Two normally functioning copies of the CFTR gene commonly exist in the DNA of most people. For a person to be affected by cystic fibrosis both of these copies need to be malfunctioning. Meaning both are not producing the functional CFTR protein. Around one in thirty people have only one working copy of the CFTR gene, which makes them the carriers of the genetic mutation even though they are not affected by cystic fibrosis themselves.

If two people who are carriers of the genetic mutation parent a child, that child will not necessarily be affected with cystic fibrosis. In fact the chances of that happening stand are only 25%. This is because it is necessary for the child to inherit the malfunctioning copies of the CFTR gene from both parents. Chances for the child to become a carrier are significantly higher at 50%.
There are over 1500 mutations of the CFTR gene that can be responsible for the development of cystic fibrosis. However, in a great majority of cases, more than two-thirds, the culprit is the ΔF508 mutation. This genetic mutation is actually a deletion of three nucleotides on the protein chain at the 508th position and a loss of the amino acid called phenylalanine. In the United States, this mutation is responsible for more than 90% of all cystic fibrosis cases.

Recommended Read: Signs & Symptoms of Cystic Fibrosis

As it is the case with most inherited conditions, family history of the disease is an important risk factor for developing cystic fibrosis. Another important risk factor is race. Statistically, the largest portion of individuals suffering from cystic fibrosis is of Caucasian and Northern European ancestry (1 in every 3000). Individuals of Latino, African, and Asian ancestry are at a lesser risk of suffering from the disease. By nationality, Ireland is the country with the highest risk, where 1 in every 1400 newborns are expected to be affected with cystic fibrosis.