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Mild forms

Hello, I am the mother of a 8-month-old little boy with cystic fibrosis. It is said that he has a mild form of the disease ( f508-r347h ) without pancreatic insufficiency for now. He has no other symptom than a loss of salt. His disease took time to be detected because the low level of sweat chloride (31), was almost normal. I am very worried for the future. I can’t have any straight answer when I ask the CF center about his disease evolution neither the symptoms' appearance. I am told that everything is possible, from a simple infertility, to an evolution towards a classic form of the disease. When can we say that the disease will indeed be mild (what does mild mean) and his life expectancy will it be the same than that for a classic form? Thank you for your answer!
CFTR mutations, leading to cystic fibrosis (CF), are numerous and have variable consequences on CFTR protein, and, thus, on disease severity. Over 2000 CFTR gene mutations are described actually in the CFTR2 database.
Your son carries 2 CFTR gene mutations: F508del and R347H. The first one (F508del) is the most frequent mutation found in CF patients (around 70%). R347H is less frequent. When combined with F508del, R347H has varying consequences: some patients having a “classical" form of cystic fibrosis and other a mild form of the disease. Your son being pancreatic sufficient, it might be considered as a mild form, but it is necessary to stay cautious and it will be important to follow the evolution of the pancreatic status. There is indeed no reliable indicator of the long-term evolution so far. In the majority of these cases, the evolution is modest with few symptoms. However, a delayed evolution towards a more classic form sometimes arises.
This information need to be cautiously considered as the number of reported patients is very low, and as there may exist an important variability in the disease expression from a patient to another. Furthermore, besides CFTR mutations, several parameters can play a role on the patients’ symptoms evolution; as the regular follow-up by a specialized team, early treatment of the infections and a good nutrition status. All these parameters could favorably influence the prognosis.
You may ask all these questions to your physician, as he/she might be able to give you more appropriate information. You could also ask to meet a geneticist or a geneticist counselor who will be able to explain these rather complexes CFTR mutations. I hope to have answered your questions and do please fill free to reply if you do have other ones.
Best regards
Dr. Harriet Corvol