Patients with the rs74551128 AA genotype (two copies of the CFTR A455E variant) and cystic fibrosis may respond to ivacaftor treatment. FDA-approved drug labeling information and CPIC guidelines indicate use of ivacaftor in cystic fibrosis patients with at least one copy of a list of 33 CFTR genetic variants, including A455E. Other genetic and clinical factors may also influence response to ivacaftor.