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Symptoms of rare mutations in our baby

My husband and I are both carriers of a CF mutation and I'm pregnant. We were told, there is a 25% chance that our baby could inherit our two mutations and we want to know what symptoms the child may have if this is the case.

My F508del mutation is common (with R668C variant, which should not be significant) but my husband is carrying a F834L mutation. We consulted the CFTR2 but we did not find any information about this change even if we read a case in ancient CFTR2 files of a woman with this mutation who had pancreatic insufficiency, respiratory problems and a dubious sweat test. This patient had F834L in conjunction with a different mutation from that I carry.
Using two predictive computer programs, the results were very different: the first predicted that there would be a simple variant / polymorphism while the second predicted there would be a "possibility of damage" with a score of 0.09 on a 0-0.10 scale, 0.10 being the most serious.

Since we have had difficulty in finding information about the F834L mutation, which is the rarest, I would like to know if you've met on your journey / experience or if you can predict the kind of symptoms that could cause the F508del.

Thank you in advance

No, the CFTR gene mutation of your husband is not carried by any of the patients registered in the French Cystic Fibrosis Registry.

In the current state of knowledge it is not possible to assume the phenotype (the evolution of symptoms) of a child with a genotype combining yours and your husband’s mutations.

In your situation (current pregnancy of a couple at risk of transmitting cystic fibrosis), given the lack of information regarding the functional mutation that your husband is a carrier of, the precautionary principle could be to get a sample of amniotic liquid for prenatal diagnosis by coupling the search for mutations with measurement of digestive enzymes. Even when carrying two fetal "mutations" the existence of a normal rate of these enzymes would be reassuring.

Hope this answer can help.
Best wishes
Gilles RAULT, MD, Roscoff CF Center