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Handklo-Jamal R, Meisel E, Yakubovich D, Vysochek L, Beinart R, Glikson M, McMullen JR, Dascal N, Nof E, Oz S. Andersen-Tawil Syndrome Is Associated With Impaired PIP 2 Regulation of the Potassium Channel Kir2.1. Front Pharmacol 2020; 11:672. [PMID: 32499698 PMCID: PMC7243181 DOI: 10.3389/fphar.2020.00672] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Accepted: 04/23/2020] [Indexed: 11/13/2022] Open
Abstract
Andersen-Tawil syndrome (ATS) type-1 is associated with loss-of-function mutations in KCNJ2 gene. KCNJ2 encodes the tetrameric inward-rectifier potassium channel Kir2.1, important to the resting phase of the cardiac action potential. Kir-channels' activity requires interaction with the agonist phosphatidylinositol-4,5-bisphosphate (PIP2). Two mutations were identified in ATS patients, V77E in the cytosolic N-terminal "slide helix" and M307V in the C-terminal cytoplasmic gate structure "G-loop." Current recordings in Kir2.1-expressing HEK cells showed that each of the two mutations caused Kir2.1 loss-of-function. Biotinylation and immunostaining showed that protein expression and trafficking of Kir2.1 to the plasma membrane were not affected by the mutations. To test the functional effect of the mutants in a heterozygote set, Kir2.1 dimers were prepared. Each dimer was composed of two Kir2.1 subunits joined with a flexible linker (i.e. WT-WT, WT dimer; WT-V77E and WT-M307V, mutant dimer). A tetrameric assembly of Kir2.1 is expected to include two dimers. The protein expression and the current density of WT dimer were equally reduced to ~25% of the WT monomer. Measurements from HEK cells and Xenopus oocytes showed that the expression of either WT-V77E or WT-M307V yielded currents of only about 20% compared to the WT dimer, supporting a dominant-negative effect of the mutants. Kir2.1 sensitivity to PIP2 was examined by activating the PIP2 specific voltage-sensitive phosphatase (VSP) that induced PIP2 depletion during current recordings, in HEK cells and Xenopus oocytes. PIP2 depletion induced a stronger and faster decay in Kir2.1 mutant dimers current compared to the WT dimer. BGP-15, a drug that has been demonstrated to have an anti-arrhythmic effect in mice, stabilized the Kir2.1 current amplitude following VSP-induced PIP2 depletion in cells expressing WT or mutant dimers. This study underlines the implication of mutations in cytoplasmic regions of Kir2.1. A newly developed calibrated VSP activation protocol enabled a quantitative assessment of changes in PIP2 regulation caused by the mutations. The results suggest an impaired function and a dominant-negative effect of the Kir2.1 variants that involve an impaired regulation by PIP2. This study also demonstrates that BGP-15 may be beneficial in restoring impaired Kir2.1 function and possibly in treating ATS symptoms.
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Affiliation(s)
| | - Eshcar Meisel
- Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.,Heart Center, Sheba Medical Center, Ramat-Gan, Israel
| | - Daniel Yakubovich
- Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.,Neonatology Department, Schneider Children's Medical Center, Petah-Tikva, Israel
| | | | - Roy Beinart
- Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.,Heart Center, Sheba Medical Center, Ramat-Gan, Israel
| | - Michael Glikson
- Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.,Heart Center, Sheba Medical Center, Ramat-Gan, Israel
| | | | - Nathan Dascal
- Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Eyal Nof
- Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.,Heart Center, Sheba Medical Center, Ramat-Gan, Israel
| | - Shimrit Oz
- Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.,Heart Center, Sheba Medical Center, Ramat-Gan, Israel
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Twigg SRF, Ousager LB, Miller KA, Zhou Y, Elalaoui SC, Sefiani A, Bak GS, Hove H, Hansen LK, Fagerberg CR, Tajir M, Wilkie AOM. Acromelic frontonasal dysostosis and ZSWIM6 mutation: phenotypic spectrum and mosaicism. Clin Genet 2016; 90:270-5. [PMID: 26706854 PMCID: PMC5025718 DOI: 10.1111/cge.12721] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2015] [Revised: 12/22/2015] [Accepted: 12/22/2015] [Indexed: 11/24/2022]
Abstract
Acromelic frontonasal dysostosis (AFND) is a distinctive and rare frontonasal malformation that presents in combination with brain and limb abnormalities. A single recurrent heterozygous missense substitution in ZSWIM6, encoding a protein of unknown function, was previously shown to underlie this disorder in four unrelated cases. Here we describe four additional individuals from three families, comprising two sporadic subjects (one of whom had no limb malformation) and a mildly affected female with a severely affected son. In the latter family we demonstrate parental mosaicism through deep sequencing of DNA isolated from a variety of tissues, which each contain different levels of mutation. This has important implications for genetic counselling.
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Affiliation(s)
- S R F Twigg
- Clinical Genetics Group, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - L B Ousager
- Department of Clinical Genetics, Odense University Hospital, Odense, Denmark
| | - K A Miller
- Clinical Genetics Group, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - Y Zhou
- Clinical Genetics Group, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - S C Elalaoui
- Human Genomics Center, Faculty of Medicine and Pharmacy of Rabat, Rabat, Morocco.,Department of Medical Genetics, National Institute of Health, Rabat, Morocco
| | - A Sefiani
- Human Genomics Center, Faculty of Medicine and Pharmacy of Rabat, Rabat, Morocco.,Department of Medical Genetics, National Institute of Health, Rabat, Morocco
| | - G S Bak
- Department of Obstetrics and Gynecology, Odense University Hospital, Odense, Denmark
| | - H Hove
- Department of Clinical Genetics, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark
| | - L K Hansen
- Department of Paediatrics, Hans Christian Andersen Children's Hospital, Odense University Hospital, Odense, Denmark
| | - C R Fagerberg
- Department of Clinical Genetics, Odense University Hospital, Odense, Denmark
| | - M Tajir
- Human Genomics Center, Faculty of Medicine and Pharmacy of Rabat, Rabat, Morocco.,Department of Medical Genetics, National Institute of Health, Rabat, Morocco
| | - A O M Wilkie
- Clinical Genetics Group, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
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Spyra M, Otto B, Schön G, Kehrer-Sawatzki H, Mautner VF. Determination of the mutant allele frequency in patients with neurofibromatosis type 2 and somatic mosaicism by means of deep sequencing. Genes Chromosomes Cancer 2015; 54:482-488. [PMID: 26031996 DOI: 10.1002/gcc.22259] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Revised: 03/20/2015] [Accepted: 03/21/2015] [Indexed: 12/17/2022] Open
Abstract
Neurofibromatosis Type 2 (NF2) is an autosomal disorder caused by mutations of the NF2 gene. More than half of all NF2 patients have unaffected parents and carry de novo mutations, which may be of prezygotic or postzygotic origin. The latter can result in mosaicism, which is relatively common in NF2 patients. Previous studies indicated that, in 50% of patients with mosaic NF2 mutations, the mutant allele is only detectable by Sanger sequencing of PCR products amplified from tumor tissue but not from blood samples. In order to establish a highly sensitive method that has the power to detect low levels of NF2 mutant alleles from blood samples of mosaic NF2 patients, we performed ultra deep sequencing and calculated the percentage of mutant and wildtype NF2 alleles. The mutant allele frequencies detected ranged from 2.6% to 19.7%. In three patients, however, the NF2 mutation previously identified in tumor tissue was not identified in blood samples by means of deep sequencing, suggesting absence of mutant cells in the blood. Remarkably, we observed a correlation between the age at onset of the disease and the mutant allele frequency. Our study indicates that ultra deep sequencing is an effective and highly sensitive method to determine the mutant allele frequency in patients with mosaic NF2 gene mutations, which enables extended phenotype/correlations in these patients. © 2015 Wiley Periodicals, Inc.
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Affiliation(s)
- Melanie Spyra
- Department of Neurology, University Hospital Hamburg-Eppendorf, Hamburg, Germany
| | - Benjamin Otto
- Department of Internal Medicine, University Hospital Hamburg-Eppendorf, Hamburg, Germany
| | - Gerhard Schön
- Department of Medical Biometry and Epidemiology, University Hospital Hamburg-Eppendorf, Hamburg, Germany
| | | | - Victor-Felix Mautner
- Department of Neurology, University Hospital Hamburg-Eppendorf, Hamburg, Germany
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