South Asian-Specific MYBPC3 Δ25bp Deletion Carriers Display Hypercontraction and Impaired Diastolic Function Under Exercise Stress

Background: A 25-base pair (25bp) intronic deletion in the MYBPC3 gene enriched in South Asians (SAs) is a risk allele for late-onset left ventricular (LV) dysfunction, hypertrophy, and heart failure (HF) with several forms of cardiomyopathy. However, the effect of this variant on exercise parameters has not been evaluated. Methods: As a pilot study, 10 asymptomatic SA carriers of the MYBPC3 Δ25bp variant (52.9 ± 2.14 years) and 10 age- and gender-matched non-carriers (NCs) (50.1 ± 2.7 years) were evaluated at baseline and under exercise stress conditions using bicycle exercise echocardiography and continuous cardiac monitoring. Results: Baseline echocardiography parameters were not different between the two groups. However, in response to exercise stress, the carriers of Δ25bp had significantly higher LV ejection fraction (%) (CI: 4.57 ± 1.93; p < 0.0001), LV outflow tract peak velocity (m/s) (CI: 0.19 ± 0.07; p < 0.0001), and higher aortic valve (AV) peak velocity (m/s) (CI: 0.103 ± 0.08; p = 0.01) in comparison to NCs, and E/A ratio, a marker of diastolic compliance, was significantly lower in Δ25bp carriers (CI: 0.107 ± 0.102; p = 0.038). Interestingly, LV end-diastolic diameter (LVIDdia) was augmented in NCs in response to stress, while it did not increase in Δ25bp carriers (CI: 0.239 ± 0.125; p = 0.0002). Further, stress-induced right ventricular systolic excursion velocity s' (m/s), as a marker of right ventricle function, increased similarly in both groups, but tricuspid annular plane systolic excursion increased more in carriers (slope: 0.008; p = 0.0001), suggesting right ventricle functional differences between the two groups. Conclusions: These data support that MYBPC3 Δ25bp is associated with LV hypercontraction under stress conditions with evidence of diastolic impairment.

Abstract P348: Pathophysiological Basis Of A Compound Variant In Calcium And Sarcomere Regulation Causing Cardiac Arrhythmias And Hypertrophic Cardiomyopathy

Rationale: Hypertrophic cardiomyopathy (HCM) is common inheritable heart disease. HCM is highly associated with arrhythmias and/or sudden death. Studies show that molecular defects in calcium handling impairing the cardiomyocyte contractility is a predominant cause. However, the pathophysiology underlying HCM with arrhythmias is not well understood, hindering the identification of novel therapies.

Objective: To investigate the pathophysiological consequences of compound variants, consisting of Histidine Rich Calcium Binding Protein gene ( HRC S96A ) and an intronic 25bp deletion in cardiac myosin binding protein-C ( MYBPC3 Δ25bp ).

Methods and Results: Clinical data revealed that co-segregation of HRC S96A and MYBPC3 ΔInt32 results in cardiac arrhythmia, heart failure, and sudden cardiac death in South Asians. To determine the cellular/molecular trigger underlying the pathophysiology of this dual variant, we used humanized, knock-in, heterozygous mouse models, including HRC S81A (equivalent to HRC S96A ) MYBPC3 Δ25bp , HRC S81A / MYBPC3 Δ25bp (double variant, DV), and wild-type controls. Echocardiography revealed a significant decrease in the percentage of ejection fraction and fractional shortening in DV mice, as well as the presence of diastolic dysfunction, at 12 weeks of age, compared to single-variant and wild-type mice. Electrocardiogram tracing of DV mice showed the presence of stress-induced arrhythmias, such as ventricular tachycardia after caffeine and epinephrine administration. Using isolated cardiomyocytes in vitro , Calcium transient experiments indicated a significant decrease in fractional shortening, Ca 2+ transient amplitude, and a higher number of after-contractions in cardiomyocytes from DV mice. DV mouse hearts showed increased phosphorylation of CaMKII and SR Ca 2+ leak by cardiomyocytes. Inclusion of the CaMKII inhibitor KN-93 rescued the increases in SR Ca 2+ leak and in aftercontractions.

Conclusion: Impaired Ca 2+ -handling, owing to the HRC S96A variant, aggravates SR Ca 2+ leak and aftercontractions in MYBPC3 Δ25bp cardiomyocytes, subsequently triggering cardiac arrhythmias and sudden death in vivo .

Genetic Modifiers of Hereditary Neuromuscular Disorders and Cardiomyopathy

Novel genetic variants exist in patients with hereditary neuromuscular disorders (NMD), including muscular dystrophy. These patients also develop cardiac manifestations. However, the association between these gene variants and cardiac abnormalities is understudied. To determine genetic modifiers and features of cardiac disease in NMD patients, we have reviewed electronic medical records of 651 patients referred to the Muscular Dystrophy Association Care Center at the University of Cincinnati and characterized the clinical phenotype of 14 patients correlating with their next-generation sequencing data. The data were retrieved from the electronic medical records of the 14 patients included in the current study and comprised neurologic and cardiac phenotype and genetic reports which included comparative genomic hybridization array and NGS. Novel associations were uncovered in the following eight patients diagnosed with Limb-girdle Muscular Dystrophy, Bethlem Myopathy, Necrotizing Myopathy, Charcot-Marie-Tooth Disease, Peripheral Polyneuropathy, and Valosin-containing Protein-related Myopathy. Mutations in COL6A1, COL6A3, SGCA, SYNE1, FKTN, PLEKHG5, ANO5, and SMCHD1 genes were the most common, and the associated cardiac features included bundle branch blocks, ventricular chamber dilation, septal thickening, and increased outflow track gradients. Our observations suggest that features of cardiac disease and modifying gene mutations in patients with NMD require further investigation to better characterize genotype–phenotype relationships.

Genetic, clinical, molecular, and pathogenic aspects of the South Asian-specific polymorphic MYBPC3Δ25bp variant

Hypertrophic cardiomyopathy (HCM) is a cardiac genetic disease characterized by ventricular enlargement, diastolic dysfunction, and increased risk for sudden cardiac death. Sarcomeric genetic defects are the predominant known cause of HCM. In particular, mutations in the myosin-binding protein C gene (MYBPC3) are associated with ~ 40% of all HCM cases in which a genetic basis has been established. A decade ago, our group reported a 25-base pair deletion in intron 32 of MYBPC3 (MYBPC3Δ25bp) that is uniquely prevalent in South Asians and is associated with autosomal dominant cardiomyopathy. Although our studies suggest that this deletion results in left ventricular dysfunction, cardiomyopathies, and heart failure, the precise mechanism by which this variant predisposes to heart disease remains unclear. Increasingly appreciated, however, is the contribution of secondary risk factors, additional mutations, and lifestyle choices in augmenting or modifying the HCM phenotype in MYBPC3Δ25bp carriers. Therefore, the goal of this review article is to summarize the current research dedicated to understanding the molecular pathophysiology of HCM in South Asians with the MYBPC3Δ25bp variant. An emphasis is to review the latest techniques currently applied to explore the MYBPC3Δ25bp pathogenesis and to provide a foundation for developing new diagnostic strategies and advances in therapeutics.

WHO/ILO work-related burden of disease and injury: Protocol for systematic reviews of occupational exposure to solar ultraviolet radiation and of the effect of occupational exposure to solar ultraviolet radiation on melanoma and non-melanoma skin cancer

BACKGROUND

The World Health Organization (WHO) and the International Labour Organization (ILO) are developing a joint methodology for estimating the national and global work-related burden of disease and injury (WHO/ILO joint methodology), with contributions from a large network of experts. In this paper, we present the protocol for two systematic reviews of parameters for estimating the number of deaths and disability-adjusted life years from melanoma and non-melanoma skin cancer (or keratinocyte carcinoma) from occupational exposure to solar ultraviolet radiation, to inform the development of the WHO/ILO joint methodology.

OBJECTIVES

We aim to systematically review studies on occupational exposure to solar ultraviolet radiation (Systematic Review 1) and systematically review and meta-analyse estimates of the effect of occupational exposure to solar ultraviolet radiation on melanoma and non-melanoma skin cancer (Systematic Review 2), applying the Navigation Guide systematic review methodology as an organizing framework and conducting both systematic reviews in tandem and in a harmonized way.

DATA SOURCES

Separately for Systematic Reviews 1 and 2, we will search electronic academic databases for potentially relevant records from published and unpublished studies, including Ovid Medline, PubMed, EMBASE, and Web of Science. We will also search electronic grey literature databases, Internet search engines and organizational websites; hand-search reference list of previous systematic reviews and included study records and consult additional experts.

STUDY ELIGIBILITY AND CRITERIA

We will include working-age (≥15 years) workers in the formal and informal economy in any WHO and/or ILO Member State, but exclude children (<15 years) and unpaid domestic workers. For Systematic Review 1, we will include quantitative studies on the prevalence of relevant levels of occupational exposure to solar ultraviolet radiation (i.e. <0.33 SED/d and ≥0.33 SED/d) and of the total working time spent outdoors, stratified by country, sex, age and industrial sector or occupation, in the years 1960 to 2018. For Systematic Review 2, we will include randomized controlled trials, cohort studies, case-control studies and other non-randomized intervention studies with an estimate of the effect of any occupational exposure to solar ultraviolet radiation (i.e., ≥0.33 SED/d) on the prevalence of, incidence of or mortality due to melanoma and non-melanoma skin cancer, compared with the theoretical minimum risk exposure level (i.e. <0.33 SED/d).

STUDY APPRAISAL AND SYNTHESIS METHODS

At least two review authors will independently screen titles and abstracts against the eligibility criteria at a first stage and full texts of potentially eligible records at a second stage, followed by extraction of data from qualifying studies. At least two review authors will assess the risk of bias and the quality of evidence, using the most suited tools currently available. For Systematic Review 2, if feasible, we will combine relative risks using meta-analysis. We will report results using the guidelines for accurate and transparent health estimates reporting (GATHER) for Systematic Review 1 and the preferred reporting items for systematic reviews and meta-analyses guidelines (PRISMA) for Systematic Review 2.

PROSPERO REGISTRATION NUMBER

CRD42018094817.

Langerhans cell histiocytosis with pulmonary involvement and unilateral pneumothorax

Langerhans cell histiocytosis (LCH) is a rare disorder of Langerhans cell with unknown etiology, which can uncommonly be associated with pneumothorax. A 14-month-old female is presented here who was referred to our center due to acute respiratory distress. Reticulonodular changes with multiple cystic areas were detected in chest X-ray, whilst extensive honeycombing and cystic changes were seen in high-resolution computed tomography scan. With deterioration of respiratory distress, chest X-ray was repeated, which revealed a unilateral pneumothorax. Meanwhile, some hyperpigmented skin plaques appeared on her skull and back. The biopsy results confirmed the diagnosis of proliferative histiocytosis. Prompt diagnosis of LCH and initiation of appropriate treatment in the patients who present with pneumothorax are vital to prevent further complications and even death in this group of patients.