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  • br Conclusions It is now clear that a number


    Conclusions It is now clear that a number of orthopoxvirus variola are involved in inherited bradyarrhythmia. Recent genetic studies have demonstrated that inherited arrhythmia is attributable to many genes with diverse functions. While the precise underlying mechanisms remain to be elucidated; these genetic defects may disrupt important cardiac functions including electrophysiological properties, development, cardioprotection, and the structural integrity of the membrane and sarcomere, ultimately leading to bradyarrhythmia. However, there are a large number of patients suffering from bradyarrhythmia whose etiologies remain unknown. As we have recently identified a novel MYH6 mutation based on the most advanced genomic findings using GWAS to investigate SSS [66], new technologies such as next generation sequencing may provide the opportunity to identify new genes for inherited bradyarrhythmia as well as novel insights into the molecular mechanisms behind cardiac rhythm regulation.
    Conflict of interest
    Acknowledgment This work was supported by Grants-in-Aid for Scientific Research 26860572 (T.I.), 15H04823 and 15K15311 (N.M.) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan; Health Science Research grants from the Ministry of Health, Labor, and Welfare of Japan for Clinical Research on Measures for Intractable Diseases (H26-002, H26-084, H27-019 and H27-032, N.M.); Translational Research Funds from the Japan Circulation Society (N.M.); the Joint Usage/Research Program of Medical Research Institute, Tokyo Medical and Dental University (N.M.); and a research grant from Takeda Science Foundation (T.I.).
    Introduction Sudden cardiac death (SCD) is a tragic complication of a number of cardiovascular diseases. The death can occur at all ages, and in the young it is often unexpected when it occurs in a previously healthy and asymptomatic person [1–3]. SCD is defined as a death occurring within an hour of the onset of symptoms, due to an underlying cardiac disease. The prevalence of SCD is significant, with at least 3 million people worldwide dying suddenly each year. In the United States, SCD occurs in up to 450,000 people each year, translating to over 1000 deaths per day, or one SCD every 1.5min [2,4]. SCD is significantly more common in older age groups, and the incidence in young people aged less than 40 years is generally low. The best estimate of the incidence of SCD in the general population aged 20–75 years is 1 in every 1000 individuals, accounting for 18.5% of all deaths [5]. In the 1–40 age group, the incidence is up to 8.5 per 100,000 person years, including competitive athletes [4–9]. While relatively uncommon, the SCD of a young person is a devastating event. In addition, the public health burden of premature death for men and women is greater for SCD than for all individual cancers and most other leading causes of death [10].
    Causes of sudden cardiac death in the young The causes of SCD can be broadly divided into structural and arrhythmogenic etiologies. In subjects over the age of 40 years, coronary artery disease and acute myocardial infarction account for over 90% of SCD cases [2,11]. Fig. 1 summarizes the causes of SCD in the young (aged 0–40), illustrating the lower prevalence of coronary artery disease and higher proportion of inherited heart diseases. Structural causes of SCD in the young include inherited cardiomyopathies, such as hypertrophic cardiomyopathy (HCM), dilated and restrictive cardiomyopathies, arrhythmogenic right ventricular cardiomyopathy (ARVC), and left ventricular non-compaction. Other structural causes of SCD in the young include myocarditis, congenital heart diseases, and coronary artery disease [12,13]. HCM is the most common inherited heart disease with a prevalence of 1 in every 200 people [14]. HCM remains the most common structural cause of SCD in the young, including competitive athletes [15]. Of note, in all structural causes of SCD in the young, the postmortem examination has a high probability of identifying the cause of death.