Vertex Pharmaceuticals Inc. said Friday that European regulators have approved its new drug Kalydeco to treat cystic fibrosis, a rare and often fatal disease.

Cambridge-based Vertex received approval to market Kalydeco in the United States earlier this year to some cystic fibrosis patients. It has been estimated that it will cost nearly $300,000 a year to treat a patient with Kalydeco.

Cystic fibrosis drugs already on the market treat symptoms of the inherited disease, which causes mucus to thicken and block the passage of air to the lungs, making it harder for patients to breathe and digest food.

Kalydeco, by contrast, is designed to target the cause of the disease in a subset of people with cystic fibrosis, Vertex said in a press release. Some patients have a genetic mutation in a particular protein that sits at the surface of cells and regulates the flow of water and salt. The Vertex drug binds to the protein and works to restores its normal function, helping patients hydrate their airways to clear mucus, absorb and digest food and gain weight.

Vertex shares closed up 24 cents at $49.32.