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Results for “Functional perturbation”

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At least 127 records · Page 7Linked to original sources

PubMed1997

Effect of a single dose of diazepam on balance measures in older people.

OBJECTIVE: This study examines the effect of a single dose of diazepam on a spectrum of balance measures in healthy older subjects. The measures include static (postural sway), dynamic (anterior tibialis muscle activation latency), and a complex self-initiated task of balance (functional reach) in addition to neuropsychological tests of attention. DESIGN: A double-blind, two-period, cross-over trial. SETTING: The community surrounding a university hospital. PARTICIPANTS: Community-dwelling, nonsmoking volunteers 65 years of age and older. MEASUREMENTS: Measures included response to unexpected perturbation (platform/EMG muscle latency), self-initiated perturbation (functional reach), and a static measure of balance (postural sway). Neurocognitive tests (digital symbol substitution test, card sorting) were included to document the cognitive effect. RESULTS: Twelve nonsmoking healthy subjects (average age = 70.4 years (66-76 years)) participated. The anterior tibalis muscle latency increased in response to a sudden perturbation with diazepam compared with placebo (TA latency 149 ms vs 142 ms, P < .001). Neurocognitive tests were adversely affected for 90 minutes after diazepam administration compared with placebo (P < .05). Other measures did not demonstrate significant effect of diazepam. CONCLUSIONS: This is among the first reports showing that benzodiazepines affect neuromuscular processing related to balance control. Increased muscle latency to sudden perturbations may represent an effect of diazepam upon the oligosynaptic spinal reflex distinct from the sedation. Surface electromyography may be a valuable noninvasive tool for future studies of drug effect on balance and falls risk among older people.

Aged↗

PubMed2004

Calculation of the vibration frequencies of alpha-quartz: the effect of Hamiltonian and basis set.

The central-zone vibrational spectrum of alpha-quartz (SiO2) is calculated by building the Hessian matrix numerically from the analytical gradients of the energy with respect to the atomic coordinates. The nonanalytical part is obtained with a finite field supercell approach for the high-frequency dielectric constant and a Wannier function scheme for the evaluation of Born charges. The results obtained with four different Hamiltonians, namely Hartree-Fock, DFT in its local (LDA) and nonlocal gradient corrected (PBE) approximation, and hybrid B3LYP, are discussed, showing that B3LYP performs far better than LDA and PBE, which in turn provide better results than HF, as the mean absolute difference from experimental frequencies is 6, 18, 21, and 44 cm(-1), respectively, when a split valence basis set containing two sets of polarization functions is used. For the LDA results, comparison is possible with previous calculations based on the Density Functional Perturbation Theory and usage of a plane-wave basis set. The effects associated with the use of basis sets of increasing size are also investigated. It turns out that a split valence plus a single set of d polarization functions provides frequencies that differ from the ones obtained with a double set of d functions and a set of f functions on all atoms by on average less than 5 cm(-1).

Journal Article↗

PubMed2004

Dielectric and vibrational properties of amino acids.

We calculate polarizability tensors and normal mode frequencies for the amino acids alanine, leucine, isoleucine, and valine using density functional perturbation theory implemented within the plane wave pseudopotential framework. It is found that the behavior of the electron density under external fields depends to a large extent on the geometrical structure of the molecule in question, rather than simply on the constituent functional groups. The normal modes are able to help distinguish between the different types of intramolecular hydrogen bonding present, and help to explain why leucine is found in the zwitterionic form for the gaseous phase. Calculated IR spectra show a marked difference between those obtained for zwitterionic and nonzwitterionic molecules. These differences can be attributed to the different chemical and hydrogen bonds present. Effective dynamical charges are calculated, and compared to atomic charges obtained from Mulliken population analysis. It is found that disagreement exists, largely due to the differing origins of these quantities.

Amino Acids↗

PubMed1992

Adhesion of a chicken myeloblast cell line to fibrinogen and vitronectin through a beta 1-class integrin.

The adhesive interactions of circulating blood cells are tightly regulated, receptor-mediated events. To establish a model for studies on regulation of cell adhesion, we have examined the adhesive properties of the HD11 chick myeloblast cell line. Function-perturbing antibodies were used to show that integrins containing the beta 1 subunit mediate HD11 cell attachment to several distinct extracellular matrix proteins, specifically fibronectin, collagen, vitronectin, and fibrinogen. This is the first evidence that an integrin heterodimer in the beta 1 family functions as a receptor for fibrinogen. While the alpha v beta 1 heterodimer has been shown to function as a vitronectin receptor on some cells, this heterodimer could not be detected on HD11 cells. Instead, results suggest that the beta 1 subunit associates with different, unidentified alpha subunit(s) to form receptors for vitronectin and fibrinogen. Results using function-blocking antibodies also demonstrate that on these cells, additional receptors for vitronectin are formed by alpha v beta 3 and alpha v associated with an unidentified 100-kD beta subunit. The adhesive interactions of HD11 cells with these extracellular matrix ligands were shown to be regulated by lipopolysaccharide treatment, making the HD11 cell line attractive for studies of mechanisms regulating cell adhesion. In contrast to primary macrophage which rapidly exhibit enhanced adhesion to laminin and collagen upon activation, activated HD11 cells exhibited reduced adhesion to most extracellular matrix constituents.

Amino Acid Sequence↗

PubMed1992

Murine monoclonal anti-DNA antibodies penetrate cells, bind to nuclei, and induce glomerular proliferation and proteinuria in vivo.

The production of relatively high quantities of autoantibodies (autoAb) that react with DNA and other intranuclear antigens is characteristic of individuals with systemic lupus erythematosus and other autoimmune diseases. However, the capacity of these Ab to penetrate cells and induce functional perturbations in vivo is not well appreciated. To address this issue, monoclonal (m) anti-DNA Ab (mAb), derived from MRL-lpr/lpr and (NZB x SWR)F1 mice, were administered to normal mice, and the animals were examined for morphologic and functional abnormalities. A subset of five mAb produced intranuclear immunoglobulin deposits in multiple organs. Intranuclear immunoglobulin deposits were also observed after cross-linking the tissue before direct immunofluorescence and after i.v. injection of F(ab')2 fragments of one anti-DNA Ab. This phenomenon was reproducible and was only associated with this subset of autoAb. Furthermore, intranuclear deposits of anti-DNA Ab within glomeruli were associated with morphologic and functional abnormalities including: hypercellularity, epithelial foot process fusion, new fiber bundle formation within the mesangium suggestive of new collagen synthesis, and proteinuria. These results indicate that a subset of autoAb may penetrate cells in vivo to influence normal cellular and nuclear function and to contribute to functional and pathologic abnormalities in individuals with systemic lupus.

Animals↗

PubMed2003

Surface chemistry modulates fibronectin conformation and directs integrin binding and specificity to control cell adhesion.

Integrin-mediated cell adhesion to proteins adsorbed onto synthetic surfaces anchors cells and triggers signals that direct cell function. In the case of fibronectin (Fn), adsorption onto substrates of varying properties alters its conformation/structure and its ability to support cell adhesion. In the present study, self-assembled monolayers (SAMs) of alkanethiols on gold were used as model surfaces to investigate the effects of surface chemistry on Fn adsorption, integrin binding, and cell adhesion. SAMs presenting terminal CH(3), OH, COOH, and NH(2) functionalities modulated adsorbed Fn conformation as determined through differences in the binding affinities of monoclonal antibodies raised against the central cell-binding domain (OH > COOH = NH(2) > CH(3)). Binding of alpha(5)beta(1) integrin to adsorbed Fn was controlled by SAM surface chemistry in a manner consistent with antibody binding (OH > COOH = NH(2) > CH(3)), whereas alpha(V) integrin binding followed the trend: COOH >> OH = NH(2) = CH(3), demonstrating alpha(5)beta(1) integrin specificity for Fn adsorbed onto the NH(2) and OH SAMs. Cell adhesion strength to Fn-coated SAMs correlated with alpha(5)beta(1) integrin binding (OH > COOH = NH(2) > CH(3)), and experiments with function-perturbing antibodies demonstrated that this receptor provides the dominant adhesion mechanism in this cell model. This work establishes an experimental framework to analyze adhesive mechanisms controlling cell-surface interactions and provides a general strategy of surface-directed control of adsorbed protein activity to manipulate cell function in biomaterial and biotechnological applications.

Animals↗

PubMed2005

Bacterial diversity promotes community stability and functional resilience after perturbation.

The relationships between bacterial community diversity and stability were investigated by perturbing soils, with naturally differing levels of diversity, to equivalent toxicity using copper sulfate and benzene. Benzene amendment led to large decreases in total bacterial numbers and biomass in both soils. Benzene amendment of an organo-mineral/improved pasture soil altered total soil bacterial community structure but, unlike amendment of the mineral/arable soil, maintained genetic diversity, based on polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis targeting DNA and RNA, until week 9 of the perturbation experiment. Assuming equivalent toxicity, the genetic diversity of the naturally more diverse soil was more resistant to benzene perturbation than the less diverse soil. The broad scale function (mineralization of 14C-labelled wheat shoot) of both benzene- and copper-treated soil communities was unaffected. However, narrow niche function (mineralization of 14C-labelled 2,4-dichlorophenol) was impaired for both benzene-polluted soils. The organo-mineral soil recovered this function by the end of the experiment but the mineral soil did not, suggesting greater resilience in the more diverse soil. Despite a large reduction in bacterial numbers and biomass in the copper-treated soils, only small differences in bacterial community diversity were observed by week 9 in the copper-polluted soils. The overall community structure was little altered and functionality, measured by mineralization rates, remained unchanged. This suggested a non-selective pressure and a degree of genetic and functional resistance to copper perturbation, despite a significant reduction in bacterial numbers and biomass. However, initial shifts in physiological profiles of both copper-polluted soils were observed but rapidly returned to those of the controls. This apparent functional recovery, accompanied by an increase in culturability, possibly reflects adaptation by the surviving communities to perturbation. The findings indicate that, although soil communities may be robust, relationships between diversity and stability need to be considered in developing a predictive understanding of response to environmental perturbations.

Bacteria↗

PubMed2004

Presenilin 1 in migration and morphogenesis in the central nervous system.

Morphogenesis of the central nervous system relies in large part upon the correct migration of neuronal cells from birthplace to final position. Two general modes of migration govern CNS morphogenesis: radial, which is mostly glia-guided and topologically relatively simple; and tangential, which often involves complex movement of neurons in more than one direction. We describe the consequences of loss of function of presenilin 1 on these fundamental processes. Previous studies of the central nervous system in presenilin 1 homozygote mutant embryos identified a premature neuronal differentiation that is transient and localized, with cortical dysplasia at later stages. We document widespread effects on CNS morphogenesis that appear strongly linked to defective neuronal migration. Loss of presenilin 1 function perturbs both radial and tangential migration in cerebral cortex, and several tangential migratory pathways in the brainstem. The inability of cells to execute their migratory trajectories affects cortical lamination, formation of the facial branchiomotor nucleus, the spread of cerebellar granule cell precursors to form the external granule layer and development of the pontine nuclei. Finally, overall morphogenesis of the mid-hindbrain region is abnormal, resulting in incomplete midline fusion of the cerebellum and overgrowth of the caudal midbrain. These observations indicate that in the absence of presenilin 1 function, the ability of a cell to move can be severely impaired regardless of its mode of migration, and, at a grosser level, brain morphogenesis is perturbed. Our results demonstrate that presenilin 1 plays a much more important role in brain development than has been assumed, consistent with a pleiotropic involvement of this molecule in cellular signaling.

Amyloid Precursor Protein Secretases↗

PubMed2002

Redox sensing properties of the ryanodine receptor complex.

The release mechanism regulating SR Ca2+ homeostasis is significantly more sensitive than the uptake mechanisms. The exquisite sensitivity exhibited by ryanodine-sensitive Ca2+ channel complexes (i.e., ryanodine receptors, RyRs) to functional perturbation by chemically diverse sulfhydryl-modifying compounds can include phases of activation and inhibition that are dependent on the concentration of the reagent used, the length of exposure, and the nature of the chemical reaction the reagent undertakes with sulfhydryl groups. However the exquisite sensitivity of RyR function to sulfhydryl modification has been generally viewed as significant only in pathophysiological processes. The present paper addresses possible physiological importance of the redox sensing properties of the ryanodine receptor complexes (RyRs) and proposes an underlying mechanism. New data is presented that directly measure the pKa of hyperreactive thiols that occur when the closed conformation of the RyR channel complex is assumed, and that appear to be an integral component of the redox sensor.

Animals↗

PubMed2004

Rubella virus and birth defects: molecular insights into the viral teratogenesis at the cellular level.

BACKGROUND: In utero rubella virus (RV) infection of a fetus can result in birth defects that are often collectively referred to as congenital rubella syndrome (CRS). In extreme cases, fetal death can occur. In spite of the availability of a safe and effective vaccine against rubella, recent worldwide estimates are that more than 100,000 infants are born with CRS annually. RECENT PROGRESS: Recently, several significant findings in the field of cell biology, as well as in the RV replication and virus-cell interactions, have originated from the authors' laboratory, and other researchers have provided insights into RV teratogenesis. It has been shown that 1) an RV protein induces cell-cycle arrest by generating a subpopulation of tetraploid nuclei (i.e., 4N DNA) cells, perhaps representative of the tetraploid state following S phase in the cell cycle, due to its interaction with citron-K kinase (CK); 2) RV infection induces apoptosis in cell culture, and 3) CK functional perturbations lead to tetraploidy, followed by apoptosis, in specific cell types. CONCLUSIONS: Based on several similarities between known RV-associated fetal and cellular manifestations and CK deficiency-associated phenotypes, it is reasonable to postulate that P90-CK interaction in RV-infected cells interferes with CK function and induces cell-cycle arrest following S phase in a subpopulation, perhaps representative of tetraploid stage, which could lead to subsequent apoptosis in RV infection. Taking all these observations to the fetal organogenesis level, it is plausible that P90-CK interaction could perhaps be one of the initial steps in RV infection-induced apoptosis-associated fetal birth defects in utero.

Apoptosis↗

PubMed1983

Adenylate cyclase is inhibited upon depletion of plasma-membrane cholesterol.

A procedure has been developed that allows for the depletion of rat liver plasma membrane cholesterol by incubation with liposomes at 4 degrees C. Upon cholesterol depletion, adenylate cyclase activity was inhibited and the membranes became more rigid, as determined by the flexibility of an incorporated fatty acid spin probe. Decreasing the cholesterol/phospholipid molar ratio elicited a pronounced drop in the net fold-stimulation of adenylate cyclase activity by glucagon. Two lipid phase separations were detected in cholesterol-depleted membranes at around 25 degrees C and 13 degrees C respectively. Breaks at these temperatures were observed in Arrhenius plots of both the mobility of the spin probe and the glucagon-stimulated adenylate cyclase activity for the range 2-40 degrees C, but only the one at the lower temperature for the fluoride-stimulated activity. It is proposed that the lipid phase separation occurring at 25 degrees C is localized in the external half of the bilayer, whereas that at 13 degrees C is due to lipids in the inner half of the bilayer. Similar structural and functional perturbations were manifest if the cholesterol-complexing polyene antibiotic amphotericin B was added to native membranes. The mechanism of adenylate cyclase inhibition achieved by cholesterol depletion and the domain structure of the plasma membrane in relation to cholesterol distribution are discussed. Native cholesterol/phospholipid ratios appear to optimize the functioning of adenylate cyclase in liver plasma membranes.

Adenylyl Cyclase Inhibitors↗

PubMed2004

Reduced expression of the insulin receptor in mouse insulinoma (MIN6) cells reveals multiple roles of insulin signaling in gene expression, proliferation, insulin content, and secretion.

The role of insulin signaling in pancreatic beta cells has become increasingly apparent. Stably transformed insulinoma cell lines (MIN6) were created with small interfering RNA resulting in the reduction of insulin receptor (IR) expression up to 80% (insulin receptor knockdown, IRKDDelta80). Functionally perturbed IR signaling was confirmed with the absence of insulin-stimulated insulin receptor substrate 1 tyrosine phosphorylation. Additionally, Akt phosphorylation was reduced and responded poorly to glucose stimulation. Gene expression profiling revealed that reduced IR expression was associated with alterations in expression of >1,500 genes with diverse functions. IRKD cells exhibited low rate of proliferation due to delay in transition from G0/G1 to S phase, whereas susceptibility to apoptosis did not differ from that of control cells. Insulin content was reduced in proportion to the reduction of IR. IRKD cells maintained glucose responsiveness as measured by NADPH generation, whereas Ca2+ responses and insulin secretion were enhanced. IRKDDelta80 and control cells were treated with glucose (25 mm) or insulin (100 nm) for 45 min, and gene expression profiles were assessed. Transcriptional activation of several hundred early response genes common to both glucose and insulin stimulation was observed in control cells. In IRKDDelta80 cells, insulin failed to activate any genes as anticipated. Importantly, glucose stimulation of gene expression in IRKDDelta80 cells showed that most genes previously activated by glucose were no longer activated, suggesting a major autocrine/paracrine effect of insulin on glucose-regulated gene expression. On the other hand, there were a number of glucose-regulated genes in the IRKDDelta80 cells that were not previously observed in control cells, suggesting a feedback regulation of insulin signaling on glucose-regulated gene expression. These results demonstrate important roles of the insulin receptor in islet beta cell gene expression and function and may serve to elucidate molecular defects in animal models with diminished beta cell insulin signaling.

Animals↗

PubMed2006

Training induced adaptations in characteristics of postural reflexes in elderly men.

The aging neuromuscular system is affected by structural and functional changes which lead to a general slowing down of neuromuscular performance and an increased risk of falling. The impact of heavy resistance (HR) training in the elderly on maximum voluntary contraction (MVC) and rate of force development (RFD) has been investigated in the past. However, the influence of sensorimotor (SENSO) training and HR training on the ability to compensate for gait perturbations has not yet been investigated in the elderly. Therefore, the purpose of the study was to examine the impact of HR and SENSO training in elderly men on unexpected treadmill perturbations. Functional reflex activity was recorded by means of surface EMG in 40 male subjects (>60 years) before and after 13 weeks of HR and SENSO training and in another 20 male subjects (>60 years), which served as a CONTROL-group. SENSO training resulted in a decrease in onset latency, an enhanced reflex activity in the prime mover as well as a decrease in maximal angular velocity of the ankle joint complex during the perturbation impulses. No significant changes were observed in the HR- and in the CONTROL-group. The results clearly indicate that SENSO training has an impact on spinal motor control mechanisms in the elderly. Training induced improvements in perception and procession of afferent information could be a possible reason for the increase in reflex contraction. Due to these adaptive processes, SENSO training could be a well-suited method for fall preventive programs in elderly people.

Adaptation, Physiological↗

PubMed2000

Intragenic and intergenic suppression of the Escherichia coli ATP synthase subunit a mutation of Gly-213 to Asn: functional interactions between residues in the proton transport site.

Subunit a of the ATP synthase F(o) sector contains a transmembrane helix that interacts with subunit c and is critical for H(+) transport activity. From a cysteine scan in the region around the essential subunit a residue, Arg-210, we found that the replacement of aGly-213 greatly attenuated ATP hydrolysis, ATP-dependent proton pumping and Delta mu(H)+-dependent ATP synthesis. Various amino acid substitutions caused similar effects, suggesting that functional perturbations were caused by altering the environment or conformation of aArg-210. aG213N, which was particularly severe in effect, was suppressed by two second-site mutations, aL251V and cD61E. These mutations restored efficient coupling; the latter also increased ATP-dependent proton transport rates. These results were consistent with the proposed functional interaction between aArg-210 and cAsp-61, the likely carrier of the transported proton. From Arrhenius analysis of steady-state ATP hydrolytic activity, the transport mutants had large increases in the transition-state enthalpic and entropic parameters. Linear isokinetic relationships demonstrate that the transport mechanism is coupled to the rate-limiting catalytic transition-state step, which we have previously shown to involve the rotation of the gamma subunit in multi-site, co-operative catalysis.

Adenosine Triphosphate↗

PubMed1998

Morphological and functional alterations to sinusoidal endothelial cells in the early phase of endotoxin-induced liver failure after partial hepatectomy in rats.

Liver failure following major hepatectomy is characterized pathologically by massive hepatic necrosis, which is thought to begin with injury of sinusoidal endothelial cells (SECs). To examine the early events of SECs leading to hepatic damage, we performed time-course analyses of the morphological and functional perturbation of SECs after endotoxin administration to hepatectomized rats. At 1.5 h after endotoxin injection, when hepatocellular damage was not yet evident, SECs showed augmented expression of intercellular adhesion molecule-1, with frequent adherence of infiltrating leucocytes and ultrastructural features of defenestration and hypertrophied cytoplasm enriched with cell organelles. The serum level of hyaluronate, as an indicator of the functional state of SECs, was significantly elevated. At 3 h, SECs underwent necrosis and disruption, accompanied by fibrin deposits with concomitant hepatocellular necrosis. The morphological and functional alterations of SECs precede necrotic changes in hepatocytes and SECs in endotoxin-induced liver failure after partial hepatectomy.

Animals↗

PubMed1997

Rescue of cardiac alpha-actin-deficient mice by enteric smooth muscle gamma-actin.

The muscle actins in higher vertebrates display highly conserved amino acid sequences, yet they show distinct expression patterns. Thus, cardiac alpha-actin, skeletal alpha-actin, vascular smooth muscle alpha-actin, and enteric smooth muscle gamma-actin comprise the major actins in their respective tissues. To assess the functional and developmental significance of cardiac alpha-actin, the murine (129/SvJ) cardiac alpha-actin gene was disrupted by homologous recombination. The majority ( approximately 56%) of the mice lacking cardiac alpha-actin do not survive to term, and the remainder generally die within 2 weeks of birth. Increased expression of vascular smooth muscle and skeletal alpha-actins is observed in the hearts of newborn homozygous mutants and also heterozygotes but apparently is insufficient to maintain myofibrillar integrity in the homozygous mutants. Mice lacking cardiac alpha-actin can be rescued to adulthood by the ectopic expression of enteric smooth muscle gamma-actin using the cardiac alpha-myosin heavy chain promoter. However, the hearts of such rescued cardiac alpha-actin-deficient mice are extremely hypodynamic, considerably enlarged, and hypertrophied. Furthermore, the transgenically expressed enteric smooth muscle gamma-actin reduces cardiac contractility in wild-type and heterozygous mice. These results demonstrate that alterations in actin composition in the fetal and adult heart are associated with severe structural and functional perturbations.

Actins↗

PubMed2026

A Phosphoproteomic Platform Identifies Erythrocyte Membrane Protein Band 4.1-Like 3-Mediated Lipid Droplet Remodeling Linked to Liver Cancer Invasion and Migration.

Aberrant lipid metabolism is a hallmark of hepatocellular carcinoma (HCC), yet the regulatory mechanisms governing lipid droplet (LD) dynamics and their contribution to tumor progression remain poorly understood. Here, we developed an ultrasensitive phosphoproteomic platform using high-affinity HPDA@Ti4+ nanospheres to map LD-associated phosphorylation events across six HCC cell lines. By correlating phosphoproteomic signatures with LD morphology, we identified distinct regulatory signatures associated with LD size and abundance. Functional perturbation screens identified two distinct phosphoprotein modules controlling LD size: silencing SH3KBP1, SLK, EHD2, EPB41L3, and NEXN reduced LD size in Huh1 cells, whereas silencing CPD, BET1, UFL1, RRP1B, OGFR, and CD2BP2 enlarged LDs in Huh7 cells. Notably, we identified EPB41L3 as a critical metabolic-metastatic link; its loss decreased LD size and accelerated HCC migration and invasion, correlating with poor clinical prognosis. Crucially, we identified five key phosphorylation sites on EPB41L3 essential for its function; substituting these with alanine completely abolished its regulatory control over both LD size and HCC metastatic potential. Together, these findings delineate a phosphorylation-based regulatory network controlling the LD architecture and metastatic potential in HCC. Our study not only identifies potential therapeutic targets but also establishes a generalizable phosphoproteomic framework for interrogating lipid signaling in cancer metabolism.

Humans↗

PubMed2005

Targeted mutational analysis of ankyrin-B in 541 consecutive, unrelated patients referred for long QT syndrome genetic testing and 200 healthy subjects.

BACKGROUND: Mutations in ANK2-encoded ankyrin-B underlie long QT syndrome type 4 (LQT4) and various other dysrhythmia phenotypes. OBJECTIVES: The purpose of this study was to determine the prevalence and spectrum of ankyrin-B mutations in a large cohort of unrelated patients referred for LQTS genetic testing and among healthy control subjects. METHODS: Between August 1997 and July 2004, 541 consecutive, unrelated patients (358 females, average age at diagnosis 24 years, average QTc 482 ms) were referred to Mayo Clinic's Sudden Death Genomics Laboratory for comprehensive mutational analysis of the five cardiac channel genes implicated in LQTS: KCNQ1 (LQT1), KCNH2 (LQT2), SCN5A (LQT3), KCNE1 (LQT5), and KCNE2 (LQT6). Based on this prior analysis, 269 of 541 cases lacked an identifiable mutation (genotype negative). In this study, targeted mutational analysis of 10 ANK2 exons (36,37,39-46) encoding the critical C-terminal regulatory domain or implicated previously as hosting pathogenic mutations was performed on genomic DNA from 541 patients and 200 control subjects using polymerase chain reaction, denaturing high-performance liquid chromatography, and direct DNA sequencing. RESULTS: Overall, 14 distinct nonsynonymous variants (10 novel) were observed in 9 (3.3%) of 269 genotype-negative LQTS patients, 5 (1.8%) of 272 genotype-positive LQTS cases, 4 (4%) of 100 white controls, and 9 (9%) of 100 black controls. Four variants found in controls (L1622I, T1626N, R1788W, and E1813K) were implicated previously as LQT4-associated mutations and displayed functional perturbations in vitro. All genotype-negative LQTS cases hosting ANK2 variants had been diagnosed as "atypical" or "borderline" cases, most presenting with normal QTc, nonexertional syncope, U waves, and/or sinus bradycardia. CONCLUSION: Nonsynonymous ankyrin-B variants were detected in nearly 3% of unrelated LQTS patients and nearly 7% of healthy control subjects. Genotype-negative LQTS patients with a single ANK2 variant displayed nonexertional syncope, U waves, sinus bradycardia, and extracardiac findings. Whether the identification of previously reported functionally significant variants residing in 2% of apparently healthy subjects suggests proarrhythmic potential or potential misclassification warrants further scrutiny.

Adolescent↗