In vivo characterization of candidate genes for heart rate variability identifies culprits for sinoatrial pauses and arrests

A meta-analysis of genome-wide association studies(GWAS) recently identified eight loci that are associated with heart rate variability (HRV) in data from 53,174 individuals. However, functional follow-up experiments - aiming to identify and characterize causal genes in these loci - have not yet been performed. We developed an image- and CRISPR- Cas9-based pipeline to systematically characterize candidate genesfor HRV in live zebrafish embryos and larvae. Nine zebrafish orthologues of six human candidate geneswere targeted simultaneously in fertilized eggs from fish that transgenically express GFP on smooth muscle cells (Tg( acta2:GFP )), to visualize the beating heart. An automated analysis of 30s recordings of 384 live zebrafish atria at 2 and 5 days post-fertilization helped identify genes that influence HRV ( kiaa1755 and gngt1); heart rate ( kiaa1755 ); sinoatrial pauses and arrests ( syt10 , hcn4 and kiaa1755 ); and early cardiac development ( gngt1, neo1a ). Hence, comprehensively characterizing candidate genesin GWAS-identified loci for HRV in vivo helped us identify previously unanticipated culpritsfor life-threatening cardiac arrhythmias.