Neuronal Voltage-gated Potassium Channels Research Articles

Discovery of a heme-binding domain in a neuronal voltage-gated potassium channel

The EAG (ether-à-go-go) family of voltage-gated K+ channels are important regulators of neuronal and cardiac action potential firing (excitability) and have major roles in human diseases such as epilepsy, schizophrenia, cancer, and sudden cardiac death. A defining feature of EAG (Kv10-12) channels is a highly conserved domain on the N terminus, known as the eag domain, consisting of a Per-ARNT-Sim (PAS) domain capped by a short sequence containing an amphipathic helix (Cap domain). The PAS and Cap domains are both vital for the normal function of EAG channels. Using heme-affinity pulldown assays and proteomics of lysates from primary cortical neurons, we identified that an EAG channel, hERG3 (Kv11.3), binds to heme. In whole-cell electrophysiology experiments, we identified that heme inhibits hERG3 channel activity. In addition, we expressed the Cap and PAS domain of hERG3 in Escherichia coli and, using spectroscopy and kinetics, identified the PAS domain as the location for heme binding. The results identify heme as a regulator of hERG3 channel activity. These observations are discussed in the context of the emerging role for heme as a regulator of ion channel activity in cells.

Heteromeric Assembly of Truncated Neuronal Kv7 Channels: Implications for Neurologic Disease and Pharmacotherapy.

Neuronal voltage-gated potassium channels (Kv) are critical regulators of electrical activity in the central nervous system. Mutations in the KCNQ (Kv7) ion channel family are linked to epilepsy and neurodevelopmental disorders. These channels underlie the neuronal "M-current" and cluster in the axon initial segment to regulate the firing of action potentials. There is general consensus that KCNQ channel assembly and heteromerization are controlled by C-terminal helices. We identified a pediatric patient with neurodevelopmental disability, including autism traits, inattention and hyperactivity, and ataxia, who carries a de novo frameshift mutation in KCNQ3 (KCNQ3-FS534), leading to truncation of ∼300 amino acids in the C terminus. We investigated possible molecular mechanisms of channel dysfunction, including haplo-insufficiency or a dominant-negative effect caused by the assembly of truncated KCNQ3 and functional KCNQ2 subunits. We also used a recently recognized property of the KCNQ2-specific activator ICA-069673 to identify assembly of heteromeric channels. ICA-069673 exhibits a functional signature that depends on the subunit composition of KCNQ2/3 channels, allowing us to determine whether truncated KCNQ3 subunits can assemble with KCNQ2. Our findings demonstrate that although the KCNQ3-FS534 mutant does not generate functional channels on its own, large C-terminal truncations of KCNQ3 (including the KCNQ3-FS534 mutation) assemble efficiently with KCNQ2 but fail to promote or stabilize KCNQ2/KCNQ3 heteromeric channel expression. Therefore, the frequent assumption that pathologies linked to KCNQ3 truncations arise from haplo-insufficiency should be reconsidered in some cases. Subtype-specific channel activators like ICA-069673 are a reliable tool to identify heteromeric assembly of KCNQ2 and KCNQ3. SIGNIFICANCE STATEMENT: Mutations that truncate the C terminus of neuronal Kv7/KCNQ channels are linked to a spectrum of seizure disorders. One role of the multifunctional KCNQ C terminus is to mediate subtype-specific assembly of heteromeric KCNQ channels. This study describes the use of a subtype-specific Kv7 activator to assess assembly of heteromeric KCNQ2/KCNQ3 (Kv7.2/Kv7.3) channels and demonstrates that large disease-linked and experimentally generated C-terminal truncated KCNQ3 mutants retain the ability to assemble with KCNQ2.

Cilantro leaf harbors a potent potassium channel-activating anticonvulsant.

Herbs have a long history of use as folk medicine anticonvulsants, yet the underlying mechanisms often remain unknown. Neuronal voltage-gated potassium channel subfamily Q (KCNQ) dysfunction can cause severe epileptic encephalopathies that are resistant to modern anticonvulsants. Here we report that cilantro (Coriandrum sativum), a widely used culinary herb that also exhibits antiepileptic and other therapeutic activities, is a highly potent KCNQ channel activator. Screening of cilantro leaf metabolites revealed that one, the long-chain fatty aldehyde (E)-2-dodecenal, activates multiple KCNQs, including the predominant neuronal isoform, KCNQ2/KCNQ3 [half maximal effective concentration (EC50), 60 ± 20 nM], and the predominant cardiac isoform, KCNQ1 in complexes with the type I transmembrane ancillary subunit (KCNE1) (EC50, 260 ± 100 nM). (E)-2-dodecenal also recapitulated the anticonvulsant action of cilantro, delaying pentylene tetrazole-induced seizures. In silico docking and mutagenesis studies identified the (E)-2-dodecenal binding site, juxtaposed between residues on the KCNQ S5 transmembrane segment and S4-5 linker. The results provide a molecular basis for the therapeutic actions of cilantro and indicate that this ubiquitous culinary herb is surprisingly influential upon clinically important KCNQ channels.-Manville, R. W., Abbott, G. W. Cilantro leaf harbors a potent potassium channel-activating anticonvulsant.

Novel KV7 ion channel openers for the treatment of epilepsy and implications for detrusor tissue contraction

Neuronal voltage-gated potassium channels, KV7s, are the molecular mediators of the M current and regulate membrane excitability in the central and peripheral neuronal systems. Herein, we report novel small molecule KV7 openers that demonstrate anti-seizure activities in electroshock and pentylenetetrazol-induced seizure models without influencing Rotarod readouts in mice. The anti-seizure activity was determined to be proportional to the unbound concentration in the brain. KV7 channels are also expressed in the bladder smooth muscle (detrusor) and activation of these channels may cause localized undesired effects. Therefore, the impact of individual KV7 isoforms was investigated in human detrusor tissue using a panel of KV7 openers with distinct activity profiles among KV7 isoforms. KCNQ4 and KCNQ5 mRNA were highly expressed in detrusor tissue, yet a compound that has significantly reduced activity on homomeric KV7.4 did not reduce detrusor contraction. This may suggest that the homomeric KV7.4 channel plays a less significant role in bladder contraction and further investigation is needed.

Neuronal Voltage Gated Potassium Channels May Modulate Nitric Oxide Synthesis in Corpus Cavernosum.

Potassium channels (K+Ch) in corpus cavernosum play an important role in the regulation of erection. Nitric oxide (NO) acts through opening of K+Ch leading to hyperpolarization and relaxation.Aim : This study aims to update knowledge about the role of voltage-gated K+Ch (KV) channels in erectile machinery and investigate their role in the control of NO action &/or synthesis in the corpus cavernosum.Methods : Tension studies using isolated rabbit corpus cavernosum (CC) strips and rat anococcygeus muscle were conducted. Results are expressed as mean ± SEM.Results : Electric field stimulation (EFS, 2–16 Hz) evoked frequency-dependent relaxations of the PE (phenylephrine)-precontracted CC strips. At 2 Hz, EFS-induced relaxation amounted to 73.17 ± 2.55% in presence 4-AP (10−3 M) compared to 41.98 ± 1.45% as control. None of the other selective K+Ch blockers tested inhibited EFS-induced relaxation. 4-AP (10−3M) significantly attenuated ACh-induced relaxation of rabbit CC where dose-response curve was clearly shifted upward, and attenuated SNP- induced relaxation, for example, to 49.28 ± 4.52% compared to 65.53 ± 3.01% as control at 10−6 M SNP. The potentiatory effect of 4-AP on EFS was abolished or reversed in presence of NG-nitro-L-arginine (L-NNA, non-selective nitric oxide synthase inhibitor, 10−5M, and 2 × 10−4M). Same results were observed in rat anococcygeus muscle which is a part of the erectile machinery in rats.Conclusion : This study provides evidence for the presence of prejunctional voltage-gated K+Ch in CC, the blockade of which may increase the neuronal synthesis of NO.

Oxidation potentials of N-modified derivatives of the analgesic flupirtine linked to potassium KV 7 channel opening activity but not hepatocyte toxicity.

Openers of neuronal voltage-gated potassium channels (KV ) are of interest as therapeutic agents for treating pain (flupirtine) and epilepsy (retigabine). In an effort to better understand the mechanisms of action and toxicity of flupirtine, we synthesized nine novel analogues with varying redox behavior. Flupirtine can be oxidatively metabolized into azaquinone diimines; thus, the oxidation potentials of flupirtine and its analogues were measured by cyclic voltammetry. KV 7.2/3 (KCNQ2/3) opening activity was determined by an established assay with HEK293 cells overexpressing these channels. A link was found between the oxidation potentials of the compounds and their EC50 values for potassium channel opening activity. On the other hand, no correlation was observed between oxidation potentials and cytotoxicity in cultures of transgenic mouse hepatocytes (TAMH). These results support the idea that oxidative metabolites of flupirtine contribute to the mechanism of action, similar to what was recently proposed for acetaminophen (paracetamol), but not to hepatotoxicity.

Can Neuronal Voltage-Gated Potassium Channels Be Associated With Parkinsonism? (P3.089)

Can Neuronal Voltage-Gated Potassium Channels Be Associated With Parkinsonism? (P3.089)

N-Linked glycan site occupancy impacts the distribution of a potassium channel in the cell body and outgrowths of neuronal-derived cells

BackgroundVacancy of occupied N-glycosylation sites of glycoproteins is quite disruptive to a multicellular organism, as underlined by congenital disorders of glycosylation. Since a neuronal component is typically associated with this disease, we evaluated the impact of N-glycosylation processing of a neuronal voltage gated potassium channel, Kv3.1b, expressed in a neuronal-derived cell line, B35 neuroblastoma cells. MethodsTotal internal reflection fluorescence and differential interference contrast microscopy measurements of live B35 cells expressing wild type and glycosylation mutant Kv3.1b proteins were used to evaluate the distribution of the various forms of the Kv3.1b protein in the cell body and outgrowths. Cell adhesion assays were also employed. ResultsMicroscopy images revealed that occupancy of both N-glycosylation sites of Kv3.1b had relatively similar amounts of Kv3.1b in the outgrowth and cell body while vacancy of one or both sites led to increased accumulation of Kv3.1b in the cell body. Further both the fully glycosylated and partially glycosylated N229Q Kv3.1b proteins formed higher density particles in outgrowths compared to cell body. Cellular assays demonstrated that the distinct spatial arrangements altered cell adhesion properties. ConclusionsOur findings provide direct evidence that occupancy of the N-glycosylation sites of Kv3.1b contributes significantly to its lateral heterogeneity in membranes of neuronal-derived cells, and in turn alters cellular properties. General significanceOur study demonstrates that N-glycans of Kv3.1b contain information regarding the association, clustering, and distribution of Kv3.1b in the cell membrane, and furthermore that decreased occupancy caused by congenital disorders of glycosylation may alter the biological activity of Kv3.1b.

Insights From LGI1 and CASPR2 Potassium Channel Complex Autoantibody Subtyping

To determine, in patients identified as seropositive for neuronal voltage-gated potassium channel (VGKC) complex autoantibodies, the spectrum of clinical presentations and frequency of leucine-rich glioma-inactivated protein 1 (LGI1) and contactin-associated protein-like 2 (CASPR2) as defined antigenic neuronal targets in the VGKC macromolecular complex. Retrospective cohort study. Clinical practice, Mayo Clinic Neuroimmunology Laboratory and Department of Neurology. A total of 54 853 patients were evaluated, of whom 1992 were found to be VGKC complex IgG positive. From June 1, 2008, to June 30, 2010, comprehensive service serologic evaluation performed on 54853 patients with unexplained neurologic symptoms identified 1992 patients (4%) who were positive for VGKC complex IgG (values ≥ 0.03 nmol/L). Among 316 seropositive patients evaluated clinically at our institution, 82 (26%) were seropositive for LGI1 IgG and/or CASPR2 IgG. Of these 82 patients, 27% had low (0.03-0.09 nmol/L), 51% had medium (0.10-0.99 nmol/L), and 22% had high (≥ 1.00 nmol/L) VGKC complex IgG values. Leucine-rich glioma-inactivated protein 1 IgG positivity was associated with higher VGKC complex IgG values (P< .001) and cortical presentations (P< .001); CASPR2 IgG was associated with peripheral motor excitability (P= .009). However, neither autoantibody was pathognomonic for a specific neurologic presentation or correlated significantly with cancer. Neurologic phenotypes were diverse. Cerebrocortical manifestations (including cognitive impairment and seizures) were recorded in 76% of patients with LGI1 IgG alone (n=46) and 29% with CASPR2 IgG alone (n=28). Peripheral motor hyperexcitability was found in 21% of patients with CASPR2 IgG alone and 6.5% of patients with LGI1 IgG alone. The study emphasizes diverse and overlapping neurologic phenotypes across a range of VGKC complex IgG values and varying LGI1 IgG and CASPR2 IgG specificities. The frequent occurrence of LGI1 IgG and CASPR2 IgG in serum samples with low and medium VGKC complex IgG values supports the clinical significance of low values in clinical evaluation. Additional antigenic components of VGKC macromolecular complexes remain to be defined.

Converging Evidence for Epistasis between ANK3 and Potassium Channel Gene KCNQ2 in Bipolar Disorder.

Genome-wide association studies (GWAS) have implicated ANK3 as a susceptibility gene for bipolar disorder (BP). We examined whether epistasis with ANK3 may contribute to the “missing heritability” in BP. We first identified via the STRING database 14 genes encoding proteins with prior biological evidence that they interact molecularly with ANK3. We then tested for statistical evidence of interactions between SNPs in these genes in association with BP in a discovery GWAS dataset and two replication GWAS datasets. The most significant interaction in the discovery GWAS was between SNPs in ANK3 and KCNQ2 (p = 3.18 × 10−8). A total of 31 pair-wise interactions involving combinations between two SNPs from KCNQ2 and 16 different SNPs in ANK3 were significant after permutation. Of these, 28 pair-wise interactions were significant in the first replication GWAS. None were significant in the second replication GWAS, but the two SNPs from KCNQ2 were found to significantly interact with five other SNPs in ANK3, suggesting possible allelic heterogeneity. KCNQ2 forms homo- and hetero-meric complexes with KCNQ3 that constitute voltage-gated potassium channels in neurons. ANK3 is an adaptor protein that, through its interaction with KCNQ2 and KCNQ3, directs the localization of this channel in the axon initial segment (AIS). At the AIS, the KCNQ2/3 complex gives rise to the M-current, which stabilizes the neuronal resting potential and inhibits repetitive firing of action potentials. Thus, these channels act as “dampening” components and prevent neuronal hyperactivity. The interactions between ANK3 and KCNQ2 merit further investigation, and if confirmed, may motivate a new line of research into a novel therapeutic target for BP.

Interaction of Voltage-gated Sodium Channel Nav1.6 (SCN8A) with Microtubule-associated Protein Map1b

The mechanism by which voltage-gated sodium channels are trafficked to the surface of neurons is not well understood. Our previous work implicated the cytoplasmic N terminus of the sodium channel Na(v)1.6 in this process. We report that the N terminus plus the first transmembrane segment (residues 1-153) is sufficient to direct a reporter to the cell surface. To identify proteins that interact with the 117-residue N-terminal domain, we carried out a yeast two-hybrid screen of a mouse brain cDNA library. Three clones containing overlapping portions of the light chain of microtubule-associated protein Map1b (Mtap1b) were recovered from the screen. Interaction between endogenous Na(v)1.6 channels and Map1b in mouse brain was confirmed by co-immunoprecipitation. Map1b did not interact with the N terminus of the related channel Na(v)1.1. Alanine-scanning mutagenesis of the Na(v)1.6 N terminus demonstrated that residues 77-80 (VAVP) contribute to interaction with Map1b. Co-expression of Na(v)1.6 with Map1b in neuronal cell line ND7/23 resulted in a 50% increase in current density, demonstrating a functional role for this interaction. Mutation of the Map1b binding site of Na(v)1.6 prevented generation of sodium current in transfected cells. The data indicate that Map1b facilitates trafficking of Na(v)1.6 to the neuronal cell surface.

Autoimmune Autonomic Ganglionopathy Associated with Voltage-Gated Potassium Channel Antibodies (P05.209)

Objective: To report a case of autoimmune autonomic ganglionopathy (AAG) associated with neuronal voltage-gated potassium channel (VGKC) antibodies. Background Ganglionic acetylcholine receptor (AChR) autoantibodies have been described in patients with idiopathic autonomic neuropathies, and with further characterization of the pathophysiologic role of these antibodies, the terminology of this condition has changed to AAG. The majority of patients fulfilling clinical and laboratory criteria for AAG are, however, seronegative and additional pathogenetic antibodies have been postulated. Recently, an association between N-type calcium channel antibodies and AAG has been described. Design/Methods: A 65 year-old woman with a one year history of orthostatic intolerance, heat intolerance, diarrhea, and sicca complex underwent comprehensive autonomic and laboratory evaluations and was diagnosed with AAG associated with VGKC antibodies. She underwent serial standardized autonomic, clinical, and laboratory evaluations for 2 years, before and during treatment with intravenous immunoglobulin (IVIG). Results: During her initial evaluation, the patient was found to have widespread anhidrosis with otherwise essentially normal autonomic function. A paraneoplastic antibody panel was positive for VGKC antibodies, which did not react to recently recognized specific VGKC-associated antigens (Lgi1, Caspr2). A search for an occult malignancy remained negative. During subsequent evaluations, progressive cardiovascular adrenergic impairment was documented with evidence of orthostatic hypotension, associated with a rise in the antibody titer. At that time, treatment with IVIG was initiated. Six months after initiation of IVIG, autonomic testing had essentially normalized, associated with a notable decrease in antibody titer. Conclusions: AAG may be associated with autoimmune antibodies other than the classic ganglionic ACHR and the recently reported calcium-channel antibodies. Whether the VGKC antibodies in our patient have a pathophysiologic role or are nonspecific indicators of an underlying immune process remains subject for further study. This association is, however, important to recognize regardless of the underlying mechanism, considering this patient9s remarkable response to immunomodulatory therapy. Supported by: R.F. Kinney Executive Dean for Research Career Development Award and NIH (BIRCWH 5K12HD065987-02 and NS44233). Disclosure: Dr. Singer has nothing to disclose. Dr. Klein has received personal compensation for activities with Pfizer Inc as a consultant. Dr. McKeon has nothing to disclose. Dr. Low has received personal compensation for activities with Chelsea, Pfizer, and WR Medical Inc. as a consultant.Dr. Low has received personal compensation in an editorial capacity for Autonomic Neuroscience.

Seronegative Neuromyotonia and Congenital Hyperinsulinism with Mutation of the Inwardly Rectifying Potassium Channel (KCNJ11) (P05.183)

Objective: We present a man with congenital hyperinsulinism due to mutation of the inwardly rectifying potassium channel (Kir6.2) and neuromyotonia. Background Patients with activating mutations in the KCNJ11 gene can have neonatal diabetes mellitus and associated DEND syndrome (developmental delay, epilepsy and hypotonia). Inactivating mutations of this ATP-sensitive potassium channel lead to congenital hyperinsulism due to insulin oversecretion from pancreatic beta-cells. Down-regulation of Kir6.2 expression in myometrium may contribute to enhanced uterine contractility with onset of labor. Neuromyotonia is a disorder of peripheral nerve hyperexcitability characterized by myokymia, muscle cramps and stiffness, usually due to autoantibodies against neuronal voltage-gated potassium channels (VGKC) or rare VGKC mutations. Design/Methods: The patient is of European descent and was born uneventfully to a family without neurologic or endocrine problems. He was hypoglycemic at birth and was eventually diagnosed with hyperinsulinism. He underwent a subtotal pancreatectomy at two months after unsuccessful medication trials and developed diabetes mellitus at 12. Around age 13, he noted muscle spasms and twitching, with difficulty relaxing his muscles after exertion and falls due to stiffness. He had no percussion or grip myotonia, muscle rippling or myokymia at rest. With hyperextension of his legs he demonstrated grouped fasciculations of the quadriceps. Results: Needle EMG captured increased neuromyotonic discharges. Antibodies against VGKC were negative. PCR and sequence analysis showed that he was heterozygous for an alanine to threonine mutation at codon 213 (p. Ala213Thr). Conclusions: Our patient has co-occurrence of congenital hyperinsulism and seronegative neuromyotonia in the setting of a known inactivating mutation in the Kir6.2 channel (KCNJ11). Inactivation of this channel decreases potassium flow into the cell and resting membrane potential. This channel is known to be expressed in the CNS; its distribution in the PNS is unknown. We speculate that KCNJ11 mutation is causally related to our patient9s peripheral nerve hyperexcitability. Disclosure: Dr. Thyerlei has nothing to disclose. Dr. Oakley has received personal compensation for activities with Neurovista as a consultant. Dr. Jayadev received personal compensation from About.com/New York Times for medical review. . . . . . . Dr. Jayadev has received personal compensation in an editorial capacity for About.com and The New York Times. Dr. Weiss has received personal compensation for activities with Walgreens, CSL Behring and Talecris Biotherapeutics as a consultant and/or speaker.

HIV-1gp120 Induces Neuronal Apoptosis through Enhancement of 4-Aminopyridine-Senstive Outward K+ Currents

Human immunodeficiency virus type 1 (HIV-1)-associated dementia (HAD) usually occurs late in the course of HIV-1 infection and the mechanisms underlying HAD pathogenesis are not well understood. Accumulating evidence indicates that neuronal voltage-gated potassium (Kv) channels play an important role in memory processes and acquired neuronal channelopathies in HAD. To examine whether Kv channels are involved in HIV-1-associated neuronal injury, we studied the effects of HIV-1 glycoprotein 120 (gp120) on outward K+ currents in rat cortical neuronal cultures using whole-cell patch techniques. Exposure of cortical neurons to gp120 produced a dose-dependent enhancement of A-type transient outward K+ currents (IA). The gp120-induced increase of IA was attenuated by T140, a specific antagonist for chemokine receptor CXCR4, suggesting gp120 enhancement of neuronal IA via CXCR4. Pretreatment of neuronal cultures with a protein kinase C (PKC) inhibitor, GF109203X, inhibited the gp120-induced increase of IA. Biological significance of gp120 enhancement of IA was demonstrated by experimental results showing that gp120-induced neuronal apoptosis, as detected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and caspase-3 staining, was attenuated by either an IA blocker 4-aminopyridine or a specific CXCR4 antagonist T140. Taken together, these results suggest that gp120 may induce caspase-3 dependent neuronal apoptosis by enhancing IA via CXCR4-PKC signaling.

Retigabine (Ezogabine)

Retigabine (ezogabine in the US) opens neuronal voltage-gated potassium channels, resulting in resting membrane potential stabilization, neuronal subthreshold excitability control and anticonvulsant effects. The clinical efficacy of adjunctive oral retigabine in adults with inadequately controlled, partial-onset seizures was demonstrated in two large, well designed, phase III trials (RESTORE-1 and RESTORE-2), generally confirming the findings of an earlier phase IIb study. In the RESTORE trials, retigabine 600, 900 or 1200 mg/day was associated with significantly higher rates of response (i.e. reduction in 28-day total partial seizure frequency of ≥50%) than placebo during both the 12-week maintenance period and the entire 16- or 18-week double-blind phase (i.e. titration plus maintenance) of the studies. Retigabine recipients also had significantly greater median reductions from baseline in 28-day total partial seizure frequency than placebo recipients during these treatment periods. These benefits of retigabine were generally seen irrespective of age, gender, race and baseline seizure frequency, and were maintained for up to 12 months according to interim data from subsequent open-label extension studies, with some patients also experiencing seizure-free periods of up to 12 months. Retigabine was generally well tolerated in adults with partial-onset seizures in the RESTORE studies, with most adverse events being of mild or moderate severity.

Biochemical engineering of the N-acyl side chain of sialic acids alters the kinetics of a glycosylated potassium channel Kv3.1

The sialic acid of complex N-glycans can be biochemically engineered by substituting the physiological precursor N-acetylmannosamine with non-natural N-acylmannosamines. The Kv3.1 glycoprotein, a neuronal voltage-gated potassium channel, contains sialic acid. Western blots of the Kv3.1 glycoprotein isolated from transfected B35 neuroblastoma cells incubated with N-acylmannosamines verified sialylated N-glycans attached to the Kv3.1 glycoprotein. Outward ionic currents of Kv3.1 transfected B35 cells treated with N-pentanoylmannosamine or N-propanoylmannosamine had slower activation and inactivation rates than those of untreated cells. Therefore, the N-acyl side chain of sialic acid is intimately connected with the activation and inactivation rates of this glycosylated potassium channel.

Autoimmune Dementia: Clinical Course and Predictors of Immunotherapy Response

To define the diagnostic characteristics and predictors of treatment response in patients with suspected autoimmune dementia. Between January 1, 2002, and January 1, 2009, 72 consecutive patients received immunotherapy for suspected autoimmune dementia. Their baseline clinical, radiologic, and serologic characteristics were reviewed and compared between patients who were responsive to immunotherapy and those who were not. Patients were classified as responders if the treating physician had reported improvement after immunotherapy (documented in 80% by the Kokmen Short Test of Mental Status, neuropsychological testing, or both). Initial immunotherapeutic regimens included methylprednisolone in 56 patients (78%), prednisone in 12 patients (17%), dexamethasone in 2 patients (3%), intravenous immune globulin in 1 patient (1%), and plasma exchange in 1 patient (1%). Forty-six patients (64%) improved, most in the first week of treatment. Thirty-five percent of these immunotherapy responders were initially diagnosed as having a neurodegenerative or prion disorder. Pretreatment and posttreatment neuropsychological score comparisons revealed improvement in almost all cognitive domains, most notably learning and memory. Radiologic or electroencephalographic improvements were reported in 22 (56%) of 39 patients. Immunotherapy responsiveness was predicted by a subacute onset (P<.001), fluctuating course (P<.001), tremor (P=.007), shorter delay to treatment (P=.005), seropositivity for a cation channel complex autoantibody (P=.01; neuronal voltage-gated potassium channel more than calcium channel or neuronal acetylcholine receptor), and elevated cerebrospinal fluid protein (>100 mg/dL) or pleocytosis (P=.02). Of 26 immunotherapy-responsive patients followed up for more than 1 year, 20 (77%) relapsed after discontinuing immunotherapy. Identification of clinical and serologic clues to an autoimmune dementia allows early initiation of immunotherapy, and maintenance if needed, thus favoring an optimal outcome.

Eliminating false‐positive results in serum tests for neuromuscular autoimmunity

In this study we describe the false-positive frequency in radioimmunoprecipitation assays for muscle acetylcholine receptor (AChR) and neuronal voltage-gated potassium channel (VGKC) autoantibodies, attributable to 125I-ligand immunoprecipitation. Sera were evaluated for AChR autoantibody (n = 34,095) and VGKC autoantibody (n = 11,028). We retested sera that yielded apparently positive results with 125I-ligand with and without detergent-solubilized cation-channel protein, indentified clinically validated fals-positive rates of 0.05% and 1.7% for AchR and VGKC autoantibodies, respectively. Specificity assurance in radioimmunoprecipitation assays requires subtraction of values for 125I-ligand binding.

Improvement of non-paraneoplastic voltage-gated potassium channel antibody-associated limbic encephalitis without immunosuppressive therapy

We describe a 61-year-old patient with clinical evidence of limbic encephalitis who improved with anticonvulsant treatment only, that is, without the use of immunosuppressive agents. Three years following occurrence of anosmia, increasing memory deficits, and emotional disturbances, he presented with new-onset temporal lobe epilepsy, with antibodies binding to neuronal voltage-gated potassium channels and bitemporal hypometabolism on FDG-PET scan; the MRI scan was normal. This is most likely a case of spontaneous remission, illustrating that immunosuppressive therapy might be suspended in milder courses of limbic encephalitis. It remains open whether treatment with anticonvulsant drugs played an additional beneficiary role through the direct suppression of seizures or, additionally, through indirect immunomodulatory side effects.

PO27-TH-15 Frequency of false positive neuronal voltage-gated potassium channel antibody detection in serological evaluation for neurological autoimmunity

PO27-TH-15 Frequency of false positive neuronal voltage-gated potassium channel antibody detection in serological evaluation for neurological autoimmunity