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CF in blood work but no symptoms

About 12 years ago it was found that i had full blown CF according to my bloods but i've never had any symptoms - this was found as i was trying to do egg donation.

I am now wondering if this is common or whether it is rare and somebody may be interested in it? Both my parents were then tested and found to be carriers obvioulsy. My brother has not been tested.

Many thanks

Dear Valerie,
If I understand your question right, CF has been diagnosed by a blood test 12 years ago—therefore I assume that your blood has been drawn and a genetic investigation of mutations in the so-called CFTR gene has been done. Obviously two mutations have been found in your test (one of each also in the test of your mother and father) and therefore the diagnosis of CF has been made to you. You report, that you do not have any symptoms (like lung symptoms, mucus, cough etc. and digestive symptoms, like fatty stools, diarrhea etc.).
There are over 1800 known mutations of the CFTR gene (the cystic fibrosis gene) that are grouped into six classes according to the way they affect the synthesis or functioning of the CFTR protein which serves as an ion channel in the cell membrane. Class I-III mutations result in defective synthesis, processing, maturation and regulation of the CFTR protein with an abolished function of the ion channel. Class IV-VI mutations result in defective conductance, reduced function/synthesis and increased degradation of the CFTR protein, though still with a residual expression and function of the ion channel.
When a patient has a mutation of a different class in each of his/her two CFTR genes, the less severe mutation affects the functioning of the protein and therefore part of the clinical expression of cystic fibrosis. In general, patients with two mutations from class I-III exhibit a phenotype associated with pancreatic insufficiency and a more severe course of the disease compared to patients with at least one class IV-VI mutation. Class IV-VI mutations are usually associated with pancreatic sufficiency and milder lung disease. However, the classification of mutations is not always conclusive and possible.
Furthermore, there are some mutations, that affect the functioning of the chloride channel so slightly, that nearly no CF symptoms occur, sometimes there are only fertility problems in male patients or chronic pancreatitis or bronchiectasis. Then we do not talk about “CF” but about “CFTR-related disorders”.
As we do not know your specific mutations, we cannot state if you probably belong to this group.
Apart from the genetic testing, an investigation of the function of the chloride channel would be interesting in your case; if you have no symptoms at all, the chloride channel in the cell membrane should have a remaining function. This can be measured by doing a so-called sweat test that measures the chloride concentration in the sweat. Classical CF patients have values over 60 mmol/l, patients with milder mutations or CFTR-related disorders have values in the borderline area (40-60 mmol/l) or sometimes even negative sweat tests (< 40 mmol/l). If this is not conclusive, there are even other test in specialized centers that measure the function of the chloride channel (nasal potential difference measurement or intestinal current measurement).
However, mutation analysis only gives a rough direction but it has to be clearly stated that the individual clinical course and especially the degree of lung involvement cannot be predicted according to the genotype, as many other genetic (modifier genes, etc.) and environmental factors play a role and the severity of disease differs substantially even between patients with the exact same mutations. If in your case, two known CFTR mutations are present, it will be of great importance to be followed up in a CF-center, with regular controls of lung function, testing of bacteria in the airways etc., as in those CFTR-related disorders or very mild forms of CF symptoms can still occur later in life and early treatment is favourable.
If there are two identified mutations in a family, testing of all other siblings (do they also carry two mutations and have to be followed up, are they only carriers but may give the mutation to their offspring?) is recommended.

Best regards,
Dr. Daniela d’Alquen (coordinator of the Central English Archive of ECORN-CF)