Flexi Says: Several genetic disorders like Marfan syndrome, Sickle cell anemia, Vitamin D-resistant rickets and Hemophilia are caused by mutations in just one gene. Cystic Fibrosis and Tay-Sachs disease are two additional severe single gene genetic disorders. Some of the disorders are caused by mutations in autosomal genes, others by mutations in X-linked genes. These are genetic conditions are often called hereditary because they can be passed from parents to their children.