The multiple problems caused by cystic fibrosis are due to the mutation of a gene called the cystic fibrosis transmembrane conductance regulator (CFTR).
Each of us inherits two CFTR genes, one from each parent. Children who inherit abnormal CFTR genes from both parents will have cystic fibrosis whereas children who inherit only one faulty gene will not have cystic fibrosis but they will be carriers of this disease.
Where both parents are carriers of the disease, there is a twenty five per cent chance that this will be passed on to the child, there is a fifty percent chance that the child will not have the diseaese but will be a carrier and a twenty five per cent chance that the child will not have the disease nor be a carrier.
Carriers do not develop cystic fibrosis because they have one normal gene which is sufficient to regulate the movement of salts and water appropriately.
The CFTR gene creates a protein that is 1480 amino acids long. The most common mutation is a deletion of three nucleotides (the structural units of RNA and DNA) from the protein which results in a loss of an amino acid at the 508th position on the protein. This particular mutation (delta 508) is responsible for two thirds of all cases of cystic fibrosis world wide. However it is important to note that there are over 1400 other mutations that can produce cystic fibrosis.
The CFTR gene is normally responsible for the channel that carries particles called chloride ions in and out of cells. The flow of these ions helps to regulate the flow of water and salts in and out of tissue which is needed for the production of thin and flowing mucus. In cystic fibrosis the chloride channel is damaged and this impairs the flow of water in and out of the cells, leaving insufficient water outside the cells, which causes the mucus to thicken and become "sticky". This mucus can clog up the airways leading to severe problems with breathing and infection. Over time the build up of mucus and consequent infections result in permanent lung damage.
Thick mucus also interferes with the functioning of the pancreas which produces insulin and the enzymes that the intestines use to digest food. Problems with digestion can lead to malnutrition, delayed puberty, large and odorous stools, poor growth and weight loss.
Where the production of insulin in the pancreas is obstructed or disrupted this can lead to diabetes. Adults with Cystic Fibrosis are much more likely to develop diabetes than children because the damage to the pancreas worsens as time progresses.
The Mayo Clinic points out that there may be a causal link between an imbalance of fatty acids and cystic fibrosis. People with cystic fibrosis have excessively high levels of arachidonic acid and a deficiency of docosahexaenoic acid but we still don't understand the relationship between this imbalance and the genetic defect that causes cystic fibrosis.