Abstract 12560: Targeted Next Generation Exomic Sequencing of Cardiac Electrophysiology Genes in Cases of Drug-Induced Torsades de Pointes
Introduction: Prolongation of the QT interval leading to torsades de pointes (TdP), the drug-induced long QT syndrome (diLQTS), is an idiosyncratic, severe adverse drug event. Previous studies screening subjects with diLQTS for mutations in congenital LQTS (cLQTS) disease genes have identified likely sub-clinical cLQTS in 10–20% suggesting rare variants contribute to risk, but the extent is unknown. We report here the incidence of rare variants in a large set of genes involved with control of heart rhythm in a cohort of patients with diLQTS.
Methods: We designed a custom Nimblegen array to capture exon and flanking sequences in 79 genes including known congenital LQTS disease genes, other genes associated with congenital arrhythmia syndromes (e.g. RYR2, GPD1L ), genes encoding known or suspected partners of disease gene proteins (e.g. KCNEx, SCNxB ), and genes identified in genome-wide studies as modulators of normal QT intervals (e.g. NOS1AP ). We developed a barcoding approach to multiplex four samples in a single lane of the Illumina Genome Analyzer II. Subjects were drawn from Vanderbilt's acquired LQTS cohort and all had documented diTdP.
Results: Targeted re-sequencing of 305 kb was attempted in 32 subjects. Over 172 million single end 43 base pair reads were generated, of which 50% uniquely mapped to the reference sequences. Mean depth of coverage was 90x before removal of duplicate reads, 20x after duplicate removal, and 61% of targeted capture sequence was covered at least 8x with Phred-like Q score 30. We identified 1,111 variants of which 121 occurred once and were not found in public databases. Of these, 72 are predicted to cause missense or splice site errors. Previously unreported mutations in cLQTS genes were identified in 19/32 subjects.
Conclusions: This novel multiplexing approach generated high quality targeted exomic sequence for 79 candidate diLQTS susceptibility genes and identified multiple previously-undescribed rare variants. Our findings suggest that the overlap between congenital and acquired long QT syndromes is greater than heretofore reported. Elucidating the functional consequences of these mutations will contribute to understanding variability in response to drug treatment and to deploying safe, targeted therapy.
- © 2010 by American Heart Association, Inc.