Cystic fibrosis is a disease of genetic cause. It is called "autosomal recessive", that is to say that it is transmitted by both parents, usually healthy carriers.
How is a genetic disease transmitted?
There are more than 6, 000 listed genetic diseases. What is a genetic disease and how can it be transmitted?
The anomaly in question is located on the gene coding for the Cystic fibrosis transmembrane conductance regulator (CFTR) present at chromosome 7.
Each parent transmits a mutated allele of this gene. Given the improvement in the life expectancy of patients, cystic fibrosis can also be transmitted by a couple in which there is a patient and a healthy carrier, or even two patients.
The CFTR protein is a protein present in the membrane of the cells of the mucous walls, and more particularly of the respiratory, digestive, and other mucous membranes. This protein functions as a channel that allows the exchange of chloride ions between the inside and the outside of the cell, for example between the cell and the digestive tract.
When its gene is mutated, the channel no longer works. This causes in particular a decrease of excretion of water in the mucous membranes. This results in inflammation and thickening of the mucus that covers the mucous walls, for example in the respiratory tract. It is this thickening of mucus, which becomes viscous (hence the name of the disease), which causes the usual symptoms of cystic fibrosis.
The CFTR gene can carry many mutations: nearly 2, 000 different alterations of the gene have already been identified.
Each can cause malfunctions whose severity is variable. The expression of cystic fibrosis is therefore more or less severe depending on the nature of the mutations carried by the patient.