Table 1. Classes of cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations.

Type of mutation	Type of CFTR mutation	Percent of people with CF who have at least 1 mutations.
Normal	CFTR protein is created and moves to the cell surface, allowing the transfer of chloride and water.
Class I	No functional CFTR protein is created	22 percent
Class II	CFTR protein is created but misfolds, keeping it from moving to the cell surface. This is called a trafficking defect.	88 percent
Class III	CFTR protein is created and moves to the cell surface but the channel gate does not open. This is called a defective channel regulation.	6 percent
Class IV	CFTR protein is created and moves to the cell surface but the channel function is faulty. This is called decreased channel conductance.	6 percent
Class V	Normal CFTR protein is created and moves correctly to the cell surface but not enough amount of the protein. This is called reduced synthesis of CFTR.	5 percent
Class VI	CFTR protein is created but it does not work properly at the cell membrane. This is called decreased CFTR stability.	5 percent