I get asked about genetic testing all the time as I do carry out some gene testing in my line of work, to aid my clinical diagnoses.
The key point to understand here is that many genes may contribute to a particular disease, some of which are yet unknown.
The other variables at play are nutrition and environment that regulate the gene expression. This has a significant bearing on whether a condition is expressed, and this is where my study and work lies.
Testing your DNA should be interpreted by someone who has a balanced view on this. The results also shouldn't go into the wrong hands.