Genetic testing is a recommended procedure whenever there is a question about the inheritance of illness in the progeny of a couple. Testing can be done on individuals before they consider marriage. In the case of Tay-Sachs disease a person can be a carrier of the mutant gene and have no symptoms of the illness. But if that person marries another person who is also a carrier, they have a 25% chance of bearing children with Tay-Sachs, which is a devastating, fatal disease with no known cause.
