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

Rare renal proximal tubular dysfunctions in primary biliary cholangitis

INTRODUCTION

Renal involvement of primary biliary cholangitis (PBC) usually presents as distal renal tubular acidosis. Proximal tubular (PT) dysfunctions in PBC were rarely reported with unclear clinicopathological characteristics and renal prognosis.

METHODS

We identified 11 cases of PBC with PT dysfunctions (PBC-PT). Their medical document, kidney pathology, and follow-up data were retrospectively reviewed and analyzed.

RESULTS

The 11 PBC-PT patients were mainly middle-aged (57.8 ± 5.2 years) females (81.8%). Most of them were asymptomatic PBC (7, 63.6%) with a high prevalence of elevated serum immunoglobulin M (IgM, 81.8%) and G (IgG, 54.5%) levels. In the kidney, they had a mean estimated glomerular filtration rate (eGFR) level of 46.54 ± 23.03 ml/min/1.73m2, and 81.8% of them had eGFR below 60 ml/min/1.73m2. They showed different degrees of PT dysfunctions, including hyperuricosuria, hypouricemia, normoglycemic glycosuria, generalized aminoaciduria, hyperphosphaturia, and hypophosphatemia. Their kidney pathology showed tubulointerstitial nephritis with lymphoplasmacytic infiltrates, brush border defects, and proximal tubulitis. After glucocorticoids treatment, the PT dysfunctions manifesting as hypophosphatemia, hypouricemia, and renal glycosuria all recovered, and the eGFR levels were improved from 43.24 ± 19.60 ml/min/1.73m2 to 55.02 ± 21.14 ml/min/1.73m2 (p = 0.028), accompanied by significant improvements of serum IgM levels (from 5.97 ± 4.55 g/L to 2.09 ± 1.48 g/L, p = 0.019).

CONCLUSIONS

The PT dysfunctions were rare in PBC patients, and glucocorticoids treatment could benefit the improvements of eGFR and tubular functions.

Navigating the multifaceted intricacies of the Na+-Cl- cotransporter, a highly regulated key effector in the control of hydromineral homeostasis

The Na+-Cl- cotransporter (NCC; SLC12A3) is a highly regulated integral membrane protein that is known to exist as three splice variants in primates. Its primary role in the kidney is to mediate the cosymport of Na+ and Cl- across the apical membrane of the distal convoluted tubule. Through this role and the involvement of other ion transport systems, NCC allows the systemic circulation to reclaim a fraction of the ultrafiltered Na+, K+, Cl-, and Mg+ loads in exchange for Ca2+ and [Formula: see text]. The physiological relevance of the Na+-Cl- cotransport mechanism in humans is illustrated by several abnormalities that result from NCC inactivation through the administration of thiazides or in the setting of hereditary disorders. The purpose of the present review is to discuss the molecular mechanisms and overall roles of Na+-Cl- cotransport as the main topics of interest. On reading the narrative proposed, one will realize that the knowledge gained in regard to these themes will continue to progress unrelentingly no matter how refined it has now become.

Hypokalaemia associated with excessive cola-flavoured drinks consumption

We present a case involving a male patient in his 30s who was admitted to hospital due to recurrent episodes of hypokalaemia over the past 5 years. His medical history revealed hypertension, attention deficit hyperactivity disorder (ADHD), autism, and paranoia. He was taking citalopram, ramipril, amlodipine, and pramipexole. Tests indicated normal levels of aldosterone/renin ratio and plasma metanephrines. On reviewing his dietary history, it was noted that he consumed 3 to 3.5 L of cola-flavoured drinks on a daily basis. Normal potassium levels were achieved after a significant reduction in cola-flavoured drinks intake and potassium replacement. Subsequent outpatient clinic follow-up revealed that normal potassium levels were maintained even after the patient ceased taking potassium replacement tablets. Given the rarity of hypokalaemia associated with fizzy drinks, the underlying mechanism for this association remains unclear. In this case report, we attempt to provide a possible explanation for the involved mechanisms.

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.

Chemotherapy-induced tubulopathy: a case report series

Acquired tubulopathies are frequently underdiagnosed. They can be characterized by the renal loss of specific electrolytes or organic solutes, suggesting the location of dysfunction. These tubulopathies phenotypically can resemble Bartter or Gitelman syndrome). These syndromes are infrequent, they may present salt loss resembling the effect of thiazides (Gitelman) or loop diuretics (Bartter). They are characterized by potentially severe hypokalemia, associated with metabolic alkalosis, secondary hyperaldosteronism, and often hypomagnesemia. Tubular dysfunction has been described as nephrotoxic effects of platinum-based chemotherapy. We present 4 cases with biochemical signs of tubular dysfunction (Bartter-like/Gitelman-like phenotype) related to chemotherapy.

"Every Cloud Has a Silver Lining": How Three Rare Diseases Defend Themselves from COVID-19 and What We Have Learnt from It

The process of SARS-CoV-2 infection, responsible for the COVID-19 pandemic, is carried out through different steps, with the interaction between ACE2 and Spike protein (S) being crucial. Besides of that, the acidic environment of endosomes seems to play a relevant role in the virus uptake into cells and its intracellular replication. Patients affected by two rare genetic tubulopathies, Gitelman's and Bartter's Syndromes, and a rare genetic metabolic disease, Fabry Disease, have shown intrinsic protection from SARS-CoV-2 infection and COVID-19 on account of specific intrinsic features that interfere with the virus uptake into cells and its intracellular replication, which will be reported and discussed in this paper, providing interesting insights for present and future research.

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.

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.

Pseudo-Gitelman Syndrome Presenting with Hypokalemic Metabolic Alkalosis and Hypocalciuria

Pseudo-Bartter syndrome is a well-known differential diagnosis that needs to be excluded in cases of normotensive hypokalemic metabolic alkalosis. Pseudo-Bartter syndrome and pseudo-Gitelman syndrome are often collectively referred to as pseudo-Bartter/Gitelman syndrome; however, pseudo-Gitelman syndrome should be considered as a separate entity because Gitelman syndrome is characterized by hypocalciuria and hypomagnesemia, while Bartter syndrome is usually associated with hypercalciuria. Herein, we report the cases of two young adult female patients who presented with severe hypokalemic metabolic alkalosis, hypocalciuria, and hypomagnesemia. Diuretic or laxative abuse and self-induced vomiting were absent, and a chloride deficit and remarkable bicarbonaturia were observed. Initial sequencing studies for SLC12A3, CLCKNB, and KCNJ10 revealed no mutations, and whole-exome sequencing revealed no pathogenic variants. The metabolic alkalosis was saline-responsive in one case, and steroid therapy was necessary in the other to relieve chronic tubulointerstitial nephritis, which was diagnosed with kidney biopsy. A new category of pseudo-Gitelman syndrome should be defined, and various etiologies should be investigated.

Ocular manifestations of the genetic renal tubulopathies

BACKGROUND

The genetic tubulopathies are rare and heterogenous disorders that are often difficult to identify. This study examined the tubulopathy-causing genes for ocular associations that suggested their genetic basis and, in some cases, the affected gene.

METHODS

Sixty-seven genes from the Genomics England renal tubulopathy panel were reviewed for ocular features, and for retinal expression in the Human Protein Atlas and an ocular phenotype in mouse models in the Mouse Genome Informatics database. The genes resulted in disease affecting the proximal tubules (n = 24); the thick ascending limb of the loop of Henle (n = 10); the distal convoluted tubule (n = 15); or the collecting duct (n = 18).

RESULTS

Twenty-five of the tubulopathy-associated genes (37%) had ocular features reported in human disease, 49 (73%) were expressed in the retina, although often at low levels, and 16 (24%) of the corresponding mouse models had an ocular phenotype. Ocular abnormalities were more common in genes affected in the proximal tubulopathies (17/24, 71%) than elsewhere (7/43, 16%). They included structural features (coloboma, microphthalmia); refractive errors (myopia, astigmatism); crystal deposition (in oxalosis, cystinosis) and sclerochoroidal calcification (in Bartter, Gitelman syndromes). Retinal atrophy was common in the mitochondrial-associated tubulopathies. Structural abnormalities and crystal deposition were present from childhood, but sclerochoroidal calcification typically occurred after middle age.

CONCLUSIONS

Ocular abnormalities are uncommon in the genetic tubulopathies but may be helpful in recognizing the underlying genetic disease. The retinal expression and mouse phenotype data suggest that further ocular associations may become apparent with additional reports. Early identification may be necessary to monitor and treat visual complications.

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.

Epithelial Transport in Disease: An Overview of Pathophysiology and Treatment

Epithelial transport is a multifaceted process crucial for maintaining normal physiological functions in the human body. This comprehensive review delves into the pathophysiological mechanisms underlying epithelial transport and its significance in disease pathogenesis. Beginning with an introduction to epithelial transport, it covers various forms, including ion, water, and nutrient transfer, followed by an exploration of the processes governing ion transport and hormonal regulation. The review then addresses genetic disorders, like cystic fibrosis and Bartter syndrome, that affect epithelial transport. Furthermore, it investigates the involvement of epithelial transport in the pathophysiology of conditions such as diarrhea, hypertension, and edema. Finally, the review analyzes the impact of renal disease on epithelial transport and highlights the potential for future research to uncover novel therapeutic interventions for conditions like cystic fibrosis, hypertension, and renal failure.

Potassium homeostasis - Physiology and pharmacology in a clinical context

Membrane voltage controls the function of excitable cells and is mainly a consequence of the ratio between the extra- and intracellular potassium concentration. Potassium homeostasis is safeguarded by balancing the extra-/intracellular distribution and systemic elimination of potassium to the dietary potassium intake. These processes adjust the plasma potassium concentration between 3.5 and 4.5 mmol/L. Several genetic and acquired diseases but also pharmacological interventions cause dyskalemias that are associated with increased morbidity and mortality. The thresholds at which serum K+ not only associates but also causes increased mortality are hotly debated. We discuss physiologic, pathophysiologic, and pharmacologic aspects of potassium regulation and provide informative case vignettes. Our aim is to help clinicians, epidemiologists, and pharmacologists to understand the complexity of the potassium homeostasis in health and disease and to initiate appropriate treatment strategies in dyskalemic patients.

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.

Gitelman Syndrome Manifesting With Acute Hypokalemic Paralysis: A Case Report

Gitelman syndrome (GS) is a rare renal tubulopathy, classically characterized by renal salt wasting and metabolic alkalosis. It is usually an incidental diagnosis, being asymptomatic or with mild symptoms. GS manifesting with acute flaccid paralysis is extremely uncommon. We report a case of GS that mimicked Guillain-Barré syndrome (GBS), manifesting with acute hypokalemic paralysis. A middle-aged male with no known comorbidities presented to our center with paresthesias of all four limbs for one month and progressive, asymmetric limb weakness over the past eight days. Neurological examination revealed hypotonia, global areflexia, and power ranging from 3/5 to 4/5 in all four limbs, leading to our initial clinical diagnosis of GBS. Our patient's laboratory panel revealed hypokalemia, hypomagnesemia, metabolic alkalosis, and hypocalcemia, characteristic of GS. Additionally, he had significantly elevated creatine phosphokinase, suggestive of rhabdomyolysis. Further urine studies revealed renal potassium wasting, confirming the diagnosis of GS. Whole exome genome sequencing for common causative genes and workup for autoimmune disease were both negative. With gradual electrolyte correction, the patient rapidly improved symptomatically. Our case highlights an uncommon initial presentation of GS and emphasizes the need for more literature on its manifestations from the Indian subcontinent.

Heart's Dangerous Symphony: Torsade De Pointes Unleashed by Gitelman Syndrome-Induced Hypomagnesemia

Gitelman syndrome (GS) is a rare autosomal recessive salt-losing renal tubular disorder associated with a mutation of SLC12A3 or CLCNKB genes which encodes the thiazide-sensitive sodium-chloride co-transporter (NCCT) in the distal renal tubule. It is inherited as an autosomal recessive disorder. Hypokalemia, metabolic alkalosis, hypomagnesemia, hypocalciuria, and renin-angiotensin-aldosterone system (RAAS) activation are characteristics of GS. GS is often misdiagnosed or underdiagnosed owing to its low incidence and lack of awareness. Its prevalence is estimated to be around 1-10 per 40,000 people. We report a case of cardiac arrest secondary to torsade de pointes (TdP) because of GS-induced hypomagnesemia. Our case highlights the importance of clinicians being aware of the potential electrolyte abnormalities and complications associated with GS, as it can lead to catastrophic consequences if not identified and corrected earlier.

Two Brothers from Macedonia with Gitelman Syndrome

Gitelman syndrome (GS) is a rare renal tubulopathy with an autosomal recessive mode of inheritance, caused by biallelic pathogenic variants in the SLC12A3 gene. The clinical features may overlap with other disorders, such as Bartter syndrome type 3, HNF1B nephropathy or even mitochondrial disease, but can be distinguished by molecular genetic analysis. Here we report on two preschool brothers, who presented with a several months' history of episodes of carpopedal spasms and muscle aches. The biochemical analyses revealed hypokalemia and hypomagnesemia without metabolic alkalosis. A 24-h urine sample demonstrated hypocalciuria. The molecular analyses showed that both patients were heterozygous for 3 (likely) pathogenic variants in SLC12A3: c.1805_1806del; p. (Tyr602Cysfs*31), c.2660+1G>A and c.2944 A>T; p. (Ile982Phe). Analysis of the parents showed that the mother was heterozygous for the c.2944 A>T p.(Ile982Phe) variant, and the father carried the other 2 variants (c.1805_1806del and c.2660+1G>A). Herein we present two children in a family from N. Macedonia with clinical manifestations and electrolyte imbalances suggestive of GS. The results of the tubulopathy next generation sequencing (NGS) panel confirmed the diagnosis. The boys are treated with a high salt diet and oral potassium and magnesium supplements.

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.

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.

Sudden cardiac arrest in a child with Gitelman syndrome: a case report and literature review

Salt-losing tubulopathies are well-recognised diseases predisposing to metabolic disturbances in affected patients. One of the most severe complications can be life-threatening arrhythmias causing sudden cardiac arrest. We present here the first case of a pediatric patient with Gitelman syndrome associated sudden cardiac arrest without precipitating event. A 10-year-old boy collapsed due to ventricular fibrillation in the Prague tram. Lay cardiopulmonary resuscitation was initiated and external defibrillation restored sinus rhythm within minutes. Initial laboratory examination revealed severe hypokalemia requiring large amounts of electrolyte supplementation. Genetic testing focused to tubulopathies was performed and the diagnosis of Gitelman syndrome was made following the identification of two pathogenic variants in SLC12A3 gene (c.2633 + 1G>A and c.2221G>A). Implantable cardioverter-defibrillator was implanted to prevent sudden cardiac death. The patient was in a good clinical condition with satisfactory electrolyte serum levels at the last follow-up. Causes of electrolyte abnormalities in children should be identified early to prevent the development of rare but potentially fatal complications.

Renal and Electrolyte Disorders and the Nervous System

OBJECTIVE

Neurologic complications are a major contributor to death and disability in patients with renal disease. Oxidative stress, endothelial dysfunction, accelerated arteriosclerosis, and uremic inflammatory milieu affect both the central and peripheral nervous systems. This article reviews the unique contributions of renal impairment to neurologic disorders and their common clinical manifestations as the prevalence of renal disease increases in a globally aging population.

LATEST DEVELOPMENT

Advances in the understanding of the pathophysiologic interplay between the kidneys and brain, also referred to as the kidney-brain axis, have led to more widespread recognition of associated changes in neurovascular dynamics, central nervous system acidification, and uremia-associated endothelial dysfunction and inflammation in the central and peripheral nervous systems. Acute kidney injury increases mortality in acute brain injury to nearly 5 times that seen in matched controls. Renal impairment and its associated increased risks of intracerebral hemorrhage and accelerated cognitive decline are developing fields. Dialysis-associated neurovascular injury is increasingly recognized in both continuous and intermittent forms of renal replacement therapy, and treatment strategies for its prevention are evolving.

ESSENTIAL POINTS

This article summarizes the effects of renal impairment on the central and peripheral nervous systems with special considerations in acute kidney injury, patients requiring dialysis, and conditions that affect both the renal and nervous systems.

Compounded Effervescent Magnesium for Familial Hypomagnesemia: A Case Report

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is a rare autosomal recessive disorder affecting <1/1,000,000 people. It is caused by mutations in the CLDN16 (FHHNC Type 1) or CLDN19 (FHHNC Type 2) genes, which are located on Chromosomes 3q27 and 1p34.2, respectively. There are no drug therapies for this condition. Although magnesium salts represent an important class of compounds and exhibit various therapeutic actions as a supplement for magnesium deficiency in FHHNC, various formulations on the market have different bioavailability. We report the case of a patient with FHNNC first treated, in our Pediatric Institute, with high doses of magnesium pidolate and magnesium and potassium citrate. The patient began to neglect this therapy after experiencing frequent daily episodes of diarrhoea. Our pharmacy received a request for an alternative magnesium supplement that would better comply by ensuring a good magnesium intake which will result in adequate blood magnesium levels. In response, we developed a galenic compound in the form of effervescent magnesium. Here, we report on the promise of this formulation not only for better compliance than pidolate, but also for better bioavailability.

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.

Gitelman Syndrome: A Case Report

Gitelman syndrome is a rare hereditary tubulopathy characterized by hypokalemic metabolic alkalosis, hypomagnesemia, and hypocalciuria. In this case report, we describe a 21-year-old male who presented with myalgias, asthenia, general muscle weakness, and hypokalemia after receiving oral potassium supplementation for six months. Additional biochemical studies showed hypomagnesemia, metabolic alkalosis, and increased urinary potassium and magnesium excretion. Calcium urinary excretion was within the normal range, but 25-hydroxycholecalciferol levels were low. Systolic arterial hypertension was found, probably reflecting chronic hyperreninemic hyperaldosteronism. Genetic testing for SCL12A3 mutations identified a pathogenic variant in homozygosity, which confirmed the Gitelman syndrome diagnosis. Treatment with chronic potassium and magnesium oral supplementation was started, as well as eplerenone and amiloride, with sustained correction of hypokalemia and hypomagnesemia.

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.

A Clinical Workflow for Cost-Saving High-Rate Diagnosis of Genetic Kidney Diseases

SIGNIFICANCE STATEMENT

To optimize the diagnosis of genetic kidney disorders in a cost-effective manner, we developed a workflow based on referral criteria for in-person evaluation at a tertiary center, whole-exome sequencing, reverse phenotyping, and multidisciplinary board analysis. This workflow reached a diagnostic rate of 67%, with 48% confirming and 19% modifying the suspected clinical diagnosis. We obtained a genetic diagnosis in 64% of children and 70% of adults. A modeled cost analysis demonstrated that early genetic testing saves 20% of costs per patient. Real cost analysis on a representative sample of 66 patients demonstrated an actual cost reduction of 41%. This workflow demonstrates feasibility, performance, and economic effect for the diagnosis of genetic kidney diseases in a real-world setting.

BACKGROUND

Whole-exome sequencing (WES) increases the diagnostic rate of genetic kidney disorders, but accessibility, interpretation of results, and costs limit use in daily practice.

METHODS

Univariable analysis of a historical cohort of 392 patients who underwent WES for kidney diseases showed that resistance to treatments, familial history of kidney disease, extrarenal involvement, congenital abnormalities of the kidney and urinary tract and CKD stage ≥G2, two or more cysts per kidney on ultrasound, persistent hyperechoic kidneys or nephrocalcinosis on ultrasound, and persistent metabolic abnormalities were most predictive for genetic diagnosis. We prospectively applied these criteria to select patients in a network of nephrology centers, followed by centralized genetic diagnosis by WES, reverse phenotyping, and multidisciplinary board discussion.

RESULTS

We applied this multistep workflow to 476 patients with eight clinical categories (podocytopathies, collagenopathies, CKD of unknown origin, tubulopathies, ciliopathies, congenital anomalies of the kidney and urinary tract, syndromic CKD, metabolic kidney disorders), obtaining genetic diagnosis for 319 of 476 patients (67.0%) (95% in 21 patients with disease onset during the fetal period or at birth, 64% in 298 pediatric patients, and 70% in 156 adult patients). The suspected clinical diagnosis was confirmed in 48% of the 476 patients and modified in 19%. A modeled cost analysis showed that application of this workflow saved 20% of costs per patient when performed at the beginning of the diagnostic process. Real cost analysis of 66 patients randomly selected from all categories showed actual cost reduction of 41%.

CONCLUSIONS

A diagnostic workflow for genetic kidney diseases that includes WES is cost-saving, especially if implemented early, and is feasible in a real-world setting.

Oxidants and Cardiorenal Vascular Remodeling—Insights from Rare Genetic Tubulopathies: Bartter’s and Gitelman’s Syndromes

Two human genetic tubulopathies, Bartter’s (BS) and Gitelman’s (GS) syndromes, have normo/hypotension and absent cardiac remodeling despite their apparent angiotensin system (RAS) activation. This seeming contradiction has led to an extensive investigation of BSGS patients, the result of which is that BSGS represents a mirror image of hypertension. BSGS’s unique set of properties has then permitted their use as a human model to probe and characterize RAS system pathways and oxidative stress in cardiovascular and renal remodeling and pathophysiology. This review details the results using GSBS patients that provide a deeper understanding of Ang II signaling and its associated oxidants/oxidative stress in humans. By providing a more complete and complex picture of cardiovascular and renal remodeling pathways and processes, studies of GSBS can inform the identification and selection of new targets and therapies to treat these and other oxidant-related disorders.

Gitelman Syndrome Presenting with Cerebellar Ataxia and Tetany

Gitelman syndrome (GS) is salt-losing tubulopathy characterized by hypokalemia, hypomagnesemia, hypocalciuria, hyperreninemia, hyperaldosteronemia, metabolic alkalosis, and rarely hypocalcemia. Here, we describe the case of a 54-year-old man who presented with cerebellar signs and tetany. On investigation, he was found to have hypokalemia, hypocalcemia, hypomagnesemia, metabolic alkalosis, and high urinary chloride levels. On correction of metabolic parameters, he became asymptomatic. In cases of unexplained recurrent hypokalemia, hypocalcemia and hypomagnesemia, the diagnosis of GS should be considered.

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.

Clinicopathological Features of Gitelman Syndrome with Proteinuria and Renal Dysfunction

INTRODUCTION

Gitelman syndrome (GS) is a rare renal tubular salt-wasting disorder. Besides kidney electrolyte loss, proteinuria and renal dysfunction were also observed. However, their incidence, risk factors, pathological features, and prognosis were unclear.

METHODS

We retrospectively reviewed 116 GS patients and analyzed their clinical, genetic, and pathological characteristics. We also systematically reviewed articles on GS with proteinuria and renal dysfunction.

RESULTS

Twenty-three GS patients had proteinuria (69.6%) and renal dysfunction (43.5%) with a mean age of 35.3 ± 13.2 years, and 65.2% were male. Compared to patients without proteinuria or renal dysfunction, these patients had elevated plasma angiotensin II level (440.2 ± 351.7 vs. 253.2 ± 187.4 pg/mL, p = 0.031) and three times higher incidence of diabetes. The renal pathology of nine biopsied patients indicated hypertrophy of the juxtaglomerular apparatus (100%), chronic tubulointerstitial changes (66.7%), intrarenal vascular changes (66.7%), and glomerulopathy (55.6%). More extensive renin staining was observed in patients with GS than in the control group with glomerular minor lesion (p < 0.001). During a median of 85 months (range, 11-205 months) of follow-up for 19 out of the 23 GS-renal patients, the renal function was generally stable, except one died of cancer and one developed end-stage renal disease because of concomitant membranous nephropathy and IgA nephropathy.

CONCLUSION

Proteinuria and renal dysfunction were more common than expected and might indicate glomerulopathy and vascular lesions besides a tubulointerstitial injury in GS. Renal function may maintain stable with effective therapy in most cases.

Total colectomy for poorly controlled hypokalaemia due to Gitelman syndrome

Gitelman syndrome (GS) is an autosomal recessive tubulopathy caused by dysfunction of the thiazide-sensitive sodium-chloride cotransporter, which leads to hypokalaemia, metabolic alkalosis, hypomagnesaemia and hypocalciuria. Patients with GS show varied clinical features due to hypokalaemia: tetany, muscle weakness, periodical paralysis and constipation, which is one of the most frequent ones. This paper presents the case of a woman in her 40s referred to our endocrinology department for severe hypokalaemia. After biochemical and genetic analyses, a diagnosis of GS was established. Concurrently, the patient suffered from refractory constipation due to hypokalaemia and underwent a total colectomy with ileorectal anastomosis, which cured both disorders without any medication for 3 years.

CRISPR-Cas9-Mediated Correction of SLC12A3 Gene Mutation Rescues the Gitelman's Disease Phenotype in a Patient-Derived Kidney Organoid System

The aim of this study is to explore the possibility of modeling Gitelman's disease (GIT) with human-induced pluripotent stem cell (hiPSC)-derived kidney organoids and to test whether gene correction using CRISPR/Cas9 can rescue the disease phenotype of GIT. To model GIT, we used the hiPSC line CMCi002 (CMC-GIT-001), generated using PBMCs from GIT patients with SLC12A3 gene mutation. Using the CRISPR-Cas9 system, we corrected CMC-GIT-001 mutations and hence generated CMC-GIT-001^corr. Both hiPSCs were differentiated into kidney organoids, and we analyzed the GIT phenotype. The number of matured kidney organoids from the CMC-GIT-001^corr group was significantly higher, 3.3-fold, than that of the CMC-GIT-001 group (12.2 ± 0.7/cm² vs. 3.7 ± 0.2/cm², p < 0.05). In qRT-PCR, performed using harvested kidney organoids, relative sodium chloride cotransporter (NCCT) mRNA levels (normalized to each iPSC) were increased in the CMC-GIT-001^corr group compared with the CMC-GIT-001 group (4.1 ± 0.8 vs. 2.5 ± 0.2, p < 0.05). Consistently, immunoblot analysis revealed increased levels of NCCT protein, in addition to other tubular proteins markers, such as LTL and ECAD, in the CMC-GIT-001^corr group compared to the CMC-GIT-001 group. Furthermore, we found that increased immunoreactivity of NCCT in the CMC-GIT-001^corr group was colocalized with ECAD (a distal tubule marker) using confocal microscopy. Kidney organoids from GIT patient-derived iPSC recapitulated the Gitelman's disease phenotype, and correction of SLC12A3 mutation utilizing CRISPR-Cas9 technology provided therapeutic insight.

Tracing angiotensin II's yin-yang effects on cardiovascular-renal pathophysiology

Adverse changes in cardiovascular and renal systems are major contributors to overall morbidity and mortality. Human cardiovascular and renal systems exhibit a complex network of positive and negative feedback that is reflected in the control of vascular tone via angiotensin II (Ang II) based signaling. This review will examine in some depth, the multiple components and processes that control the status and reflect the health of these various cardiovascular and renal systems, such as pathways associated to monomeric G proteins, RhoA/Rho kinase system and ERK, oxidative stress and NO balance. It will specifically emphasize the "yin-yang" nature of Ang II signaling by comparing and contrasting the effects and activity of various systems, pathways and components found in hypertension to those found in Gitelman's and Bartter's syndromes (GS/BS), two rare autosomal recessive tubulopathies characterized by electrolytic imbalance, metabolic alkalosis, sodium wasting and prominent activation of the renin-angiotensin-aldosterone system. Notwithstanding the activation of the renin-angiotensin-aldosterone system, GS/BS are normo-hypotensive and protected from cardiovascular-renal remodeling and therefore can be considered the mirror image, the opposite of hypertension.

Pathophysiologic approach in genetic hypokalemia: An update

The pathophysiology of genetic hypokalemia is close to that of non-genetic hypokalemia. New molecular pathways physiologically involved in renal and extrarenal potassium homeostasis have been highlighted. A physiological approach to diagnosis is illustrated here, with 6 cases. Mechanisms generating and sustaining of hypokalemia are discussed. After excluding acute shift of extracellular potassium to the intracellular compartment, related to hypokalemic periodic paralysis, inappropriate kaliuresis (>40mmol/24h) concomitant to hypokalemia indicates renal potassium wasting. Clinical analysis distinguishes hypertension-associated hypokalemia, due to hypermineralocorticism or related disorders. Genetic hypertensive hypokalemia is rare. It includes familial hyperaldosteronism, Liddle syndrome, apparent mineralocorticoid excess,11beta hydroxylase deficiency and Geller syndrome. In case of normo- or hypo-tensive hypokalemia, two etiologies are to be considered: chloride depletion or salt-wasting tubulopathy. Diarrhea chlorea is a rare disease responsible for intestinal chloride depletion. Due to the severity of hypokalemic metabolic alkalosis, this disease can be misdiagnosed as pseudo-Bartter syndrome. Gitelman syndrome is the most frequent cause of genetic hypokalemia. It typically associates renal sodium and potassium wasting, hypomagnesemia, conserved chloride excretion (>40mmol/24h), and low-range calcium excretion (urinary Ca/creatinine ratio<0.20mmol/mmol). Systematic analysis of hydroelectrolytic disorder and dynamic hormonal investigation optimizes indications for and orientation of genotyping of hereditary salt-losing tubulopathy.

A genomic deep field view of hypertension

Blood pressure is regulated by a complex neurohumoral system including the renin-angiotensin-aldosterone system, natriuretic peptides, endothelial pathways, the sympathetic nervous system, and the immune system. This review charts the evolution of our understanding of the genomic basis of hypertension at increasing resolution over the last 5 decades from monogenic causes to polygenic associations, spanning ∼30 monogenic rare variants and >1500 single nucleotide variants. Unexpected early wins from blood pressure genomics include deepening of our understanding of the complex causation of hypertension; refinement of causal estimates bidirectionally between blood pressure, risk factors, and outcomes through Mendelian randomization; risk stratification using polygenic risk scores; and opportunities for precision medicine and drug repurposing.

Novel Intronic Mutations of the SLC12A3 Gene in Patients with Gitelman Syndrome

Aim

Mutations in the SLC12A3 gene have been reported to cause Gitelman syndrome (GS), characterized by hypokalemic metabolic alkalosis. The aim of this research is to investigate the genetic mutations and clinical features of patients with clinical suspicion of GS.

Methods

Six families were enrolled. The symptoms, clinical examination, laboratory results, genotypes, and effect of mutations on mRNA splicing were analyzed. Genomic DNA was screened for gene variations using whole exome sequence and Sanger sequencing. DNA sequences were compared with reference sequences.

Results

Genetic analysis revealed nine genetic variants of SLC12A3, including three novel heterozygous mutations (c.1096-2A>G, c.1862A>G, and c.2747+4del) and six previously characterized mutations (c.965-1_976delinsACCGAAAATTTT, c.506-1G>A, c.602-16G>A, c.533C >T, c.1456 G>A, and c.1108 G>C). Probands presented with the clinical syndrome of hypokalemia, increased plasma renin, hypocalciuria and hypokalemic alkalosis.

Conclusion

These clinical manifestations and genotypes were consistent with the diagnostic criteria of GS. The study described the phenotypes and genotypes of six pedigrees involving GS patients, demonstrating the importance of SLC12A3 gene screening for GS. This study expands the mutation spectrum of SLC12A3 gene in GS.

A clinical approach to tubulopathies in children and young adults

Kidney tubules are responsible for the preservation of fluid, electrolyte and acid-base homeostasis via passive and active mechanisms. These physiological processes can be disrupted by inherited or acquired aetiologies. The net result is a tubulopathy. It is important to make a prompt and accurate diagnosis of tubulopathies in children and young adults. This allows timely and appropriate management, including disease-specific therapies, and avoids complications such as growth failure. Tubulopathies can present with a variety of non-specific clinical features which can be diagnostically challenging. In this review, we build from this common anatomical and physiological understanding to present a tangible appreciation of tubulopathies as they are likely to be clinically encountered among affected children and young adults.

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

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

Gitelman syndrome diagnosed in the first trimester of pregnancy: a case report and literature review

Objectives

Gitelman syndrome is a rare salt-losing tubulopathy caused by inactivating mutations in the SLC12A3 gene, which is expressed in the distal convoluted tubule and accounts for 5–10% of renal sodium reabsorption. Atypical symptoms and insidious conditions generally delay diagnosis until childhood or even adulthood. Here, we report the case of a 22-year-old Chinese woman who was admitted to our endocrinology department for severe hypokalemia during pregnancy.

Case presentation

The patient had no specific symptoms but exhibited hypokalemia, metabolic alkalosis, hypomagnesemia, hypocalciuria, hyperreninemia, hyperaldosteronism, and normal blood pressure. Together, these symptoms indicated the clinical diagnosis of Gitelman syndrome, which was confirmed by genetic analysis. Many drugs have limited safety data during early pregnancy, and optimum potassium and magnesium levels are necessary for a successful pregnancy.

Conclusions

Diagnosis and management of Gitelman syndrome are crucial during pregnancy to ensure the safety of the mother and fetus, especially during the first trimester.

The genetic spectrum of Gitelman(-like) syndromes

PURPOSE OF REVIEW

Gitelman syndrome is a recessive salt-wasting disorder characterized by hypomagnesemia, hypokalemia, metabolic alkalosis and hypocalciuria. The majority of patients are explained by mutations and deletions in the SLC12A3 gene, encoding the Na+-Cl--co-transporter (NCC). Recently, additional genetic causes of Gitelman-like syndromes have been identified that should be considered in genetic screening. This review aims to provide a comprehensive overview of the clinical, genetic and mechanistic aspects of Gitelman(-like) syndromes.

RECENT FINDINGS

Disturbed Na+ reabsorption in the distal convoluted tubule (DCT) is associated with hypomagnesemia and hypokalemic alkalosis. In Gitelman syndrome, loss-of-function mutations in SLC12A3 cause impaired NCC-mediated Na+ reabsorption. In addition, patients with mutations in CLCKNB, KCNJ10, FXYD2 or HNF1B may present with a similar phenotype, as these mutations indirectly reduce NCC activity. Furthermore, genetic investigations of patients with Na+-wasting tubulopathy have resulted in the identification of pathogenic variants in MT-TI, MT-TF, KCNJ16 and ATP1A1. These novel findings highlight the importance of cell metabolism and basolateral membrane potential for Na+ reabsorption in the DCT.

SUMMARY

Altogether, these findings extend the genetic spectrum of Gitelman-like electrolyte alterations. Genetic testing of patients with hypomagnesemia and hypokalemia should cover a panel of genes involved in Gitelman-like syndromes, including the mitochondrial genome.

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 case of Gitelman syndrome with membranous nephropathy

Background

Gitelman syndrome (GS) is a rare autosomal recessive inherited salt-losing tubulopathy (SLT). Here, we report, for the first time, a case of GS overlapping nephrotic syndrome (NS) related to PLA2R-associated membranous nephropathy (MN).

Case presentation

We described a male patient had a 4-year history of recurrent fatigue. Serum biochemistry revealed hypokalemia with renal potassium wasting, hypomagnesemia, metabolic alkalosis, hyperreninemia, hypocalciuria, as well as nephrotic-range proteinuria, hypoalbuminemia, and elevated serum anti-phospholipase A2 receptor (PLA2R) antibody. Gene sequencing identified compound heterozygous mutations in SLC12A3 [c.536T > A(p.V179D) and c.1456G > A(p.D486N)]. The unusual association of SLTs and nephrotic-range glomerular proteinuria prompted us to perform a renal biopsy. Renal biopsy showed idiopathic MN. Due to the potential to activate the sodium-chloride co-transporter (NCC) and cause hyperkalemia, tacrolimus was selected to treat NS. Following treatment with potassium chloride, magnesium oxide, low-dose glucocorticoid combined with tacrolimus, the fatigue significantly improved, and concurrently hypokalemia, hypomagnesemia were corrected and NS was remitted.

Conclusions

Renal biopsy should be warranted for GS patients with moderate to nephrotic-range proteinuria. Tacrolimus was preferred to the management of GS patients with NS.