Cystic fibrosis

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Cystic fibrosis

Mutations of the CFTR gene

Cystic fibrosis (CF, cystic fibrosis, mucoviscidosis) is one of the most prevalent congenital diseases, which is caused by alterations (mutations) in the CFTR (cystic fibrosis transmembrane conductance regulator) gene.

In Hungary, one in every 28 persons carries a defective copy of the CFTR gene. To date, more than 1500 alterations have been identified in the CFTR gene. Mutation ΔF508del should be highlighted since this deletion is responsible for the clinical aspects of the disease in approximately two-thirds of the patients. The remaining one-third of the mutations is dispersed in the gene.

The prevalence of CF justifies the mutational analysis of the CFTR gene. This test, as yet, is not included in routine neonatal screening in Hungary, but several developed countries have already incorporated it in their routine neonatal screening.

In CF patients the CFTR protein is missing or malfunctioning leading to the following symptoms:

  • In the pancreas: digestive problems.
  • In the respiratory system: chronic coughs and bouts of coughing, recurrent and chronic pneumonia. Respiratory difficulties develop; thick mucus is deposited in the airways, and the lung does not get sufficient oxygen, which leads to its gradual necrosis.
  • In the epididymis: due to the obstruction of the epididymis ducts, 95% of the male patients are infertile.
  • The thick mucus blocks the exit ducts of the exocrine glands as demonstrated by a change in mucus production.
  • In newborns, the disease is indicated by meconium ileus, that is, bowel obstruction due to the thickening of the bowel content.
  • Protein deficiency
  • Symptoms of deficiency of fat-soluble vitamins (A, D, E, K)..
  • Inflammatory alterations are typical in almost all of the glands.

The CFTR Diagnostic Kit developed in our lab enables the analysis of the whole gene, that is, it is capable of detecting all of the mutations.

Child suffering from cystic fibrosis

Babies suffering from mucoviscidosis are born with normal lungs, but the glands of the mucous membranes continuously secrete thick mucus, which blocks the alveoli, and the respiratory surface decreases significantly. The thick mucus cannot clear up the normal way, so the little patients try to get rid of it with long bouts of coughing. At the beginning, the cough is dry, intermittent, later it seems to clear up. The thick mucus is a hotbed for different upper respiratory tract pathogens. Staphylococcus aureus and Pseudomonas species are the most frequent causes of infection. Pseudomonas aeruginosa is the most dangerous pathogen, which can cause fatal infections.

Inheritance of the disease from parents to children

If, in a given case, both parents carry a mutation in their CFTR genes they have a 25% probability that their child will be ill.

FREQUENTLY ASKED QUESTIONS

When can the CFTR gene cause problem, how does the disease develop?
The CFTR gene is present in everyone. Since every gene we have, except those on the sex chromosomes, is present in two copies we have two copies of the CFTR gene as well. The CFTR protein, which controls the movement of salts and water through the cell membrane, is transcribed and produced indirectly from these genes. If one of the copies is defective, the amount of correctly functioning proteins decreases, but this does not necessarily lead to health damage. However, if both copies carry the mutation the disease develops. As in Hungary one in every 28 people carries a defective copy of the CFTR gene, there is a high probability that the child to be born will inherit the defective copy from his/her parents.
Can everyone be a carrier of cystic fibrosis?
Yes, both sexes are affected by the disease at equal frequency.
What is the prevalence of cystic fibrosis?
In Hungary, one in every 28 people is a carrier of a CFTR mutation, and the disease manifests in about one out of every 2500 babies born. This means that, on average, 40 babies suffering from CFTR are born every year in Hungary.
When do the symptoms of the disease appear?
The symptoms can appear at any age, but they manifest most frequently already in the first few years of life affecting mainly the respiratory or the digestive system. After birth, in about 15% of the cases, ileus indicates the problem. It is worth paying attention to symptoms such as recurrent coughing and/or pulmonary infiltration and lag of physical development already from birth.
What other effects does the disease have?
Fortunately, intelligence is not influenced by the disease. However, it may have serious consequences for fertility. Depending on the mutation, fertility may be impaired even in carriers. This accounts for 1-2% of male infertility, which is important to know because the disease impairs only the release of sperms; thus, participation in assisted reproduction programmes can be successful. In case of infertility, the board of clinical genetics suggests testing the CFTR gene.
I am planning to have a family; should I have a test?
Testing is particularly indicated in both parents before having children because one in every 28 people, that is, 4% of the population is asymptomatic carrier. If two carriers have a child, they have a 25% probability that their child will be ill. If someone suffers from the disease in the family, there is a higher-than-average risk for the baby to be born with cystic fibrosis.
How efficient is the test; does it surely detect the mutation?
The CFTR gene is 230 000 base pair long, and mutations have been described in nearly 2000 positions. The frequency of these mutations varies over a wide range. Screening tests focus on those positions that are present in at least 1% of the population, thus, rare variations remain hidden. In contrast, the CE IVD certified test we use identifies all the mutations, regardless of their frequency by reading the whole coding sequence of the gene.
What should I do to have the test performed?
You only have to contact our genetic counsellor who will be glad to give you advice on whether the test is recommended for you or for a member of your family. If it is recommended, a simple blood draw is enough for the test.
When can I expect to have the result?
The result is ready within 4-6 weeks of sample taking; our genetic counsellor will contact you and provide all the information necessary for the interpretation of the result and for the further steps if required.

Scientific background

The most common hereditary disease, cystic fibrosis, is caused by defects in the CFTR gene as known since 1989. However, the number of gene variants causing the disease continuously increases as the genetic testing of new patients with different severity of the disease reveals new and new defects in the gene or the protein encoded.


Targeted therapeutic drugs under development for the treatment of cystic fibrosis patients (CF Foundation drug development pipeline)
New and emerging targeted therapies for cystic fibrosis
Bradley S Quon, clinician-scientist1 and Steven M Rowe, director2

These results form the basis of choosing the targeted molecules that can be used for the different variants of this heterogeneous disease.

Cystic fibrosis genetics: from molecular understanding to clinical application.
Cutting GR. Nat Rev Genet. 2015 Jan;16(1):45-56. doi: 10.1038/nrg3849. Epub 2014 Nov 18. Review.