ABSTRACT
AIMS: Atrial fibrillation (AF) is a common arrhythmia with an important heritable aspect. The genetic factors underlying AF have not been fully elucidated. METHODS AND RESULTS: We screened six candidate genes (CAV1, KCNJ2, KCNQ1, NKX2.5, PITX2, and TBX5) for novel mutations in 139 patients of Chinese descent with early-onset AF and 576 controls. Four missense TBX5 mutations, p.R355C, p.Q376R, p.A428S, and p.S372L, were identified in evolutionarily conserved regions. We did not find any mutations in CAV1, KCNJ2, KCNQ1, NKX2.5, and PITX2. These mutations increased the expression of atrial natriuretic peptide (ANP) and connexin-40 (CX40) in the primarily cultured rat atrial myocytes but did not alter the expression of cardiac structural genes, atrial myosin heavy chain-α (MHC-α) and myosin light chain-2α (MLC-2α). Overexpression of p.R355C developed an atrial arrhythmia suggestive of paroxysmal AF in the zebrafish model. To replicate our findings, we screened TBX5 in 527 early-onset AF cases from the Massachusetts General Hospital AF study. A novel TBX5 deletion (ΔAsp118, p.D118del) was identified, while no TBX5 mutations were identified in 1176 control subjects. CONCLUSION: Our results provide both genetic and functional evidence to support the contribution of TBX5 gene in the pathogenesis of AF. The potential mechanism of arrhythmia may be due in part to the disturbed expression of ANP and CX40.
Subject(s)
Atrial Fibrillation/genetics , Genetic Predisposition to Disease , Mutation/genetics , T-Box Domain Proteins/genetics , Adult , Age of Onset , Aged , Asian People , Atrial Fibrillation/metabolism , Connexins/genetics , Female , Homeodomain Proteins/genetics , Humans , Middle Aged , Mutation, Missense/genetics , Pregnancy , T-Box Domain Proteins/metabolism , Transcription Factors/metabolism , White People , Gap Junction alpha-5 ProteinABSTRACT
BACKGROUND: Atrial fibrillation (AF) is the most common arrhythmia, and a recent genome-wide association study identified the hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) as a novel AF susceptibility locus. HCN4 encodes for the cardiac pacemaker channel, and HCN4 mutations are associated with familial sinus bradycardia and AF. OBJECTIVE: The purpose of this study was to determine whether novel variants in the coding region of HCN4 contribute to the susceptibility for AF. METHODS: We sequenced the coding region of HCN4 for novel variants from 527 cases with early-onset AF from the Massachusetts General Hospital AF Study and 443 referents from the Framingham Heart Study. We used site-directed mutagenesis, cellular electrophysiology, immunocytochemistry, and confocal microscopy to functionally characterize novel variants. RESULTS: We found the frequency of novel coding HCN4 variants was 2-fold greater for individuals with AF (7 variants) compared to the referents (3 variants). We determined that of the 7 novel HCN4 variants in our AF cases, 1 (p.Pro257Ser, located in the amino-terminus adjacent to the first transmembrane spanning domain) did not traffic to cell membrane, whereas the remaining 6 were not functionally different from wild type. In addition, the 3 novel variants in our referents did not alter function compared to wild-type. Coexpression studies showed that the p.Pro257Ser mutant channel failed to colocalize with the wild-type HCN4 channel on the cell membrane. CONCLUSION: Our findings are consistent with HCN4 haploinsufficiency as the likely mechanism for early-onset AF in the p.Pro257Ser carrier.
Subject(s)
Atrial Fibrillation/genetics , Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels/genetics , Muscle Proteins/genetics , Potassium Channels/genetics , Age of Onset , Animals , Atrial Fibrillation/epidemiology , CHO Cells , Cricetulus , Electrophysiologic Techniques, Cardiac , Female , Haploinsufficiency , Humans , Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels/metabolism , Male , Microscopy, Confocal , Middle Aged , Muscle Proteins/metabolism , Mutagenesis, Site-Directed , Potassium Channels/metabolism , Protein TransportABSTRACT
BACKGROUND: Dilated cardiomyopathy (DCM) is a leading cause of heart failure and death. The etiology of DCM is genetically heterogeneous. OBJECTIVES: We sought to define the prevalence of mutations in the RNA splicing protein RBM20 in a large cohort with DCM and to determine whether genetic variation in RBM20 is associated with clinical outcomes. METHODS: Subjects included in the Genetic Risk Assessment of Defibrillator Events (GRADE) study were aged at least 18 years, had an ejection fraction of ≤30%, and an implantable cardioverter-defibrillator (ICD). The coding region and splice junctions of RBM20 were screened in subjects with DCM; 2 common polymorphisms in RBM20, rs942077 and rs35141404, were genotyped in all GRADE subjects. RESULTS: A total of 1465 subjects were enrolled in the GRADE study, and 283 with DCM were screened for RBM20 mutations. The mean age of subjects with DCM was 58 ± 13 years, 64% were males, and the mean follow-up time was 24.2 ± 17.1 months after ICD placement. RBM20 mutations were identified in 8 subjects with DCM (2.8%). Mutation carriers had a similar survival, transplantation rate, and frequency of ICD therapy compared with nonmutation carriers. Three of 8 subjects with RBM20 mutations (37.5%) had atrial fibrillation (AF), whereas 19 subjects without mutations (7.4%) had AF (P = .02). Among all GRADE subjects, rs35141404 was associated with AF (minor allele odds ratio = 0.62; 95% confidence interval = 0.44-0.86; P = .006). In the subset of GRADE subjects with DCM, rs35141404 was associated with AF (minor allele odds ratio = 0.58; P = .047). CONCLUSIONS: Mutations in RBM20 were observed in approximately 3% of subjects with DCM. There were no differences in survival, transplantation rate, and frequency of ICD therapy in mutation carriers.
