Single Cell Transcriptomic and Genomic Characterization of Brugada Syndrome Associated Genes

Brugada syndrome (BrS) is a rare, inherited arrhythmia with high risk of sudden cardiac death. Complex genetic background of BrS primarily involves mutations in genes encoding ion channels and regulatory/structural proteins. However, the molecular pathways and single cell expression patterns linked to clinically associated genes in BrS are not well defined. To evaluate the convergence of key genes, domains, motifs, molecular pathways, and single cell expression associated with BrS, we collected 733 mutations represented by 16 sodium, calcium, potassium channels, regulatory and structural genes related to BrS reported between 1999-2019.266 of the clinically relevant mutations (splice site, stop, frame shift and deleterious missense) in genes occurred once and 88 mutations were recurrent in nature, which appeared at two to forty-three instances. We observed an over-representation of clinically relevant mutations (~80%) in SCN5A gene, and also identified several candidate genes, including GPD1L, TRPM4, and SCN10A. Single cell transcriptomic analysis revealed restrictive expression of highly mutated BrS genes. Furthermore, protein domain enrichment analysis revealed that a large proportion of the mutations impacted ion-transport domains in multiple genes, SCN5A, TRPM4 and SCN10A. Gene enrichment analysis identified the action potential pathway as the most significant pathway involving the mutated genes in BrS. A comparative protein domain analysis of the SCN5A further established a significant (p=0.04) relation between mutation distribution and ion-transport domain. A strong association (p=0.00003) was also observed between mutation distribution across the ion transport domain and early/late onset of BrS. The significant role of the mutations in the ion transport domain leading to BrS manifestation was further established by window-based and MEME motif analysis which identified residue 1321-1380 (part of ion transport domain) as one of the significant (p=0.02) hotspot regions. Our study identified genomic and proteomic hotspots and a convergent pathway (ion transport) that provides in-depth insight into the complex pathophysiology of BrS. Single cell transcriptome profile of heart tissue shows that highly mutated genes (SCN5A and GPD1L) in BrS are restrictively expressed in ventricular cardiomyocyte cell type.