Hypomagnesemia induces impaired glucose metabolism and insulin resistance in patients with Gitelman syndrome

AIMS

To investigate the contributing factors of impaired glucose metabolism in patients with Gitelman syndrome (GS).

METHODS

This study collected clinical data and conducted oral glucose tolerance tests (OGTT) on 44 GS patients, with 60 non-functioning adrenal incidentaloma (NFAI) patients serving as controls.

RESULTS

Compared to NFAI patients, GS patients exhibited a significantly higher prevalence of impaired glucose metabolism (P < 0.001), with markedly higher homeostasis model assessment of insulin resistance (HOMA-IR), lower quantitative insulin sensitivity check index, and lower Matsuda index compared to NFAI patients (all P < 0.001). The homeostasis model assessment for β cells was elevated (P = 0.003) and the insulin secretion sensitivity index-2 was reduced (P = 0.007) in GS patients relative to NFAI patients. Logistic regression identified hypomagnesemia (P = 0.042) and hypokalemia (P = 0.046) as risk factors for dysregulated glucose metabolism in GS patients. Additionally, higher body mass index (BMI) (P = 0.016) and hypomagnesemia (P = 0.045) were significant contributors to IR. Notably, GS patients had a steeper linear regression slope between BMI and HOMA-IR compared to NFAI patients (P = 0.016). A negative linear correlation between plasma magnesium and BMI (R = 0.54, P < 0.001) was found in GS patients.

CONCLUSIONS

Hypomagnesemia may contribute to increased BMI, exacerbating impaired glucose metabolism and IR in GS patients.

Recurrent falls as the presentations of Gitelman syndrome in an octogenarian

Gitelman syndrome (GS) is the most common hereditary renal tubular disorder, with a higher carrier frequency among Asians often overlooked in older adults. Electrolyte imbalances, such as those seen in GS, are crucial considerations for older adults experiencing recurrent falls. We described an 83-year-old diabetic female on metformin, who was admitted due to recurrent falls with the preceding dizziness and palpitations when standing. She had the history of chronic hypokalemia and hypomagnesemia on regular potassium (K+) and magnesium (Mg++) supplementation for 10 years and gout-like arthritis episodes over her shoulder and ankle joints. Her consciousness was alert with normal blood pressure but reduced tendon reflex over bilateral knees. Pertinent laboratory findings included hypokalemic (K+ 2.2 mmol/L) with metabolic alkalosis and high urine K+ excretion, hypomagnesemia (1.1 mg/dl) with hypermagnesuria, but hypocalciuria (UCa/Cr ratio 0.01 mg/mg), high urine salt excretion, and hyperreninemia. X-ray of bilateral knees and shoulders demonstrated typical chondrocalcinosis with dense calcification band in the joint space. Targeted Sanger sequencing confirmed GS, identifying a biallelic homozygous deletion mutation (2881-2 delAG) in the exon 24 of SLC12A3 gene as the potential causes of recurrent falls. After aggressive electrolytes correction, her potassium and magnesium levels stabilized, and the patient did not experience further falls. This case, probably the oldest documented patient with GS emphasizes the importance of recognizing atypical presentations of GS in older adults. Careful evaluation and management of electrolyte disturbances in this population may prevent fall recurrence and complications.

Functional evaluation of novel compound heterozygous variants in SLC12A3 of Gitelman syndrome

BACKGROUND

Gitelman syndrome (GS) is an inherited renal tubular disorder characterized by hypokalemic alkalosis and hypomagnesemia, due to biallelic pathogenic variants in the solute carrier family 12 member 3 (SLC12A3) gene encoding a sodium-chloride (Na-Cl) cotransporter (NCC). This work aimed at identifying SLC12A3 variants in the GS pedigree and reveal the effect of the mutations on protein structure and function.

METHODS

Whole-exome sequencing (WES) and Sanger sequencing were performed in the pedigree. Configuration prediction of two mutant NCC proteins were achieved using SWISS-MODEL. The SLC12A3 missense mutants were generated by site-specific mutagenesis, and the protein expression, location and Na+ uptake activity were assessed by using the HEK293T cell line.

RESULTS

Genetic analysis identified novel compound heterozygous SLC12A3 variants (c.718G > A/p.E240K and c.2675T > C/p.L892P) in the patient with typical GS phenotype. Both of her parents, elder brother and her son carried the heterozygous p.L892P variant, but only the elder brother exhibited mild hypokalemia. Bioinformatics tools predicted that both mutations were highly species conserved and pathogenic. The prediction of mutant protein indicated that p.E240K and p.L892P altered protein's secondary and three-dimensional (3D) structure and stability. Functional experiments revealed decreased protein expression and Na+ uptake activity caused by these two variants, especially the p.L892P variant.

CONCLUSION

Our study presents the genetic and functional evidence for the novel compound heterozygous loss-of-function variants in SLC12A3 that may synergistically cuase GS, and expands the mutation spectrum of SLC12A3 variants in patients with GS.

A novel homozygous SLC12A3 mutation causing Gitelman syndrome with co-existent autoimmune thyroiditis: a case report and review of the literature

Gitelman syndrome is a rare, autosomal recessively inherited tubulopathy manifesting with hypokalemia, hypomagnesemia, hypocalciuria, and metabolic alkalosis. Common symptoms include fatigue, myalgia, reduced performance capacity, tetany, paresthesia, and delayed growth. However, as reported in the literature, diagnosis in some patients is prompted by an incidental finding of hypokalemia. GS develops due to mutations in the SLC12A3 gene, which encodes the thiazide-sensitive Na-Cl cotransporter. Many variants in the SLC12A3 gene causing GS have been reported in literature. A new pathogenic homozygous mutation (c.2612G > T), absence of hypomagnesemia, and accompanying autoimmune thyroiditis are remarkable in our patient. There are a few Gitelman syndrome cases that are complicated with autoimmune thyroiditis in the literature. In this study, we present a case of Gitelman syndrome with a novel homozygous mutation and accompanying autoimmune thyroiditis and review of the literature.

Case report: Two novel compound heterozygous variant of SLC12A3 gene in a gitelman syndrome family and literature review

A 36-year-old unmarried male chef was incidentally diagnosed with hypokalemia during an evaluation for an acute perianal abscess. Despite potassium supplementation, he developed progressive weakness in his lower limbs, culminating in an inability to stand. Investigations confirmed severe hypokalemia, metabolic alkalosis, hypomagnesemia, secondary hyperaldosteronism, and low urinary calcium excretion, with normotension. The patient's long-standing stunted growth and lean physique since childhood were noted. Biochemical assays further identified type 2 diabetes mellitus and metabolic syndrome. Genetic analysis revealed three heterozygous SLC12A3 mutations (M1: c.421G>A: p.G141R, M2: c.509T>A:p.L170Q, and M3: c.704C>A: p.T235K), compound heterozygo us and derived from both parents, with M1 and M3 reported here for the first time. Treatment with spironolactone and oral potassium chloride stabilized his potassium levels. Following the administration of SGLT2 inhibitors in patients receiving hypoglycemic therapy, we observed a mild decrease in serum sodium levels. This case highlights the criticality of vigilant metabolic surveillance in Gitelman syndrome and advises prudence with SGLT2 inhibitors in those with concurrent type 2 diabetes, given the risk of potentially aggravate sodium loss.

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 compound heterozygous variants of SLC12A3 gene in a Chinese patient with Gitelman syndrome: a case report

Background: The Gitelman syndrome (GS) is an autosomal recessive disorder of renal tubular salt handling. Gitelman syndrome is characterized by hypokalemia, metabolic alkalosis, hypomagnesemia, hypocalciuria, and renin-angiotensin-aldosterone system (RAAS) activation, and is caused by variants in the SLC12A3 gene. Gitelman syndrome has a heterogeneous phenotype, which may or may not include a range of clinical signs, posing certain difficulties for clinical diagnosis. Case presentation: A 49-year-old man was admitted to our hospital due to muscular weakness. The patient's history revealed previous recurrent muscular weakness events associated with hypokalemia, featured by a minimum serum potassium value of 2.3 mmol/L. The reported male patient had persistent hypokalemia, hypocalciuria and normal blood pressure, without presenting obvious metabolic alkalosis, growth retardation, hypomagnesemia, hypochloremia or RAAS activation. We performed whole-exome sequencing and identified a novel compound heterozygous variant in the SLC12A3 gene, c.965-1_976delGCGGACATTTTTGinsACCGAAAATTTT in exon8 and c.1112T>C in exon9 in the proband. Conclusion: This is a study to report a heterogeneous phenotype Gitelman syndrome with a novel pathogenic compound heterozygous variant in the SLC12A3 gene. This genetic study expands the variants spectrum, and improve the diagnostic accuracy of Gitelman syndrome. Meanwhile, further functional studies are required to investigate the pathophysiological mechanisms of Gitelman syndrome.

Gitelman syndrome with Graves' disease leading to rhabdomyolysis: a case report and literature review

A 14-year-old male patient who suffered from limb numbness, fatigue, and hypokalemia was considered Graves' disease (GD) complicated with thyrotoxic periodic paralysis (TPP) at the first diagnosis. Although with the treatment of antithyroid drugs, he developed severe hypokalemia and rhabdomyolysis (RM). Further laboratory tests revealed hypomagnesemia, hypocalciuria, metabolic alkalosis, hyperrenin, and hyperaldosteronemia. Genetic testing revealed compound heterozygous mutations in the SLC12A3 gene (c.506-1G > A, c.1456G > A) encoding the thiazide-sensitive sodium-chloride cotransporter, which presented a definitive diagnosis of Gitelman syndrome (GS). Moreover, gene analysis revealed his mother diagnosed with subclinical hypothyroidism due to Hashimoto's thyroiditis carried the c.506-1G > A heterozygous mutation in the SLC12A3 gene and his father carried the c.1456G > A heterozygous mutation in the SLC12A3 gene. His younger sister who had hypokalemia and hypomagnesemia carried the same compound heterozygous mutations as the proband and was diagnosed with GS as well, but with a much milder clinical presentation and better treatment outcome. This case suggested the potential relationship between GS and GD, clinicians should strengthen the differential diagnosis to avoid missed diagnosis.

Genetic diagnosis and treatment of hereditary renal tubular disease with hypokalemia and alkalosis

Renal tubules play an important role in maintaining water, electrolyte, and acid-base balance. Renal tubule dysfunction can cause electrolyte disorders and acid-base imbalance. Clinically, hypokalemic renal tubular disease is the most common tubule disorder. With the development of molecular genetics and gene sequencing technology, hereditary renal tubular diseases have attracted attention, and an increasing number of pathogenic genes related to renal tubular diseases have been discovered and reported. Inherited renal tubular diseases mainly occur due to mutations in genes encoding various specific transporters or ion channels expressed on the tubular epithelial membrane, leading to dysfunctional renal tubular reabsorption, secretion, and excretion. An in-depth understanding of the molecular genetic basis of hereditary renal tubular disease will help to understand the physiological function of renal tubules, the mechanism by which the kidney maintains water, electrolyte, and acid-base balance, and the relationship between the kidney and other systems in the body. Meanwhile, understanding these diseases also improves our understanding of the pathogenesis of hypokalemia, alkalosis and other related diseases and ultimately promotes accurate diagnostics and effective disease treatment. The present review summarizes the most common hereditary renal tubular diseases (Bartter syndrome, Gitelman syndrome, EAST syndrome and Liddle syndrome) characterized by hypokalemia and alkalosis. Further detailed explanations are provided for pathogenic genes and functional proteins, clinical manifestations, intrinsic relationship between genotype and clinical phenotype, diagnostic clues, differential diagnosis, and treatment strategies for these diseases.

Machine Learning to Identify Genetic Salt-Losing Tubulopathies in Hypokalemic Patients

Introduction

Clinically distinguishing patients with the inherited salt-losing tubulopathies (SLTs), Gitelman or Bartter syndrome (GS or BS) from other causes of hypokalemia (LK) patients is difficult, and genotyping is costly. We decided to identify clinical characteristics that differentiate SLTs from LK.

Methods

A total of 66 hypokalemic patients with possible SLTs were recruited to a prospective observational cohort study at the University College London Renal Tubular Clinic, London. All patients were genotyped for pathogenic variants in genes which cause SLTs; 39 patients had pathogenic variants in genes causing SLTs. We obtained similar data sets from cohorts in Taipei and Kobe, as follows: the combined data set comprised 419 patients; 291 had genetically confirmed SLT. London and Taipei data sets were combined to train machine learning (ML) algorithms, which were then tested on the Kobe data set.

Results

Single biochemical variables (e.g., plasma renin) were significantly, but inconsistently, different between SLTs and LK in all cohorts. A decision table algorithm using serum bicarbonate and urinary sodium excretion (FE_Na) achieved a classification accuracy of 74%. This was superior to all the single biochemical variables identified previously.

Conclusion

ML algorithms can differentiate true SLT in the context of a specialist clinic with some accuracy. However, based on routine biochemistry, the accuracy is insufficient to make genotyping redundant.

A Practical Guide to Genetic Testing for Kidney Disorders of Unknown Etiology

Genetic testing is increasingly used in the workup and diagnosis of kidney disease and kidney-related disorders of undetermined cause. Out-of-pocket costs for clinical genetic testing have become affordable, and logistical hurdles overcome. The interest in genetic testing may stem from the need to make or confirm a diagnosis, guide management, or the patient's desire to have a more informed explanation or prognosis. This poses a challenge for providers who do not have formal training in the selection, interpretation, and limitations of genetic tests. In this manuscript, we provide detailed discussion of relevant cases in which clinical genetic testing using a kidney gene panel was applied. The cases demonstrate identification of pathogenic variants for monogenic diseases-contrasting them from genetic risk alleles-and bring up diagnostic limitations and diagnostic utility of these tests in nephrology. This review aims to guide clinicians in formulating pretest conversations with their patients, interpreting genetic variant nomenclature, and considering follow-up investigations. Although providers are gaining experience, there is still risk of testing causing more anxiety than benefit. However, with provider education and support, clinical genetic testing applied to otherwise unexplained kidney-related disorders will increasingly serve as a valuable diagnostic tool with the potential to reshape how we consider and treat many kidney-related diagnoses.

Detecting pathogenic deep intronic variants in Gitelman syndrome

Gitelman syndrome (GS) is a rare, autosomal recessive, salt-losing tubulopathy caused by loss of function in the SLC12A3 gene (NM_000339.2), which encodes the natrium chloride cotransporter. The detection of homozygous or compound heterozygous SLC12A3 variants is expected in GS, but 18%-40% of patients with clinical GS carry only one mutant allele. Previous reports identified some pathogenic deep intronic variants in SLC12A3. Here, we report the screening of SLC12A3 deep intronic variants in 13 patients with suspected GS carrying one mutated SLC12A3 allele. Variant screening used the HaloPlex Target Enrichment System Kit capturing whole introns and the promotor region of SLC12A3, followed by SureCall variant analysis. Rare intronic variants (<1% frequency) were identified, and pathogenicity evaluated by the minigene system. Deep intronic variant screening detected seven rare SLC12A3 variants from six patients. Only one variant showed pathogenicity in the minigene system (c.602-16G>A, intron 4) through activation of a cryptic acceptor site. No variants were detected in the promotor region. Deep intronic screening identified only one pathogenic variant in patients with suspected GS carrying monoallelic SLC12A3 variants. Our results suggest that deep intronic variants partially explain the cause of monoallelic variants in patients with GS.

Novel compound heterozygous mutation of SLC12A3 in Gitelman syndrome co-existent with hyperthyroidism: A case report and literature review

BACKGROUND

Gitelman syndrome (GS) is a rare inherited autosomal recessive tubulopathy, characterized clinically by hypokalemia, hypomagnesemia, hypocalciuria, and metabolic alkalosis, and is caused by an inactivating mutation in SLC12A3. GS is prone to misdiagnosis when occurring simultaneously with hyperthyroidism. It is important to consider the possibility of other diseases when hyperthyroidism is combined with hypokalemia, which is difficult to correct.

CASE SUMMARY

A female patient with hyperthyroidism complicated with limb weakness was diagnosed with thyrotoxic hypokalemic periodic paralysis for 4 mo. However, the patient’s serum potassium level remained low despite sufficient potassium replacement and remission of hyperthyroidism. GS was confirmed by whole exome and Sanger sequencing. Gene sequencing revealed compound heterozygous mutations of c.488C>T (p.Thr163Met), c.2612G>A (p.Arg871His), and c.1171_1178dupGCCACCAT (p.Ile393fs) in SLC12A3. Protein molecular modeling was performed to predict the effects of the identified missense mutations. All three mutations cause changes in protein structure and may result in abnormal protein function. All previously reported cases of GS coexisting with autoimmune thyroid disease are reviewed.

CONCLUSION

We have identified a novel compound heterozygous mutation in SLC12A3. The present study provides new genetic evidence for GS.

A novel mutation of SLC12A3 gene causing Gitelman syndrome

A 48-year-old patient with a history of diabetes mellitus, presented to a surgical ward with abdominal pain. She was found to have hypokalemia. Her younger sister had passed away due to sudden cardiac death at the age of 25 years. Further evaluation revealed an elevated trans-tubular potassium gradient suggestive of renal potassium loss, normal blood pressure, hypomagnesemia, hypocalciuria, and alkalosis. Moreover, there was evidence of secondary hyperaldosteronism. Genetic studies revealed two heterozygous mutations of the SLC12A3 gene, including a novel mutation which has not been reported before anywhere in the world. She was treated with intravenous potassium supplementation and was later converted to oral potassium and oral magnesium supplementation with spironolactone. Her potassium and magnesium levels normalized and glycaemic control also improved. Hypokalemia and hypomagnesemia found in Gitelman syndrome may be associated with insulin resistance and correction of electrolytes can lead to better glycaemic control.

Genetic and Biological Effects of SLC12A3, a Sodium-Chloride Cotransporter, in Gitelman Syndrome and Diabetic Kidney Disease

The SLC12A3 (Solute carrier family 12 member 3) gene encodes a sodium-chloride cotransporter and mediates Na+ and Cl− reabsorption in the distal convoluted tubule of kidneys. An experimental study has previously showed that with knockdown of zebrafish ortholog, slc12a3 led to structural abnormality of kidney pronephric distal duct at 1-cell stage, suggesting that SLC12A3 may have genetic effects in renal disorders. Many clinical reports have demonstrated that the function-loss mutations in the SLC12A3 gene, mainly including Thr60Met, Asp486Asn, Gly741Arg, Leu859Pro, Arg861Cys, Arg913Gln, Arg928Cys and Cys994Tyr, play the pathogenic effects in Gitelman syndrome. This kidney disease is inherited as an autosomal recessive trait. In addition, several population genetic association studies have indicated that the single nucleotide variant Arg913Gln in the SLC12A3 gene is associated with diabetic kidney disease in type 2 diabetes subjects. In this review, we first summarized bioinformatics of the SLC12A3 gene and its genetic variation. We then described the different genetic and biological effects of SLC12A3 in Gitelman syndrome and diabetic kidney disease. We also discussed about further genetic and biological analyses of SLC12A3 as pharmacokinetic targets of diuretics.

Early diagnosis of Gitelman syndrome in a young child: A case report

BACKGROUND

Gitelman syndrome (GS) is an autosomal recessive renal tubular disorder characterized by renal wasting hypokalemia, metabolic alkalosis, hypomagnesemia, and hypocalciuria. It is usually caused by mutations in the gene SLC12A3, which encodes the thiazide-sensitive Na-Cl cotransporter. GS is not usually diagnosed until late childhood or adulthood.

CASE SUMMARY

Here, we report the case of a one-year-old girl who was brought to the emergency department due to persistent vomiting for two days. On admission to our hospital, generalized weakness was observed, and laboratory investigations revealed severe hypokalemia (1.9 mmol/L). However, persistent hypokalemia was observed during outpatient follow-up. Suspicion of the GS phenotype was assessed via the patient’s clinical presentation, family history, and biochemical analysis of blood and urine. Further genetic analysis was performed for her and her family by exon-wide sequencing analysis of the gene SLC12A3. The genetic diagnosis of GS was established in the Taiwanese family with three affected individuals, two of whom were children (7 years/17 years) without obvious symptoms, with the youngest being only one year old (patient in our case).

CONCLUSION

We successfully demonstrated the early diagnosis of GS using family genetic analysis. Any instances of hypokalemia should not be neglected, as early detection of GS with suitable treatment can prevent patients from potentially life-threatening complications.

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.

Novel mutations of the SLC12A3 gene in patients with Gitelman syndrome

Mutations in the SLC12A3 gene have been reported to cause Gitelman syndrome (GS). This study aimed to investigate the genetic mutations and clinical features of patients with GS. Four pedigrees (4 GS patients and 14 family members) were enrolled. The symptoms, laboratory results, management, and genotypes were analyzed. Genomic DNA was screened for gene variations using Sanger sequencing. DNA sequences were compared with reference sequences. The effects of the mutations were predicted using prediction tools (Mutation Taster, PolyPhen-2, SIFT, and PROVEAN). Genetic analysis revealed six genetic variants of SLC12A3, including three novel heterozygous mutations (c.2T > C, c.1609C > T, c.3055G > A) and three previously characterized mutations (c.1456G > A, c.2542G > A, c.1077C > G). These mutations were predicted to exert a damaging effect based on predictive in silico tools. GS patients had low blood pressure and low levels of serum K⁺, serum Mg²⁺, and 24-h urinary Ca²⁺ but high levels of 24-h urinary K⁺. These clinical manifestations and genotypes were consistent with the diagnostic criteria of GS. The study described the phenotypes and genotypes of 4 pedigrees involving GS patients, demonstrating the importance of SLC12A3 gene screening for GS.

Allele-specific RT-PCR for the rapid detection of recurrent SLC12A3 mutations for Gitelman syndrome

Recurrent mutations in the SLC12A3 gene responsible for autosomal recessive Gitelman syndrome (GS) are frequently reported, but the exact prevalence is unknown. The rapid detection of recurrent SLC12A3 mutations may help in the early diagnosis of GS. This study was aimed to investigate the prevalence of recurrent SLC12A3 mutations in a Taiwan cohort of GS families and develop a simple and rapid method to detect recurrent SLC12A3 mutations. One hundred and thirty independent Taiwan families with genetically confirmed GS were consecutively enrolled to define recurrent SLC12A3 mutations and determine their prevalence. Using TaqMan probe-based real-time polymerase chain reaction, we designed a mutation detection plate with all recurrent mutations. We validated this mutation detection plate and tested its feasibility in newly diagnosed GS patients. A total of 57 mutations in the SLC12A3 gene were identified and 22 including 2 deep intronic mutations were recurrent mutations consisting of 87.1% (242/278, 18 triple) of all allelic mutations. The recurrent mutation-based TaqMan assays were fully validated with excellent sensitivity and specificity in genetically diagnosed GS patients and healthy subjects. In clinical validation, recurrent mutations were recognized in 92.0% of allelic mutations from 12 GS patients within 4 h and all were confirmed by direct sequencing. Recurrent SLC12A3 mutations are very common in Taiwan GS patients and can be rapidly identified by this recurrent mutation-based SLC12A3 mutation plate.

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

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

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

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

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

BACKGROUND

Potassium levels regulate multiple physiologic processes. The heritability of serum potassium level is moderate, with published estimates varying from 17% to 60%, suggesting genetic influences. However, the genetic determinants of potassium levels are not generally known.

METHODS

A whole-exome sequencing association study of serum potassium levels in 5812 subjects of the Old Order Amish was performed. A dietary salt intervention in 533 Amish subjects estimated interaction between p.R642G and sodium intake.

RESULTS

A cluster of variants, spanning approximately 537 kb on chromosome 16q13, was significantly associated with serum potassium levels. Among the associated variants, a known pathogenic variant of autosomal recessive Gitelman syndrome (p.R642G SLC12A3) was most likely causal; there were no homozygotes in our sample. Heterozygosity for p.R642G was also associated with lower chloride levels, but not with sodium levels. Notably, p.R642G showed a novel association with lower serum BUN levels. Heterozygotes for p.R642G had a two-fold higher rate of self-reported bone fractures and had higher resting heart rates on a low-salt diet compared with noncarriers.

CONCLUSIONS

This study provides evidence that heterozygosity for a pathogenic variant in SLC12A3 causing Gitelman syndrome, a canonically recessive disorder, contributes to serum potassium concentration. The findings provide insights into SLC12A3 biology and the effects of heterozygosity on electrolyte homeostasis and related subclinical phenotypes that may have implications for personalized medicine and nutrition.

Type 2 diabetes mellitus caused by Gitelman syndrome-related hypokalemia: A case report

INTRODUCTION

Gitelman syndrome (GS) is an autosomal-recessive disease caused by SLC12A3 gene mutations. It is characterized by hypokalemic metabolic alkalosis in combination with hypomagnesemia and hypocalciuria. Recently, patients with GS are found at an increased risk for developing type 2 diabetes mellitus (T2DM). However, diagnosis of hyperglycemia in GS patients has not been thoroughly investigated, and family studies on SLC12A3 mutations and glucose metabolism are rare. Whether treatment including potassium and magnesium supplements, and spironolactone can ameliorate impaired glucose tolerance in GS patients, also needs to be investigated.

PATIENT CONCERNS

We examined a 55-year-old Chinese male with intermittent fatigue and persistent hypokalemia for 17 years.

DIAGNOSES

Based on the results of the clinical data, including electrolytes, oral glucose tolerance test (OGTT), and genetic analysis of the SLC12A3 gene, GS and T2DM were newly diagnosed in the patient. Two mutations of the SLC12A3 gene were found in the patient, one was a missense mutation p.N359K in exon 8, and the other was a novel insert mutation p.I262delinsIIGVVSV in exon 6. SLC12A3 genetic analysis and OGTT of 9 other family members within 3 generations were also performed. Older brother, youngest sister, and son of the patient carried the p.N359K mutation in exon 8. The older brother and the youngest sister were diagnosed with T2DM and impaired glucose tolerance by OGTT, respectively.

INTERVENTIONS

The patient was prescribed potassium and magnesium (potassium magnesium aspartate, potassium chloride) oral supplements and spironolactone. The patient was also suggested to maintain a high potassium diet. Acarbose was used to maintain the blood glucose levels.

OUTCOMES

The electrolyte imbalance including hypokalemia and hypomagnesemia, and hyperglycemia were improved with a remission of the clinical manifestations.

CONCLUSION

GS is one of the causes for manifestation of hypokalemia. SLC12A3 genetic analysis plays an important role in diagnosis of GS. Chinese male GS patients characterized with heterozygous SLC12A3 mutation should be careful toward occurrence of T2DM. Moreover, the patients with only 1 SLC12A3 mutant allele should pay regular attention to blood potassium and glucose levels. GS treatment with potassium and magnesium supplements, and spironolactone can improve impaired glucose metabolism.

The challenges of diagnosis and management of Gitelman syndrome

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

Resistance to Insulin in Patients with Gitelman Syndrome and a Subtle Intermediate Phenotype in Heterozygous Carriers: A Cross-Sectional Study

BACKGROUND

Gitelman syndrome is a salt-losing tubulopathy caused by mutations in the SLC12A3 gene, which encodes the thiazide-sensitive sodium-chloride cotransporter. Previous studies suggested an intermediate phenotype for heterozygous carriers.

METHODS

To evaluate the phenotype of heterozygous carriers of pathogenic SLC12A3 mutations, we performed a cross-sectional study of patients with Gitelman syndrome, heterozygous carriers, and healthy noncarriers. Participants measured their BP at home for three consecutive days before hospital admission for blood and urine sampling and an oral glucose tolerance test.

RESULTS

We enrolled 242 participants, aged 18-75 years, including 81 heterozygous carriers, 82 healthy noncarriers, and 79 patients with Gitelman syndrome. The three groups had similar age, sex ratio, and body mass index. Compared with healthy noncarriers, heterozygous carriers showed significantly higher serum calcium concentration (P=0.01) and a trend for higher plasma aldosterone (P=0.06), but measures of home BP, plasma and urine electrolytes, renin, parathyroid hormone, vitamin D, and response to oral glucose tolerance testing were similar. Patients with Gitelman syndrome had lower systolic BP and higher heart rate than noncarriers and heterozygote carriers; they also had significantly higher fasting serum glucose concentration, higher levels of markers of insulin resistance, and a three-fold higher sensitivity to overweight. According to oral glucose tolerance testing, approximately 14% of patients with Gitelman syndrome were prediabetic, compared with 5% of heterozygous carriers and 4% of healthy noncarriers.

CONCLUSIONS

Heterozygous carriers had a weak intermediate phenotype, between that of healthy noncarriers and patients with Gitelman syndrome. Moreover, the latter are at risk for development of type 2 diabetes, indicating the heightened importance of body weight control in these patients.

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.

Gitelman Syndrome Presenting with Hypomagnesemia, Hypokalemia and Hypocalciuria: A Case Report

Gitelman syndrome is a a rarely seen autosomal recessive renal tubulopathy characterized by inherited hypokalemic metabolic alkalosis with hypomagnesemia and hypocalciuria. The diagnosis of Gitelman syndrome is usually established during adolescence, but is also observed in childhood and even in the adulthood period. In this case report, we presented a 19-year-old male patient who was diagnosed as Gitelman Syndrome and admitted to the hospital with symptoms of muscle weakness, cramps and weakness.

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.

Genetic screening for Bartter syndrome and Gitelman syndrome pathogenic genes among individuals with hypertension and hypokalemia

PURPOSE

Bartter syndrome (BS) and Gitelman syndrome (GS) are hereditary diseases characterized by hypokalemia with decreased or normal blood pressure (BP). However, BS or GS patients who present with elevated BP levels have been increasingly reported recently. Therefore, this study aimed to investigate the presence of BS and GS among individuals with unexplained hypokalemia with hypertension in a clinical setting.

METHODS

Patients presented with unexplained hypertension and hypokalemia admitted to Hypertension Center of Fuwai Hospital from November 2015 to February 2017 were enrolled. High-throughput sequencing for five BS and GS causative genes were performed. Variants were classified using American College of Medical Genetics (ACMG) consensus guidelines.

RESULTS

Thirty-four patients with unexplained hypertension and hypokalemia were included for genetic analysis. A total number of 10 rare variants were identified in six individuals (mutation detection rate, 17.65%). One homozygous variant carried by one of the 34 patients, KCNJ1 c.941A> G (p.Tyr314Cys), were categorized as likely pathogenic variant and resulted in a diagnostic yield of 2.94%. Eight of the remaining nine variants were predicted to be deleterious by ≥ three bioinformatics software and may give additional potential diagnostic yields.

CONCLUSIONS

This is the first study performing combined genetic screening for BS and GS pathogenic genes among individuals with unexplained hypertension and hypokalemia. Our data suggested that BS or GS may contribute to the etiology of patients presented with hypertension and hypokalemia. Genetic testing for BS and GS pathogenic genes are recommended to facilitate precision diagnoses and targeted treatment.

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

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

SLC12A3 variants modulate LDL cholesterol levels in the Mongolian population

Background

Abnormalities in lipid metabolism are crucial factors in the pathogenesis of cardiovascular disease (CVD). Variants of many genes have been verified to confer risk for lipid metabolism abnormalities. However, the relationship between genetic variants of the NCC-encoding SLC12A3 gene and lipid metabolism in the Mongolian population remains unclear. In the present study, we aimed to elucidate the effects of SLC12A3 variants on Mongolian lipid metabolism, including total cholesterol (TCHO), triglycerides (TG), low-density lipoprotein cholesterol (LDL-c), and high-density lipoprotein cholesterol (HDL-c).

Methods

A randomly selected population of Mongolians (n = 331) from China underwent clinical testing. An ANOVA test, Kruskal-Wallis H test (K-W test) and haplotype analysis were used to evaluate the association between the levels of lipids (TCHO, TG, LDL-c, and HDL-c) and polymorphisms in SLC12A3 loci.

Results

We identified three single nucleotide polymorphisms (SNPs) rs5803, rs2010501 and rs711746 in the SLC12A3 gene that were significantly associated with an individual’s serum LDL-c level. Haplotypes combining these SNPs also showed the same trend (all p values < 0.01). Furthermore, the influence of SLC12A3 genetic polymorphisms on differences in individual serum LDL-c levels remained significant, even after we controlled gender, and demographic and other non-genetic factors.

Conclusion

These results suggest that variants of the SLC12A3 gene confer susceptibility to the abnormal serum LDL-c level in the Mongolian population.