Genetic Disorders

Statistics and twin studies are often used to determine the genetic basis for multi-factorial genetic disorders (MFGDs). Because environment can play an important role in the development of these diseases, identical and fraternal twins who have been raised in different homes are ideally studied. MFGD include some disorders associated with diet and metabolism, such as obesity, diabetes, alcoholism, rickets, and high blood pressure. And the tendency of contracting certain infections such as measles, scarlet fever, and tuberculosis can be considered MFGDs. In addition, schizophrenia and some other psychological illnesses represent as well as congenital hip, club foot, and cleft lip are also inherited in this manner. Cancer, where the risk is associated with the environmental exposure also falls into this class of disorders. Certain breast, colon, skin, and small-cell lung cancers have been shown to have a genetic link. Certain genes predisposed people to a certain type of cancer and this risk is enhanced when there is a specific environmental exposure. This susceptibility is influenced by inherited variations in genes, which encode proteins that may be more or less functional. For example, if the protein is involved in the metabolism of a carcer causing substance and an individual inherits a variation in the gene sequence, this might affect the function of the protein it encodes. If it reduced its function, this might lead to more damaging effects of the cancer causing substance.