NEXN Gene in Cardiomyopathies and Sudden Cardiac Deaths: Prevalence, Phenotypic Expression, and Prognosis

BACKGROUND

Few clinical data are available on NEXN mutation carriers, and the gene's involvement in cardiomyopathies or sudden death has not been fully established. Our objectives were to assess the prevalence of putative pathogenic variants in NEXN and to describe the phenotype and prognosis of patients carrying the variants.

METHODS

DNA samples from consecutive patients with cardiomyopathy or sudden cardiac death/sudden infant death syndrome/idiopathic ventricular fibrillation were sequenced with a custom panel of genes. Index cases carrying at least one putative pathogenic variant in the NEXN gene were selected.

RESULTS

Of the 9516 index patients sequenced, 31 were carriers of a putative pathogenic variant in NEXN only, including 2 with double variants and 29 with a single variant. Of the 29 unrelated probands with a single variant (16 males; median age at diagnosis, 32.0 [26.0-49.0] years), 21 presented with dilated cardiomyopathy (prevalence, 0.33%), and 3 presented with hypertrophic cardiomyopathy (prevalence, 0.14%). Three patients had idiopathic ventricular fibrillation, and there were 2 cases of sudden infant death syndrome (prevalence, 0.46%). For patients with dilated cardiomyopathy, the median left ventricle ejection fraction was 37.5% (26.25-50.0) at diagnosis and improved with treatment in 13 (61.9%). Over a median follow-up period of 6.0 years, we recorded 3 severe arrhythmic events and 2 severe hemodynamic events.

CONCLUSIONS

Putative pathogenic NEXN variants were mainly associated with dilated cardiomyopathy; in these individuals, the prognosis appeared to be relatively good. However, severe and early onset phenotypes were also observed-especially in patients with double NEXN variants. We also detected NEXN variants in patients with hypertrophic cardiomyopathy and sudden infant death syndrome/idiopathic ventricular fibrillation, although a causal link could not be established.

[Is Tako-tsubo cardiomyopathy really reversible ?]

Tako-tsubo cardiomyopathy is characterized by a total reversibility of wall motion abnormalities of the left ventricle (LV) as well as normalization of LV ejection fraction after the acute phase. However, recent studies have shown that some patients present functional, metabolic, and morphologic abnormalities away from the acute phase suggesting an incomplete recovery of the disease. In this revue we discuss about this topic through several tools used in those studies (echocardiography, exercise test, MRI, nuclear imaging, biology, as well).

Evolution of non-invasive myocardial work in tako-tsubo cardiomyopathy

Tako-tsubo cardiomyopathy (TTC) is characterized by left ventricular (LV) systolic dysfunction with transient wall motion abnormalities (WMA). However, whether systolic performance fully recovers is unclear. Non-invasive myocardial work (MW) is a new tool to assess the LV performance, never described in this setting. To assess MW in apical TTC. Fifty patients with the apical variant TTC (77 ± 10 years, 47 women) were enrolled and underwent a transthoracic echocardiography within 24 h of admission and a median of 36 days at follow-up (FU). Constructive work (CW), wasted work (WW), MW index (MWI) and efficiency (MWE) were derived from a strain- pressure loop obtained from non-invasive brachial blood pressure and 2D strain. Hospital complications (HC) were defined as heart failure, LV apical thrombus, and ventricular arrhythmia. A control group of 24 matched-subjects was used. Myocardial work improved significantly between the acute phase and follow-up (global, and all apical and middle segments for all indices, all, p < 0.01; and some basal segments for MWI and CW, all p < 0.05). The degree of impairment of MW followed an apical-basal gradient (worse in apical segments), which inverted at follow-up. Furthermore, in TTC, global CW and MWI were significantly impaired in patients with HC (n = 10, all p < 0.05). At follow-up, global and regional MW remained significantly reduced by comparison to the control group (CW, MWI, MWE, WW, all p < 0.01), despite similar hemodynamics, LVEF and 2D-strain (all, p = NS). Myocardial work is transiently altered in apical TTC and significantly associated to HC. Despite total recovery of WMA, subtle dysfunction of myocardial performance persists at FU.

Symmetric and asymmetric shocked gas jets for laser-plasma experiments

Shocks in supersonic flows offer both high density and sharp density gradients that are used, for instance, for gradient injection in laser-plasma accelerators. We report on a parametric study of oblique shocks created by inserting a straight axisymmetric section at the end of a supersonic "de Laval" nozzle. The effect of different parameters, such as the throat diameter and straight section length on the shock position and density, is studied through computational fluid dynamics (CFD) simulations. Experimental characterizations of a shocked nozzle are compared to CFD simulations and found to be in good agreement. We then introduce a newly designed asymmetric shocked gas jet, where the straight section is only present on one lateral side of the nozzle, thus providing a gas profile well adapted for density transition injection. In this case, full-3D fluid simulations and experimental measurements are compared and show excellent agreement.

Evaluation of non-invasive myocardial work in tako-tsubo cardiomyopathy

Funding Acknowledgements

Type of funding sources: None.

Background

Tako-tsubo cardiomyopathy (TTC) is characterized by the presence of transient left ventricular (LV) wall motion abnormalities (WMA). However, whether systolic performance fully recover is unclear. Non-invasive myocardial work (MW) is a new index of global and regional myocardial performance which has never been described in this setting. Objective: to assess global and regional MW in typical TTC (apical variant). Methods: fifty patients with typical TTC (mean age, 77 ± 10 years, 47 women) were prospectively enrolled and underwent a transthoracic Doppler echocardiography within 24 hours of admission and a median of 32 days at follow-up (FU). MW is derived from the non-invasive strain-pressure loop obtained from the 2D strain data, integrating in its calculation the non-invasive brachial arterial pressure. Constructive MW (CMW), MW index (MWI), MW efficiency (MWE), and wasted work (WW) were measured. Hospital complications (HC) were defined as a composite of heart failure, right ventricular extension, and LV apical thrombus. A control group of 24 patients matched for age and sex without overt cardiovascular disease served as a comparative group. Results: In the TTC group, global and regional MW improved significantly between the two examinations (global, regional apical and medial CMW, MWI, MWE, WW, and regional basal CMW, and MWI, all p &lt; 0.01). The acute apical –basal gradient of MW inverted at FU. In TTC, global CMW and MWI were significantly correlated to acute LV systolic function parameters and their change, and were significantly impaired in patients with HC (n = 13) (all, p &lt; 0.01). At FU, despite total recovery of WMA, global and regional MW was significantly reduced in TTC by comparison to the control group (p &lt; 0.01 for all components), although hemodynamics, LV ejection fraction, and 2D global longitudinal strain were similar (all, p = NS). Conclusion: Global and regional myocardial performance is transiently impaired in typical TTC and significantly associated to HC. And despite total recovery of WMA, subtle dysfunction of myocardial performance persist at FU.

Limitations in ionization-induced compression of femtosecond laser pulses due to spatio-temporal couplings

It was recently proposed that ionization-induced self-compression could be used as an effective method to further compress femtosecond laser pulses propagating freely in a gas jet [He et al., Phys. Rev. Lett. 113, 263904 2014]. Here, we address the question of the homogeneity of the self-compression process and show experimentally that homogeneous self-compression down to 12fs can be obtained by finding the appropriate focusing geometry for the laser pulse. Simulations are used to reproduce the experimental results and give insight into the self-compression process and its limitations. Simulations suggest that the ionization process induces spatio-temporal couplings which lengthen the pulse duration at focus, possibly making this method ineffective for increasing the laser peak intensity.

Demonstration of a strong Rydberg blockade in three-atom systems with anisotropic interactions

We study the Rydberg blockade in a system of three atoms arranged in different two-dimensional geometries (linear and triangular configurations). In the strong blockade regime, we observe high-contrast, coherent collective oscillations of the single excitation probability and an almost perfect van der Waals blockade. Our data are consistent with a total population in doubly and triply excited states below 2%. In the partial blockade regime, we directly observe the anisotropy of the van der Waals interactions between |nD> Rydberg states in the triangular configuration. A simple model that only uses independently measured two-body van der Waals interactions fully reproduces the dynamics of the system without any adjustable parameter. These results are extremely promising for scalable quantum information processing and quantum simulation with neutral atoms.

Direct measurement of the van der Waals interaction between two Rydberg atoms

We report the direct measurement of the van der Waals interaction between two isolated, single Rydberg atoms separated by a controlled distance of a few micrometers. Working in a regime where the single-atom Rabi frequency for excitation to the Rydberg state is comparable to the interaction, we observe partial Rydberg blockade, whereby the time-dependent populations of the various two-atom states exhibit coherent oscillations with several frequencies. Quantitative comparison of the data with a simple model based on the optical Bloch equations allows us to extract the van der Waals energy, and observe its characteristic C6/R6 dependence. The measured C6 coefficients agree well with ab initio calculations, and we observe their dramatic increase with the principal quantum number n of the Rydberg state.

Enhanced frequency up-conversion in Rb vapor

We demonstrate highly efficient generation of coherent 420 nm light via up-conversion of near-infrared lasers in a hot rubidium vapor cell. By optimizing pump polarizations and frequencies we achieve a single-pass conversion efficiency of 260% per Watt, significantly higher than in previous experiments. A full exploration of the coherent light generation and fluorescence as a function of both pump frequencies reveals that coherent blue light is generated close to (85)Rb two-photon resonances, as predicted by theory, but at high vapor pressure is suppressed in spectral regions that do not support phase matching or exhibit single-photon Kerr refraction. Favorable scaling of our current 1 mW blue beam power with additional pump power is predicted.

Cytokine production by human epithelial and endothelial cells following exposure to oral viridans streptococci involves lectin interactions between bacteria and cell surface receptors

In order to examine the possible implication of human epithelial and endothelial cells in the pathogenesis of various diseases associated with oral viridans streptococci, we tested the immunomodulatory effects of 11 representative strains of oral viridans streptococci on human epithelial KB cells and endothelial cells. We then examined the possible role of two major adhesins from oral viridans streptococci, protein I/II and rhamnose-glucose polymers (RGPs), in this process. In this study we demonstrate that oral viridans streptococci are potent stimulators of interleukin-8 (IL-8) production from KB cells and of IL-6 and IL-8 production from endothelial cells. The ability of protein I/II and RGPs to contribute to these effects was then examined. Using biotinylated protein I/IIf and RGPs from Streptococcus mutans OMZ 175, we showed that these adhesins bind to KB and endothelial cells through specific interactions and that the binding of these molecules initiates the release of IL-8 from KB cells and of IL-6 and IL-8 from endothelial cells. These results suggest that protein I/IIf and RGPs play an important role in the interactions between bacteria and KB and endothelial cells in that similar cytokine profiles are obtained when cells are stimulated with bacteria or surface components. We also provide evidence that protein I/IIf binds to and stimulates KB and endothelial cells through lectin interactions and that N-acetyl neuraminic acid (NANA) and fucose present on cell surface glycoproteins may form the recognition site since binding and cytokine release can be inhibited by dispase and periodate treatment of cells and by NANA and fucose. These results demonstrate that oral viridans streptococci, probably by engaging two cell surface adhesins, exert immunomodulatory effects on human KB and endothelial cells.

Antioxidant lazaroids enhance differentiation of C2 skeletal muscle cells

We have examined the incidence of new antioxidant compounds, so-called lazaroids, on the morphological and biochemical aspects of differentiation of C2 mouse skeletal muscle cells. We show that three lazaroids (U-74006F, U-74389F and U-83836E) enhance fusion of myogenic cells when added at the day of fusion. A parallel increase in nicotinic acetylcholine receptor expression and skeletal muscle alpha-actin content was observed. This promoting effect of lazaroids on myogenesis could be related to inhibition of free radical-mediated muscle damage. Therefore, one could expect that lazaroids might be useful in the treatment of degenerating muscle diseases such as Duchenne muscular dystrophy.

Lazaroids enhance skeletal myogenesis in primary cultures of dystrophin-deficient mdx mice

Growing evidence suggests a role for free radicals in the degeneration of dystrophin-deficient muscle (as observed in Duchenne muscular dystrophy). We therefore decided to test the action of the lazaroid antioxidant compounds on primary skeletal muscle cell cultures derived from an animal model of Duchenne muscular dystrophy, the mdx mouse. Both vitamin E-derived U-83836E and glucocorticoid-derived U-74389F enhanced myogenesis of dystrophin-deficient cultures as determined by the number of myotubes, the amount of nicotinic acetylcholine receptor, skeletal muscle alpha-actin levels and myosin light chain. U-83836E enhanced myogenesis of control congenic C57BL/10 mouse-derived muscle cultures whereas U-74389F had no detectable effect. This enhanced myogenesis was in most respects similar to the one triggered by alpha-methylprednisolone which is the only drug known to be beneficial in Duchenne muscular dystrophy.