Cystic Fibrosis

Synonyms in a broader sense

Cystic fibrosis, lung

Definition Cystic Fibrosis

Cystic fibrosis is a hereditary disease. The inheritance is medically called autosomal – recessive. Cystic fibrosis (cystic fibrosis) is therefore not inherited on the sex chromosomes X and Y, but on autosomal chromosome no.

7. The mutation lies on the so-called CFTR gene. Recessive means that two defective gene copies must be present for the disease to break out.

If a person has a healthy and mutated gene locus on the corresponding chromosome 7, the disease does not occur. The result is a diseased gene product. The chloride channels encoded by this gene are defective. The defective chloride channels lead to the formation of thick mucus in all exocrine glands. These exocrine glands, i.e. glands that release their secretion to the outside, include

  • The Pancreas
  • The small intestine
  • The respiratory system with lungs and bronchial system
  • The bile ducts and
  • Also the sweat glands

Summary

Since it is a recessively inherited disease pattern, there are people who carry the altered gene but do not suffer from the disease itself. Such persons are called carriers or conductors. These people do not suffer from cystic fibrosis because the other gene copy is intact and the diseased one is not strong enough to assert itself.

However, they can pass on this defective gene copy to their offspring. If one altered gene would already be sufficient to cause a disease, it would be a so-called dominant inheritance. Such an inheritance is found for example in Chorea Huntington.

You can learn more about this disease under our topic Huntington’s disease. The disease rate in newborns in Germany is about 1:2500. About one in 25 of the population is a carrier.

The cause of cystic fibrosis is a mutation of a gene on chromosome 7, which is an autosomal chromosome, i.e. not a sex chromosome. Every human being has 44 autosomal chromosomes (two of each of the same type) and two sex chromosomes. This mutation on chromosome 7 leads to the formation of defective chloride channels.

The reabsorption (reabsorption) of chloride from glandular secretions is not possible, because the receptor, the docking site for chloride, is not built into the glandular ducts. Instead, it is used for degradation due to its incorrect appearance and structure. The natural exchange of chloride by certain chloride channels is disturbed.

These so-called channels consist of proteins. A wide variety of proteins are encoded on our DNA. Due to the genetic defect of the chloride channels, there is a low water content and viscous production of mucus from all glands, which release their secretion to the outside.

Sometimes the mucus then blocks the excretory ducts, or in the lungs the respiratory tract. The typical symptoms, which begin as early as infancy, point the way forward in the diagnosis of cystic fibrosis. This suspicion is further substantiated by a positive family history (illness of father-mother or close relatives).

A positive family history means that there are or have been cases of cystic fibrosis within the family – on the mother’s or father’s side. The absence of pancreatic enzymes can also be detected in stool. By x-raying the thorax, possible blockages of the airways can be detected.

A sweat test, which measures the chloride content of the sweat, also helps in the diagnosis of cystic fibrosis. If a certain value is exceeded and the other symptoms also apply, the diagnosis is relatively certain. Often the parents themselves notice the increased salt content in the sweat already in the infant. The unborn child can also be tested for this hereditary disease. By means of an amniocentesis, fetal cells are removed and examined for the mutated gene.