Cystic fibrosis (CF) is a lifelong genetic condition. It primarily impacts the lungs and digestive system, leading to various health challenges. Understanding how CF is passed down through families involves examining specific genetic factors.
The CFTR Gene
Cystic fibrosis results from a mutation in a specific gene called the Cystic Fibrosis Transmembrane Conductance Regulator, or CFTR gene. This gene provides instructions for creating the CFTR protein, which regulates the movement of salt and water in and out of cells. When a mutation occurs in the CFTR gene, it leads to the production of a faulty or absent protein. This malfunction causes the mucus produced in various organs to become unusually thick and sticky.
Understanding Recessive Inheritance
For an individual to develop cystic fibrosis, they must inherit two copies of the mutated CFTR gene. One mutated copy comes from each biological parent. This pattern is known as autosomal recessive inheritance, where two altered copies are necessary for the condition to manifest. Inheriting only one mutated copy of the CFTR gene does not cause the disease.
The Role of Carriers
Individuals who inherit one normal CFTR gene and one mutated CFTR gene are considered “CF carriers.” These carriers do not exhibit symptoms of cystic fibrosis. This is because the single healthy gene can produce enough functional CFTR protein to prevent the disease’s full effects. Many carriers are unaware of their status unless they undergo specific testing or have a family history of CF.
Calculating Inheritance Probabilities
The likelihood of a child inheriting cystic fibrosis depends on the genetic status of both parents. If both parents are CF carriers, each child has a 25% chance of developing CF, a 50% chance of being a carrier like their parents, and a 25% chance of being unaffected and not a carrier. When one parent has CF and the other is a carrier, there is a 50% chance for each child to have CF and a 50% chance to be a carrier. If one parent has CF and the other is not a carrier, every child will be a carrier, but none will have CF.
Genetic Testing for CF
Several types of genetic testing are available for cystic fibrosis. Carrier screening is offered to individuals or couples planning a family, determining if they carry a mutated CFTR gene. Newborn screening is a routine test performed shortly after birth to identify newborns who may have CF, allowing for early diagnosis and treatment. Diagnostic testing, which often includes a sweat test or genetic test, is used for individuals who are showing symptoms of CF to confirm a diagnosis.