Unexpected clinical sequelae of Gitelman syndrome: hypertension in adulthood is common and females have higher potassium requirements

Genotype-phenotype correlations in children with Gitelman syndrome

BACKGROUND

This study aimed to analyze genotype-phenotype correlations in children with Gitelman syndrome (GS).

METHODS

This multicenter retrospective study included 50 Korean children diagnosed with SLC12A3 variants in one or both alleles and the typical laboratory findings of GS. Genetic testing was performed using the Sanger sequencing except for one patient.

RESULTS

The median age at the diagnosis was 10.5 years (interquartile range, 6.8;14.1), and 41 patients were followed up for a median duration of 5.4 years (interquartile range, 4.1;9.6). A total of 30 different SLC12A3 variants were identified. Of the patients, 34 (68%) had biallelic variants, and 16 (32%) had monoallelic variants on examination. Among the patients with biallelic variants, those (n = 12) with the truncating variants in one or both alleles had lower serum chloride levels (92.2 ± 3.2 vs. 96.5 ± 3.8 mMol/L, P = 0.002) at onset, as well as lower serum potassium levels (3.0 ± 0.4 vs. 3.4 ± 0.3 mMol/L, P = 0.016), and lower serum chloride levels (96.1 ± 1.9 vs. 98.3 ± 3.0 mMol/L, P = 0.049) during follow-up than those without truncating variants (n = 22). Patients with monoallelic variants on examination showed similar phenotypes and treatment responsiveness to those with biallelic variants.

CONCLUSIONS

Patients with GS who had truncating variants in one or both alleles had more severe electrolyte abnormalities than those without truncating variants. Patients with GS who had monoallelic SLC12A3 variants on examination had almost the same phenotypes, response to treatment, and long-term prognosis as those with biallelic variants.

Gitelman Syndrome and Hypertension: A Case Report

In a patient with persistent hypokalemia, it is important to consider Gitelman syndrome, a rare, salt-wasting tubulopathy inherited in an autosomal recessive pattern. Gitelman syndrome leads to electrolyte abnormalities like hypokalemia, hypomagnesemia, and metabolic alkalosis. Typical clinical features include muscle cramps, fatigue, polydipsia, and salt cravings. Our case involves a female patient in her early 40s who visited the endocrinology clinic with symptoms of polyuria, constipation, muscle weakness, and fatigue. Electrolyte abnormalities included hypokalemia, hypomagnesemia, hypochloremia, and hyperreninemia. Initial tests, such as renal function tests, renal ultrasound, and CT scan, yielded normal results. Differential diagnosis of Gitelman syndrome and Bartter syndrome was considered due to the mutual electrolyte abnormalities of hypokalemia and metabolic alkalosis. Bartter syndrome was ruled out in our patient due to the presence of hypomagnesemia, which indicates a different defective receptor. Ultimately, genetic testing would be necessary to confirm the diagnosis of Gitelman syndrome considering the characteristic electrolyte disturbances and classic clinical presentation of fatigue, weakness, and salt craving.

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 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.

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.

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.

Successful living kidney donation from a patient with a Gitelman's syndrome

Living kidney donation from Gitelman's syndrome (GS) patients remains very rare. Long-term renal prognosis of donor and recipient patients remains unknown. We report a 67-year-old man with GS, harbouring a mutation of the SLC12A3 gene, who donated his kidney for transplant. Five years post-transplantation, his clinical condition and biochemical parameters remained stable with close monitoring and follow-up. Patients with non-complicated GS can be considered eligible to donate their kidney for transplant.

Potassium and the kidney: a reciprocal relationship with clinical relevance

By controlling urinary potassium excretion, the kidneys play a key role in maintaining whole-body potassium homeostasis. Conversely, low urinary potassium excretion (as a proxy for insufficient dietary intake) is increasingly recognized as a risk factor for the progression of kidney disease. Thus, there is a reciprocal relationship between potassium and the kidney: the kidney regulates potassium balance but potassium also affects kidney function. This review explores this relationship by discussing new insights into kidney potassium handling derived from recently characterized tubulopathies and studies on sexual dimorphism. These insights reveal a central but non-exclusive role for the distal convoluted tubule in sensing potassium and subsequently modifying the activity of the sodium-chloride cotransporter. This is another example of reciprocity: activation of the sodium-chloride cotransporter not only reduces distal sodium delivery and therefore potassium secretion but also increases salt sensitivity. This mechanism helps explain the well-known relationship between dietary potassium and blood pressure. Remarkably, in children, blood pressure is related to dietary potassium but not sodium intake. To explore how potassium deficiency can cause kidney injury, we review the mechanisms of hypokalemic nephropathy and discuss if these mechanisms may explain the association between low dietary potassium intake and adverse kidney outcomes. We discuss if potassium should be repleted in patients with kidney disease and what role dietary potassium plays in the risk of hyperkalemia. Supported by data and physiology, we reach the conclusion that we should view potassium not only as a potentially dangerous cation but also as a companion in the battle against kidney disease.

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.

Gitelman syndrome with a novel frameshift variant in SLC12A3 gene accompanied by chronic kidney disease and type 2 diabetes mellitus

Gitelman syndrome is an autosomal recessive genetic disease caused by pathogenic variants in SLC12A3 resulting in the loss of function of the Na-Cl co-transporter (NCC) in the distal tubules. Hypokalemia and diuretic effects can cause secondary type 2 diabetes and renal function decline. Here, we present the case of a 49-year-old male patient with chronic persistent treatment-resistant hypokalemia for the past 13 years who had been receiving treatment for type 2 diabetes mellitus for 6 years. He was referred to our department due to the presence of urinary protein, impaired renal function, high renin activity, and hyperaldosteronism. Laboratory test results showed hypokalemia, hypomagnesemia, hypocalciuria, and metabolic alkalosis. Using next-generation and Sanger sequencing, we identified a novel stop-gain variant (NM_000339.3:c.137del [p.His47fs]) and a missense variant (NM_000339.3:c.2927C > T [p.Ser976Phe]) in the SLC12A3 gene. This novel pathogenic variant was located at the intracellular N-terminus of the NCC. Based on these findings, the patient was diagnosed with Gitelman syndrome. The use of next-generation sequencing facilitated the exclusion of diseases with similar clinical symptoms.

Genetic analysis of the Gitelman syndrome coexisting with Osteogenesis imperfecta

Gitelman syndrome (GS) is an autosomal recessive disorder caused by loss-of-function mutations in SLC12A3, which encodes the Na-Cl cotransporter (NCC). Osteogenesis imperfecta (OI) is an autosomal dominant disorder caused by the inheritance of mutations mainly in the COL1A1 gene, resulting in bone fragility and deformity. In this study, we aimed to investigate the clinical and genetic manifestations in a 7-year-old boy with OI, who had electrolyte abnormalities and his four family members. Complete sequence analysis of COL1A1 revealed a novel mutation, c.268G>T, p.Glu90del. The gene mutation of OI in the patient's older brother was inherited from his mother, and the younger brother had no mutation. Two pathogenic mutations (c.179C>T, p.Thr60Met and c.1763C>T, p.Ala588Val) in SLC12A3 resulting in GS were also identified in the patient. The OI-related genetic mutation in the patient was consistent with that in the patient's mother. The GS-related genetic mutations were inherited from each parent. This study is the first to identify compound heterozygous variants in the SLC12A3 gene and a novel mutation in the COL1A1 gene in patients with OI and GS. Our findings indicate that genetic analysis is recommended to differentiate GS from BS, as clinical manifestations do not provide an accurate diagnosis.

Multi-centre study of the clinical features and gene variant spectrum of Gitelman syndrome in Chinese children

Based on the Chinese Children Genetic Kidney Disease Database (CCGKDD), we established a pediatric Gitelman syndrome (GS) cohort to explore the phenotype and genotype characteristics. Thirty-two patients with SLC12A3 gene variants were collected. Five cases (16%) were homozygous, 16 (50%) were compound heterozygous, 10 (31%) carried only a single variant, and the other one harbored two de novo variants beyond classification. p.(T60M) was found in eight patients. The average diagnosis age was 7.79 ± 3.54 years. A total of 31% of the patients were asymptomatic. Muscle weakness was the most common symptom, accounting for 50%. Earlier age of onset (4.06 ± 1.17 yr vs. 8.10 ± 3.46 yr vs. 8.61 ± 3.56 yr, p< 0.05) and lower urinary calcium-creatinine ratio (p = 0.024) were found in the homozygous group than those in the heterozygous and compound heterozygous group. Patients with p.(T60M) variant had an earlier age of onset (4.01 ± 2.83 yr vs. 6.92 ± 3.07 yr, p = 0.025) and lower urinary calcium-creatinine ratio (p = 0.056). Thus, more than 30% of GS children have no clinical symptoms. Homozygous variant and the p.(T60M) variant may be associated with earlier onset and lower urinary calcium excretion in Chinese pediatric GS.

Clinical and laboratory features of female Gitelman syndrome and the pregnancy outcomes in a Chinese cohort

AIM

Gitelman syndrome (GS) is a rare inherited salt-losing renal tubulopathy. Data on clinical features and the pregnancy outcome for female GS patients in a large cohort are lacking. The study was aimed to explore the phenotype and pregnant issue for female GS patients.

METHODS

GS cases from the National Rare Diseases Registry System of China (NRSC) were collected, and detailed clinical, laboratory and genetic data were analysed. Articles on pregnancy in GS were also systemically reviewed.

RESULTS

A total of 101 GS patients were included; among them, 42.6% were female and 79.2% showed hypomagnesaemia. A lower proportion of female patients presented before 18 years of age, with less frequently reported polyuria, higher serum potassium and less urine sodium and chloride excretions. There was no gender difference in the sodium-chloride cotransporter (NCC) dysfunction evaluated by hydrochlorothiazide test. Twelve of the 43 female GS patients delivered after disease symptom onset, and their pregnancies were generally uneventful. As a group, pregnant GS patients had lower potassium levels in the first-trimester (P = .002) requiring higher potassium supplementation. After delivery, serum potassium (P = .02) and magnesium (P = .03) increased significantly. Both caesarean section and vaginal delivery were safe.

CONCLUSION

Female GS patients may have a less severe phenotype with generally favourable outcomes of pregnancy. Intensive monitoring and increased potassium supplementation are necessary during pregnancy, especially in the first-trimester.

Gitelman syndrome in pregnancy: a case series

OBJECTIVE

To evaluate maternal and fetal outcomes in women with Gitelman syndrome (GS).

METHODS

Retrospective analysis of the clinical data of five patients with the clinical diagnosis of GS during pregnancy, who were admitted to Beijing Shijitan Hospital, Capital Medical University between 2013 and 2019, was conducted.

RESULTS

Five women with GS during pregnancy who finally gave birth to a total of eight newborns have been included. Three cases were primiparas and two cases were multiparas. Two cases were diagnosed before pregnancy and three cases were diagnosed in first or second trimester. The primary treatment was oral or intravenous electrolytes supplement. Three patients delivered through the vagina, and shoulder dystocia occurred in one patient. Two patients delivered by cesarean section, with one because of symptom of limb weakness during the course of labor and the other owing to gestational diabetes with fetal macrosomia. Postpartum hemorrhage and urinary retention were not reported in these cases. In perinatal period all the infants had good outcome. The children, aged between six months and five years, were healthy and well-developed during follow-up.

CONCLUSION

The maternal and perinatal outcome is usually favorable. We should pay attention to electrolyte examination in the first trimester in order to diagnose and manage the GS efficiently. Well-controlled patients with Gitelman syndrome can deliver through the vagina.

Early onset children's Gitelman syndrome with severe hypokalaemia: a case report

Background

Hypokalaemia is a common condition among paediatric patients, but severe hypokalaemia is rare and can be life-threatening if not treated properly. The causes of hypokalaemia are complex. Finding the root cause is the key.

Case presentation

This article reports on a 2-year-old boy with severe hypokalaemia who was diagnosed with pneumonia. The child’s lab findings were low blood potassium minimum level of 1.7 mmol/L, hypomagnesemia, and metabolic alkalosis. However, he was without the common features of hypokalaemia, such as respiratory paralysis, severe arrhythmia, weakness and decreased blood pressure. After recovering from pneumonia, his potassium levels did not return to normal. This outcome was suspected to be due to chronic renal loss of potassium. After undergoing second-generation gene sequencing tests, it was discovered he carried the SLC12A3 gene mutation with an Asp486Asn mutation site, which he had inherited from his mother. The final diagnosis was made, confirming the child suffered from Gitelman syndrome.

Conclusions

Genetic predisposition is an important cause of hypokalaemia in children. Children with unexplained persistent hypokalaemia should be examined for the possibility of Gitelman syndrome, which should be distinguished from Bartter syndrome. Genetic testing is the gold standard.

Bartter and Gitelman syndromes: Questions of class

Bartter and Gitelman syndromes are rare inherited tubulopathies characterized by hypokalaemic, hypochloraemic metabolic alkalosis. They are caused by mutations in at least 7 genes involved in the reabsorption of sodium in the thick ascending limb (TAL) of the loop of Henle and/or the distal convoluted tubule (DCT). Different subtypes can be distinguished and various classifications have been proposed based on clinical symptoms and/or the underlying genetic cause. Yet, the clinical phenotype can show remarkable variability, leading to potential divergences between classifications. These problems mostly relate to uncertainties over the role of the basolateral chloride exit channel CLCNKB, expressed in both TAL and DCT and to what degree the closely related paralogue CLCNKA can compensate for the loss of CLCNKB function. Here, we review what is known about the physiology of the transport proteins involved in these disorders. We also review the various proposed classifications and explain why a gene-based classification constitutes a pragmatic solution.

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.

A case of Gitelman syndrome: our experience with a patient treated in clinical practice on a local island

Background: Gitelman syndrome (GS) is an autosomal recessive salt-losing renal tubulopathy resulting from mutations in the thiazide-sensitive Na-Cl cotransporter (NCC) gene. Notably, lack of awareness regarding GS and difficulty with prompt diagnosis are observed in clinical practice, particularly in rural settings.

Case presentation: We report a case of a 48-year-old man with GS who presented to a local clinic on a remote island. Occasional laboratory investigations incidentally revealed a reduced serum potassium level of 2.6 mmol/L. A careful medical interview revealed episodes of intermittent paralysis of the lower extremities and muscular weakness for >30 years. Subsequent laboratory investigations revealed hypomagnesemia, hypocalciuria, and hypokalemic metabolic alkalosis. Based on the patient’s history, clinical presentation, and laboratory investigations, we suspected GS. Genetic testing revealed a rare homozygous in-frame 18 base insertion in the NCC gene that might have resulted from the founder effect, consequent to his topographically isolated circumstances.

Conclusion: More case studies similar to our study need to be added to the literature to gain a deeper understanding of the functional consequences of this mutation and to establish optimal management strategies for this condition, particularly in rural clinical settings.

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.

Hypocalcaemia and hyponatraemia masquerading the diagnosis of Gitelman syndrome

Gitelman syndrome is the most common renal tubulopathy, recently exhibiting a dramatic rise of incidence in Asia.A 50-year-old woman presented with vomiting, fatigue and quadriparesis. Physical examination revealed a positive Trousseau sign , hypotonia and areflexia.Suspecting hypocalcaemia, she was given intravenous 10% calcium gluconate (10 mL administered slowly over 10 min) but her manifestations persisted. An exhaustive laboratory work up revealed the diagnosis of Gitelman syndrome.The peculiarity of this case however, is entailed in its coexistence with hypocalcaemia and hyponatraemia. In addition, the age of primary presentation being 50 years further culminates its atypicality.Multiple electrolyte imbalances were corrected by oral and intravenous supplementation and a high sodium-potassium diet was advocated. Administration of spironolactone imposed a pitfall in the management of our patient due to exacerbation of pre-existing hyponatraemia.On follow-up, her electrolyte profile was stable and corresponding symptoms were alleviated.

Changes in biochemical tests in pregnancy and their clinical significance

Interpretation of laboratory investigations relies on reference intervals. Physiological changes in pregnancy may result in significant changes in normal values for many biochemical assays, and as such results may be misinterpreted as abnormal or mask a pathological state. The aims of this review are as follows: 1. To review the major physiological changes in biochemical tests in normal pregnancy. 2. To outline where these physiological changes are important in interpreting laboratory investigations in pregnancy. 3. To document the most common causes of abnormalities in biochemical tests in pregnancy, as well as important pregnancy-specific causes.

A case of hypokalemia and proteinuria with a new mutation in the SLC12A3 Gene

Background

Gitelman syndrome is an autosomal recessive inherited renal disorder characterized by hypokalemia, hypomagnesemia, and hypocalciuria. Since the symptoms are not severe and laboratory results are not always clear, Gitelman syndrome can go unnoticed by physicians. Here, we report our experiences with a patient that presented with hypokalemia and proteinuria; genetic analysis revealed a new homozygous mutation in the SLC12A3 gene.

Case presentation

A 47-year-old man presented with hypokalemia and proteinuria. He had come to the hospital with the same symptoms 11 months and 3 years prior. His laboratory tests showed hypokalemia, hypocalciuria, and increased plasma angiotensin-2 activity. His renal pathology was consistent with the development of minimal lesions. Genetic analysis found a new homozygous mutation in exon 6 on the SLC12A3 gene (p.Trp281Arg) in the patient and in his brother; his mother and sister were diagnosed as heterozygous carriers of the same gene mutation. Finally, the patient was diagnosed with Gitelman syndrome.

Conclusions

This case is the first to report a homozygous mutation in the 841th nucleotide of exon 6 on the SLC12A3 gene (p.Trp281Arg), which may cause Gitelman syndrome. At the same time, this report might stimulate interest in discussing the relationship between different mutations in the SLC12A3 gene and renal pathology.

Transplantation of a Gitelman Syndrome Kidney Ameliorates Hypertension: A Case Report

Gitelman syndrome is caused by inactivating mutations of the gene that encodes the renal sodium/chloride cotransporter (NCC; encoded by SLC12A3), resulting in hypokalemia, hypomagnesemia, hypocalciuria, and metabolic alkalosis. Renal salt wasting commonly provokes mild hypotension. The paucity of previous kidney transplants from donors with known tubulopathies suggests that such conditions may be considered contraindications to donation. A 76-year-old man received a live unrelated kidney transplant from a donor with known Gitelman syndrome secondary to a pathogenic mutation of SLC12A3. Immediate graft function preceded the emergence of the Gitelman syndrome biochemical phenotype and blood pressure subsequently improved. The recipient developed unexpected hyponatremia. Potential causes are discussed, including the possibility that it paralleled the physiologic changes seen in the high-volume state of thiazide-induced hyponatremia. Transplanted kidneys are subject to nephrotoxicity from the use of calcineurin inhibitors. Acquired Gitelman syndrome may confer a potential long-term advantage to the recipient through both improved blood pressure control and protection against the calcineurin inhibitor-induced side-effect profile caused by NCC overactivation. Both the donor and recipient remain well. In conclusion, Gitelman syndrome need not preclude kidney donation and transference of the phenotype may have benefits for the recipient.

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.

Future considerations based on the information from Barrter's and Gitelman's syndromes

PURPOSE OF REVIEW

Bartter and Gitelman syndromes are typical normotensive salt losing hypokalaemic tubulopathies. Their pathogenesis was gradually deciphered in the past 5 decades, first by typical salt balance studies and histopathology, followed by genetic characterization and discovery of the affected different ion channels. Although the different genotypic subtypes were originally thought to show a similar phenotype, important clinical and biochemical differences can now be found. New findings on the regulation of these channels, as well as the recent discovery of newly affected genes, merit an update on this topic.

RECENT FINDINGS

Na-K-2CL cotransporter and NaCl cotransporter, the two main luminal channels in the thick ascending limb and distal convoluted tubule were found to be regulated by Ste 20-related proline alanine-rich kinase and oxidative stress response kinase. Knockout mice to these channels express a Bartter-like phenotype. MAGE-D2 is new gene found to cause severe polyhydramnios and transient postnatal Bartter-like syndrome. Variants in the different channels causing Bartter syndromes/Gitelman syndromes may also confer susceptibility for hypertension or protect against it.

SUMMARY

It remains to be determined if polymorphism or epigenetic changes in these genes and proteins may affect salt handling, explaining, apart from Bartter syndromes and Gitelman syndromes, also hypertension or stroke tendency, or both.

Review article: Investigations and the pregnant woman in the emergency department - part 1: Laboratory investigations

Accurate assessment of the pregnant patient in the ED depends on knowledge of physiological changes in pregnancy, and how these changes may impact on pathology tests, appearance on point-of-care ultrasound and electrocardiography. In addition the emergency physician needs to be cognisant of disorders that are unique to or more common in pregnancy. Part 1 of this review addresses potential deviations in laboratory investigation reference intervals resulting from physiological alterations in pregnancy, and the important causes of abnormal laboratory results in pregnancy. Part 2 will address the role of point-of-care ultrasound in pregnancy, physiological changes that may affect interpretation of point-of-care ultrasound, physiological changes in electrocardiography, and the safety of radiological procedures in the pregnant patient.

Two cases of successful pregnancy in patients with Gitelman's syndrome

Gitelman's syndrome (GS) is a distal convoluted tubule (DCT) defect clinically characterized by hypokalemic metabolic alkalosis. Pregnancy in women with GS often results in severe hypomagnesemia and hypokalemia. We report two cases of successful pregnancies, after previous fetal loss, in patients with GS managed with aggressive oral and intravenous electrolyte repletion. These cases illustrate increased potassium and magnesium requirements over the course of the pregnancies and are notable due to the high doses of electrolytes required. They also demonstrate the possibility of successful pregnancy outcomes with frequent laboratory monitoring and aggressive titration of electrolyte replacement either orally or intravenously to maintain appropriate serum levels necessary to provide a suitable environment for fetal development.

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.

Magnesium lactate in the treatment of Gitelman syndrome: patient-reported outcomes

Background: Gitelman syndrome (GS) is a rare recessively inherited renal tubulopathy associated with renal potassium (K) and magnesium (Mg) loss. It requires lifelong K and Mg supplementation at high doses that are at best unpalatable and at worst, intolerable. In particular, gastrointestinal side effects often limit full therapeutic usage.

Methods: We report here the analysis of a cohort of 28 adult patients with genetically proven GS who attend our specialist tubular disorders clinic, in whom we initiated the use of a modified-release Mg preparation (slow-release Mg lactate) and who were surveyed by questionnaire.

Results: Twenty-five patients (89%) preferred the new treatment regimen. Of these 25, 17 (68%) regarded their symptom burden as improved and seven reported no worsening. Of the 25 who were not Mg-treatment naïve, 13 (59%) patients reported fewer side effects, 7 (32%) described them as the same and only 2 (9%) considered side effects to be worse. Five were able to increase their dose without ill-effect. Overall, biochemistry improved in 91% of the 23 patients switched from therapy with other preparations who chose to continue the modified-release Mg preparation. Eleven (48%) improved both their Mg and K mean levels, 3 (13%) improved Mg levels only and in 7 cases (30%), K levels alone rose.

Conclusions: Patient-reported and biochemical outcomes using modified-release Mg supplements were very favourable, and patient choice should play a large part in choosing Mg supplements with GS patients.

Gitelman syndrome: an analysis of the underlying pathophysiologic mechanisms of acid-base and electrolyte abnormalities

Gitelman syndrome is the most common inherited tubular disease resulting from mutations of the SLC12A3 gene that encodes the thiazide-sensitive sodium-chloride cotransporter in the early distal convoluted tubules. The review presents the underlying pathophysiologic mechanisms of acid-base and electrolyte abnormalities observed in patients with Gitelman syndrome. The syndrome is usually characterized by hypokalemic metabolic alkalosis in combination with hypomagnesemia and hypocalciuria. Additionally, increased chloride excretion and renin/aldosterone levels, hypophosphatemia (occasionally), hyponatremia (rarely) and glucose intolerance/insulin resistance have been reported. The knowledge of the pathophysiologic mechanisms is useful for the treatment of patients with Gitelman syndrome as well as for the understanding of other tubular diseases.

Genetics of Magnesium Disorders

Background

Magnesium (Mg²⁺), the second most abundant cation in the cell, is woven into a multitude of cellular functions. Dysmagnesemia is associated with multiple diseases and, when severe, can be life-threatening.

Summary

This review discusses Mg²⁺ homeostasis and function with specific focus on renal Mg²⁺ handling. Intrarenal channels and transporters related to Mg²⁺ absorption are discussed. Unraveling the rare genetic diseases with manifestations of dysmagnesemia has greatly increased our understanding of the complex and intricate regulatory network in the kidney, specifically, functions of tight junction proteins including claudin-14, -16, -19, and -10; apical ion channels including: TRPM6, K_v1.1, and ROMK; small regulatory proteins including AC3 and ANK3; and basolateral proteins including EGF receptor, γ-subunit (FXYD2) of Na-K-ATPase, K_ir4.1, CaSR, CNNM2, and SLC41A. Although our understanding of Mg²⁺ handling of the kidney has expanded considerably in the last two decades, many questions remain. Future studies are needed to elucidate a multitude of unknown aspects of Mg²⁺ handling in the kidney.

Key Message

Understanding rare and genetic diseases of Mg²⁺ dysregulation has expanded our knowledge and furthers the development of strategies for preventing and managing dysmagnesemia.

Gitelman syndrome in a South African family presenting with hypokalaemia and unusual food cravings

BACKGROUND

Gitelman syndrome (GS) is an autosomal recessive renal tubular disorder characterised by renal salt wasting with hypokalaemia, metabolic alkalosis, hypomagnesaemia and hypocalciuria. It is caused by mutations in SLC12A3 encoding the sodium-chloride cotransporter on the apical membrane of the distal convoluted tubule. We report a South African family with five affected individuals presenting with hypokalaemia and unusual food cravings.

METHODS

The affected individuals and two unaffected first degree relatives were enrolled into the study. Phenotypes were evaluated through history, physical examination and biochemical analysis of blood and urine. Mutation screening was performed by sequencing of SLC12A3, and determining the allele frequencies of the sequence variants found in this family in 117 ethnically matched controls.

RESULTS

The index patient, her sister, father and two aunts had a history of severe salt cravings, fatigue and tetanic episodes, leading to consumption of large quantities of salt and vinegar. All affected individuals demonstrated hypokalaemia with renal potassium wasting. Genetic analysis revealed that the pseudo-dominant pattern of inheritance was due to compound heterozygosity with two novel mutations: a S546G substitution in exon 13, and insertion of AGCCCC at c.1930 in exon 16. These variants were present in the five affected individuals, but only one variant each in the unaffected family members. Neither variant was found in any of the controls.

CONCLUSIONS

The diagnosis of GS was established in five members of a South African family through clinical assessment, biochemical analysis and mutation screening of the SLC12A3 gene, which identified two novel putative pathogenic mutations.

Pseudo Gitelman Syndrome Associated With Pregnancy

BACKGROUND

Gitelman syndrome is a rare inherited renal tubulopathy associated with metabolic alkalosis and electrolyte disorders. Pseudo Gitelman syndrome presents with the same clinical characteristics as Gitelman syndrome, yet without genetic mutations in SLC12A3.

CASE

A 32-year-old woman with no remarkable medical and family history developed hypokalemia at 32 weeks of gestation. Laboratory findings were consistent with Gitelman syndrome and potassium supplementation was initiated. The patient delivered a healthy neonate at 40 weeks of gestation and the electrolyte disorders drastically improved. After delivery, genomic analysis revealed no evidence of mutations in SLC12A3, and pseudo Gitelman syndrome was finally diagnosed.

CONCLUSION

Pseudo Gitelman syndrome, presenting with Gitelman syndrome-like renal tubulopathy without mutations in SLC12A3, can cause a temporary electrolyte imbalance based on the physiologic changes of pregnancy. Although pregnant women with isolated hypokalemia need not be evaluated for Gitelman or pseudo Gitelman syndrome, if it is accompanied by metabolic alkalosis, hypocalciuria, hypomagnesia, and activation of the renin-angiotensin-aldosterone system without hypertension, this evaluation should be considered.

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

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

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

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

Dopamine receptor DRD4 gene and stressful life events in persistent attention deficit hyperactivity disorder

We performed a case-control association study in persistent ADHD considering eight candidate genes (DRD4, DAT1/SLC6A3, COMT, ADRA2A, CES1, CYP2D6, LPHN3, and OPRM1) and found additional evidence for the involvement of the Dup 120bp and VNTR 48bp functional variants within the dopamine receptor DRD4 gene in the etiology of adult ADHD. We subsequently investigated the interaction of stressful life events with these two DRD4 polymorphisms, and the impact of such events on the severity of ADHD symptomatology. The gene-by-environment analysis revealed an independent effect of stressful experiences on the severity of persistent ADHD, and a gene-by-environment interaction on the inattentive dimension of the disorder, where non carriers of the Dup 120bp (L) - VNTR 48bp (7R) haplotype were more sensitive to environmental adversity than carriers. These results are in agreement with previous works reporting a relationship between DRD4 and the effect of adverse experiences, which may explain the discordant findings in previous genetic studies and strengthen the importance of gene-by-environment interactions on the severity of ADHD. © 2015 Wiley Periodicals, Inc.

Hypokalemic paralysis due to thyrotoxicosis accompanied by Gitelman's syndrome

A 35-year-old male patient was admitted with fatigue and muscle weakness. He had been on methimazole due to thyrotoxicosis for 2 weeks. Laboratory tests showed overt hyperthyroidism and hypokalemia. Potassium replacement was started with an initial diagnosis of thyrotoxic hypokalemic periodic paralysis. Later on, despite the euthyroid condition and potassium chloride treatment, hypokalemia persisted. Further investigations revealed hyperreninemic hyperaldosteronism. The patient was considered to have Gitelman's syndrome (GS) and all genetic analysis was done. A c. 1145C>T, p. Thr382Met homozygote missense mutation located on solute carrier family 12, member gene 3, exon 9 was detected and GS was confirmed.