Molecular Genetic And Clinical Studies Of Hypertrophic Cardiomyopathy

Background:Hypertrophic Cardiomyopathy(HCM)is the most common genetic heart disease caused by mutations that encode sarcomeric protein,affects one in every 500 people in the general population and represents a major cause of sudden cardiac death(SCD)in adolescent athletes.The biggest challenge of HCM is the heterogeneity of genotype and phenotype.Heterogeneity can be explained by the causative gene,the position of the amino acid residue affected by a mutation within the protein and modifying genetic and environmental factors.In addition to that,multiple mutations were associated with a more severe phenotype compared with single-mutation carriers.It implys that the gene dose effect may contribute to HCM heterogeneity as well.However the basic molecular genetics of this mechanism is not clear.Objective:We aim to investigate the association between mutilple mutations and clinical heterogeneity within the proband who had double-ventricular hypertrophy with right ventricular outflow tract obstruction and her parents who had left ventricular hypertrophy without obstruction by next generations sequencing(NGS),such as Whole-Genome Sequencing(WGS)and Whole-Exon Sequencing(WES).Methods:Two HCM families were studied.Family l was comprising of 3 generations and 27 members and family 2 was comprising of 3 generations and 11 members.Proband(?:11)was a shared member of both family 1 and fanily 2,because her parents were ?:14 of family 1 and ?:15 of family 2.Clinical,electrocardiographic(ECG),and echocardiography in all the members of the two families were collected.WES(Illumina,San Diego,CA)were performed in 2 HCM phenotype positive(?:2,?:14)and 1 HCM phenotype negative(?:2)members in family 1 and 3 HCM phenotype positive(?:3,?:15,?:16)and 1 HCM phenotype negative(?:19)members in family 2 while WGS(Illumina,San Diego,CA)was performed in the proband(?:11).The identified mutations were confirmed by bi-directional Sanger sequencing in all family members and 216 healthy controls.The study was approved by our institutional review board and written informed consent was obtained from all subjects.Results:1.Six members(?:2,?:3,?:8,?:14,?:6,?:11)of family 1 were diagnosed as HCM and the remaining members were not diagnosed as HCM;four members(1:3,?:15,?:16,?:11)of family 2 were diagnosed as HCM and the remaining members were not diagnosed as HCM;2.After advanced bioinformatics analysis of WES data,34 candidate mutations in family 1 and 9 candidate mutations in family 2 were selected as possibly pathogenic mutations;3.Based on the genotype-phenotype analysis of the 43 candidate mutations,four candidate mutations(SYNE2 E6435K,LTBP1 D591H,LAMA1 A2022T,IRF9 c.496-5C>T)in family 1 and two candidate mutations(CTNNA1 N257S And FOXM1 R754H)in family 2 were picked out as pathogenic mutations;4.After Sanger sequencing of the 4 mutations in family 1 and 2 mutations in family 2,SYNE2 E6435K and IRF9 c.496-5C>T segregated with HCM in family 1 and CTNNA1 N257S and FOXM1 R754H segregated with HCM in family 2;5.Regard to the associations between effect of the amino acid residue affected by the mutation within the related protein and HCM,we finally confirmed that SYNE2 E6435K was the pathogenic mutation of family 1 and CTNNA1 N257S was the pathogenic mutation of family 2;5.Double mutations(SYNE2 E6435K,CTNNA1 N257S)of the proband(?:11)aggravated its clinical phenotype.For the first time,this study directly identified the source of multiple mutations in HCM patients and investigates the mechanism of multiple mutations in the significant heterogeneity of HCM.Conclusions:In this study,two new mutations(SYNE2 E6435K and CTNNA1 N257S)were found in two unrelated HCM families by using WES.Mutiple mutations may contribute to phenotypic heterogeneity of HCM by the interaction between S YNE2 E6435K and CTNNA1 N257S.BACKGROUD&OBJECTIVE:Hypertrophic cardiomyopathy(HCM)is the most common genetic heart disease,with a prevalence of approximately 0.02?0.23%among the overall population,and leads to early death and congestive heart failure.Apical hypertrophic cardiomyopathy(AHCM)is a relatively rare form of HCM,originally described in Japan and later in the Western hemisphere.Patients with HCM have been found to have a high prevalence of myocardial bridging(MB),with reported rates of 30%-50%on angiography.The clinical significance and prognostic value of MB of the coronary arteries in AHCM patients have rarely been described.We sought to determine the prevalence and clinical effects of myocardial bridging(MB)in patients with apical hypertrophic cardiomyopathy(AHCM).METHODS:We screened 212 consecutive AHCM patients who underwent coronary angiography at Fuwai Hospital in Beijing,China from January 1994 to February 2016.Inclusion criteria:1.Patients with compression of MB of the tunnelled segment>50%as AHCM with MB group;2.Patients without MB or coronary atherosclerotic stenosis as AHCM without MB group.Exclusion criteria:1.Patients with coronary atherosclerotic stenosis;2.Patients with left out-flow obstruction and mid-ventricular obstruction.The primary clinical endpoint was cardiovascular(CV)mortality including the following:(1)SCD(unexpected within 1 h of witnessed collapse or nocturnal in previously stable patients);(2)heart failure(HF)-related death occurring in patients with progressive cardiac decompensation ? 1 year before death;(3)stroke-related death that occurred as a consequence of a probable or proven embolic stroke;(4)aborted cardiac arrest or appropriate discharge of an implantable cardioverter defibrillator(ICD)for ventricular fibrillation,and(5)patients who underwent heart transplantation for drug-refractory HF were recorded as having surrogate HF-related death.The secondary endpoints included CV-related morbidity as follows:unexplained syncope;non-sustained ventricular tachycardia(NSVT,<30 consecutive ventricular beats);atrial fibrillation;myocardial infarction;mural thrombus;and embolic stroke(ES),transient ischaemic attack(TIA)or progressive HF,with an increase of at least one NYHA functional class.We also reviewed patient information regarding cardiovascular(CV)risk factors,symptoms,and occurrence of CV events.RESULTS:Of 212 AHCM patients,60 patients with MB and 100 patients without MB or coronary atherosclerotic stenosis were included,while 48 patients with coronary artery disease(10 of them also had MB)and 4 patients with obstructions and MB simultaneously were excluded.Patients with MB showed higher rates of angina(63.2%vs.40%;p=0.003),symptoms mimicking non-ST-segment elevation myocardial infarction(NSTEMI)(15%vs.3%,p=0.013)and New York Heart Association(NYHA)class III/IV(14.7%vs.4%;p=0.01)than patients without MB.The mean follow-up periods(56.9±49.9 vs.55.7±45 months;p=0.378)and CV mortality(2.9%vs.2%;p=0.9)were similar between patients with and without MB.Kaplan-Meier estimates demonstrated patients with MB to have lower CV event-free survival rates than those without MB(73.5%vs.88%;p=0.031).MB(HR:2.69,95%CI,1.14-6.38),female(HR:2.42,95%CI,1.02-5.75)and late gadolinium enhancement(LGE)(HR:3.62,95%CI,1.34-9.75)emerged as independent risk factors for CV events in multivariate Cox regression analysis after adjusting for other risk factors.CONCLUSION:For patients with AHCM,the presence of MB was associated with a worsening of symptoms,including higher prevalence of angina and mimicking of NSTEMI than AHCM patients without MB.Moreover,AHCM patients with MB had increased incidence of cardiovascular events than those without MB.However,the presence of MB did not increase the cardiovascular mortality in AHCM patients.After adjusting for other risk factors of CV events,MB was one of the independent risk factors for CV events in patients with AHCM.