 At the first study visit Visit 1, the participant will come to the Diabetes Center after an overnight fast of at least 8 hours. The following will occur at this study visit: informed consent; brief medical history; weight and height; vital signs and blood pressure; blood draw for DNA extraction, and an extra research tube for storage; administration of 75g Glucola load as per a standard oral glucose tolerance test OGTT protocol; and blood work for glucose and insulin at 30, 60, 90 and 120 minutes after the glucose load. This will be scheduled at a time that is convenient to the patient, with an attempt to coordinate with the patients visit to the CF clinic prior to starting lumacaftor-ivacaftor combination drug. 