CF Gene Mutation Testing

The CF gene mutation test identifies mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene on chromosome 7. Each cell in the human body (except sperm and eggs) has 46 chromosomes (23 inherited from the mother and 23 from the father). Genes on these chromosomes form the body’s blueprint for producing proteins that control body functions. Cystic fibrosis is caused by a mutation in each of the two copies of the CFTR gene located on chromosomes 7. Both copies (alleles) of this gene must be abnormal to cause CF. If only one copy of the gene pair is mutated, the individual is a CF carrier. Carriers are not ill; they generally do not have any CF symptoms, but they can pass their abnormal CF gene copy on to their children.

To date, more than 1,000 different mutations of the CFTR gene have been identified, but only a few of the mutations are common. The majority of cystic fibrosis cases in the U.S. are caused by a mutation called deltaF508 (F508). Recommendations by the American College of Medical Genetics (ACMG) and the American College of Obstetricians and Gynecologists (ACOG) have led to the adoption of a standard CF gene mutation panel. It includes 23 of the most common mutations (those with frequencies greater than 0.1% in the general U.S. population). Some laboratories use expanded panels of as many as 97 mutations designed to pick up more rare mutations particular to specific ethnic populations. The vast majority of rare CF mutations are "private" and unique to a single individual or family.

In CF gene mutation testing, the laboratory specifically examines the CFTR gene on each chromosome 7 for the 23 mutations. If the initial panel of 23 mutations demonstrates a mutation, additional testing for other less common mutations may be indicated if the individual is suspected of having the disease.

A blood sample is drawn from an infant’s heel, a spot of blood is put onto filter paper, or a blood sample is obtained by inserting a needle into a vein in the arm. A scraping of the inner cheek, called a buccal swab sample, or prenatal (amniocentesis or chorionic villus) specimens may also be used.

No test preparation is needed.