For example, the treatments for Reiters have only limited effectiveness, there is no cure. If you have a disease that is similar to Reiters and it does have an effective treatment or cure, you may suffer needlessly. A rheumatologist is usually required to diagnose Reiters. There is no medical test that proves Reiters. There is a gene marker, but it only indicates a predisposition for Reiters.
Nobody knows if the gene is part of the cause.
Also it is possible not to have the gene marker, but to have Reiters.