STUDY OBJECTIVES: The goal of this study was to evaluate the association between a polygenic risk score (PRS) for QT prolongation (QTc-PRS), corrected QT intervals (QTc) and sudden cardiac death (SCD) in participants enrolled in the UK Biobank with and without sleep-disordered breathing (SDB). METHODS: The QTc-PRS was calculated using allele copy number and previously reported effect estimates for each single nuclear polymorphism. Competing-risk regression models adjusting for age, sex, body mass index, QT prolonging medication, race, and comorbid cardiovascular conditions were used for SCD analyses. RESULTS: A total of 500,584 participants were evaluated (56.5 ± 8 years, 54% female, 1.4% diagnosed with sleep apnea). A higher QTc-PRS was independently associated with the increased QTc interval duration ( CONCLUSIONS: In the UK Biobank population, the QTc-PRS was associated with SCD among participants with SDB but not among those without SDB, indicating that SDB is a significant modifier of the genetic risk. Black participants with SDB had a particularly high risk of SCD. CITATION: Arora A, Zareba W, Woosley RL, et al. Genetic QT score as a predictor of sudden cardiac death in participants with sleep-disordered breathing in the UK Biobank.