Hereditary diseases are diseases that are caused by defective genetic information transmitted from parents to their children. Such errors can unsettle the delicate balance of the organism and cause a disease. Hemophilia is one of the most well-known hereditary diseases. It is caused by the mutation of only one single gene. The affected gene contains the genetic information for a coagulation protein. Hemophilia patients cannot properly produce this coagulation protein any longer and, as a result, have difficulty in stemming bleeding in even small wounds.

But it is rare that diseases are caused by one single mutation of the genetic material. Usually, several genetic mutations and environmental stressors are involved in the outbreak of the disease (complex diseases).