A novel homozygous mutation (p.N958K) of SLC12A3 in Gitelman syndrome is associated with endoplasmic reticulum stress.

PURPOSE: Gitelman syndrome (GS) is an autosomal recessive renal tubular disease that arises as a consequence of mutations in the SLC12A3 gene, which codes for an Na-Cl cotransporter (NCC) in distal renal tubules. This study was designed to explore the mutations associated with GS in an effort to more fully understand the molecular mechanisms governing GS. METHODS: We analyzed SLC12A3 mutations in a pedigree including a 42-year-old male with GS as well as four related family members over three generations using Sanger and next generation sequencing approaches. We additionally explored the functional ramifications of identified mutations using both Xenopus oocytes and the HEK293T cell line. RESULTS: We found that the subject with GS exhibited characteristic symptoms including sporadic thirst, fatigue, excess urination, and substantial hypokalemia and hypocalciuria, although magnesium levels were normal. Other analyzed subjects in this pedigree had normal laboratory findings and did not exhibit clear signs of GS. Sequencing analyses revealed that the GS subject exhibited a homozygous missense mutation (c.2874C > G, p.N958K) in exon 24 of SLC12A3. Both parents of this GS subject, as well as his older brother and daughter all exhibited heterozygous mutations at this same site. Functional analyses in Xenopus oocytes indicated that this mutated SLC12A3 gene encodes a protein which fails to mediate normal sodium transport, and when this mutant gene was expressed in HEK293T cells, we observed significant increases in endoplasmic reticulum (ER)-stress pathway activation. CONCLUSION: The p.N958K mutation in exon 24 of SLC12A3 can trigger GS at least in part via enhancing ER stress responses.

Hypokalaemic paralysis and metabolic alkalosis in a patient with Sjögren syndrome: a case report and literature review.

BACKGROUND: Acquired Gitelman syndrome is a very rare disorder reported in association with autoimmune disorders, mostly Sjögren syndrome. It is characterized by the presence of hypokalaemic metabolic alkalosis, hypocalciuria, hypomagnesaemia and hyper-reninaemia, in the absence of typical genetic mutations associated with inherited Gitelman syndrome. CASE PRESENTATION: A 20 year old woman who was previously diagnosed with primary Sjögren syndrome and autoimmune thyroiditis presented with two week history of lower limb weakness and salt craving. Examination revealed upper limb and lower limb muscle weakness with muscle power of 3/5 on MRC scale and diminished deep tendon reflexes. On evaluation, she had hypokalaemia with high trans-tubular potassium gradient, metabolic alkalosis and hypocalciuria, features suggestive of Gitelman syndrome. New onset hypokalaemic alkalosis in a previously normokalaemic patient with Sjögren syndrome strongly favored a diagnosis of acquired Gitelman syndrome. Daily potassium supplementation and spironolactone resulted in complete clinical recovery. CONCLUSIONS: Acquired Gitelman syndrome associated with Sjögren syndrome is rare. It should be considered as a differential diagnosis during evaluation of acute paralysis and hypokalaemic metabolic alkalosis in patients with autoimmune disorders, especially Sjögren syndrome.

Loss of sodium chloride co-transporter impairs the outgrowth of the renal distal convoluted tubule during renal development.

BACKGROUND: Loss-of-function mutations in the sodium chloride (NaCl) co-transporter (NCC) of the renal distal convoluted tubule (DCT) cause Gitelman syndrome with hypokalemic alkalosis, hypomagnesemia and hypocalciuria. Since Gitelman patients are usually diagnosed around adolescence, we tested the idea that a progressive regression of the DCT explains the late clinical onset of the syndrome. METHODS: NCC wild-type and knockout (ko) mice were studied at Days 1, 4 and 10 and 6 weeks after birth using blood plasma analysis and morphological and biochemical methods. RESULTS: Plasma aldosterone levels and renal renin messenger RNA expression were elevated in NCC ko mice during the first days of life. In contrast, plasma ion levels did not differ between genotypes at age 10 days, but a significant hypomagnesemia was observed in NCC ko mice at 6 weeks. Immunofluorescent detection of parvalbumin (an early DCT marker) revealed that the fractional cortical volume of the early DCT is similar for mice of both genotypes at Day 4, but is significantly lower at Day 10 and is almost zero at 6 weeks in NCC ko mice. The DCT atrophy correlates with a marked reduction in the abundance of the DCT-specific Mg2+ channel TRPM6 (transient receptor potential cation channel subfamily M member 6) and an increased proteolytic activation of the epithelial Na+ channel (ENaC). CONCLUSION: After an initial outgrowth, DCT development lags behind in NCC ko mice. The impaired DCT development associates at Day 1 and Day 10 with elevated renal renin and plasma aldosterone levels and activation of ENaC, respectively, suggesting that Gitelman syndrome might be present much earlier in life than is usually expected. Despite an early downregulation of TRPM6, hypomagnesemia is a rather late symptom.

[Severe hypokalemic rhabdomyolysis. Report of six cases]. / Rabdomiólisis por hipopotasemia severa.

Rhabdomyolysis results from acute necrosis of skeletal muscle fibers and consequent leakage of muscle constituents into the circulation. It ranges from an asymptomatic state to a severe condition associated with extreme elevations in creatine kinase and acute renal failure. Reported etiologies of rhabdomyolysis include alcohol abuse, drugs, muscle trauma and muscle overexertion. Less common causes include muscle enzyme deficiencies, electrolyte abnormalities, infectious causes, toxins and endocrine disorders. Hypokalemia is a rare cause of rhabdomyolysis. We report six patients aged 31 to 57 years (three women) with a severe hypokalemic rhabdomyolysis, secondary to chronic diarrhea in two patients, treatment with loop diuretics in one and Gitelman syndrome in three. Rhabdomyolysis may be underdiagnosed in the context of hypokalemia, because the neuromuscular symptoms can be attributed solely to the electrolyte disorder.

Hypokalaemia and failure to thrive: report of a misleading onset.

AIM: We report a case of Gitelman Syndrome (GS) in a 9-year-old girl, previously diagnosed as a Bartter syndrome at one year of life. METHODS: She had been treated with potassium, for over 8 years and was admitted because of fatigue, numbness and weakness of both legs. The patient has typical laboratory findings, including hypokalemia, metabolic alkalosis, hypomagnesemia, and hypocalciuria, thus GS was suspected. RESULTS: Genetic analysis was performed two mutations IVS9(+1)G>T were detected in the thiazide-sensitive Na-Cl cotransporter (TSC) gene (SLC12A3), thus she was diagnosed as having GS. She was treated with oral potassium and magnesium supplements with resolution of the symptoms. CONCLUSION: This case reminded us that doctors should be alert to the initial presentation of renal tubular diseases. Detailed electrolyte analysis, hormone evaluations and clinic follow-up are mandatory for their correct differential diagnosis.

Systemic lupus erythematosus complicated by a Gitelman-like syndrome in an 8-year-old girl.

An 8-year-old girl with recently diagnosed Systemic Lupus Erythematosus (SLE) (class 4 lupus nephritis with autoimmune hemolytic anemia) presented to the pediatric nephrology clinic with polyuria, tiredness and cramps; laboratory investigations revealed refractory hypokalemia, hypomagnesemia, metabolic alkalosis, hypocalciuria and hyperchloriuria. There was no history of diuretic administration. These features were consistent with the Gitelman syndrome. She required large doses of potassium and magnesium supplementation along with spironolactone, for normalization of the serum potassium and magnesium levels. Immunosuppressive therapy was continued with cyclophosphamide pulses administered on a monthly basis. The doses of potassium and magnesium supplements were tapered off over the next 6 months. The clinical exome sequencing was negative for any mutations in the SLC12A3 gene. An 'acquired' form of Gitelman syndrome has been reported earlier in association with Sjogren syndrome and systemic sclerosis. Though tubular disorders such as renal tubular acidosis have been reported in association with SLE, a Gitelman-like syndrome has not been reported earlier. This case adds Gitelman-like tubulopathy to the clinical spectrum of tubular disorders complicating SLE.

Novel mutations in the SLC12A3 gene causing Gitelman's syndrome in Swedes.

PURPOSE: Gitelman's syndrome (GS) is an inherited autosomal recessive disorder due to loss of function mutations in the SLC12A3 gene encoding the Na-Cl co-transporter (NCCT), the target of thiazide diuretics. The defective function of the NCCT, which normally is expressed in the apical membrane of the distal convolute tubule in the kidney, leads to mild hypotension, hypokalemia, hyperreninemic hyperaldosteronism, mild metabolic alkalosis, hypomagnesemia and hypocalciuria. Up to now, more than 100 mutations of the SLC12A3 gene have been described in GS patients. METHODS: We have collected 30 patients from Sweden with a clinical diagnosis of GS and undertaken a mutation screening by SSCP and successive sequencing of the 26 exons and intronic boundaries. Both mutations were identified in most (n = 28, 93%) and at least one mutation was identified in all patients. RESULTS: We found 22 different mutations evenly distributed throughout the gene, 11 of which have not been described previously. The new variants include 8 missense mutations (Glu68Lys, His69Asn, Argl45His, Vall53Met, Gly230Asp, Gly342Ala, Val677Leu and Gly867Ser), 1 insertion (c.834_835insG on exon 6) and 2 splice-site mutations (c.2667 + lT>G substitution in splicing donor site after exon 22, c.1569-1G>A substitution in the splicing acceptor site before exon 13). CONCLUSION: In Swedish patients with the clinical features of GS, disease-causing mutations in the SLC12A3 gene were identified in most patients. The spectrum of GS mutations is wide making full mutation screening of the SLC12A3 gene necessary to confirm the diagnosis.

Gitelman's syndrome and pregnancy: new potential pathophysiological influencing factors, therapeutic approach and materno-fetal outcome.

In the last twenty years the knowledge of biochemical, hormonal and molecular abnormalities of Gitelman's syndrome, the most common phenotype of inherited hypokalemic salt losing renal tubular disorders, is increased in the medical community. In parallel with the increasing number of adult population affected by the syndrome and the remarkable improvement of its management, pregnancy have become an important issue for patients affected and their physicians. There are, however, few reports of pregnancies in Gitelman's patients. We review here the cases of pregnancies in Gitelman's patients reported in literature and report three more cases from our cohort of Gitelman's patients, giving particular attention to the materno-fetal outcome and therapeutic approach. The possible influences on pregnancy of Gitelman's patient of other main hemodynamic, hormonal and molecular features of Gitelman's syndrome such as cardiovascular hyporesponsiveness, abnormal vascular tone regulation, upregulation of nitric oxide and Angiotensin 1-7 systems with their possible influence on the reported alteration of cardiac rhythm and function, are also considered.

Rabdomiólisis por hipopotasemia severa: Report of six cases / Severe hypokalemic rhabdomyolysis

Rhabdomyolysis results from acute necrosis of skeletal muscle fibers and consequent leakage of muscle constituents into the circulation. It ranges from an asymptomatic state to a severe condition associated with extreme elevations in creatine kinase and acute renal failure. Reported etiologies of rhabdomyolysis include alcohol abuse, drugs, muscle trauma and muscle overexertion. Less common causes include muscle enzyme deficiencies, electrolyte abnormalities, infectious causes, toxins and endocrine disorders. Hypokalemia is a rare cause of rhabdomyolysis. We report six patients aged 31 to 57 years (three women) with a severe hypokalemic rhabdomyolysis, secondary to chronic diarrhea in two patients, treatment with loop diuretics in one and Gitelman syndrome in three. Rhabdomyolysis may be underdiagnosed in the context of hypokalemia, because the neuromuscular symptoms can be attributed solely to the electrolyte disorder.

Transcriptional and functional analyses of SLC12A3 mutations: new clues for the pathogenesis of Gitelman syndrome.

Gitelman syndrome (GS) is a recessive salt-losing tubulopathy that is caused by mutations in the SLC12A3 gene that encodes the sodium-chloride co-transporter (NCC). GS is characterized by significant inter- and intrafamilial phenotype variability, with early onset and/or severe clinical manifestations in some patients. No correlations between the disease variability and the position/nature of SLC12A3 mutations have been investigated thus far. In this study, extensive mutational analyses of SLC12A3 were performed in 27 patients with GS, including genomic DNA sequencing, multiplex ligation-dependent probe amplification, cDNA analysis, and quantification of allele-specific transcripts, in parallel with functional analyses in Xenopus laevis oocytes and detailed phenotyping. Twenty-six SLC12A3 mutations were identified in 25 patients with GS, including eight novel (detection rate 80%). Transcript analysis demonstrated that splicing mutations of SLC12A3 lead to frameshifted mRNA subject to degradation by nonsense-mediated decay. Heterologous expression documented a novel class of NCC mutants with defective intrinsic transport activity. A subgroup of patients presented with early onset, growth retardation, and/or detrimental manifestations, confirming the potential severity of GS. The mutations that were associated with a severe presentation were the combination at least for one allele of a missplicing resulting in a truncated transcript that was downregulated by nonsense-mediated decay or a nonfunctional, cell surface-absent mutant. The most recurrent mutation on the second allele was a newly described NCC mutant that affected the functional properties of the co-transporter. These data suggest that the nature/position of SLC12A3 mutation, combined with male gender, is a determinant factor in the severity of GS and provide new insights in the underlying pathogenic mechanisms of the disease.