Reported by ClinVar to cause Long QT Syndrome (https://www.ncbi.nlm.nih.gov/clinvar/variation/14443/). In ClinVar, it is reported as “likely pathogenic” or “pathogenic” by submissions from Blueprint Genetics, Invitae, and OMIM, however it’s listed as “uncertain significance” by GeneDx.
These resources reference a couple of papers, including Kapplinger et al. 2009 (https://www.ncbi.nlm.nih.gov/pubmed/19716085), which found this variant in 5 out of 2500 patients tested.