That illness you're genetically predisposed toward could be a thing of the past within the next 50 years.
Gene modification is one of those things that people wring their hands about. And while, yes, there are risks involved, and ethical implications to consider, the potential benefit is much too large to ignore.
And as proof of that, genetic engineers have made a massive breakthrough recently. They have successfully created their own "designer" eukaryotic chromosome, removed the original DNA, spliced in their new one, and then ... the brewer's yeast this experiment was conducted on passed along the new chromosome!
I don't want to minimize the work ahead, because it is immense, but this is pretty huge news. Just think of all the times you've been to a new doctor and had to check off all the illnesses that run in your family, all the conditions that might ultimately cause your brief blip of existence to end. Now imagine a world where what your grandparent died of was no longer relevant because your DNA had been rewritten so that you were no longer predisposed toward ANYTHING.
That is monumental. But, like I said, this is just a small step. And, in addition to the actual scientific work ahead, there will also be those who question the ethics of messing with our DNA, people who worry that this will only create a new set of problems. They may be right, the may be wrong, but either way people will stand in the way of this kind of progress.
It'll be fascinating to see what will come of this development in the future. And in the meanwhile, it will certainly inspire science fiction writers to revisit the topic of gene manipulation.