Cystic fibrosis (CF) is a genetic disorder impacting multiple organ systems, including the respiratory, digestive, and reproductive systems. It results in the body producing thick, sticky mucus that can clog airways and ducts. Understanding risk factors for CF or being a carrier of the CF gene is helpful for individuals and families.
The Genetic Foundation
Cystic fibrosis is caused by a mutation in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. This gene provides instructions for making a protein that regulates the movement of chloride ions and water in and out of cells. When the CFTR gene is mutated, this protein does not function correctly, leading to the production of unusually thick and sticky mucus.
CF is inherited in an autosomal recessive pattern. This means an individual must inherit two copies of the mutated CFTR gene, one from each parent, to develop the condition. If a person inherits only one mutated gene copy and one normal copy, they are considered a carrier. Carriers do not experience CF symptoms but can pass the mutated gene to their children. For two carriers, each pregnancy carries a 25% chance of the child having CF and a 50% chance of the child being a carrier.
Family History
A family history of cystic fibrosis or a known CF carrier increases the likelihood of being a carrier or having the condition. The closer the genetic relationship to someone with CF, the higher the risk. Parents of an individual with CF are carriers of the mutated gene.
Siblings of a person with CF who do not have the condition themselves have a two-thirds chance of being carriers. Aunts, uncles, and grandparents of an affected individual also have a 50% chance of being carriers. Knowing one’s family medical history regarding CF is an important step in assessing personal risk.
Ancestry and Population Risk
The prevalence of CFTR gene mutations varies among different ethnic and racial groups. Individuals of Northern European (Caucasian) descent have the highest incidence of CF and a significant carrier rate.
Other populations also have notable carrier rates, including Ashkenazi Jewish, Hispanic American, and African American individuals. While CF occurs in all races, it is less common in some groups, which can lead to a later diagnosis.
Understanding Your Risk Through Testing
Genetic testing provides definitive information about an individual’s carrier status or the presence of CF. Carrier screening is available for prospective parents to determine if they carry a CFTR gene mutation, performed using a blood sample or a cheek swab. These tests can identify 85% to 90% of common CFTR mutations in the Caucasian population, though rarer mutations may not be detected.
Newborn screening for CF is performed in the United States, detecting the condition before symptoms appear. For individuals with symptoms or a strong family history, diagnostic testing can confirm a CF diagnosis. Genetic counseling is also available to help interpret test results and understand the implications for personal health and family planning.