thirteen pedigrees (86 members, 17 GS patients) were enrolled. Symptoms and management, laboratory findings, and genotype-phenotype associations among all the members were analyzed.

RESULTS

The average ages at onset and diagnosis were 27.6 ± 10.2 years and 37.9 ± 11.6 years, respectively. Males were an average of 10 years younger and exhibited more profound hypokalemia than females. Eighteen mutations were detected. Two novel mutations (p.W939X, p.G212S) were predicted to be pathogenic by bioinformatic analysis. GS patients exhibited the lowest blood pressure, serum K⁺, Mg²⁺, and 24-h urinary Ca²⁺ levels. Although blood pressure, serum K⁺ and Mg²⁺ levels were normal in heterozygous carriers, 24-h urinary Na⁺ excretion was significantly increased. During follow-up, only 41.2% of patients reached a normal serum K⁺ level. Over 80% of patients achieved a normal Mg²⁺ level. Patients were taking 2-3 medications at higher doses than usual prescription to stabilize their K⁺ levels. Six patients were taking spironolactone simultaneously, but no significant elevation in the serum K⁺ level was observed.

CONCLUSION

The phenotypic variability of GS and therapeutic strategies deserve further research to improve GS diagnosis and prognosis. Even heterozygous carriers exhibited increased 24-h Na⁺ urine excretion, which may make them more susceptible to diuretic-induced hypokalemia.

A novel heterozygous duplication of the SLC12A3 gene in two Gitelman syndrome pedigrees: indicating a founder effect

Gitelman syndrome is an autosomal recessive salt-wasting tubulopathy caused by mutations in the SLC12A3 gene. A female and a male sibling from two unrelated Greek-Cypriot families presenting with a severe salt-wasting tubulopathy due to compound heterozygous mutations of a novel duplication and a previously reported missense mutation in the SLC12A gene are described. Sanger sequencing was used to identify possible mutations in the SLC12A3 gene. For the detection of duplications/conversions and deletions in the same gene, Multiplex ligation probe amplification (MLPA) analysis was performed. Direct sequencing and MLPA analysis of the SLC12A3 gene identified two compound heterozygous mutations in both unrelated probands. Both probands were identified to carry in compound heterozygosity the known p.Met581Lys and a novelheterozygous duplication of exons 9-14 (E9_E14dup). The diagnosis of Gitelman syndrome was made through clinical assessment, biochemical screening and genetic analysis. The identification of the novel SLC12A3 duplication seems to be characteristic of Greek-Cypriot patients and suggests a possible ancestral mutational event that has spread in Cyprus due to a possible founder effect. Testing for Gitelman syndrome probable variants can be performed before proceeding to a full gene sequencing dropping the diagnostic cost. In addition, this report adds to the mutational spectrum observed.

Complicated Gitelman syndrome and autoimmune thyroid disease: a case report with a new homozygous mutation in the SLC12A3 gene and literature review

BACKGROUND

Gitelman syndrome (GS) is an inherited autosomal recessive renal tubular disorder characterized by low levels of potassium and magnesium in the blood, decreased excretion of calcium in the urine, and elevated blood pH. GS is caused by an inactivating mutation in the SLC12A3 gene, which is located on the long arm of chromosome 16 (16q13) and encodes a thiazide-sensitive sodium chloride cotransporter (NCCT).

CASE PRESENTATION

A 45-year-old man with Graves' disease complicated by paroxysmal limb paralysis had a diagnosis of thyrotoxic periodic paralysis for 12 years. However, his serum potassium level remained low despite sufficiently large doses of potassium supplementation. Finally, gene analysis revealed a homozygous mutation in the SLC12A3 gene. After his thyroid function gradually returned to normal, his serum potassium level remained low, but his paroxysmal limb paralysis resolved.

CONCLUSIONS

GS combined with hyperthyroidism can manifest as frequent episodes of periodic paralysis; to date, this comorbidity has been reported only in eastern Asian populations. This case prompted us to more seriously consider the possibility of GS associated with thyroid dysfunction.

A NOVEL COMPOUND HETEROZYGOUS VARIANT OF SLC12A3 GENE IN A PEDIGREE WITH GITELMAN SYNDROME CO-EXISTENT WITH THYROID DYSFUNCTION

OBJECTIVE

Gitelman syndrome (GS) is an autosomal recessive disorder characterized by salt wasting and hypokalemia resulting from mutations in the SLC12A3 (solute carrier family 12 member 3) gene, which encodes the thiazide-sensitive sodium-chloride cotransporter. To date, more than 488 mutations of the SLC12A3 gene have been discovered in patients with GS. In this study, we reported a GS pedigree complicated by thyroid diseases or thyroid dysfunction.

METHODS

Sanger sequencing and next-generation sequencing analysis were performed to determine the SLC12A3 gene mutations in a GS pedigree including the 16-year old male patient with GS and his family members within 3 generations. Chemiluminescence immunoassays were used to detect thyroid hormone and antibody concentrations.

RESULTS

Genetic analysis of the SLC12A3 gene identified 2 mutations in the 16-year old male patient with GS concomitant with Graves disease (GD) and his younger sister accompanied by abnormal thyroid function. Additionally, one mutation site (c.1456G>A) in SLC12A3 gene was found in his father, paternal uncle and elder female cousin, who were complicated by subclinical hypothyroidism or autoantibody against thyroid. The other mutation site (c.2102_2107 delACAAGA) in SLC12A3 gene, a novel mutated variant of SLC12A3 gene, was carried by his mother and maternal grandfather.

CONCLUSION

Two mutation sites were documented in the pedigree with GS, and one has not been reported before. Moreover, we found a mutation at nucleotide c.1456 G>A in the SLC12A3 gene that may affect thyroid function. However, further studies are needed to explore the underlying molecular mechanisms.

ABBREVIATIONS

FT3 = free triiodothyronine; FT4 = free tetraiodothyronine; GD = Graves disease; GS = Gitelman syndrome; SLC12A3 = solute carrier family 12 member 3; TGAb = thyroglobulin antibody; TPOAb = thyroid peroxidase antibody; TSH = thyroid-stimulating hormone; TT3 = total triiodothyronine; TT4 = total tetraiodothyronine.

Renal Mg handling, FXYD2 and the central role of the Na,K-ATPase

This article examines the central role of Na,K-ATPase (α1β1FXYD2) in renal Mg handling, especially in distal convoluted tubule (DCT), the segment responsible for final regulation of Mg balance. By considering effects of Na,K-ATPase on intracellular Na and K concentrations, and driving forces for Mg transport, we propose a consistent rationale explaining basal Mg reabsorption in DCT and altered Mg reabsorption in some human diseases. FXYD2 (γ subunit) is a regulatory subunit that adapts functional properties of Na,K-ATPase to cellular requirements. Mutations in FXYD2 (G41R), and transcription factors (HNF-1B and PCBD1) that affect FXYD2 expression are associated with hypomagnesemia with hypermagnesuria. These mutations result in impaired interactions of FXYD2 with Na,K-ATPase. Renal Mg wasting implies that Na,K-ATPase is inhibited, but in vitro studies show that FXYD2 itself inhibits Na,K-ATPase activity, raising K0.5 Na. However, FXYD2 also stabilizes the protein by amplifying specific interactions with phosphatidylserine and cholesterol within the membrane. Renal Mg wasting associated with impaired Na,K-ATPase/FXYD2 interactions is explained simply by destabilization and inactivation of Na,K-ATPase. We consider also the role of the Na,K-ATPase in Mg (and Ca) handling in Gitelman syndrome and Familial hyperkalemia and hypertension (FHHt). Renal Mg handling serves as a convenient marker for Na,K-ATPase activity in DCT.

Consideration of the diagnosis of hypertension accompanied with hypokalaemia: monism or dualism?

This case report describes a 53-year-old male patient with persistent hypertension and hypokalaemia. Laboratory tests showed that the patient had hypokalaemia, hypocalcaemia and reduced urine calcium/creatinine. Levels of aldosterone and renin activity were increased significantly. Serum levels of adrenocorticotropic hormone, plasma total cortisol level, 24-h urinary-free cortisol, catecholamines, thyroid stimulating hormone and free tetraiodothyronine were normal. A novel single heterozygous mutation (c.836T> G [E6]) was found after full sequencing of the solute carrier family 12 member 3 ( SLC12A3) gene exons. The patient was diagnosed as having primary hypertension with Gitelman syndrome (GS). These findings triggered the careful consideration of whether a monistic or dualist approach to the diagnosis of this patient was the most appropriate. Monism may not always be the most appropriate approach for the diagnosis of coexistent hypertension and hypokalaemia. Consideration should be given to the possibility of the independent existence of distinct diseases (i.e. dualism) when secondary hypertension cannot be confirmed by conventional examinations and when a genetic diagnosis is crucial. As a common cause of hypokalaemia with a high level of clinical phenotypic variation, GS does not conform to the usual diagnostic criteria. It should also be noted that single heterozygous SLC12A3 gene mutations can cause disease symptoms and other genetic mutations might be involved in the pathogenesis of GS.

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

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

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.

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.

Genetic Features of Chinese Patients with Gitelman Syndrome: Sixteen Novel SLC12A3 Mutations Identified in a New Cohort

BACKGROUND

Gitelman syndrome (GS) is an autosomal recessive renal tubulopathy caused by inactivating mutations in the SLC12A3 gene. Although hundreds of different mutations across the SLC12A3 gene have been reported worldwide, data from mainland China are limited. We investigated the clinical manifestations and genetic features of Chinese patients with GS.

METHODS

Fifty-four unrelated Chinese patients with clinically diagnosed GS were included. Clinical manifestations and biochemical parameters were collected and analyzed. All exons and flanking regions of the SLC12A3 and CLCNKB genes were screened by direct sequencing.

RESULTS

Weakness was the most commonly reported symptom in this cohort of patients with GS. In gender-based analyses, higher systolic blood pressure and urine protein excretion were observed in male patients. For genetic screening, 2 pathogenic SLC12A3 mutations were identified in 38 patients (70.4%), 1 mutation in 11 patients (20.4%) and no mutation in 5 patients (9.3%). In total, 42 distinct pathogenic mutations throughout SLC12A3 were identified; 16 were novel, including 9 missense, 1 deletion, 1 insertion, 3 splice site and 2 nonsense mutations. Eleven mutations were recurrently found in different patients. Among them, T60M and D486N were identified in 11 individuals. No CLCNKB mutations were found.

CONCLUSION

Sixteen novel SLC12A3 pathogenic mutations were identified in a cohort of Chinese patients with GS. T60M and D486N were most frequent and appear to be important candidate alleles in Chinese patients with GS.

A novel SLC12A3 gene homozygous mutation of Gitelman syndrome in an Asian pedigree and literature review

OBJECTIVES

Gitelman syndrome (GS) is an autosomal recessive disease characterized by hypokalemic metabolic alkalosis in combination with significant hypomagnesemia and hypocalciuria which is caused by mutations in the SLC12A3 gene. In this study, we reported a case of GS pedigree and reviewed pertinent literature so as to explore the relationship between clinical characteristics and genotype meanwhile provide recommendations for the diagnosis and treatment of GS.

DESIGN AND METHODS

This is a pedigree-based genetic study of GS and 11 members from one family were included. We summarized their clinical features, analyzed laboratory parameters related to GS and SLC12A3 gene.

RESULTS

The proband experienced intermittent severe symptoms of weakness accompanied by significant hypokalemia, hypomagnesemia and hypocalciuria in laboratory test with poor treatments. His mother had more slight symptoms of weakness than him with mild hypokalemia and hypocalciuria. Mild hypomagnesemia was also observed in his sister with occasional weakness. All other pedigree members had normal laboratory test with no GS-related symptoms. A homozygous mutation of SLC12A3 gene (c.488C > T) was detected by genetic testing in three members, and six were carriers of this mutation.

CONCLUSIONS

Genotype and phenotype vary significantly among GS patients. Male patients tend to experience more severe symptoms and poor treatment effect. Further large-scale population, animal, and molecular biology experiments are required to investigate the complexity of GS and to find a better treatment regimen for this disease.

Analysis of mutations of two Gitelman syndrome family SLC12A3 genes and proposed treatments using Chinese medicine

OBJECTIVE

To determine the gene location of two Gitelman syndrome (GS) family SLC12A3 genes and explore treatments using Chinese medicine (CM) prescriptions.

METHODS

In order to locate the two GS mutations, samples were collected from 11 people from two different pedigrees for direct genetic sequencing and comparison of the 26 exons of SLC12A3. Furthermore, the change of serum potassium was monitored throughout the therapy and those two probands undertook a sequential superposition of Western medicine (including potassium, Panangin and potassium-sparing diuretics) with CM prescription based on Buyang Huanwu Decoction () and Sijunzi Decoction (). The treatment included three stages, oral potassium chloride for the first 2 weeks (stage 1), potassium-sparing diuretic and Panangin with potassium chloride for the next 2 weeks (stage 2), CM along with the medicine in stage 2 for the final 2 weeks (stage 3).

RESULTS

The three mutations occurring in proband 1 from pedigree I were Thr60Met, 965-1_976del13ins12 (small indels mutation) and Ala122Ala (homozygous silent mutation). Likewise, three mutations, Asn359Lys, Thr382Met and Arg913Gln, appeared in the proband 2 from pedigree II. The serum potassium levels increasing from baseline to sequential stages were 1.63 mmol/L (baseline), 2.5 mmol/L (stage 1), 3.1 mmol/L (stage 2) and 3.9 mmol/L (stage 3) in the proband 1, and 2.8 mmol/L (baseline), 3.1 mmol/L (stage 1), 3.5 mmol/L (stage 2) and 4.3 mmol/L (stage 3) in the proband 2, respectively. The symptoms (numbness of limbs, weakness, palpitations, etc.) of both probands were all alleviated.

CONCLUSIONS

The mutations of both GS pedigrees can be defined as compound heterozygous mutations, most of which are known as missense mutations. Applying CM could be an appropriate choice for future intervention of GS.

Mutations in SLC12A3 and CLCNKB and Their Correlation with Clinical Phenotype in Patients with Gitelman and Gitelman-like Syndrome

Gitelman's syndrome (GS) is caused by loss-of-function mutations in SLC12A3 and characterized by hypokalemic metabolic alkalosis, hypocalciuria, and hypomagnesemia. Long-term prognosis and the role of gene diagnosis in GS are still unclear. To investigate genotype-phenotype correlation in GS and Gitelman-like syndrome, we enrolled 34 patients who showed hypokalemic metabolic alkalosis without secondary causes. Mutation analysis of SLC12A3 and CLCNKB was performed. Thirty-one patients had mutations in SLC12A3, 5 patients in CLCNKB, and 2 patients in both genes. There was no significant difference between male and female in clinical manifestations at the time of presentation, except for early onset of symptoms in males and more profound hypokalemia in females. We identified 10 novel mutations in SLC12A3 and 4 in CLCNKB. Compared with those with CLCNKB mutations, patients with SLC12A3 mutations were characterized by more consistent hypocalciuria and hypomagnesemia. Patients with 2 mutant SLC12A3 alleles, compared with those with 1 mutant allele, did not have more severe clinical and laboratory findings except for lower plasma magnesium concentrations. Male and female patients did not differ in their requirement for electrolyte replacements. Two patients with concomitant SLC12A3 and CLCNKB mutations had early-onset severe symptoms and showed different response to treatment. Hypocalciuria and hypomagnesemia are useful markers in differentiation of GS and classical Bartter's syndrome. Gender, genotypes or the number of SLC12A3 mutant alleles cannot predict the severity of disease or response to treatment.

[Gitelman´s syndrome as common cause of hypokalemia and hypomagnesemia]

The Gitelman syndrome (GS) is an autosomal recessive disorder characterized by hypokalemic metabolic alkalosis and presence of hypocalciuria and hypomagnesemia. It is one of the most common congenital "salt-wasting" tubulo-pathies, where the impairment of function of the Na+-Cl- cotransporter (NCCT) in the distal convoluted tubule is primary and hypokalemia secondary. Hypomagnesemia is caused by the impairment of magnesium reabsorption through TRPM6 channel which is located just by NCCT. Clinically, patients suffer from fatigue and hypotension due to loss of salt and water and also have cramps and tetany. In some patients chondrocalcinosis can be identified which leads to protracted pain and repeated aseptic inflammations in the joints. The course of the disease, though, is typically benign, and it rarely leads to structural changes in the kidneys or renal impairment. In the period of 2004-2006 we commenced examination of patients with suspected GS based on clinical and laboratory findings within a grant project in the Czech Republic, and in the following years this methodology was introduced to the common laboratory practice. By the year 2011 we had identified 7 different causal mutations in the gene SLC12A3 (4 of them new) among the Czech population, which is responsible for the origin of this disease. The majority of patients, whose clinical findings indicated the presence of GS, had the mutation actually detected, specifically in heterozygous form; 4 individuals were then homozygous. Most of the identified mutations were missense mutations and the most common type found among the Czech population was the change 1315 G>A within the geneSLC12A3, which causes impairment of glycosylation of the NCCT transporter. Further a great number of single-nucleotide polymorphisms were found that may be involved in clinical manifestation of the disease.Key words: gene mutation - gene sequence - Gitelman´s syndrome - NCC channel - PCR.

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.

Identification of two novel mutations in SLC12A3 gene in two Chinese pedigrees with Gitelman syndrome and review of literature

OBJECTIVE

Gitelman syndrome (GS) is one of the most common causes of inherited hypokalaemia. As it was caused by mutations in the SLC12A3 gene, GS is a highly heterogeneous disease. Here, we aimed to investigate the clinical and genetic characteristics of two Chinese pedigrees and summarize the advance in GS genetics, diagnosis and management.

SUBJECTS AND METHODS

Two three-generation families with GS were identified and screened for mutations in the SLC12A3 gene. Genotype-phenotype correlations were analysed.

RESULTS

The two probands (A and B) were characterized by hypokalaemia, hypomagnesaemia and hypocalciuria without hypertension. Complete DNA sequencing of the SLC12A3 gene revealed two novel compound heterozygous mutations (c.179C>T and c.234delG; c.486-490delTACGGinsA and c.1925G>A), which are predicted to drastically affect normal protein structure. The female members of the pedigrees showed mild-to-no phenotype, although they carried the same mutations as the probands. Moreover, proband B presented with more severe symptoms than did proband A, which might be related to a lower serum magnesium level. During the 1-year follow-up, both probands showed satisfactory symptom improvement following the use of potassium and magnesium supplements.

CONCLUSION

Our findings strongly suggested that the two novel mutations in the SLC12A3 gene are the causative agents of GS, which may provide further insights into the function of this gene and help clinicians better understand this disorder.

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

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

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.

Thiazide-sensitive Na+-Cl- cotransporter: genetic polymorphisms and human diseases

The thiazide-sensitive Na(+)-Cl(-) cotransporter (TSC) is responsible for the major sodium chloride reabsorption pathway, which is located in the apical membrane of the epithelial cells of the distal convoluted tubule. TSC is involved in several physiological activities including transepithelial ion absorption and secretion, cell volume regulation, and setting intracellular Cl(-) concentration below or above its electrochemical potential equilibrium. In addition, TSC serves as the target of thiazide-type diuretics that are the first line of therapy for the treatment of hypertension in the clinic, and its mutants are also reported to be associated with the hereditary disease, Gitelman's syndrome. This review aims to summarize the publications with regard to the TSC by focusing on the association between TSC mutants and human hypertension as well as Gitelman's syndrome.

Integrated compensatory network is activated in the absence of NCC phosphorylation

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