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Cystic fibrosis is a genetically inherited, lethal disease. CF occurs in all ethnic groups with the highest incidence occurring in the caucasian population. CF is a multi-organ disease affecting primarily the lungs and the digestive system. In the lungs, CF causes severe breathing problems. A build-up of thick mucus makes it difficult to clear bacteria and leads to cycles of infection and inflammation, which damage the delicate lung tissues. People with CF must follow a demanding daily routine of physical therapy to keep the lungs free of congestion and infection.
In the digestive tract, CF makes it extremely difficult to digest and absorb adequate nutrients from food. Thick mucus blocks the ducts of the pancreas, preventing enzymes from reaching the intestines to digest food. Therefore, most persons with CF must consume a large number of artificial enzymes (on average 20 pills a day) with every meal and snack, to help them absorb adequate nutrition from their food.
Genetics and CF: Our hereditary information is arranged into rod-like structures called chromosomes. In a typical individual, there are 46 chromosomes which come in pairs, giving us a total of 23 pairs. One of each pair of chromosomes comes from each parent. Chromosomes contain genes, which tell our bodies how to grow and develop. Since we have two copies of each chromosome, we have two copies of each gene. Mutations or changes in a particular gene can cause the gene not to work properly. CF is caused by mutations in the CFTR gene. Genes work in the body by being translated into proteins, which actually carries out the functions in the body. A mutation causes the gene to be unable to be translated into a functional protein, thereby, resulting in the symptoms of CF.
CF can only be transmitted when both parents are carriers. It is inherited in an autosomal recessive pattern. This means that in order to be affected with CF, an individual must have mutations on both copies of their CFTR genes. Carriers have one copy of the CFTR gene with a mutation, while the second copy does not have a mutation. Carriers are usually asymptomatic. However, when two carriers have children together, there is a 25% chance for each of their offspring to be affected with cystic fibrosis.
The following diagram illustrates this.
Chances of transmission when both parents are carriers of the CFTR gene with a mutation.