1. a susceptibility to developing a disorder or disease, the actual development of which may be initiated by the interaction of certain biological, psychological, or environmental factors.

2. in genetics, any hereditary factor that, given the necessary conditions, will lead to the development of a certain trait or disease. Predisposition testing is genetic testing for mutations that are less than 100% penetrant (see penetrance). Thus, a positive test result indicates that the individual has an increased predisposition to develop the disease but might not necessarily do so. If a mutation is fully penetrant, the testing is referred to as predictive testing, since all those who carry the mutated gene will develop the disease.