Cystic fibrosis (CF) was one of the first diseases whose causative gene, CFTR, was identified by human genetic mapping. Subsequent work over two decades revealed that each of the disease mutations in CFTR affects the protein differently, making corrective therapy very challenging. A small molecule screening approach identified a compound that partially corrected the defect caused by the G551D mutation, present in about 4% of patients with CF. A version of this compound, known as ivacaftor, was later shown to improve health and lung function in patients over 5 years of age who received the drug over 48 weeks [Ramsey et al 2011]. Ivacaftor has not yet been shown to affect survival in G551D carriers, and apparently has no benefit for the majority of CF patients, who carry other mutations. Despite these limitations, ivacaftor is one of the first examples of an effective treatment that targets patients carrying a particular disease mutation.
