Cystic fibrosis, mutation testing

Clinical significance
Cystic fibrosis (CF) is a serious, chronic, progressive inherited disease; one baby in every 2,700 is born with it. It is inherited in an autosomal recessive pattern and is caused by DNA changes, called “mutations”, in the CFTR (cystic fibrosis transmembrane conductance regulator) gene. Genes are inherited in pairs, one from the father and one from the mother: in people with the disease both copies of the CF gene are altered, while people with a mutation on only one chromosome are called “healthy carriers”. Children with CF can only be born if both parents are healthy carriers. Two healthy carrier parents have a 25% chance of having a child with CF. From the same couple, each child has a one in two (50%) chance of being a healthy carrier, like the parents. There is currently a tendency to test all couples attending assisted reproduction centres to identify healthy carriers. Guidelines also recommend testing men with some forms of infertility: in males the T5 “variant”, inherited from both parents or together with a true mutation, is associated with congenital absence of the vas deferens and therefore with azoospermia (no sperm in the ejaculate).