Cystic fibrosis is a genetic disease caused by a mutation in the CFTR gene. This pathology usually causes problems in the pancreas and the lungs, but also fertility problems.
Most men diagnosed with cystic fibrosis have azoospermia, that is, there are no sperm in the ejaculate. This is due to the fact that patients lack the ducts in charge of transporting the sperm, the vas deferens.
However, cystic fibrosis is a recessive disease. Therefore, a man can be a carrier of the mutation and not suffer from the disease, since two copies are necessary.