Gitelman-Like Syndrome Caused by Pathogenic Variants in mtDNA

Background: Gitelman syndrome (GS) is the most frequent hereditary salt-losing tubulopathy characterized by hypokalemic alkalosis and hypomagnesemia. GS is caused by biallelic pathogenic variants in SLC12A3, encoding the Na+-Cl- cotransporter (NCC) expressed in the distal convoluted tubule. Pathogenic variants of CLCNKB, HNF1B, FXYD2, or KCNJ10 may result in the same renal phenotype of GS, as they can lead to reduced NCC activity. For approximately 10 percent of patients with a GS phenotype, the genotype is unknown. Methods: We identified mitochondrial DNA (mtDNA) variants in three families with GS-like electrolyte abnormalities, then investigated 156 families for variants in MT-TI and MT-TF, which encode the transfer RNAs for phenylalanine and isoleucine. Mitochondrial respiratory chain function was assessed in patient fibroblasts. Mitochondrial dysfunction was induced In NCC-expressing HEK293 cells to assess the effect on thiazide-sensitive 22Na+ transport. Results: Genetic investigations revealed four mtDNA variants in 13 families: m.591C>T (n=7), m.616T>C (n=1), m.643A>G (n=1) (all in MT-TF) and m.4291T>C (n=4, in MT-TI). Variants were near homoplasmic in affected individuals. All variants were classified as pathogenic, except for m.643A>G, which was classified as a variant of uncertain significance. Importantly, affected members of six families with an MT-TF variant additionally suffered from progressive chronic kidney disease. Dysfunction of oxidative phosphorylation complex IV reduced maximal mitochondrial respiratory capacity in patient fibroblasts. In vitro pharmacological inhibition of complex IV, mimicking the effect of the mtDNA variants, inhibited NCC phosphorylation and NCC-mediated sodium uptake. Conclusion: Pathogenic mtDNA variants in MT-TF and MT-TI can cause a GS-like syndrome. Genetic investigation of mtDNA should be considered in patients with unexplained GS-like tubulopathies.

Abstract P103: A PATIENT'S 45 YEAR STORY AFTER 1 3/4 ADRENALECTOMY FOR PRIMARY ALDOSTERONISM DUE TO ADRENAL HYPERPLASIA: IMPROVED CONTOL WITH LO NA DASH DIET.

This report relies on detailed hospital/clinic records from the UK provided by the patient(PK) and his physicians for review and synthesis. In 1976 an asymptomatic, 24 y/o college lad had a routine health screening BP of 245/125. He was admitted. HPI was negative for symptoms or prior history of HBP. FH was - for low K or HBP, + for CAD in men <50. PE: ? increased heart size, Fundi Grade II. Hypokalemic alkalosis was noted, a renal arteriogram was normal. Adrenal (Ad) CT showed a normal L Ad but the R was not visualized, plasma aldosterone (PALDO) was elevated but 24 hr urine ALDO was not. PRA was not available at this time. Ad venography was negative, but the R Ad could not be cannulated. The DX was bilateral disease. Spironolactone (S) was started at 300 mg/d. He was readmitted for surgery 2 months later. BP = 160/100 and K was normal. At surgery, L Ad was said to be 2x normal and it and 3/4 of the R Ad were excised. Oral cortisol coverage was needed for 2 months, then ACTH gel for 2 months. BP was lowered for about 2 months off medications but then returned to 200/110. S was restarted at 400 mg/d with good control but gynecomastia developed. BP control was attempted with S and hydralazine for several years but despite being normal at home was always high in the office. Age 33 noted to have K of 3.2 and muscle “fasciculations”. S was increased. AFIB developed at 51. He converted to NSR with Amiodarone. BP continued to be difficult to control till age 56 when he began to move to the DASH diet recommended by my (CEG) patient online support Group which I have managed now for 19+ years. At 58, he retired from teaching early to care for his wife. At 62, PALDO was 1300 and Renin was 10 on S+DASH diet (ENa 55, EK 139 mM/d). Then 600/1 off S + on high salt intake (ENa 125, EK 100 mM/d). At 60, MRI showed “adenoma R” Ad. Rx with S/enalapril continued with home BPs 122/84. At 65, non-ST MI diagnosed, PTA/stenting was performed. BP has been stable for last 3 years with home BP 120/80 on DASH Diet, Spiro 100/enalapril 20 mg/d. Statin myalgia prevented statins. Lipids and BP have improved on DASH. HBP returns when he deviates from DASH. This case shows that long-term survival after 1 3/4 adrenalectomy for Conn’s (due to hyperplasia) is possible and suggests moving to the DASH diet improves BP control (last 3 year AVE 112/73).

An Unusual Case of Bilateral Adrenal Hyperplasia

Background: Thrombocytopenia, anasarca, fever, reticulin fibrosis/renal failure, and organomegaly (TAFRO) syndrome is a variant of Castleman Disease, which is a rare lymphoproliferative disease that can be life threatening. Diagnosis is often delayed because of its nonspecific presentation. Bilateral adrenal hyperplasia has been a reported complication, however the majority of cases reported have been in Asian patients. Prior accounts of elevated ACTH in TAFRO have been in the context of adrenal insufficiency. Clinical Case: A 28-year-old Caucasian male with a history of multiple sclerosis was seen in the ED with abdominal pain. On presentation, he was afebrile and normotensive. Physical exam was notable for cervical lymphadenopathy and abdominal tenderness. There was no facial rounding/plethora, bruising, abnormal striae, or proximal muscle weakness. He had normal blood counts, serum chemistry and liver function. An abdominal CT scan showed marked bilateral adrenal hyperplasia with pre-aortic, peri-aortic and retroperitoneal lymphadenopathy. An 8AM serum cortisol was 14.1 mcg/dl (4.8–19.6 mcg/dl) and adrenocorticotrophic hormone (ACTH) was elevated at 152 pg/ml (7.2–63 pg/ml). A repeat serum 8AM cortisol following low dose dexamethasone suppression test (LDDST) was 14.7 mcg/dl, however at that point the patient had developed new fevers and thrombocytopenia. Blood pressure, blood glucose and potassium remained normal. An MRI of the brain showed a normal appearing pituitary gland. An extensive infectious and rheumatologic evaluation was negative, and he underwent an inguinal lymph node biopsy which showed nodal expansion with histiocytes, consistent with TAFRO. High dose methylprednisolone and Siltuximab (an IL-6 inhibitor) were started, and his fever and abdominal pain resolved. He was discharged home on oral prednisone. Conclusion: We describe a case of bilateral adrenal hyperplasia with elevated ACTH and non-suppressed cortisol on LDDST suggestive of ACTH-driven cortisol excess. However, interpretation of his LDDST is made difficult in the context of persistent fevers. Although we cannot definitively exclude pathologic hypercortisolism at this time, given his lack of suggestive features such as proximal muscle weakness, abnormal striae or hypokalemic alkalosis, his over-all presentation was more consistent with hyperplasia secondary to TAFRO rather than an underlying pathologic hypercortisolism. Adrenal hyperplasia has been noted in TAFRO, however its pathogenesis remains poorly understood. TAFRO should be added among the differentials for bilateral adrenal hyperplasia to facilitate early diagnosis and treatment. References: Ducoux G, et al. Thrombocytopenia, Anasarca, Fever, Reticulin Fibrosis/Renal Failure, and Organomegaly (TAFRO) Syndrome with Bilateral Adrenal Hemorrhage in Two Caucasian Patients. Am J Case Rep. 2020;21:e919536.

Defects in KCNJ16 Cause a Novel Tubulopathy with Hypokalemia, Salt Wasting, Disturbed Acid-Base Homeostasis, and Sensorineural Deafness

BackgroundThe transepithelial transport of electrolytes, solutes, and water in the kidney is a well-orchestrated process involving numerous membrane transport systems. Basolateral potassium channels in tubular cells not only mediate potassium recycling for proper Na+,K+-ATPase function but are also involved in potassium and pH sensing. Genetic defects in KCNJ10 cause EAST/SeSAME syndrome, characterized by renal salt wasting with hypokalemic alkalosis associated with epilepsy, ataxia, and sensorineural deafness.MethodsA candidate gene approach and whole-exome sequencing determined the underlying genetic defect in eight patients with a novel disease phenotype comprising a hypokalemic tubulopathy with renal salt wasting, disturbed acid-base homeostasis, and sensorineural deafness. Electrophysiologic studies and surface expression experiments investigated the functional consequences of newly identified gene variants.ResultsWe identified mutations in the KCNJ16 gene encoding KCNJ16, which along with KCNJ15 and KCNJ10, constitutes the major basolateral potassium channel of the proximal and distal tubules, respectively. Coexpression of mutant KCNJ16 together with KCNJ15 or KCNJ10 in Xenopus oocytes significantly reduced currents.ConclusionsBiallelic variants in KCNJ16 were identified in patients with a novel disease phenotype comprising a variable proximal and distal tubulopathy associated with deafness. Variants affect the function of heteromeric potassium channels, disturbing proximal tubular bicarbonate handling as well as distal tubular salt reabsorption.

Simultaneous Homozygous Mutations in SLC12A3 and CLCNKB in an Inbred Chinese Pedigree

Gitelman syndrome (GS) and Bartter syndrome (BS) type III are both rare, recessively inherited salt-losing tubulopathies caused by SLC12A3 and CLCNKB mutations, respectively. We described a 48-year-old male patient with fatigue, carpopedal spasm, arthralgia, hypokalemic alkalosis, mild renal dysfunction, hypomagnesemia, hypocalciuria, hyperuricemia, normotension, hyperreninemia and chondrocalcinosis in knees and Achilles tendons. His parents are first cousin. Genetic analysis revealed simultaneous homozygous mutations in SLC12A3 gene with c.248G>A, p.Arg83Gln and CLCNKB gene with c.1171T>C, p.Trp391Arg. The second younger brother of the proband harbored the same simultaneous mutations in SLC12A3 and CLCNKB and exhibited similar clinical features except normomagnesemia and bilateral kidney stones. The first younger brother of the proband harbored the same homozygous mutations in CLCNKB and exhibited clinical features of hypokalemia, normomagnesemia, hypercalciuria and hyperuricemia. Potassium chloride, spironolactone and potassium magnesium aspartate were prescribed to the proband to correct electrolytic disturbances. Benzbromarone and febuxostat were prescribed to correct hyperuricemia. The dose of potassium magnesium aspartate was subsequently increased to alleviate arthralgia resulting from calcium pyrophosphate deposition disease (CPPD). To the best of our knowledge, we are the first to report an exceptionally rare case in an inbred Chinese pedigree with simultaneous homozygous mutations in SLC12A3 and CLCNKB. GS and BS type III have significant intrafamilial phenotype heterogeneity. When arthralgia is developed in patients with GS and BS, gout and CPPD should both be considered.

Apparent mineralocorticoid excess caused by novel compound heterozygous mutations in HSD11B2

Background Apparent mineralocorticoid excess (AME) is a rare autosomal recessive genetic disorder caused by a mutation in the 11β-hydroxysteroid dehydrogenase type 2 gene (HSD11B2). AME is characterized by early-onset and severe hypertension, hypokalemia, and metabolic alkalosis. Purpose This study aimed to study the molecular genetics, clinical presentation, biochemical parameters, and treatment in the proband with AME from a non-consanguineous Chinese family. Methods Genomic DNA was recovered from peripheral blood leukocytes from nine subjects in this family. Next-generation sequencing and Sanger sequencing were performed to identify the HSD11B2 variants. In silico and genotype-phenotype correlations analyses were used to predict pathogenicity of candidate variants. A tailored therapy was performed for identified mutations carriers. Results Genetic analysis identified novel compound heterozygous HSD11B2 mutations (c.343-348del/c.1099-1101del) in the proband. In silico analysis predicted these HSD11B2 mutations were deleterious. The structural change and predicted consequences owing to the compound mutations have been modeled. The same compound mutations were not found in any other family members, 100 hypertensives, or 100 healthy controls. The proband had typical manifestations of AME, including early-onset and severe hypertension, hypokalemia, low plasma aldosterone concentration, hypokalemic alkalosis and nephrolithiasis. The probands' blood pressure and serum potassium level had returned to normal after treatmennt with dexamethasone (1.5 mg/day) and spirolactone (40 mg/day) for three months. Conclusions We conclude that this novel compound mutations are responsible for AME in the proband. These genetic and clinical data expand the genetic spectrum of HSD11B2 and demonstrate the pathogenic effects of identified mutations and genotype-phenotype correlations. It is emphasized that genetic diagnosis and specific treatment play an important role in patients with AME. Figure 1 Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): National Key Research and Development Program of China; PUMC Youth Fund and the Fundamental Research Funds for the Central Universities

Differential diagnosis of perinatal Bartter, Bartter and Gitelman syndromes

The common finding of hypokalemic alkalosis in several unrelated disorders may confound the early diagnosis of salt-losing tubulopathy (SLT). Antenatal Bartter syndrome (BS) must be considered in idiopathic early-onset polyhydramnios. Fetal megabladder in BS may allow its distinction from third-trimester polyhydramnios that occurs in congenital chloride diarrhea (CCD). Fetal megacolon occurs in CCD while fecal chloride &gt;90 mEq/L in infants is diagnostic. Failure-to-thrive, polydipsia and polyuria in early childhood are the hallmarks of classic BS. Unlike BS, there is low urinary chloride in hypokalemic alkalosis of intractable emesis and cystic fibrosis. Rarely, renal salt wasting may result from cystinosis, Dent disease, disorders of paracellular claudin-10b and Kir4.1 potassium-channel deficiency. Acquired BS may result from calcimimetic up-regulation of a calcium-sensing receptor or autoantibody inactivation of sodium chloride co-transporters in Sjögren syndrome. A relatively common event of heterozygous gene mutations for Gitelman syndrome increases the likelihood of its random occurrence in certain diseases of adult onset. Finally, diuretic abuse is the most common differential diagnosis of SLT. Unlike the persistent elevation in BS, urinary chloride concentration losses waxes and wanes on day-to-day assessment in patients with diuretic misuse.

Mutations in transcription factor CP2-like 1 may cause a novel syndrome with distal renal tubulopathy in humans

Background An underlying monogenic cause of early-onset chronic kidney disease (CKD) can be detected in ∼20% of individuals. For many etiologies of CKD manifesting before 25 years of age, &gt;200 monogenic causative genes have been identified to date, leading to the elucidation of mechanisms of renal pathogenesis. Methods In 51 families with echogenic kidneys and CKD, we performed whole-exome sequencing to identify novel monogenic causes of CKD. Results We discovered a homozygous truncating mutation in the transcription factor gene transcription factor CP2-like 1 (TFCP2L1) in an Arabic patient of consanguineous descent. The patient developed CKD by the age of 2 months and had episodes of severe hypochloremic, hyponatremic and hypokalemic alkalosis, seizures, developmental delay and hypotonia together with cataracts. We found that TFCP2L1 was localized throughout kidney development particularly in the distal nephron. Interestingly, TFCP2L1 induced the growth and development of renal tubules from rat mesenchymal cells. Conversely, the deletion of TFCP2L1 in mice was previously shown to lead to reduced expression of renal cell markers including ion transporters and cell identity proteins expressed in different segments of the distal nephron. TFCP2L1 localized to the nucleus in HEK293T cells only upon coexpression with its paralog upstream-binding protein 1 (UBP1). A TFCP2L1 mutant complementary DNA (cDNA) clone that represented the patient’s mutation failed to form homo- and heterodimers with UBP1, an essential step for its transcriptional activity. Conclusion Here, we identified a loss-of-function TFCP2L1 mutation as a potential novel cause of CKD in childhood accompanied by a salt-losing tubulopathy.

A Case Report: Gitelman Syndrome or Bartter Syndrome?

Background: Gitelman syndrome (GS) is a rare autosomal recessive inherited tubular disease which is caused by mutation in the SLC12A3 gene. It is characterized by hypokalemic alkalosis with hypomagnesemia and hypocalciuria, and can cause serious complications such as arrhythmia, syncope, sudden death, etc. Bartter syndrome (BS) is similar to Gitelman syndrome in clinical and laboratory examinations. If lack of sufficient understanding of the disease, it is easy to cause misdiagnosis and missed diagnosis. Case presentation: A 6-year-old Chinese girl presented with history of hand and foot spasms and was diagnosed with hypokalemia. Although multiple symptomatic treatments of potassium supplementation was given, is the concentration of potassium was still at a low level. Gene analysis revealed that the presence of two heterozygous mutations, i.e. a missense mutation c.248G> A and a frameshift mutation c.2875_2876del, in the SLC12A3 gene.The child was diagnosed with Gitelman syndrome(GS) due to SLC12A3 compound heterozygous mutation. Through treatment, the level of ion metabolism in children remains stable. Conclusions: By reviewing its clinical characteristics and diagnosis and treatment ideas, we can help improve clinicians' understanding of children's GS.

Clinico-genetic specifications of Bartter and Gitelman syndrome in children

Molecular genetic research has led to the discovery of new genes encoding proteins – transporters, cotransporters and exchangers involved in the transport of sodium, potassium and chlorine in the thick ascending part of the Henle loop and in the distal convoluted tubule. The article presents modern literature data on the genetic types of tubulopathy with the leading syndrome of hypokalemia and alkalosis – Bartter and Gitelman syndromes in children. The clinical and genetic features of the six types of Bartter syndrome with autosomal recessive and X-linked inheritance, classification approaches, diagnosis, and modern treatment methods are described. Since the first description of Bartter syndrome, 6 clinical genetic options have been known, including antenatal I, II, IVa, IVb, V types, which are potentially life-threatening diseases. Bartter type III syndrome is characterized by the manifestation of hypokalemic alkalosis in children at an early and preschool age. Treatment of Bartter syndrome in children includes the correction of water – electrolyte disturbances, the use of non-steroidal anti-inflammatory drugs (NSAIDs) to inhibit the excessive formation of renal prostaglandin PgE 2. Gitelman syndrome with an autosomal recessive type of inheritance manifests itself in children at school age, later on in adolescents and adults there is an increase in clinical manifestations (with severe hypomagnesemic seizures of the upper and lower extremities, arterial hypertension) requiring correction. The review presents the clinical and genetic features of the rare, atypical form of the autosomal recessive Gitelman syndrome with a manifestation in school age, which is characterized by progressive bilateral calcifications of the subcortical parts of the cerebral hemispheres, calcifications in the basal ganglia and subcortical cerebellum. Unlike Bartter syndrome, with more severe clinical manifestations in newborns, infants and young children, Gitelman syndrome tends to increase clinical manifestations in adolescents and adults. Treatment of Gitelman syndrome in children and adolescents includes the correction of water – electrolyte disturbances, the use of magnesium preparations and salt subsidy.