Another example of a successful similarity search was the discovery of the
cystic fibrosis gene. Cystic fibrosis is a fatal disease associatedwith abnormal
secretions, and is diagnosed in children at a rate of 1 in 3900. A defective gene
causes the body to produce abnormally thick mucus that clogs the lungs and
leads to lifethreatening lung infections. More than 10 million Americans are
unknowing and symptomless carriers of the defective cystic fibrosis gene;
each time two carriers have a child, there is a 25% chance that the child will
have cystic fibrosis.