Abstract 17963: Novel loss of Function Mutations in HCN4 Identified in Early-Onset Atrial Fibrillation
Introduction: Atrial fibrillation (AF) is the most common arrhythmia, affecting nearly 3 million Americans. In a recent meta-analysis of genome-wide association studies for AF, we identified a novel susceptibility locus on chromosome 15q24 located in the first intron of HCN4 (hyperpolarization-activated cyclic nucleotide-gated channel 4). HCN4 is highly expressed in the sinoatrial node, contributes to spontaneous pacemaking, and mutations in HCN4 lead to sinus node dysfunction. Therefore, we hypothesized that mutations in HCN4 may be present in individuals with AF.
Methods: We screened 553 cases with early-onset AF from Massachusetts General Hospital and 525 referents without AF from the Framingham Heart Study. The coding region (exons 1-8) of HCN4 was screened using high-resolution melting and direct sequencing. Variants not found in controls or the exome variant server were considered novel. Novel HCN4 variants were constructed using site-directed mutagenesis and were expressed in Chinese Hamster Ovary cells. Wild type and variant HCN4 currents were measured 24-48 hours post transfection using patch clamp electrophysiology.
Results: We identified eight novel HCN4 variants in the early-onset AF cases and four novel HCN4 variants in the referents. Of the eight novel variants in the AF cases two resulted in a loss of function. However, none of the four novel variants in the control population had functional effects. The two loss of function mutations were P257S (proximal N-terminus) and L385P (middle of fourth transmembrane - voltage sensor) which produced no measurable current. The individual with the P257S mutation had persistent AF, a family history of AF and the age of onset was 30 years. The individual with the L385P mutation had paroxysmal AF, no family history and the age of onset was 51 years.
Conclusion: We have identified novel loss of function mutations in the HCN4 channel that are associated with early-onset AF.
- © 2012 by American Heart Association, Inc.