Genetics is believed to play a role in almost every human disease. Even for diseases traditionally described as environmental, such as tuberculosis and HIV, scientists are discovering that genetics is implicated either in the susceptibility to infection or in the severity of the disease. In some disorders a variation within a single gene is sufficient to cause disease, while in other disorders variations within a gene must interact with the environment and other genes to cause disease. The goal of human medical genetics is to identify all the genes that are involved in human disease and determine how the genes function to cause susceptibility to disease. This knowledge leads to the development of successful therapies that improve the quality of life of affected individuals and their families.

Mendelian and Complex Disorders

Geneticists typically classify genetic disorders into two main categories: Mendelian and complex disorders...