I was shaking my head the whole time I was reading this article:
Over-the-counter DNA kit worries genetics experts...
It's really hard to explain just how complicated genetic testing is. I think an early assumption many people make is that you do the test to look for 'the gene' and it's either there or it isn't - simple! When the fact of the matter is we all have 'the gene' i.e. basically the same set of around 30,000 genes, and genetic testing searches for miniscule changes within genes (and even that's a simplification of the process!).
One single letter change amongst a million letter long piece of DNA is pretty easy to miss, yet one single letter change can have vast consequences (such as leading to an 100% lifetime risk of bowel cancer in the case of the genetic disease FAP). These over the counter DNA kits simply cannot test for everything. Not even close. There is a very real chance that the results people get back from these tests will be misinterpreted.