recessive CF carrier and pancreatic problems

Question

I am a possibly carrier of the CF-gene, the disease being present in my family. I know that mild forms of the disease may be present in CF-carriers, for example resulting in infertility (a disease also prevalent in my family). My question is the following: “Is it possible, being a carrier, not to have complaints like infertility, but presenting with decreased pancreatic function, resulting for example in loose fatty stools when eating fatrich food. Is there a lab-test to detect these forms? Or does this type of disease not exist? Testing for CF carriership is planned soon. Thanks for your answer. With kind regards

Answer

Dear questioner,
Cystic fibrosis or CF is a inheritable disease, which means that the disease is caused by ‘mistakes’ or mutations in our chromosomes (our genetic material). Cystic fibrosis is caused by a mutation in the CF-gene. CF is an autosomal recessive disease. ‘Autosomal’ means that the disease is inherited independent of the sex (it’s as frequent in boys as in girls). ‘Recessive’ means that a CF patient inherited the diseased CF gene from both parents and does not have a normal copy of the CFTR gene. Many people carry one mutation and are called “carriers”. However, they do not have disease. Only if two mutations are present (one on the gene inherited from the father, and one on the gene inherited from the mother) disease will be present. You should therefore not confuse carriership (having 1 mutation and thus not being ill, however possibly passing on the mutation to your kindred) with having two abnormal genes, causing disease.

Carriers of the recessive disease do not have complaints. There are however more than 1.600 different CFTR-mutations known. When a person is tested for CF-carriership, the most common mutations are tested (30 to 36), covering about 94% of existing mutations. However, when one of the mutations is an unusual or less frequent mutation, it may not be picked up by the standard tests and only one mutation will be found while the other remains unknown. If the doctor suspects the diagnosis of cystic fibrosis, he or she can order to test a patient for rare mutations.

Most CF-patients carry 2 severe mutations and have the classical picture of cystic fibrosis (early disease, mainly with digestive problems and lung disease). About 10% of CF-patients have a combination of a severe and a mild mutation and present with less severe disease. Rarely, patients have 2 mild mutations and in this case it may happen that you are not sick at all. Mutations causing less severe disease are called mild mutations.
Some mutations in the CFTR gene can give rise to a rare form of male infertility, namely ‘congenital bilateral absence of the vas deferens’, without having lung disease. Digestion is mostly disturbed in CF patients carrying 2 severe mutations. There are of course other causes of disturbed digestion, outside CF and there are other diseases of the pancreas, other than CF. Detection of the enzyme elastase in the stool is an easy test to diagnose digestive problems related to cystic fibrosis. If the digestive problem is suspected, you should consult your physician to see what the cause may be. We hope that our answer clarifies your question.

Kind regards
K. De Boeck

23.03.2010