THURSDAY, July 2, 2015 (HealthDay News) -- Orkambi (lumacaftor and ivacaftor) has been approved by the U.S. Food and Drug Administration to treat cystic fibrosis in patients who have inherited two copies of a specific gene mutation from their parents.

The F508del mutation causes production of an abnormal protein that disrupts transport of water and chloride through the body, the FDA said Thursday in a news release. Having two copies of this gene mutation is the leading cause of cystic fibrosis, accounting for about half of all cases.

"The FDA encourages manufacturers to develop new and innovative treatments for serious rare diseases like cystic fibrosis," Dr. John Jenkins, director of the Office of New Drugs, Center for Drug Evaluation and Research, said in the news release. "Today's approval significantly broadens the availability of targeted treatments for the specific defects that cause cystic fibrosis."

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CF is an often-fatal genetic disorder that causes development of thick mucus that gathers in the lungs and digestive tract. This can lead to severe breathing and digestive problems, the agency said. Some 30,000 people in the United States have been diagnosed with the disease.

Orkambi was evaluated in clinical studies involving more than 1,100 people aged 12 and older with two copies of the F508del mutation. Improved lung function was seen in the treatment group, compared to those who got a placebo.

The drug's safety and effectiveness among cystic fibrosis patients who don't have the genetic mutation has not been evaluated, the FDA said.

Orkambi's most common side effects include shortness of breath, upper respiratory tract infection, nausea, diarrhea and rash. An increase in menstrual problems such as bleeding were reported among female users of childbearing age.

Orkambi is produced by Vertex Pharmaceuticals, based in Boston.

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The FDA has more about this approval.