New scientific knowledge has found its application in medicine also. The advancements in medical technology has brought us right to the very core of a disease, i.e. to the gene responsible for appearance not only of hereditary but also of acquired diseases. Medical genetics, molecular biology and genetic engineering have focused on the attempts to replace "diseased" genes, to "restore" them or to make them functional and in this way make possible the remission of a disease or by the screening techniques to detect DNA defect and accomplish the prevention or early detection of a disease before the manifestation of its evident signs.