Can carriers of the CF gene can also have CF-like complaints ?

Question

My daughter has serious lung problems and after many tests the conclusion is that she does no suffer from cystic fibrosis, but my daughter is a carrier. Can this contribute to her lung problems or is it not part of it ?

Answer

Dear parent,

From your question I understand that extensive examinations have been done in your daughter and that the conclusion is that she does not suffer from cystic fibrosis. Probably the fact that she carries a frequently occurring mutation in the CF gene was the reason to do more extensive tests.

We cannot judge the health of your daughter but we can give you general information about the disease. First of all, being carrier of one CF-mutation does not lead to the disease. CF is a disease that only comes to expression when a person carries two mutations that cause CF, one on the gene inherited from the father and one on the gene inherited from the mother. In case a person has serious lung problems and is carrier of one mutation (for instance DF508) the treating physician may have reasons to still consider the diagnosis of CF. In that case the first test needed will be a sweat test. The sweat chloride is elevated in patients with CF (higher than 60 mmol/L), a test result in the grey zone (30-60 mmol/L) can be a reason to do more tests in a person with symptoms suggestive of cystic fibrosis. A test result lower than 30 mmol/L makes CF very unlikely as explanation for the symptoms.

In case of atypical form of cystic fibrosis, serious lung problems at a young age are very unlikely. In case one tests for mutations in the CF gene, only the 36 most frequent mutations are being considered. With these test in patients of Dutch or Belgian decent 49% of the patients will be found to have two mutations. But if a patient has a really rare mutation it is possible that only one mutation is found. And then it may be needed to search for these rare mutations. This is not easy because more than 1600 different mutations are known. To do such a test (sequencing) the whole CF gene is “read”. If no mutations are found it is very unlikely that there is problem of cystic fibrosis. But it is not still totally excluded. Additional tests can evaluate the function of the CFTR protein directly. In the nose with a special test such as nasal PD or in a small biopsy taken from the rectum with the intestinal current measurement. Read more about these tests in the archives on diagnosis.
More on carriers and cystic fibrosis you can read in the archives of ECORN under carriers.
As last note we can say that the frequency of mutations in the CF gene is higher in other lung diseases than in cystic fibrosis so it is known that in people with bronchiectasis CF mutations are found more often than in general healthy population but reversely a carrier does not have an increased risk of severe lung disease.
In case a person has all these tests done and the tests are negative, it is very unlikely that they have cystic fibrosis. For the discussions whether the diagnosis of cystic fibrosis is possible in your daughter and whether the CF mutation contributes to the disease I refer you to your doctor.

Kind regards
Jeannette Dankert, Pediatrician

05.10.2010