In the past, geneticists have looked at so-called disease genes, but a lot of people have changes in their genes and don't get these diseases. There have to be other parts of physiology and genetics that compensate.
One of the things about genetics that has become clearer as we've done genomes - as we've worked our way through the evolutionary tree, including humans - is that we're probably much more genetic animals than we want to confess we are.