Some diseases do not follow simple patterns of inheritance. Many factors influence how a gene works or who will get a disease and when. Mutations in several different genes can lead to the same disease, as we see in some forms of Alzheimer's disease. Genes that increase one's risk of getting a certain disease are called susceptibility genes. Usually a blood sample is taken, and a molecular genetics lab performs special tests to look for mutations in a gene that lead to disease.
Genetic testing is available for only a fraction of the many genetic conditions in existence.
There is no test that analyzes a person's DNA and gives him or her a clean bill of health. Genetic testing can be done to confirm or rule out a certain diagnosis. Some of the more common genetic diseases for which genetic tests are available include sickle cell disease, myotonic dystrophy, cystic fibrosis, Duchenne's muscular dystrophy, and Fragile X syndrome. Alzheimer's disease Persons with Alzheimer's disease have progressive impairment in multiple cognitive areas. These areas may include memory, language, calculation, orientation, judgment and personality.