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Question

Hello my son was diagnosed CF at birth. His mutations are 508 del F and P5L. 3 sweat tests showed very diferent results (from positive to negative). He’s regularly followed in a CF Center, is today 3 years of age and luckily does not present any symptom of the disease. Is there an identical genotype in your archives? May symptoms of the disease occur late?

Answer

Hello,
your child's genotype 508 del F/P5L is extremely rare because of the rarity of the mutation P5L. Consultation of the international database of mutations in the CFTR gene (Http://www.genet.sickkids.on.ca) only refers to one another case of a 9 y. boy who was diagnosed CF regarding to the detection of 2 mutations (the same as your child's ones) and a sweat test frankly positive. He is there indicated as having a " pancreatic sufficiency » (pancreas secretes normally the enzymes that help digest food) and a normal pulmonary function.
The presence of this mutation P5L results in a partial functioning of the chloride channel and consequently in the possibility of mild symptoms or no symptoms at all. Those situations known as « borderline » are currently better identified after having implemented the systematic CF newborn screening. Their diagnosis and the name one should assign them can be problematic when the sweat test is not positive, eventhough normal (should we call them cystic fibrosis, or give them another name: CFTR Related Disorders, cyfitrosis ...?). Anyway, we don’t have nowadays reliable markers of the long term evolution. Although most of those situations are associated with a development of moderate, poor symptomatic or eventhough no symptomatic status at all, an evolution towards a more delayed classical disease may occur. These are all arguments, firstly, to observe lifestyle precautions (avoid environment potentially harmful to the respiratory tract, including active and passive smoking; be even more vigilant to detect and prevent dehydration which can be promoted through an abnormally salty sweat) secondly, keep on following in your CF Center according to arrangements that should be discussed with his doctor. Note that a national observational study of the evolution of these particular forms is to be implemented in France in the beginning of 2011: its aim is to better understand the long term evolution and to adjust the procedures for monitoring (frequency of consultations and type of examinations to perform). Hoping to have answered your questions, I wish you and to all your loved ones a happy new year.
Dr. Gilles Rault

02.02.2011