A new pill may help in the fight with cystic fibrosis.

A study, funded in part by Vertex Pharmaceuticals, found the drug ivacaftor (pronounced eye va kaf tor) caused patients with a specific type of cystic fibrosis to improve lung function, gain weight, and fight other aspects of the disease.

“This is the first time that we have a therapy that is directed at the cause of cystic fibrosis,” says Dr. Michael Konstan, the chair of the Department of Pediatrics at Rainbow Babies and Children’s Hospital in Cleveland and one of the authors of the study. There is no cure for this disease and existing treatments just help alleviate some of the symptoms.

“This is a big deal,” says Robert Beall, the president and CEO of the Cystic Fibrosis Foundation. “The fact is it is obviously going to make a very big difference in the lives of patients.”

Cystic fibrosis is a genetic disease that causes problems with the balance of salt going in and out of cells. A sticky mucus clogs organs, particularly the lungs and liver. It can also cause digestive problems. About 1,000 new cases are diagnosed each year, according to the Cystic Fibrosis Foundation, and the average person with the disease dies before age 40.

Ivacaftor works for people with the G551D mutation of cystic fibrosis. Konstan says that only about 4% of the people with the disease have this specific mutation. “It really is a major milestone in the treatment of cystic fibrosis,” he says. “Even thought it only affects a small percentage (of patients) the hope is there that we can finally do something about this disease.”

The study, published in the New England Journal of Medicine Wednesday, looked at 84 people who got the drug. Those taking ivacaftor saw improvements within two weeks, which continued for the nearly yearlong trial. Drug recipients could blow out more than 10% more air from their lungs compared with patients who were not taking the drug, and were about half as likely to have a “pulmonary exacerbation” or a worsening of their lung disease that often requires hospitalization. On average, patients taking the drug grew more and put on more weight than the placebo group, according to the study, and had lower sweat chloride – an indicator of the disease.

Beall says the improved lung function helped patients double their ability to walk and one patient even started going the gym for the first time.

“We have an incredible proof of concept,” Beall says. He points to other research under way with ivacaftor combined with another drug that could help people with the most common mutation of cystic fibrosis. That trial is ongoing and the treatment is at least four or five years away from approval, but if it works, Beall says, it could help 90% of the people with cystic fibrosis.

In an editorial accompanying the study, Dr. Pamela Davis, of Case Western University paraphrased Winston Churchill, “This study is also a great victory in the war against genetic diseases and marks the end of the beginning for the treatment of the cystic fibrosis defect.”

Ivacaftor has been submitted to the FDA for approval, and could be available next year, according to Konstan. When it goes on sale it will be sold under the brand name Kalydeco (pronounced kuh-LYE-deh-koh).