How does a person inherit cystic fibrosis?
Cystic fibrosis (CF) is an autosomal recessive genetic disorder, meaning that a person must inherit two copies of the defective gene (one from each parent) to develop the condition. The inheritance pattern of CF can be explained as follows:
1. Normal Allele (CFTR): The normal gene responsible for producing the cystic fibrosis transmembrane conductance regulator (CFTR) protein is denoted as CFTR. This protein helps regulate the movement of chloride and sodium ions across cell membranes, particularly in the lungs, pancreas, and other organs.
2. CF Allele (CF): The defective gene responsible for CF is denoted as CF. It contains mutations that impair the function or production of the CFTR protein.
3. Inheritance Patterns:
- Carriers (CF/CFTR): Individuals who carry one copy of the normal CFTR allele and one copy of the CF allele are called carriers. They do not have CF but can pass on the CF allele to their offspring.
- Affected Individuals (CF/CF): Individuals who inherit two copies of the CF allele (one from each parent) have CF. They lack functional CFTR proteins, leading to the development of the characteristic symptoms and complications of the condition.
- Non-Carriers (CFTR/CFTR): Individuals who have two copies of the normal CFTR allele do not have CF and are not carriers.
4. Risk of Inheriting CF:
- Parents Both Carriers: If both parents are carriers (CF/CFTR), each pregnancy has a 25% chance of resulting in a child with CF, a 50% chance of a carrier child (CF/CFTR), and a 25% chance of a non-carrier child (CFTR/CFTR).
- One Parent Affected and One Carrier: If one parent is affected (CF/CF) and the other is a carrier (CF/CFTR), each pregnancy has a 50% chance of resulting in a carrier child (CF/CFTR) and a 50% chance of an affected child (CF/CF).
- Both Parents Affected: If both parents are affected (CF/CF), all offspring will inherit two copies of the CF allele and will have CF.
It's important to note that while the inheritance pattern of CF is well-understood, the specific mutations in the CFTR gene can vary, and the severity of the condition can also vary among individuals with CF. Genetic counseling is recommended for individuals with a family history of CF or those who are considering having children to assess their risk and make informed decisions about reproductive planning.