Patients with coronary heart disease, dilated cardiomyopathy and idiopathic ventricular tachycardia share overlapping patterns of pathogenic variation in cardiac risk genes.

BACKGROUND: Ventricular tachycardia (VT) is a major cause of sudden cardiac death (SCD). Clinical investigations can sometimes fail to identify the underlying cause of VT and the event is classified as idiopathic (iVT). VT contributes significantly to the morbidity and mortality in patients with coronary artery disease (CAD) and dilated cardiomyopathy (DCM). Since mutations in arrhythmia-associated genes frequently determine arrhythmia susceptibility screening for disease-predisposing variants could improve VT diagnostics and prevent SCD in patients. METHODS: Ninety-two patients diagnosed with coronary heart disease (CHD), DCM, or iVT were included in our study. We evaluated genetic profiles and variants in known cardiac risk genes by targeted next generation sequencing (NGS) using a newly designed custom panel of 96 genes. We hypothesized that shared morphological and phenotypical features among these subgroups may have an overlapping molecular base. To our knowledge, this was the first study of the deep sequencing of 96 targeted cardiac genes in Kazakhstan. The clinical significance of the sequence variants was interpreted according to the guidelines developed by the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology (AMP) in 2015. The ClinVar and Varsome databases were used to determine the variant classifications. RESULTS: Targeted sequencing and stepwise filtering of the annotated variants identified a total of 307 unique variants in 74 genes, totally 456 variants in the overall study group. We found 168 mutations listed in the Human Genome Mutation Database (HGMD) and another 256 rare/unique variants with elevated pathogenic potential. There was a predominance of high- to intermediate pathogenicity variants in LAMA2, MYBPC3, MYH6, KCNQ1, GAA, and DSG2 in CHD VT patients. Similar frequencies were observed in DCM VT, and iVT patients, pointing to a common molecular disease association. TTN, GAA, LAMA2, and MYBPC3 contained the most variants in the three subgroups which confirm the impact of these genes in the complex pathogenesis of cardiomyopathies and VT. The classification of 307 variants according to ACMG guidelines showed that nine (2.9%) variants could be classified as pathogenic, nine (2.9%) were likely pathogenic, 98 (31.9%) were of uncertain significance, 73 (23.8%) were likely benign, and 118 (38.4%) were benign. CHD VT patients carry rare genetic variants with increased pathogenic potential at a comparable frequency to DCM VT and iVT patients in genes related to sarcomere function, nuclear function, ion flux, and metabolism. CONCLUSIONS: In this study we showed that in patients with VT secondary to coronary artery disease, DCM, or idiopathic etiology multiple rare mutations and clinically significant sequence variants in classic cardiac risk genes associated with cardiac channelopathies and cardiomyopathies were found in a similar pattern and at a comparable frequency.

RYR2 sequencing reveals novel missense mutations in a Kazakh idiopathic ventricular tachycardia study cohort.

Channelopathies, caused by disturbed potassium or calcium ion management in cardiac myocytes are a major cause of heart failure and sudden cardiac death worldwide. The human ryanodine receptor 2 (RYR2) is one of the key players tightly regulating calcium efflux from the sarcoplasmic reticulum to the cytosol and found frequently mutated (<60%) in context of catecholaminergic polymorphic ventricular tachycardia (CPVT1). We tested 35 Kazakhstani patients with episodes of ventricular arrhythmia, two of those with classical CPVT characteristics and 33 patients with monomorphic idiopathic ventricular arrhythmia, for variants in the hot-spot regions of the RYR2 gene. This approach revealed two novel variants; one de-novo RYR2 mutation (c13892A>T; p.D4631V) in a CPVT patient and a novel rare variant (c5428G>C; p.V1810L) of uncertain significance in a patient with VT of idiopathic origin which we suggest represents a low-penetrance or susceptibility variant. In addition we identified a known variant previously associated with arrhythmogenic right ventricular dysplasia type2 (ARVD2). Combining sets of prediction scores and reference databases appeared fundamental to predict the pathogenic potential of novel and rare missense variants in populations where genotype data are rare.

Sequence Alterations of I(Ks) Potassium Channel Genes in Kazakhstani Patients with Atrial Fibrillation.

INTRODUCTION: Atrial fibrillation (AF) is the most common sustained arrhythmia, and it results in significant morbidity and mortality. However, the pathogenesis of AF remains unclear to date. Recently, more pieces of evidence indicated that AF is a multifactorial disease resulting from the interaction between environmental factors and genetics. Recent studies suggest that genetic mutation of the slow delayed rectifier potassium channel (I(Ks)) may underlie AF. OBJECTIVE: To investigate sequence alterations of I(Ks) potassium channel genes KCNQ1, KCNE1 and KCNE2 in Kazakhstani patients with atrial fibrillation. METHODS: Genomic DNA of 69 cases with atrial fibrillation and 27 relatives were analyzed for mutations in all protein-coding exons and their flanking splice site regions of the genes KCNQ1 (NM_000218.2 and NM_181798.1), KCNE1 (NM_000219.2), and KCNE2 (NM_172201.1) using bidirectional sequencing on the ABI 3730xL DNA Analyzer (Applied Biosystems, Foster City, CA, USA). RESULTS: In total, a disease-causing mutation was identified in 39 of the 69 (56.5%) index cases. Of these, altered sequence variants in the KCNQ1 gene accounted for 14.5% of the mutations, whereas a KCNE1 mutation accounted for 43.5% of the mutations and KCNE2 mutation accounted for 1.4% of the mutations. The majority of the distinct mutations were found in a single case (80%), whereas 20% of the mutations were observed more than once. We found two sequence variants in KCNQ1 exon 13 (S546S G1638A) and exon 16 (Y662Y, C1986T) in ten patients (14.5%). In KCNE1 gene in exon 3 mutation, S59G A280G was observed in 30 of 69 patients (43.5%) and KCNE2 exon 2 T10K C29A in 1 patient (1.4%). Genetic cascade screening of 27 relatives to the 69 index cases with an identified mutation revealed 26.9% mutation carriers who were at risk of cardiac events such as syncope or sudden unexpected death. CONCLUSION: In this cohort of Kazakhstani index cases with AF, a disease-causing mutation was identified in 56.5 % of the referred patients. Further screening of mutations in other genes encoding cardiac ion channels is needed to clarify possible disease causing and founder mutations in Kazakhstani atrial fibrillation patients.