Major improvements were observed in persons with CF and the G551D-CFTR mutation for several CF disease parameters including a decrease in sweat chloride concentration to values approximating normal values, an average increase in the percent predicted forced expiratory volume in one second (ppFEV1) of 10%, significant weight gain, particularly in children and a 55% decrease in the frequency of respiratory exacerbations [17,25,26]. Here, CFTR is linked to cystic fibrosis.