Interpreting epigenetic causes of recurrent hypokalemia and seizures: Gitelman syndrome co-exist with pseudohypoparathyroidism type 1B

We describe a unique case of 27-year-old male with Gitelman syndrome (GS) co-exist with pseudohypoparathyroidism type 1B (PHP1B). The patient presented with a 5-year history of seizures, tetany, and numbness of the extremities. Further examinations showed recurrent hypokalemia, inappropriate kaliuresis, hypocalcemia, hyperphosphatemia, and elevated PTH levels. A novel variant of autosomal recessive GS (p.Val287Met SLC12A3) and a novel 492.3Kb deletion containing the whole of STX16, were discovered by a whole-exome sequencing. Following the diagnosis, calcitriol, calcium, and potassium supplements were started. Hematuria calcium and phosphorus levels, as well as blood potassium levels, have recovered and remained within normal ranges after 3 years of follow-up. Our findings have important consequences for supporting the idea that heterozygosity for variants have effects on the patients' clinical performance with autosomal recessive inheritance disorders. Further study is need for the putative effects of the variant. Likewise, further investigation with regards to the gene-gene interaction relations between GS and other electrolyte imbalance disorders is warranted.

Clinical and genetic analysis of a case of Gitelman syndrome accompanied with Graves disease and adrenocortical adenoma: A case report

RATIONALE

Gitelman syndrome (GS), also known as familial hypokalemia and hypomagnesemia, is a rare autosomal recessive inherited disease caused by primary renal desalinization caused by impaired reabsorption of sodium and chloride ions in the distal renal tubules. We report a case of clinical and genetic characteristics of GS accompanied with Graves disease and adrenocorticotrophic hormone (ACTH)-independent adrenocortical adenoma.

PATIENT CONCERNS

The patient is a 45 year old female, was admitted to our hospital, due to a left adrenal gland occupying lesion as the chief complaint.

DIAGNOSIS

The patient was finally diagnosed as GS with Graves disease and adrenocortical adenoma.

INTERVENTIONS

Potassium magnesium aspartate (1788 mg/d, taken orally 3 times a day (supplement a few times a day, intake method, treatment duration). Contains 217.2 mg of potassium and 70.8 mg of magnesium, and potassium chloride (4.5 g/d, taken orally 3 times a day (supplement a few times a day, intake method, and treatment duration); Potassium 2356 mg), spironolactone (20 mg/d, taken orally once a day (supplement a few times a day, intake method, treatment duration). After 3 months of treatment, the patient's blood potassium fluctuated between 3.3-3.6 mmol/L, and blood magnesium fluctuated between 0.5-0.7 mmol/L, indicating a relief of fatigue symptoms.

OUTCOMES

On the day 6 of hospitalization, the symptoms of dizziness, limb fatigue, fatigue and pain were completely relieved on patient. In the follow-up of the following year, no recurrence of the condition was found.

LESSONS

The novel c.1444-10(IVS11)G > A variation may be a splicing mutation. The compound heterozygous mutations of the SLC12A3 gene may be the pathogenic cause of this GS pedigree.

[Genetic analysis of two patients with Gitelman syndrome]

OBJECTIVE

To explore the genetic etiology of two patients with Gitelman syndrome (GS).

METHODS

Two patients who had presented at the Linyi People's Hospital in January and June 2022 respectively were selected as the study subjects. Peripheral blood samples of them were collected and subjected to whole exome sequencing (WES). Electrolyte levels in their serum and urine were detected. Candidate variants were verified by Sanger sequencing. PyMOL software was used to predict the impact of the variants on the protein structure.

RESULTS

Patient 1 was a 27-year-old female with decreased serum levels of sodium, potassium, chloride and magnesium, along with decreased urine chloride and calcium. WES revealed that she has harbored compound heterozygous variants of the SLC12A3 gene, namely c.1456G>A (p.D486N) and c.179C>T (p.T60M). The former was inherited from her mother and known to be pathogenic. Patient 2 was a 4-year-old male with lower serum sodium, chloride and magnesium levels, and his serum potassium level was found to be critically low. He was found to harbor compound heterozygous variants of c.602-16G>A and c.805_806insTTGGCGTGGTCTCGGTCA (p.V268_T269insIGVVSV) of the SLC12A3 gene, which were inherited from his mother and father, respectively. Based on the guidelines from the American College of Medical Genetics and Genomics, both variants were predicted to be pathogenic (PVS1+PM2_Supporting+PP3; PVS1+PM2_Supporting+PM4).

CONCLUSION

The above heterozygous variants of the SLC12A3 gene probably underlay the GS in these patients.

The first compound heterozygous mutations in SLC12A3 and PDX1 genes: a unique presentation of Gitelman syndrome with distinct insulin resistance and familial diabetes insights

Background

Gitelman Syndrome (GS) patients frequently exhibit disrupted glucose metabolism, attributed to hypokalemia, hypomagnesemia and heightened aldosterone. This study delved into the genetic underpinnings linked to insulin resistance and diabetes in a GS patient, contextualized within his family history.

Methods

The hydrochlorothiazide and furosemide loading test were performed to ascertain the presence of GS. Oral glucose tolerance test (OGTT) evaluated glucose metabolism and insulin sensitivity. Whole-exome sequencing, validated by Sanger sequencing, was employed to confirm gene mutations, which were then tracked among the patient's relatives.

Results

Symptoms and laboratory examination confirmed the clinical diagnosis of GS. Comprehensive whole-exome sequencing, augmented by Sanger sequencing validation, revealed a compound heterozygous mutation within the SLC12A3 gene (c.1108G>C in exon 9, c.676G>A in exon 5 and c.2398G>A in exon 20) in the patient. The OGTT affirmed diabetes and heightened insulin resistance, distinct from previous patients with GS we evaluated. Further genetic analysis identified a missense heterozygous mutation (c.97C>G in exon 1) within the PDX1 gene, inherited from the patient's diabetic mother without GS. Furthermore, the patient's brother, with impaired glucose tolerance but regular potassium levels, also bore this mutation, hinting at additional impacts of the PDX1 gene mutation on glucose metabolism regulation beyond the known impacts of GS.

Conclusion

This study unveils unprecedented compound heterozygous mutations in the SLC12A3 and PDX1 genes in a GS patient. These findings illuminate the potential complex genetic factors influencing glucose metabolism disruptions in GS.

Take-home message

This research uncovers a novel combination of SLC12A3 and PDX1 gene mutations in a Gitelman Syndrome patient, revealing intricate genetic factors that potentially disrupt glucose metabolism and shedding light on familial diabetes links.

Gitelman syndrome combined with diabetes mellitus: A case report and literature review

RATIONALE

Gitelman syndrome (GS) is an uncommon autosomal recessive tubulopathy resulting from a functional deletion mutation in the SLC12A3 gene. Its onset is typically insidious and challenging to discern, and it is characterized by hypokalemia, metabolic alkalosis, and reduced urinary calcium excretion. There is limited literature on the diagnosis and management of GS in individuals with concomitant diabetes.

PATIENT CONCERNS

A 36-year-old male patient with a longstanding history of diabetes exhibited suboptimal glycemic control. Additionally, he presented with concurrent findings of hypokalemia, hypomagnesemia, hypocalciuria, and metabolic alkalosis.

DIAGNOSIS

Building upon the patient's clinical manifestations and extensive laboratory evaluations, we conducted thorough genetic testing, leading to the identification of a compound heterozygous mutation within the SLC12A3 gene. This definitive finding confirmed the diagnosis of GS.

INTERVENTIONS

We have formulated a detailed medication regimen for patients, encompassing personalized selection of hypoglycemic medications and targeted electrolyte supplementation.

OUTCOMES

Following 1 week of comprehensive therapeutic intervention, the patient's serum potassium level effectively normalized to 3.79 mmol/L, blood glucose parameters stabilized, and there was significant alleviation of clinical symptoms.

LESSONS

GS has a hidden onset and requires early diagnosis and intervention based on patient related symptoms and laboratory indicators in clinical practice, and personalized medication plans need to be provided according to the specific situation of the patient.

Long-Term Indomethacin Treatment in a Chinese Child with Gitelman Syndrome: Case Report and Literature Review on its Efficacy and Tolerance

BACKGROUND Gitelman syndrome (GS) is a rare inherited autosomal recessive salt-losing renal tubulopathy. Early-onset GS is difficult to differentiate from Bartter syndrome (BS). It has been reported in some cases that cyclooxygenase (COX) inhibitors, which pharmacologically reduce prostaglandin E2(PGE2) synthesis, are helpful for GS patients, especially in children, but the long-term therapeutic effect has not yet been revealed. CASE REPORT A 4-year-old boy was first brought to our hospital for the chief concern of short stature and growth retardation. Biochemical tests demonstrated severe hypokalemia, hyponatremia, and hypochloremic metabolic alkalosis. The patient's serum magnesium was normal. He was diagnosed with BS and treated with potassium supplementation and indomethacin and achieved stable serum potassium levels and slow catch-up growth. At 11.8 years of age, the patient showed hypomagnesemia and a genetic test confirmed that he had GS with compound heterozygous mutations in the SLC12A3 gene. At the age of 14.8 years, when indomethacin had been taken for nearly 10 years, the boy reported having chronic stomachache, while his renal function remained normal. After proton pump inhibitor and acid inhibitor therapy, the patient's symptoms were ameliorated, and he continued to take a low dose of indomethacin (37.5 mg/d divided tid) with good tolerance. CONCLUSIONS Early-onset GS in childhood can be initially misdiagnosed as BS, and gene detection can confirm the final diagnosis. COX inhibitors, such as indomethacin, might be tolerated by pediatric patients, and long-term therapy can improve the hypokalemia and growth retardation without significant adverse effects.

Spectrum of variants in a large Chinese Gitelman syndrome cohort

Gitelman syndrome (GS) is caused by SLC12A3 biallelic variants. A previous study showed that large rearrangements (LRGs) of SLC12A3 accounted for the low sensitivity of genetic testing. However, a systematic screening for LRGs in Chinese GS patients is lacking. Massively parallel sequencing (MPS) and multiplex ligation-dependent probe amplification (MLPA) were performed to sequence the genomic DNA of patients with clinically diagnosed GS. Of 165 index cases, MPS identified 151 cases with two or more affected alleles and 14 cases with one variant allele. LRGs were detected by MLPA in 20 out of 27 cases, including 15 cases with suspected LRGs by MPS. Among these 20 cases with LRGs, the results of MPS and MLPA were identical in only 8 cases. Additional LRGs in 6 cases were detected by MLPA alone. In 6 cases, E4_E6del was identified by MPS, while E4_E5del and Intron6del were identified by MLPA. Among the 102 distinct variants, 30 are novel. LRGs were found in 20 cases (12.1%). LRGs were found in 12.1% of our Chinese GS patients cohort. We show that MPS and MLPA are two complementary techniques with the ability to improve the diagnostic yield of GS.

[Clinical and genetic analysis of a case of Gitelman syndrome with comorbid Graves disease and adrenocortical adenoma]

OBJECTIVE

To report the clinical and genetic characteristics of a rare case of Gitelman syndrome with comorbid Graves disease and ACTH-independent adrenocortical adenoma.

METHODS

A patient who had presented at the Nanchong Central Hospital on December 21, 2020 was selected as the study subject. Clinical data of the patient was collected. Whole-exome sequencing was carried out on DNA extracted from peripheral venous blood samples from the patient and her family members.

RESULTS

The patient, a 45-year-old woman, was found to have Graves disease, ACTH-independent Cushing syndrome, hypokalemia and hypomagnesemia following the discovery of an adrenal incidentaloma. MRI scan had revealed a 3.8 cm × 3.2 cm mass in the left adrenal gland. The mass was removed by surgery and confirmed as adrenocortical adenoma. DNA sequencing revealed that the patient and her sister have both harbored compound heterozygous variants of the SLC12A3 gene, namely c.1444-10(IVS11)G>A and c.179(exon1)C>T (p.T60M), which were respectively inherited from their father and mother. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), the c.1444-10(IVS11)G>A and c.179(exon1)C>T (p.T60M) were respectively classified as a variant of uncertain significance (PM2_Supporting+PP3) and a likely pathogenic variant (PM3_Strong+PM1+PP3).

CONCLUSION

The conjunction of Gitelman syndrome with Graves disease and adrenal cortex adenoma is rather rare. The newly discovered c.1444-10(IVS11)G>A variant of the SLC12A3 gene, together with the heterozygous variant of c.179(exon1)C>T (p.T60M), probably underlay the pathogenesis in this patient.

Novel SLC12A3 gene mutations and clinical characteristics in two pedigrees with Gitelman syndrome

OBJECTIVE

Gitelman syndrome (GS) is an autosomal recessive tubulopathy resulting from inactivating mutations in the SLC12A3 gene that encodes the thiazide-sensitive sodium-chloride cotransporter (NCC). To date, more than 500 mutations have been identified in the SLC12A3 gene. In this study, we identified two new mutations in the SLC12A3 gene in two Chinese GS pedigrees.

DESIGN, PATIENTS AND MEASUREMENTS

The clinical characteristics and laboratory examination of two suspected GS patients in our hospital were analyzed. In addition, two pedigrees including 11 members and 2 patients underwent SLC12A3 gene analysis.

RESULTS

Both patients were middle-aged women with characteristics of hypokalemic metabolic alkalosis, hypomagnesemia, low level of urinary calcium and the elevated levels of renin-angiotensin-aldosterone system. So, they were clinically diagnosed as GS. Patient 2 also had type 2 diabetes and Graves' disease. Both patients were found to carry two mutations of SLC12A3 gene by Sanger direct sequencing, which were all compound heterozygous mutations. We identified three mutations in these two Chinese GS pedigrees, one of which was c.179C>T (Thr60Met). The novel c.2159G>T (p. Gly720Val) and c.2675T>C (p. Leu892Pro) mutations were strongly predicted to be pathogenic using four network programs-Polyphen-2, SIFT, Mutation Taster and LRT.

CONCLUSIONS

We identified two novel SLC12A3 genetic variant [c.2159G>T (p.Gly720Val) and c.2675T>C (p.Leu892Pro)] in two Chinese GS pedigrees. The discovery of new mutations has enriched the spectrum of SLC12A3 genotypes.

Novel heterozygous mutations of SLC12A3 gene in a Chinese pedigree with Gitelman syndrome: A care-compliant case report

RATIONALE

The diagnosis of Gentleman syndrome (GS) is usually delayed because the clinical symptoms are easily mistaken.

PATIENT CONCERNS

A 19-year-old male patient was referred to endocrinology due to intermittent twitch of extremities for approximately 7 years.

DIAGNOSES

The diagnosis of GS was made based on the laboratory and gene detection results. We identified 2 new variants in the SLC12A3 gene [c.857 A > C (exon7) and c.2089_2095del (exon17)] in his Asian family.

INTERVENTIONS

The patient received the treatment of potassium chloride sustained release tablets, potassium magnesium aspartate and spironolactone. After given potassium supplement through enema, his serum potassium level was corrected to normal.

OUTCOMES

The electrolyte imbalance including hypokalemia and hypomagnesemia were improved with a remission of the clinical manifestations. But the patient's condition still could not remain stable for his irregular oral potassium supplementation during the follow-up of nearly 3 months.

LESSONS

Our finding broadens the variant spectrum of SLC12A3 and contributes to a more quickly genetic counseling. As a result, when a patient presents with persistent, unspecified, and inadequately treated hypokalemia, tests for GS should indeed be considered. For suspected cases of GS, genetic testing should always be considered in the diagnosis.

Case report: Gitelman syndrome with diabetes: Confirmed by both hydrochlorothiazide test and genetic testing

RATIONALE

Gitelman syndrome (GS) is an autosomal recessive tubulopathy caused by mutations of the SLC12A3 gene. It is characterized by hypokalemic metabolic alkalosis, hypomagnesemia and hypocalciuria. Hypokalemia, hypomagnesemia, and increased renin-angiotensin-aldosterone system (RAAS) activity can cause glucose metabolism dysfunction. The diagnosis of GS includes clinical diagnosis, genetic diagnosis and functional diagnosis. The gene diagnosis is the golden criterion while as functional diagnosis is of great value in differential diagnosis. The hydrochlorothiazide (HCT) test is helpful to distinguish GS from batter syndrome, but few cases have been reported to have HCT testing.

PATIENT CONCERNS

A 51-year-old Chinese woman presented to emergency department because of intermittent fatigue for more than 10 years.

DIAGNOSES

Laboratory test results showed hypokalemia, hypomagnesemia, hypocalciuria and metabolic alkalosis. The HCT test showed no response. Using next-generation and Sanger sequencing, we identified 2 heterozygous missense variants (c.533C > T:p.S178L and c.2582G > A:p.R861H) in the SLC12A3 gene. In addition, the patient was diagnosed with type 2 diabetes mellitus 7 years ago. Based on these findings, the patient was diagnosed with GS with type 2 diabetic mellitus (T2DM).

INTERVENTIONS

She was given potassium and magnesium supplements, and dapagliflozin was used to control her blood glucose.

OUTCOMES

After treatments, her fatigue symptoms were reduced, blood potassium and magnesium levels were increased, and blood glucose levels were well controlled.

LESSONS

When GS is considered in patients with unexplained hypokalemia, the HCT test can be used for differential diagnosis, and genetic testing can be continued to confirm the diagnosis when conditions are available. GS patients often have abnormal glucose metabolism, which is mainly caused by hypokalemia, hypomagnesemia, and secondary activation of RAAS. When a patient is diagnosed with GS and type 2 diabetes, sodium-glucose cotransporter 2 inhibitors (SGLT2i) can be used to control the blood glucose level and assist in raising blood magnesium.

A case report of Gitelman syndrome in children

RATIONALE

Giltelman syndrome (GS) is an autosomal recessive infectious disease, which is caused by the mutation of SLC12A3 gene encoding thiazide diuretic sensitive sodium chloride cotransporter located in the distal convoluted tubule of the kidney.

PATIENT CONCERNS

A 7-year-old and 3-month-old male patient has poor appetite, slow growth in height and body weight since the age of 3, body weight: 16 kg (-3 standard deviation), height: 110 cm (-3 standard deviation), normal exercise ability and intelligence. One year ago, he was diagnosed with hypokalemia. After potassium supplement treatment, the blood potassium returned to normal. The patient developed abdominal pain, vomiting, limb weakness, and tetany 1 day before admission.

DIAGNOSES

After admission examination, the patient was found to have hypokalemia (2.27-2.88 mmol/L), hypomagnesemia (0.47 mmol/L), hypophosphatemia (1.17 mmol/L), hypocalcemia (1.06 mmol/24 hours), and metabolic alkalosis (PH 7.60). The blood pressure is normal, and the concentration of aldosterone is 791.63 pg/mL. The adrenocorticotropic hormone and cortisol detected at 8 am are 4.95 pmol/L and 275.09 nmol/L, respectively. Twenty-four hours of urine potassium is 32.52 mmol. Gene sequencing results showed 2 pathogenic variants in the GS-related SLC12A3 gene, which are related to the phenotype of the subject.

INTERVENTIONS

After admission, the patients were given potassium and magnesium supplements, as well as oral spironolactone. The symptoms of limb weakness and tetany were significantly relieved. After discharge, the patients continued to maintain treatment to keep the blood potassium at more than 3.0 mmol/L, and the blood magnesium at more than 0.6 mmol/L.

OUTCOMES

Follow-up at 1 month after discharge, in the patient's self-description, he had no symptoms such as limb weakness and tetany, and his height was increased by 1 cm and the body weight increased by 1.5 kg.

LESSONS

For patients with hypokalemia, hypomagnesemia, and metabolic alkalosis, the possibility of GS should be given priority. After the diagnosed by gene sequencing of SLC12A3 gene, potassium and magnesium supplementation could significantly improve symptoms.

Long-Read Sequencing Identifies Novel Pathogenic Intronic Variants in Gitelman Syndrome

BACKGROUND

Gitelman syndrome is a salt-losing tubulopathy characterized by hypokalemic alkalosis and hypomagnesemia. It is caused by homozygous recessive or compound heterozygous pathogenic variants in SLC12A3 , which encodes the Na + -Cl - cotransporter (NCC). In up to 10% of patients with Gitelman syndrome, current genetic techniques detect only one specific pathogenic variant. This study aimed to identify a second pathogenic variant in introns, splice sites, or promoters to increase the diagnostic yield.

METHODS

Long-read sequencing of SLC12A3 was performed in 67 DNA samples from individuals with suspected Gitelman syndrome in whom a single likely pathogenic or pathogenic variant was previously detected. In addition, we sequenced DNA samples from 28 individuals with one variant of uncertain significance or no candidate variant. Midigene splice assays assessed the pathogenicity of novel intronic variants.

RESULTS

A second likely pathogenic/pathogenic variant was identified in 45 (67%) patients. Those with two likely pathogenic/pathogenic variants had a more severe electrolyte phenotype than other patients. Of the 45 patients, 16 had intronic variants outside of canonic splice sites (nine variants, mostly deep intronic, six novel), whereas 29 patients had an exonic variant or canonic splice site variant. Midigene splice assays of the previously known c.1670-191C>T variant and intronic candidate variants demonstrated aberrant splicing patterns.

CONCLUSION

Intronic pathogenic variants explain an important part of the missing heritability in Gitelman syndrome. Long-read sequencing should be considered in diagnostic workflows for Gitelman syndrome.

Structure and thiazide inhibition mechanism of the human Na-Cl cotransporter

The sodium-chloride cotransporter (NCC) is critical for kidney physiology1. The NCC has a major role in salt reabsorption in the distal convoluted tubule of the nephron2,3, and mutations in the NCC cause the salt-wasting disease Gitelman syndrome4. As a key player in salt handling, the NCC regulates blood pressure and is the target of thiazide diuretics, which have been widely prescribed as first-line medications to treat hypertension for more than 60 years5-7. Here we determined the structures of human NCC alone and in complex with a commonly used thiazide diuretic using cryo-electron microscopy. These structures, together with functional studies, reveal major conformational states of the NCC and an intriguing regulatory mechanism. They also illuminate how thiazide diuretics specifically interact with the NCC and inhibit its transport function. Our results provide critical insights for understanding the Na-Cl cotransport mechanism of the NCC, and they establish a framework for future drug design and for interpreting disease-related mutations.

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 leads them to be protected from hypertension, 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 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.

Whole-exome sequencing in diagnosing 2 cases of Gitelman syndrome

Two patients with Gitelman syndrome were admitted to the Department of Endocrinology, Third Xiangya Hospital of Central South University. The genomic DNA from the patients' peripheral blood was extracted and the whole-exome sequencing was performed to detect the possible mutations. The function of the mutation sites was analyzed by bioinformatics software. Through whole-exome sequencing and Sanger sequencing, we have found that 2 patients with Gitelman syndrome carried compound heterozygous mutations of SLC12A3 gene, which were c.486_490delTACGGinsA, p.R943W, p.D486N, and p.R928C. Among them, c.486_490delTACGGinsA insertion deletion mutation causes frame shift and protein truncation. The p.R943W, p.D486N, and p.R928C of SLC12A3 gene were predicted to be pathogenic mutations by SIFT, PolyPhen2, and Mutation Taster. These 4 mutations were all reported, but p.R943W was first reported in Chinese population. Gitelman syndrome is rare in clinic and the rate of missed diagnosis is high. Early genetic analysis in patients with Gitelman syndrome is helpful to determine the etiology and guide the treatment.

Rapidly Progressing to ESRD in an Individual with Coexisting ADPKD and Masked Klinefelter and Gitelman Syndromes

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenetic hereditary renal disease, promoting end-stage renal disease (ESRD). Klinefelter syndrome (KS) is a consequence of an extra copy of the X chromosome in males. Main symptoms in KS include hypogonadism, tall stature, azoospermia, and a risk of cardiovascular diseases, among others. Gitelman syndrome (GS) is an autosomal recessive disorder caused by SLC12A3 variants, and is associated with hypokalemia, hypomagnesemia, hypocalciuria, normal or low blood pressure, and salt loss. The three disorders have distinct and well-delineated clinical, biochemical, and genetic findings. We here report a male patient with ADPKD who developed early chronic renal failure leading to ESRD, presenting with an intracranial aneurysm and infertility. NGS identified two de novo PKD1 variants, one known (likely pathogenic), and a previously unreported variant of uncertain significance, together with two SLC12A3 pathogenic variants. In addition, cytogenetic analysis showed a 47, XXY karyotype. We investigated the putative impact of this rare association by analyzing possible clinical, biochemical, and/or genetic interactions and by comparing the evolution of renal size and function in the proband with three age-matched ADPKD (by variants in PKD1) cohorts. We hypothesize that the coexistence of these three genetic disorders may act as modifiers with possible synergistic actions that could lead, in our patient, to a rapid ADPKD progression.

Bartter and Gitelman syndromes

Bartter and Gitelman syndromes belong to salt-losing tubulopathies. These rare diseases may be associated with severe electrolyte disorders. Early identification of tubulopathies is essential for appropriate management. Progress in molecular genetics enabled the identification of genes and pathophysiologic mechanisms associated with these diseases. Here, we review etiology and diagnostics of these disorders from the light of current knowledge. Additionally, we discuss contemporary therapeutic approaches.

Molecular Basis, Diagnostic Challenges and Therapeutic Approaches of Bartter and Gitelman Syndromes: A Primer for Clinicians

Gitelman and Bartter syndromes are rare inherited diseases that belong to the category of renal tubulopathies. The genes associated with these pathologies encode electrolyte transport proteins located in the nephron, particularly in the Distal Convoluted Tubule and Ascending Loop of Henle. Therefore, both syndromes are characterized by alterations in the secretion and reabsorption processes that occur in these regions. Patients suffer from deficiencies in the concentration of electrolytes in the blood and urine, which leads to different systemic consequences related to these salt-wasting processes. The main clinical features of both syndromes are hypokalemia, hypochloremia, metabolic alkalosis, hyperreninemia and hyperaldosteronism. Despite having a different molecular etiology, Gitelman and Bartter syndromes share a relevant number of clinical symptoms, and they have similar therapeutic approaches. The main basis of their treatment consists of electrolytes supplements accompanied by dietary changes. Specifically for Bartter syndrome, the use of non-steroidal anti-inflammatory drugs is also strongly supported. This review aims to address the latest diagnostic challenges and therapeutic approaches, as well as relevant recent research on the biology of the proteins involved in disease. Finally, we highlight several objectives to continue advancing in the characterization of both etiologies.

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

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

Glomerular podocyte dysfunction in inherited renal tubular disease

BACKGROUND

Hereditary renal tubular disease can cause hypercalciuria, acid-base imbalance, hypokalemia, hypomagnesemia, rickets, kidney stones, etc. If these diseases are not diagnosed or treated in time, they can cause kidney damage and electrolyte disturbances, which can be detrimental to the maturation and development of the child. Glomerular involvement in renal tubular disease patients has only been considered recently.

METHODS

We screened 71 papers (including experimental research, clinical research, etc.) about Dent's disease, Gitelman syndrome, and cystinosis from PubMed, and made reference.

RESULTS

Glomerular disease was initially underestimated among the clinical signs of renal tubular disease or was treated merely as a consequence of the tubular damage. Renal tubular diseases affect glomerular podocytes through certain mechanisms resulting in functional damage, morphological changes, and glomerular lesions.

CONCLUSIONS

This article focuses on the progress of changes in glomerular podocyte function in Dent disease, Gitelman syndrome, and cystinosis for the purposes of facilitating clinically accurate diagnosis and scientific treatment and improving prognosis.

[Identification of pathological variants of SLC12A3 gene in a pedigree affected with Gitelman syndrome]

OBJECTIVE

To detect pathological variants of the SLC12A3 gene in a Chinese pedigree affected with Gitelman syndrome (GS).

METHODS

Clinical data and peripheral blood samples of the proband and his family members were collected. All exons of the SLC12A3 gene were amplified by PCR and subjected to Sanger sequencing.

RESULTS

Sanger sequencing has revealed that the proband has carried a c.486_489 delTACG (p.Ile162Met fs*8) deletion and a heterozygous c.2890C>T (p.Arg964Trp) missense variant in the SLC12A3 gene. Neither variant was reported previously and was not found among healthy controls.

CONCLUSION

The c.486_489delTACG (p.Ile162Met fs*8) and c.2890C>T (p.Arg964Trp) variants of the SLC12A3 gene probably underlay the GS in the proband. Above discovery has enriched the variant spectrum of GS.

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.

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.