More than 20 years after scientists discovered the mutated gene responsible for cystic fibrosis (CF), a drug based on that finding may be on the cusp of reaching patients.

VX-770, a drug that targets a mutation found in some CF patients passed a phase III clinical trial of 161 patients age 12 and older, said its manufacturer Vertex Pharmaceuticals, based in Cambridge, Massachusetts, and the Cystic Fibrosis Foundation, which kicked in $75 million to develop the drug.

Patients who received the drug, which opens an ion channel defective in CF, reported better lung function, fewer heart and respiratory problems and gained more weight, compared to those on placebo.

About 1800 different mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene have been implicated in the disease. The gene encodes a molecular channel that shuttles chloride ions across cellular membranes, and people with two mutated copies develop mucus-filled lungs susceptible to infection. Few patients live to see their 30s.

In 1989, CF became the first disease pinned to a specific gene mutation, without the benefit of knowing the protein first. For the whole story, read our award-winning feature on the discovery and efforts to translate it into treatments like VX-770.

Vertex plans to file for FDA approval soon. Only about 4% of CF patients possess the mutation that VX-770 targets, but the drug might also benefit patients with other mutations. Vertex is also developing a drug, VX-809, that targets the most common CF mutation and is now testing it in combination with VX-770, with results expected later this year.

Image of a structural model of the CFTR protein courtesy Wikimedia Commons