The practice of medicine has a long tradition of making a diagnosis by building up a composite picture of the symptoms and their history, a clinical examination and specialist investigations. A diagnosis enables the course of the disease to be predicted and the appropriate treatment , scientific developments in genetics, by allowing us to detect specific abnormalities in chromosomes and in individual genes, are beginning to throw light on the mechanisms involved at a biochemical and molecular a result the genetic and environmental factors involved in many disorders can be separated
