scholarly journals Epilepsy and neurobehavioral abnormalities in mice with a KCNB1 pathogenic variant that alters conducting and non-conducting functions of KV2.1

2019 ◽  
Author(s):  
Nicole A. Hawkins ◽  
Sunita N. Misra ◽  
Manuel Jurado ◽  
Nicholas C. Vierra ◽  
Kimberly Nguyen ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
De Novo ◽  
Pathogenic Variant ◽  
Repetitive Behaviors ◽  
Dominant Negative ◽  
Dominant Negative Effect ◽  
Delayed Rectifier ◽  
Eeg Abnormalities ◽  
Surface Ecg

AbstractDevelopmental and epileptic encephalopathies (DEE) are a group of severe epilepsies that usually present with intractable seizures, developmental delay and are at a higher risk for premature mortality. Numerous genes have been identified as a monogenic cause of DEE, including KCNB1. The voltage-gated potassium channel KV2.1, encoded by KCNB1, is primarily responsible for delayed rectifier potassium currents that are important regulators of excitability in electrically excitable cells, including neurons and cardiomyocytes. The de novo pathogenic variant KCNB1-p.G379R was identified in an infant with epileptic spasms, atonic, focal and tonic-clonic seizures that were refractory to treatment with standard antiepileptic drugs. Previous work demonstrated deficits in potassium conductance, but did not assess non-conducting functions. To determine if the G379R variant affected clustering at endoplasmic reticulum-plasma membrane junctions KV2.1-G379R was expressed in HEK293T cells. KV2.1-G379R expression did not induce formation of endoplasmic reticulum-plasma membrane junctions, and co-expression of KV2.1-G379R with KV2.1-WT lowered induction of these structures relative to KV2.1-WT alone, suggesting a dominant negative effect. To model this variant in vivo, we introduced Kcnb1G379R into mice using CRISPR/Cas9 genome editing. We characterized neurological and neurobehavioral phenotypes of Kcnb1G379R/+ (Kcnb1R/+) and Kcnb1G379R/G379R (Kcnb1R/R) mice, and screened for cardiac abnormalities. Immunohistochemistry studies on brains from Kcnb1+/+ (WT), Kcnb1R/+ and Kcnb1R/R mice revealed genotype-dependent differences in the levels and subcellular localization of KV2.1, with reduced plasma membrane expression of the KV2.1-G379R protein, consistent with in vitro data. Kcnb1R/+ and Kcnb1R/R mice displayed profound hyperactivity, repetitive behaviors, impulsivity and reduced anxiety. In addition, both Kcnb1R/+ and Kcnb1R/R mice exhibited abnormal interictal EEG abnormalities, including isolated spike and slow waves. Spontaneous seizure events were observed in Kcnb1R/R mice during exposure to novel environments and/or handling, while both Kcnb1R/+ and Kcnb1R/R mutants were more susceptible to induced seizures. Kcnb1R/+ and Kcnb1R/R mice exhibited prolonged rate-corrected QT interval on surface ECG recording. Overall, the Kcnb1G379R mice recapitulate many features observed in individuals with DEE due to pathogenic variants in KCNB1. This new mouse model of KCNB1 associated DEE will be valuable for improving the understanding of the underlying pathophysiology and will provide a valuable tool for the development of therapies to treat this pharmacoresistant DEE.

scholarly journals DNM1 encephalopathy

Neurology ◽  
2017 ◽  
Vol 89 (4) ◽  
pp. 385-394 ◽  
Author(s):  
Sarah von Spiczak ◽  
Katherine L. Helbig ◽  
Deepali N. Shinde ◽  
Robert Huether ◽  
Manuela Pendziwiat ◽  
...  
Keyword(s):  
Functional Data ◽  
De Novo ◽  
Structural Modeling ◽  
Dominant Negative ◽  
Dominant Negative Effect ◽  
Global Developmental Delay ◽  
Epilepsy Syndrome ◽  
De Novo Mutations ◽  
Phenotypic Data ◽  
Phenotypic Spectrum

Objective:To evaluate the phenotypic spectrum caused by mutations in dynamin 1 (DNM1), encoding the presynaptic protein DNM1, and to investigate possible genotype-phenotype correlations and predicted functional consequences based on structural modeling.Methods:We reviewed phenotypic data of 21 patients (7 previously published) with DNM1 mutations. We compared mutation data to known functional data and undertook biomolecular modeling to assess the effect of the mutations on protein function.Results:We identified 19 patients with de novo mutations in DNM1 and a sibling pair who had an inherited mutation from a mosaic parent. Seven patients (33.3%) carried the recurrent p.Arg237Trp mutation. A common phenotype emerged that included severe to profound intellectual disability and muscular hypotonia in all patients and an epilepsy characterized by infantile spasms in 16 of 21 patients, frequently evolving into Lennox-Gastaut syndrome. Two patients had profound global developmental delay without seizures. In addition, we describe a single patient with normal development before the onset of a catastrophic epilepsy, consistent with febrile infection-related epilepsy syndrome at 4 years. All mutations cluster within the GTPase or middle domains, and structural modeling and existing functional data suggest a dominant-negative effect on DMN1 function.Conclusions:The phenotypic spectrum of DNM1-related encephalopathy is relatively homogeneous, in contrast to many other genetic epilepsies. Up to one-third of patients carry the recurrent p.Arg237Trp variant, which is now one of the most common recurrent variants in epileptic encephalopathies identified to date. Given the predicted dominant-negative mechanism of this mutation, this variant presents a prime target for therapeutic intervention.

scholarly journals Characterization of the R162W Kir7.1 mutation associated with snowflake vitreoretinopathy

2013 ◽  
Vol 304 (5) ◽  
pp. C440-C449 ◽  
Author(s):  
Wei Zhang ◽  
Xiaoming Zhang ◽  
Hui Wang ◽  
Anil K. Sharma ◽  
Albert O. Edwards ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Expression System ◽  
Dominant Negative ◽  
Dominant Negative Effect ◽  
Xenopus Laevis Oocyte ◽  
Cation Selectivity ◽  
Negative Effect ◽  
Dominant Disease ◽  
Vitreoretinal Degeneration ◽  
Inwardly Rectifying

KCNJ13 encodes Kir7.1, an inwardly rectifying K+ channel that is expressed in multiple ion-transporting epithelia. A mutation in KCNJ13 resulting in an arginine-to-tryptophan change at residue 162 (R162W) of Kir7.1 was associated with snowflake vitreoretinal degeneration, an inherited autosomal-dominant disease characterized by vitreous degeneration and mild retinal degeneration. We used the Xenopus laevis oocyte expression system to assess the functional properties of the R162W (mutant) Kir7.1 channel and determine how wild-type (WT) Kir7.1 is affected by the presence of the mutant subunit. Recordings obtained via the two-electrode voltage-clamp technique revealed that injection of oocytes with mutant Kir7.1 cRNA resulted in currents and cation selectivity that were indistinguishable from those in water-injected oocytes, suggesting that the mutant protein does not form functional channels in the plasma membrane. Coinjection of oocytes with equal amounts of mutant and WT Kir7.1 cRNAs resulted in inward K+ and Rb+ currents with amplitudes that were ∼17% of those in oocytes injected with WT Kir7.1 cRNA alone, demonstrating a dominant-negative effect of the mutant subunit. Similar to oocytes injected with WT Kir7.1 cRNA alone, coinjected oocytes exhibited inwardly rectifying Rb+ currents that were more than seven times larger than K+ currents, indicating that mutant subunits did not alter Kir7.1 channel selectivity. Immunostaining of Xenopus oocytes or Madin-Darby canine kidney cells expressing mutant or WT Kir7.1 demonstrated distribution of both proteins primarily in the plasma membrane. Our data suggest that the R162W mutation suppresses Kir7.1 channel activity, possibly by negatively impacting gating by membrane phosphadidylinositol 4,5-bisphosphate.

scholarly journals Clinical and molecular analysis of three families with autosomal dominant neurohypophyseal diabetes insipidus associated with a novel and recurrent mutations in the vasopressin-neurophysin II gene

2002 ◽  
pp. 649-656 ◽  
Author(s):  
J Rutishauser ◽  
P Kopp ◽  
MB Gaskill ◽  
TJ Kotlar ◽  
GL Robertson
Keyword(s):  
Diabetes Insipidus ◽  
Autosomal Dominant ◽  
De Novo ◽  
Index Patient ◽  
Dominant Negative ◽  
Dominant Negative Effect ◽  
Heterozygous Mutation ◽  
Posterior Pituitary ◽  
Recurrent Mutations ◽  
Neurophysin Ii

OBJECTIVE: To test further the hypothesis that autosomal dominant neurohypophyseal diabetes insipidus (adFNDI) is caused by heterozygous mutations in the vasopressin-neurophysin II (AVP-NPII) gene that exert a dominant negative effect by producing a precursor that misfolds, accumulates and eventually destroys the neurosecretory neurons. METHODS: Antidiuretic function, magnetic resonance imaging (MRI) of the posterior pituitary and AVP-NPII gene analysis were performed in 10 affected members of three unreported families with adFNDI. RESULTS: As in previously studied patients, adFNDI apparently manifested after birth, was due to a partial or severe deficiency of AVP, and was associated with absence or diminution of the hyperintense MRI signal normally emitted by the posterior pituitary, and with a heterozygous mutation in the AVP-NPII gene. In family A, a transition 275G-->A, which predicts replacement of cysteine 92 by tyrosine (C92Y), was found in the index patient, but not in either parent, indicating that it arose de novo. The six affected members of family B had a transversion 160G-->C, which predicts replacement of glycine 54 by arginine (G54R). It appeared de novo in the oldest affected member, and was transmitted in a dominant manner. In family C, six of 15 living affected members were tested and all had a novel transition, 313T-->C, which predicts replacement of cysteine 105 by arginine (C105R). It, too, was transmitted in a dominant manner. As in other patients with adFNDI, the amino acids replaced by the mutations in these three families are known to be particularly important for correct and efficient folding of the precursor. CONCLUSIONS: These findings are consistent with the malfolding/toxicity hypothesis underlying the pathogenesis of adFNDI. Moreover, they illustrate the value of genetic analysis in all patients who develop idiopathic diabetes insipidus in childhood, even if no other family members are affected.

Heterozygous Missense Pathogenic Variants Within the Second Spectrin Repeat of SPTBN2 Lead to Infantile-Onset Cerebellar Ataxia

2019 ◽  
Vol 35 (2) ◽  
pp. 106-110 ◽  
Author(s):  
Andrea Accogli ◽  
Judith St-Onge ◽  
Nassima Addour-Boudrahem ◽  
Joël Lafond-Lapalme ◽  
Alexandre Dionne Laporte ◽  
...  
Keyword(s):  
Cognitive Impairment ◽  
Cerebellar Ataxia ◽  
De Novo ◽  
Dominant Negative ◽  
Dominant Negative Effect ◽  
Adult Onset ◽  
Spinocerebellar Ataxias ◽  
Spectrin Repeat ◽  
Missense Variants ◽  
Pathogenic Variants

The term spinocerebellar ataxia encompasses a heterogeneous group of neurodegenerative disorders due to pathogenic variants in more than 100 genes, underlying 2 major groups of ataxia: autosomal dominant cerebellar ataxias (ADCA, also known as spinocerebellar ataxias [SCAs]) due to heterozygous variants or polyglutamine triplet expansions leading to adult-onset ataxia, and autosomal recessive spinocerebellar ataxias (ARCAs, also known as SCARs) due to biallelic variants, usually resulting in more severe and earlier-onset cerebellar ataxia. Certain ataxia genes, including SPTBN2 which encodes β-III spectrin, are responsible for both SCA and SCAR, depending on whether the pathogenic variant occurs in a monoallelic or biallelic state, respectively. Accordingly, 2 major phenotypes have been linked to SPTBN2: pathogenic heterozygous in-frame deletions and missense variants result in an adult-onset, slowly progressive ADCA (SCA5) through a dominant negative effect, whereas biallelic loss-of-function variants cause SCAR14, an allelic disorder characterized by infantile-onset cerebellar ataxia and cognitive impairment. Of note, 2 heterozygous missense variants (c.1438C>T, p.R480 W; c.1309C>G, p.R437G), both lying in the second spectrin repeat of SPTBN2, have been linked to infantile-onset cerebellar ataxia, similar to SCAR14. Here, we report a novel de novo heterozygous pathogenic missense variant (c.1310G>A) in SPTBN2 in a child with infantile-onset cerebellar ataxia and mild cognitive impairment. This variant affects the same R437 residue of the second spectrin repeat but results in a different amino acid change (p.R437Q). We review previously reported cases and discuss possible pathomechanisms responsible for the early-onset cerebellar phenotype due to disease-causing variants in the second spectrin repeat.

scholarly journals Mutational Analysis of PHEX Gene in X-Linked Hypophosphatemia1

1998 ◽  
Vol 83 (10) ◽  
pp. 3615-3623 ◽  
Author(s):  
Peter H. Dixon ◽  
Paul T. Christie ◽  
Carol Wooding ◽  
Dorothy Trump ◽  
Marvin Grieff ◽  
...  
Keyword(s):  
Untranslated Region ◽  
De Novo ◽  
Mutational Analysis ◽  
Extracellular Domain ◽  
Phosphate Transport ◽  
Dominant Negative ◽  
Hypophosphatemic Rickets ◽  
Dominant Negative Effect ◽  
Conformational Polymorphism ◽  
Single Stranded Conformational Polymorphism

Hypophosphatemic rickets is commonly an X-linked dominant disorder (XLH or HYP) associated with a renal tubular defect in phosphate transport and bone deformities. The XLH gene, referred to as PHEX, or formerly as PEX (phosphate regulating gene with homologies to endopeptidases on the X-chromosome), encodes a 749-amino acid protein that putatively consists of an intracellular, transmembrane, and extracellular domain. PHEX mutations have been observed in XLH patients, and we have undertaken studies to characterize such mutations in 46 unrelated XLH kindreds and 22 unrelated patients with nonfamilial XLH by single stranded conformational polymorphism and DNA sequence analysis. We identified 31 mutations (7 nonsense, 6 deletions, 2 deletional insertions, 1 duplication, 2 insertions, 4 splice site, 8 missense, and 1 within the 5′ untranslated region), of which 30 were scattered throughout the putative extracellular domain, together with 6 polymorphisms that had heterozygosity frequencies ranging from less than 1% to 43%. Single stranded conformational polymorphism was found to detect more than 60% of these mutations. Over 20% of the mutations were observed in nonfamilial XLH patients, who represented de novo occurrences of PHEX mutations. The unique point mutation (a→g) of the 5′untranslated region together with the other mutations indicates that the dominant XLH phenotype is unlikely to be explained by haplo-insufficiency or a dominant negative effect.

scholarly journals Determinants of thetrans-Dominant Negative Effect of Truncated Forms of the CCR5 Chemokine Receptor

2001 ◽  
Vol 276 (50) ◽  
pp. 46975-46982 ◽  
Author(s):  
Maurice Chelli ◽  
Marc Alizon
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Chemokine Receptor ◽  
Transmembrane Domains ◽  
Viral Envelope ◽  
Dominant Negative ◽  
Dominant Negative Effect ◽  
Wild Type ◽  
Ccr5 Chemokine Receptor ◽  
Hiv 1

The human immunodeficiency virus, type 1 (HIV-1) entry process is triggered by interaction between the viral envelope and a seven membrane-spanning domain receptor at the cell surface, usually the CCR5 chemokine receptor. Different naturally occurring mutations in theCCR5gene abolish receptor function, the most frequent being a 32-nucleotide deletion resulting in a truncated protein (Δ32) lacking the last three transmembrane domains (TM5–7). This mutant is retained in the endoplasmic reticulum and exerts atrans-dominant negative (TDN) effect on the wild type, preventing its exit from this compartment. This TDN effect is often considered as evidence for the oligomerization of CCR5 during transport to the cell surface. Here we use a genetic approach to define the structural determinants of the TDN effect of the Δ32 mutant. It was abolished by certain deletions and by mutations of cysteine residues preventing formation of a disulfide link between the first and second extracellular loops, suggesting that conformation of Δ32 is important for its interaction with CCR5. To circumvent this problem, we used chimeric forms of the Δ32 and wild type CCR5, consisting in substitutions with homologous domains from the mouse CCR5. All chimeric full-length receptors were expressed at the cell surface and were functional for interaction with HIV-1 or with a chemokine ligand, when assayed. The TDN effect was only observed if both the TM3 domain in CCR5 and the TM4 domain in Δ32 were from human origin, whereas the rest of the proteins could be from either origin. This suggests that the TDN effect involves some form of interaction between these transmembrane domains. Alternatively, but less likely to us, substitutions in TM4 could affect the conformation of CCR5 in the endoplasmic reticulum but not at the cell surface. However that may be, it seems that the TDN effect of the Δ32 mutant has no bearing to the issue of CCR5 dimerization and to its possible role in the processing of the receptor to the cell surface.

scholarly journals Pharmacological correction of long QT-linked mutations in KCNH2 (hERG) increases the trafficking of Kv11.1 channels stored in the transitional endoplasmic reticulum

2013 ◽  
Vol 305 (9) ◽  
pp. C919-C930 ◽  
Author(s):  
Jennifer L. Smith ◽  
Allison R. Reloj ◽  
Parvathi S. Nataraj ◽  
Daniel C. Bartos ◽  
Elizabeth A. Schroder ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Therapeutic Potential ◽  
Functional Expression ◽  
Small Gtpase ◽  
Dominant Negative ◽  
Delayed Rectifier ◽  
Protein Synthesis Inhibitor ◽  
Missense Mutations ◽  
Long Qt ◽  
Pharmacological Correction

KCNH2 encodes Kv11.1 and underlies the rapidly activating delayed rectifier K+ current ( IKr) in the heart. Loss-of-function KCNH2 mutations cause the type 2 long QT syndrome (LQT2), and most LQT2-linked missense mutations inhibit the trafficking of Kv11.1 channels. Drugs that bind to Kv11.1 and block IKr (e.g., E-4031) can act as pharmacological chaperones to increase the trafficking and functional expression for most LQT2 channels (pharmacological correction). We previously showed that LQT2 channels are selectively stored in a microtubule-dependent compartment within the endoplasmic reticulum (ER). We tested the hypothesis that pharmacological correction promotes the trafficking of LQT2 channels stored in this compartment. Confocal analyses of cells expressing the trafficking-deficient LQT2 channel G601S showed that the microtubule-dependent ER compartment is the transitional ER. Experiments with E-4031 and the protein synthesis inhibitor cycloheximide suggested that pharmacological correction promotes the trafficking of G601S stored in this compartment. Treating cells in E-4031 or ranolazine (a drug that blocks IKr and has a short half-life) for 30 min was sufficient to cause pharmacological correction. Moreover, the increased functional expression of G601S persisted 4–5 h after drug washout. Coexpression studies with a dominant-negative form of Rab11B, a small GTPase that regulates Kv11.1 trafficking, prevented the pharmacological correction of G601S trafficking from the transitional ER. These data suggest that pharmacological correction quickly increases the trafficking of LQT2 channels stored in the transitional ER via a Rab11B-dependent pathway, and we conclude that the pharmacological chaperone activity of drugs like ranolazine might have therapeutic potential.

scholarly journals Biallelic and monoallelic variants in PLXNA1 are implicated in a novel neurodevelopmental disorder with variable cerebral and eye anomalies

2021 ◽  
Author(s):  
Gabriel C. Dworschak ◽  
Jaya Punetha ◽  
Jeshurun C. Kalanithy ◽  
Enrico Mingardo ◽  
Haktan B. Erdem ◽  
...  
Keyword(s):  
Developmental Delay ◽  
De Novo ◽  
Neurodevelopmental Disorder ◽  
Structural Modeling ◽  
Dominant Negative ◽  
Dominant Negative Effect ◽  
Global Developmental Delay ◽  
Downstream Signaling ◽  
Negative Effect

Abstract Purpose To investigate the effect of PLXNA1 variants on the phenotype of patients with autosomal dominant and recessive inheritance patterns and to functionally characterize the zebrafish homologs plxna1a and plxna1b during development. Methods We assembled ten patients from seven families with biallelic or de novo PLXNA1 variants. We describe genotype–phenotype correlations, investigated the variants by structural modeling, and used Morpholino knockdown experiments in zebrafish to characterize the embryonic role of plxna1a and plxna1b. Results Shared phenotypic features among patients include global developmental delay (9/10), brain anomalies (6/10), and eye anomalies (7/10). Notably, seizures were predominantly reported in patients with monoallelic variants. Structural modeling of missense variants in PLXNA1 suggests distortion in the native protein. Our zebrafish studies enforce an embryonic role of plxna1a and plxna1b in the development of the central nervous system and the eye. Conclusion We propose that different biallelic and monoallelic variants in PLXNA1 result in a novel neurodevelopmental syndrome mainly comprising developmental delay, brain, and eye anomalies. We hypothesize that biallelic variants in the extracellular Plexin-A1 domains lead to impaired dimerization or lack of receptor molecules, whereas monoallelic variants in the intracellular Plexin-A1 domains might impair downstream signaling through a dominant-negative effect.

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