The first drug that treats the root cause of cystic fibrosis won approval Tuesday, offering a life-changing treatment for a handful of patients with the deadly illness and broader hope for thousands more patients with the inherited disease.

This is a great step forward for those of us with CF and the G551D mutation, while the damage is already done in my case this will help so many people suffering around the world.

"Even though this drug isn't for the majority of people, it proves that you can look at the mistake in the genes and design a drug in a rational way that will fix the problem," said Dr. Drucy Borowitz of the State University of New York at Buffalo, where she directs the cystic fibrosis program..

Vertex executives said Kalydeco would cost $294,000 for a year's supply, placing it among the most expensive prescription drugs sold in the U.S. Specialty drugmakers are known to charge $300,000 or more for drugs that treat very small groups of patients.

"The drug is priced for the value it will deliver to this very small group of patients," Vertex Executive Vice President Nancy Wysenski told analysts.

Wysenski said Vertex would provide the medicine for free to people with no insurance and household income of $150,000 or less. The company will also cover 30 percent of copay costs for select patients who have insurance