Skip Navigation


Human Molecular Genetics Advance Access originally published online on February 26, 2007
Human Molecular Genetics 2007 16(8):900-906; doi:10.1093/hmg/ddm034
This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
16/8/900    most recent
ddm034v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (2)
Right arrowRequest Permissions
Google Scholar
Right arrow Articles by Bendahhou, S.
Right arrow Articles by Barhanin, J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Bendahhou, S.
Right arrow Articles by Barhanin, J.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

© The Author 2007. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Corticosteroid-exacerbated symptoms in an Andersen's syndrome kindred

Saïd Bendahhou1,*, Emmanuel Fournier2, Serge Gallet3, Dominique Ménard4, Marie-Madeleine Larroque1 and Jacques Barhanin1

1 Institut de Pharmacologie Moléculaire et Cellulaire, UMR 6097 CNRS, Université de Nice Sophia Antipolis, France, 2 Fédération de Neurophysiologie Clinique and Centre de Référence des Canalopathies Musculaires, Pitié-Salpêtrière Hospital, Paris, France, 3 Department of Pediatrics, Montluçon Hospital, Montluçon, France and 4 Neurology Department, Rennes Hospital, Rennes, France

* To whom correspondence should be addressed at: Université de Nice Sophia Antipolis, UMR 6097 CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, 660 Route des Lucioles, Sophia-Antipolis 06560, Valbonne, France. Tel: +33 493957741; Fax: +33 493957708; Email: bendahhou{at}ipmc.cnrs.fr

Received January 10, 2007; Revised January 10, 2007; Accepted February 15, 2007


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 RESULTS
 DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
Periodic paralysis, cardiac arrhythmia and bone features are the hallmark of Andersen's syndrome (AS), a rare disorder caused by mutations in the KCNJ2 gene that encodes for the inward rectifier K+-channel Kir2.1. Rest following strenuous physical activity, carbohydrate ingestion, emotional stress and exposure to cold are the precipitating triggers. Most of the mutations act in a dominant-negative fashion, either through a trafficking dysfunction or through Kir2.1-phosphatidyl inositol bisphosphate binding defect. We have identified two families that were diagnosed with periodic paralysis and cardiac abnormalities, but only discrete development features. The proband in one of the two families reported having his symptoms occurring twice within the day following corticosteroids ingestion, and alleviated after stopping the corticosteroid treatment. Electromyographic evaluations pointed out to a typical hypokalemic periodic paralysis pattern. Molecular screening of the KCNJ2 gene identified two mutations leading to C54F and T305P substitutions in the Kir2.1 protein. Functional expression in mammalian cells revealed a loss-of-function of the mutated channels and a dominant-negative effect when both mutants and wild-type channels are present in the same cell. However, channel trafficking and assembly are not affected. Substitutions at these residues may interfere with phosphatidyl inositol bisphosphate binding to Kir2.1 channels. Sensitivity of our patients to multiple corticosteroid administrations shows that care must be taken in the use of such treatments in AS patients. Taken together, our data suggest the inclusion of the KCNJ2 gene in the molecular screening of patients with periodic paralysis, even when the classical AS dysmorphic features are not present.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
RESULTS
 DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
K+ channels are involved in a number of cellular processes that include repolarization, setting rest membrane potential and maintaining the electrolyte balance. Inward rectifier K+ channels are widely expressed in human tissues and are involved in many aspects of cell functions including excitability and differentiation. In excitable and non-excitable tissues, the Kir family has been shown to contribute to the resting of membrane potential, pacing of neuronal and cardiac myocytes, regulation of insulin secretion and renal transport (1). The Kir2 subfamily exhibits a strong inward rectification because of polyamines and Mg2+ block (2–5). The peptide consists of 428 amino acid residues that are predicted to have a secondary structure with an N terminus, followed by two membrane-spanning domains (M1 and M2) and a C-terminal part. The Kir2.1 inward rectifier channel may assemble as a homo- or hetero-tetramer to fashion a complex pore-forming protein (6). The Kir2.1 protein is encoded by the KCNJ2 gene, which has been associated with Andersen's syndrome (AS), short QT syndrome and atrial fibrillation (7–9). Over 20 KCNJ2 mutations have been described in many AS kindreds (7,10–18). AS patients share many clinical phenotypes that include periodic paralysis, cardiac arrhythmia and bone malformation as has been described in the first AS family (19). These diagnostic criteria have recently been extended to include skeletal and dental aspects (17,20). In AS, episodes of periodic paralysis are usually triggered by rest post-exercise, stress and carbohydrate intake. The precipitating factors reported in AS patients are quite similar to those reported for patients with other forms of periodic paralyses. However, corticosteroid intake has not been reported as a precipitating trigger in any of the AS patients. Here, we report two independent families carrying two novel KCNJ2 mutations. One of the identified AS families is of a particular interest because the proband has reported corticosteroids as being the trigger for two major attacks of periodic paralysis, that led to the diagnosis. We have successfully developed an electromyographic test on patients with discrete phenotype that can provide valuable information towards patient diagnosis. In addition, we carried out functional characterization of the two mutations to understand how they underlay the disease in the two families.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
Electromyography
Electromyographic tests were performed in proband 1 (Fig. 1). The long exercise test (5-min duration) revealed a drastic and prolonged decrement in compound muscle action potential (CMAP) amplitude of the exercised muscle, beginning 10 min after exercise completion (Fig. 2) and worsening during the post-exercise rest (nadir: –69% reached 40 min after the end of the exercise). There was neither increment in the CMAP amplitude during the first seconds immediately after long exercise nor CMAP change after short exercise. These results were typical of the electromyographic (EMG) signs of abnormal, decreased muscle excitability described in HypoPP because of CACNA1S mutations, SCN4A mutations (21) or KCNJ2 mutations (16,22). As first molecular analyses failed to reveal the most recurrent CACNA1S and SCN4A mutations responsible for HypoPP, EMG pattern suggested searching for KCNJ2 mutations, which turned out to be positive.


Figure 1
View larger version (6K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Figure 1. Pedigrees of two AS families. Pedigrees of two families with AS phenotypes and are associated to mutation in the KCNJ2 gene. Circles represent females, squares represent males, affected members are shown with solid symbols. Arrows indicate probands. Genotyped individuals are shown with (+) for mutation carriers and with (–) for non-carriers. Deceased individuals are shown with a cross-bar.

 


Figure 2
View larger version (9K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Figure 2. Long exercise test of the AS patient with C54F mutation. The CMAPs of the ADM were recorded with skin electrodes following the ulnar nerve stimulation at wrist before and after exercise. (A) Pre-exercise (top trace) and post-exercise recordings (below) at different times following the trial (Ex) as indicated left to the tracings. Scale between two dots: 5 ms, 5 mV. (B) Changes in CMAP amplitude of ADM muscle following long exercise. The amplitude of the CMAP expressed as a percentage of its pre-exercise value is plotted against the time elapsed after the exercise trial. Open circles: changes of CMAP amplitude in 30 control subjects (mean ± S.E.M.). Solid circles and squares: changes of CMAP amplitude in patient with C54F substitution.

 
Novel Kir2.1 mutations at residues C54 and T305
Using direct sequencing of the solely known AS gene, we identified two novel mutations in two unrelated families with AS phenotype. Both probands were heterozygous for each mutation. Mutation G489T found in family 1 (the proband, the brother and the father) yield to C54F mutation in the kir2.1 protein, and is located in a well-conserved region of the N terminus. Mutation A1141C changed the threonine residue at position 305 to proline (T305P), located in the C-terminal part of the protein and is conserved as well among inward rectifier K+-channel family (Fig. 3), suggesting an important role of these residues in channel function.


Figure 3
View larger version (76K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Figure 3. (A) Alignment of amino acid sequences around the residues that have been modified in the Kir2.1 protein for AS patients. The modified residues are shown in bold in Kir2.1 and in the other Kir channels when they are conserved. (B) A cartoon of one subunit of the kir2.1 protein showing the localization of C54 and T305 residues where two AS mutations occurred. (C) Localization of residue T305 on the crystal structure of the kirBac1.1. Residue C54 cannot be shown on this representation, it corresponds to residue 33 in the kirbac1.1 primary sequence that has known crystal structure from residue 39 only.

 
Dominant-negative pattern
KCNJ2 wild-type (WT) as well as G489T and A1141C mutants were subcloned into the pXOOM mammalian expression vector, and expressed in COS-7 cells. This vector is a bi-cistronic vector expressing KCNJ2 genes in the first site and enhanced green fluorescent protein (EGFP) in the second site, allowing the identification of positively transfected cells. Whole-cell patch-clamp technique was employed to monitor currents in transfected cells. As shown in Figure 4, WT channels showed normal inward rectifier currents. However, we were unable to record any current from both type of cells transfected with either kir2.1-C54F or kir2.1-T305P.


Figure 4
View larger version (8K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Figure 4. (A) Whole-cell current traces from COS-7 cells that were transfected with KCNJ2WT, KCNJ2C54F, and KCNJ2T305P. Cells were held to –80 mV, then depolarized to various test potentials (–120 to +40 mV) for 200-ms duration in 20-mV increment. Both mutants failed to produce any current when expressed alone. (B) Current density is shown for a range of test potentials starting at – 120 mV. Each value represents the average of n cells for KCNJ2WT-DsRed (10), KCNJ2C54F (10), KCNJ2T305P (12), KCNJ2C54F-GFP/KCNJ2WT-DsRed (10), KCNJ2T305P-GFP/ KCNJ2WT-DsRed (9). Values are mean±S.E.M.

 
As both patients were heterozygous for the mutations, and because most of the AS mutants had a dominant-negative effects, we set to test the effect of co-expression of WT and mutants in the same cells. To make sure that both WT and mutant DNA are introduced into the same cell, we fused WT channels to DsRed monomer protein and mutant channels to EGFP. We and others have shown that fusion of fluorescent tags to kir2.1 protein did not affect either its biophysical properties nor its cell trafficking behavior (23). C54F-EGFP and T305P-EGFP were introduced into the first cloning site of the pIRES bi-cistronic vector. WT-DsRed fusion protein was introduced into the second cloning site of the same vector. We have also engineered pIRES constructs with WT-EGFP in the first site and WT-DsRed in the second site to allow accurate comparison of current density between all of our constructs. Figure 4 shows that both mutations have a dominant-negative behavior when co-expressed with WT channels. A small current was recorded with C54F-EGFP/WT-DsRed and T305P-GfP/WT-DsRed constructs which may represent the small fraction (1/16) of the proteins made of WT channels only.

Cellular distribution
Confocal microscopy imaging was used to monitor channel distribution of EGFP- and DsRed-fused channels. Our data show that all the constructs had a normal membrane localization (Fig. 5), suggesting that these mutations did not alter or interfere with any trafficking signal on the kir2.1 protein. After merging the two pictures (mutant-EGFP and WT-DsRed constructs), a yellow color was present at cell membrane suggesting that WT-DsRed and mutant-EGFP channels are in a very close vicinity.


Figure 5
View larger version (59K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Figure 5. Assembly and trafficking of AS mutant channels. Confocal microscopy images of KCNJ2 clones expressed in COS-7 cells. Cells were transiently transfected and images were taken 48 h later. Each KCNJ2 clone was fused to either DsRedmonomer (WT) or EGFP (C54F and T305P). Both EGFP (B) and DsRed monomer (C) show a cytoplasmic diffuse fluorescent pattern. However, KCNJ2-DsRedmonomer (A,D,G), KCNJ2C54F-EGFP (E) and KCNJ2T305P-EGFP (H) are localized to the plasma membrane. Magnification: 63x, using a Leica microscope. For cellular co-localization (D–I), cells were transfected with pIRES plasmids containing KCNJ2-EGFP, KCNJ2C154F-EGFP or KCNJ2T309I-EGFP in the first cloning site and KCNJ2-DsRed monomer in the second cloning site. Yellow color indicates overlapping localization.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
 DISCUSSION
MATERIALS AND METHODS
 REFERENCES
 
We have identified two unrelated families with AS clinical phenotypes: periodic paralysis, cardiac abnormalities and discreet developmental aspects. The proband in family 1 suffered severe episodic paralysis that was first triggered by corticosteroid intake. Three years later, despite his acetazolamide and potassium supplement treatment, he went through another severe attack (periodic paralysis, arrhythmia) just after starting another corticosteroid therapy. Twenty-four hours later, all his problems returned to normal after stopping the corticosteroid treatment in both cases. However, EMG evaluation revealed a delayed decrease in CMAP amplitude after long exercise. This decrease in muscle membrane excitability could account for exercise-induced episodes of weakness. After a negative patient DNA screening for known mutations in SCN4A and CNCA1S genes, in the absence of clear clinical phenotype, our EMG tests revealed a pattern that fits with HypoPP patients. Molecular patient diagnosis became easier to identifying a mutation on the KCNJ2 gene. Both the father and the brother of proband 1, presenting with the same mutation, have normal life without any signs related to AS. The absence of any AS phenotype in the brother and the father is reminiscent of incomplete penetrance that has already been observed among AS families. AS phenotype may vary from family to family, and even between affected members of the same family, with a significant degree of non-penetrance (11,12,24). To our knowledge, this is the first case of an AS patient that has symptoms triggered with corticosteroid intake. Another case has been recently described but for a patient having thyrotoxic periodic paralysis (25). Muscle weakness and wasting are common complications of corticosteroid administration (26). In our patient, corticosteroid intake may have produced a depletion of serum K+-ions likely through their mineralocorticoid activity leading to hypokalemia, or may have affected K+-channel activity.

Family 2 has a classical AS pattern without dysmorphic features: periodic paralysis and cardiac dysrhythmia are prominent in the proband and family members.

Molecular screening of the KCNJ2 gene in both probands identified two novel mutations: C54F and T305P. C54 and T305 are located in the N and C terminus portions, respectively, of the Kir2.1 protein and are well conserved within the inward rectifier channel family. C54 is located in a region of the Kir2.1 protein that has been involved in PIP2 binding. Indeed, Lopes et al. (27) demonstrated that arginine 50 and histidine 53 altered channel–kir2.1-PIP2 interaction when they were neutralized. In addition, this region is quite conserved between kir family members. It has been suggested that C49 of kir1.1 (corresponding to C54 in Kir2.1) is involved in a pH-dependent gating of this channel (28). This gating mechanism involves interaction of the proximal N terminus and the middle C terminus of the kir channels (29). These interactions would contribute to the formation of a gating ring just inside the cytoplasm in a similar way to that described for Ca2+-activated K+-channel MthK (30,31). Garneau et al. (32) failed to provide evidence for significant changes in gating properties when C54 residue was mutated to either a valine or a serine. Taken together, these data do not support the involvement of residue C54 in a disulfide bond but may rather participate to a structure that is important for Kir2.1-channel gating.

Residue T305 is located in a quite complex region: this residue is located in a close vicinity to residues that have already been involved in Kir2.1-PIP2 binding (K303, R312) and in channel trafficking (S314, Y315, L316). However, our confocal imaging data show normal trafficking of the mutated channels ruling out the involvement of this residue in any trafficking signaling on this channel. We hypothesize that T305 may destabilize Kir2.1-PIP2 binding leading to non-functional channels. This region of the channel, starting at residue 300 and ending at residue 315, seems to be a hotspot for AS mutations, as eight substitutions have been reported (G300V/D, V302M, E303K, T305P, T309I, R312C and {Delta}SY314-315). Pegan et al. (33) have recently resolved the structure of this region of the channel to 2.0 Å, and have shown that this region belongs to the G-loop that is involved in intra- and inter-subunit salt bridges that mainly affect channel gating.

Both mutations showed a loss-of-function when expressed alone and a dominant-negative behavior when co-expressed with the WT channels in mammalian cells, suggesting that the defective channels do co-assemble with WT channels to poison the protein complex, a behavior that is similar to that seen for most AS mutations. The amplitude of the current recorded in the presence of both WT and mutated channels suggests that only one defective subunit in the protein complex may be required for channel silencing. These data suggest that these two residues are not involved in channel assembly or trafficking. This conclusion is supported by confocal microscopy images showing normal trafficking of the mutated channels and a more likely normal assembly.

In conclusion, we report clinical and functional characterizations of two novel AS mutations that have classical dominant-negative behavior. Our clinical data reveal that AS patients may have their symptoms triggered by corticosteroid intake. It would be of interest to determine the nature of corticosteroids that are involved, the mechanism underlying the exacerbation of the phenotype and the incidence of such phenomenon on a larger AS population. Until then, care must be taken in using corticosteroid with patient harboring AS phenotypes. In addition, our study reveal that, in addition to AS triad phenotypes, KCNJ2 mutations may lead to periodic paralysis and abnormal EMG tests with mild or no AS dysmorphic features. This suggests to search for KCNJ2 mutations in patients with periodic paralysis, when molecular screening fails to reveal CACNA1S or SCN4A mutations.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
 DISCUSSION
 MATERIALS AND METHODS
REFERENCES
 
Case histories
Clinical studies were conducted after patients signed a consent form approved by the French and European Union bioethics law, and conformed with the Declaration of Helsinki. Patients were examined by one of the authors (S.G., D.M. or E.F.). Exams included electrocardiogram (ECG), EMG, CT scan and clinical electrophysiological study.

In family 1, the proband is a 19-year-old man with no family history (Fig. 1). He has a small chin, but no other noticeable dysmorphic features.

At the age of 15, the proband has experienced a restricted chin eruption that was first thought to be a herpes infection, and was later extended to the whole chin. He had then a local treatment associated with prednisolone, a corticosteroid-based anti-inflammatory drug. The first day of the corticosteroid intake, he reported important fatigue and difficulty to walk upstairs. When he woke up the next day, he was unable to sit down. At the hospital, he had hard time moving the upper limbs, and was unable to stand up. He complained from small muscle pain. The ECG showed extrasystoles, U waves and bigeminy. His blood exam revealed hypokalemia (2.2 mEq/L). His creatine phosphokinase (CPK) level was slightly over normal at 211 U/I (normal <174 U/I). His symptoms disappeared 24 h later: he recovered almost all his movements, ECG was normal (with no extrasystolis), and kalemia returned to normal. During the following 4 weeks, he did not develop paralysis but he complained of muscle pain. No other corticosteroid side effect has been reported. His CPK level was as high as 997 U/I. He is under Diomax, Tenormine (ß-blocker) and a potassium supplement. Since then, he had few periodic paralysis attacks, that were severe, and one of them was again triggered by corticosteroid therapy following an important urticaria of the upper and lower limbs. Beside corticosteroid intake, we were unable to determine other periodic paralysis triggering factors.

The proband in family 2 is a 23-year-old woman with no noticeable dysmorphic features. She reported having difficulties practicing sport at school at younger age. She described pain in lower limbs making it harder to walk during couple of days. Pain and weakness were not particularly triggered by exercise, rest after exercise, food or cold. She has full strength in upper limbs but permanent motor deficit in lower limbs. No muscle atrophy or myotonia was observed during her clinical examination. Muscle biopsy was normal. Clinical examination and muscle biopsy are in favor of a hypokalemic periodic paralysis pattern. ECG revealed ventricular arrhythmia, bidirectional tachycardia and extrasystolis. Family history shows cardiac arrhythmia in the mother, her aunt and grandmother (has a pacemaker), but a healthy brother (Fig. 1).

Electromyography
Electromyographic evaluations were performed using a protocol recently described (21). CMAP was recorded at the right and left abductor digiti minimi (ADM) muscles following supramaximal stimulation of ulnar nerves at the wrist. The effects of two kinds of exercises were tested: (1) short exercise (10 s) of the left ADM muscle, with recording of the CMAP immediately after exercise cessation and then every 10 s for 1 min; (2) long exercise (5 min) of the right ADM muscle, with CMAP recording immediately after exercise completion, and then every minute for 5 min and every 5 min for 40 min. CMAP amplitude, duration and area were expressed as a percentage of the reference values measured before exercise. Changes in CMAP amplitude were compared to those observed in 30 healthy individuals.

Molecular diagnosis
Patients' DNA was extracted from peripheral blood leukocytes and used as a template for screening and subcloning. Whole KCNJ2 open reading frame was PCR-amplified using pfu taq DNA polymerase (Promega, USA). PCR product was cloned into the pGEM-T vector (Promega, USA), and the clones were directly sequenced. Mutation-containing clones were PCR-amplified with primers flanked with restriction enzyme sequences: BamHI for cloning into the pXOOM vector, or EcoRI and SacII for cloning into the pEGFP vector. The latter allowed fusion of the EGFP to the C terminus of the Kir2.1 WT or mutant protein. Kir2.1 WT protein (WT human cardiac KCNJ2 was obtained in the plasmid pBluescript KS (-) as a gift from Dr Vandenberg, University of California San Francisco, USA) was also fused to DsRed monomer fluorescent protein using the same restriction enzymes.

The mutated fusion proteins were PCR-amplified using primers flanked with NheI and EcoRI sequences for subsequent cloning into the first cloning site of the pIRES vector (Clontech) under CMV promoter. Kir2.1-DsRed fusion was amplified with primers flanked with NotI site and subcloned into the second cloning site to generate a plasmid allowing simultaneous expression of WT and mutant protein. All PCR products and final constructs were sequenced to ensure fidelity.

Electrophysiology
COS-7 cells were maintained in Dulbecco's modified Eagle media supplemented with 10% fetal bovine serum and 100 µg/mL streptomycin, 100 U/mL penicillin, at 37°C in a humidified 5% CO2 atmosphere. COS-7 cells were transiently transfected by DEAE-Dextran precipitate method using 200 ng Kir2.1WT or mutant DNA per 35-mm culture dish. Currents were recorded 48 h after transfection.

Recordings were conducted in the whole-cell configuration (34) at room temperature (~22°C), using an EPC 10 amplifier (HEKA Electronic, Germany). The pipette solution contained (mM): 150 KCl, 0.5 MgCl2, 5 EGTA and 10 HEPES, pH 7.3. The bathing media were (mM): 150 NaCl, 5 KCl, 2 CaCl2, 1 MgCl2 and 10 HEPES, pH 7.3. Pipette resistance was 1.5–4 Mohm. Membrane currents were elicited by depolarizations ranging from – 120 to +40 mV, from a holding potential of – 80 mV. Only cells with series resistance less than 5 Mohm were used for analysis. Data acquisition and analysis were performed using Patchmaster and Pulsefit (HEKA Electronic, Germany) and IgorPro (WaveMetrics, Inc., Oregon, USA) softwares.

Confocal microscopy imaging
COS-7 cells were transiently transfected with DNA encoding for EGFP, DsRed monomer (DsRed), Kir2.1-EGFP, Kir2.1-DsRed, Kir2.1C54F-EGFP, Kir2.1T305P-EGFP, Kir2.1-DsRed/Kir2.1-EGFP, Kir2.1-DsRed/Kir2.1C54F-EGFP and Kir2.1-DsRed/Kir2.1T305P-EGFP. COS-7 cells were cultured on a cover slip and transiently transfected with 750 ng of each DNA per 35-mm culture dish using DEAE Dextran. Confocal microscopy (Leica) images were taken 48 h later with 63-magnification lens.


   ACKNOWLEDGEMENTS
 
The authors thank the patients for their kind participation. We also thank Drs B. Fontaine, S. Vicart and D. Sternberg for their contribution to this work. We thank N. Leroudier for DNA sequencing and F. Brau for his help with confocal microscopy. This work was supported by the Centre National de la Recherche Scientifique, AFM grant (S.B. and J.B.) and Résocanaux.

Conflict of Interest statement. None declared.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
 DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 

  1. Hille B. Ionic Channels of Excitable Membranes. Massachusetts: Sinauer Associates.

  2. Fakler B., Brandle U., Glowatzki E., Weidemann S., Zenner H.P., Ruppersberg J.P. Strong voltage-dependent inward rectification of inward rectifier K+ channels is caused by intracellular spermine. Cell (1995) 80:149–154.[CrossRef][ISI][Medline]

  3. Lu Z., MacKinnon R. Electrostatic tuning of Mg2+ affinity in an inward-rectifier K+ channel. Nature (1994) 371:243–246.[CrossRef][Medline]

  4. Silver M.R., DeCoursey T.E. Intrinsic gating of inward rectifier in bovine pulmonary artery endothelial cells in the presence or absence of internal Mg2+. J. Gen. Physiol. (1990) 96:109–133.[Abstract/Free Full Text]

  5. Ficker E., Taglialatela M., Wible B.A., Henley C.M., Brown A.M. Spermine and spermidine as gating molecules for inward rectifier K+ channels. Science (1994) 266:1068–1072.[Abstract/Free Full Text]

  6. Yang J., Jan Y.N., Jan L.Y. Determination of the subunit stoichiometry of an inwardly rectifying potassium channel. Neuron (1995) 15:1441–1447.[CrossRef][ISI][Medline]

  7. Plaster N.M., Tawil R., Tristani-Firouzi M., Canun S., Bendahhou S., Tsunoda A., Donaldson M.R., Iannaccone S.T., Brunt E., Barohn R., et al. Mutations in Kir2.1 cause the developmental and episodic electrical phenotypes of Andersen's syndrome. Cell (2001) 105:511–519.[CrossRef][ISI][Medline]

  8. Priori S.G., Pandit S.V., Rivolta I., Berenfeld O., Ronchetti E., Dhamoon A., Napolitano C., Anumonwo J., di Barletta M.R., Gudapakkam S., et al. A novel form of short QT syndrome (SQT3) is caused by a mutation in the KCNJ2 gene. Circ. Res (2005) 96:800–807.[Abstract/Free Full Text]

  9. Xia M., Jin Q., Bendahhou S., He Y., Larroque M.M., Chen Y., Zhou Q., Yang Y., Liu Y., Liu B., et al. A Kir2.1 gain-of-function mutation underlies familial atrial fibrillation. Biochem. Biophys. Res. Commun. (2005) 332:1012–1019.[CrossRef][ISI][Medline]

  10. Ai T., Fujiwara Y., Tsuji K., Otani H., Nakano S., Kubo Y., Horie M. Novel KCNJ2 mutation in familial periodic paralysis with ventricular dysrhythmia. Circulation (2002) 105:2592–2594.[Abstract/Free Full Text]

  11. Andelfinger G., Tapper A.R., Welch R.C., Vanoye C.G., George A.L. Jr, Benson D.W. KCNJ2 mutation results in Andersen syndrome with sex-specific cardiac and skeletal muscle phenotypes. Am. J. Hum. Genet. (2002) 71:663–668.[CrossRef][ISI][Medline]

  12. Tristani-Firouzi M., Jensen J.L., Donaldson M.R., Sansone V., Meola G., Hahn A., Bendahhou S., Kwiecinski H., Fidzianska A., Plaster N., et al. Functional and clinical characterization of KCNJ2 mutations associated with LQT7 (Andersen syndrome). J. Clin. Invest. (2002) 110:381–388.[CrossRef][ISI][Medline]

  13. Donaldson M.R., Jensen J.L., Tristani-Firouzi M., Tawil R., Bendahhou S., Suarez W.A., Cobo A.M., Poza J.J., Behr E., Wagstaff J., et al. PIP2 binding residues of Kir2.1 are common targets of mutations causing Andersen syndrome. Neurology (2003) 60:1811–1816.[Abstract/Free Full Text]

  14. Hosaka Y., Hanawa H., Washizuka T., Chinushi M., Yamashita F., Yoshida T., Komura S., Watanabe H., Aizawa Y. Function, subcellular localization and assembly of a novel mutation of KCNJ2 in Andersen's syndrome. J. Mol. Cell. Cardiol. (2003) 35:409–415.[CrossRef][ISI][Medline]

  15. Chun T.U., Epstein M.R., Dick M. II, Andelfinger G., Ballester L., Vanoye C.G., George A.L. Jr, Benson D.W. Polymorphic ventricular tachycardia and KCNJ2 mutations. Heart Rhythm (2004) 1:235–241.[CrossRef][ISI][Medline]

  16. Bendahhou S., Fournier E., Sternberg D., Bassez G., Furby A., Sereni C., Donaldson M.R., Larroque M.M., Fontaine B., Barhanin J. In vivo and in vitro functional characterization of Andersen's syndrome mutations. J. Physiol. (2005) 565:731–741.[Abstract/Free Full Text]

  17. Davies N.P., Imbrici P., Fialho D., Herd C., Bilsland L.G., Weber A., Mueller R., Hilton-Jones D., Ealing J., Boothman B.R., et al. Andersen–Tawil syndrome: new potassium channel mutations and possible phenotypic variation. Neurology (2005) 65:1083–1089.[Abstract/Free Full Text]

  18. Ballester L.Y., Benson D.W., Wong B., Law I.H., Mathews K.D., Vanoye C.G., George A.L., Jr. Trafficking-competent and trafficking-defective KCNJ2 mutations in Andersen syndrome. Hum. Mutat. (2006) 27:388.[Medline]

  19. Andersen E.D., Krasilnikoff P.A., Overvad H. Intermittent muscular weakness, extrasystoles, and multiple developmental anomalies: a new syndrome? Acta Paediatr. Scand. (1971) 60:559–564.[ISI][Medline]

  20. Yoon G., Oberoi S., Tristani-Firouzi M., Etheridge S.P., Quitania L., Kramer J.H., Miller B.L., Fu Y.H., Ptacek L.J. Andersen–Tawil syndrome: prospective cohort analysis and expansion of the phenotype. Am. J. Med. Genet. A (2006) 140:312–321.[Medline]

  21. Fournier E. Electromyography guides towards subgroups of ion channel mutations in periodic paralyses and myotonias. Ann. Neurol. (2004) 56:650–661.[CrossRef][ISI][Medline]

  22. Katz J.S., Wolfe G.I., Iannaccone S., Bryan W.W., Barohn R.J. The exercise test in Andersen syndrome. Arch. Neurol. (1999) 56:352–356.[Abstract/Free Full Text]

  23. Bendahhou S., Donaldson M.R., Plaster N.M., Tristani-Firouzi M., Fu Y.H., Ptacek L.J. Defective potassium channel Kir2.1 trafficking underlies Andersen–Tawil syndrome. J. Biol. Chem. (2003) 278:51779–51785.[Abstract/Free Full Text]

  24. Sansone V., Griggs R.C., Meola G., Ptacek L.J., Barohn R., Iannaccone S., Bryan W., Baker N., Janas S.J., Scott W., et al. Andersen's syndrome: a distinct periodic paralysis. Ann. Neurol. (1997) 42:305–312.[CrossRef][ISI][Medline]

  25. Liu Z., Braverman L.E., Malabanan A. Thyrotoxic periodic paralysis in a Hispanic man after the administration of prednisone. Endocr. Pract. (2006) 12:427–431.[Medline]

  26. Kaminski H.J., Ruff R.L. Endocrine myopathies (hyper- and hypo-function of adrenal, thyroid, pituitary, and parathyroid glands) and iatrogenic corticosteroid myopathy. In: Myology—Engel A., Franzini-Armstrong C., eds. (1994) New York: McGraw-Hill. 1726–1753.

  27. Lopes C.M., Zhang H., Rohacs T., Jin T., Yang J., Logothetis D.E. Alterations in conserved Kir channel-PIP(2) interactions underlie channelopathies. Neuron (2002) 34:933–944.[CrossRef][ISI][Medline]

  28. Schulte U., Hahn H., Wiesinger H., Ruppersberg J.P., Fakler B. pH-dependent gating of ROMK (Kir1.1) channels involves conformational changes in both N and C termini. J. Biol. Chem. (1998) 273:34575–34579.[Abstract/Free Full Text]

  29. Guo Y., Waldron G.J., Murrell-Lagnado R. A role for the middle C terminus of G-protein-activated inward rectifier potassium channels in regulating gating. J. Biol. Chem. (2002) 277:48289–48294.[Abstract/Free Full Text]

  30. Jiang Y., Lee A., Chen J., Cadene M., Chait B.T., MacKinnon R. The open pore conformation of potassium channels. Nature (2002) 417:523–526.[CrossRef][Medline]

  31. Jiang Y., Lee A., Chen J., Cadene M., Chait B.T., MacKinnon R. Crystal structure and mechanism of a calcium-gated potassium channel. Nature (2002) 417:515–522.[CrossRef][Medline]

  32. Garneau L., Klein H., Parent L., Sauve R. Contribution of cytosolic cysteine residues to the gating properties of the Kir2.1 inward rectifier. Biophys. J. (2003) 84:3717–3729.[ISI][Medline]

  33. Pegan S., Arrabit C., Slesinger P.A., Choe S. Andersen's syndrome mutation effects on the structure and assembly of the cytoplasmic domains of Kir2.1. Biochemistry (2006) 45:8599–8606.[CrossRef][Medline]

  34. Hamill O.P., Marty A., Neher E., Sakmann B., Sigworth F.J. Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. Pflugers Arch. (1981) 391:85–100.[CrossRef][ISI][Medline]


Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?



This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
16/8/900    most recent
ddm034v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (2)
Right arrowRequest Permissions
Google Scholar
Right arrow Articles by Bendahhou, S.
Right arrow Articles by Barhanin, J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Bendahhou, S.
Right arrow Articles by Barhanin, J.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?