In the ideal world, a doctor could look at your genetic profile and determine your health risks. More study of genetic factors, and how they interact with each other and the environment, is needed. This is a genetic condition in which its victims' bodies tend to absorb and hoard iron in otherwise healthy tissue. Perhaps three to five people out of every 1,000 have this trait. A smaller percentage of them will develop hemachromatosis.
Treatment is called de-ironing.
Doctors remove iron from the body by removing iron-rich blood in several sessions. So that's a genetic test where the outcome offers an effective treatment. But some tests may do you more harm than good. There's a test of a protein, APOE 4, that can tell you if you have an increased risk of developing Alzheimer's disease. Unlike the example of hemachromatosis, there is nothing you can do about the results.