When talking about genetic pre-disposition to a condition, make sure you understand both the increased risk factor and the general risk.As the geneticist at the Ask a Geneticist blog, I get a lot of questions about diseases that run in the family. They usually run along the lines of, "My mother had diabetes, what is my risk for getting it?"
What I try to do in answering these questions is give them a feel for what the disease is, how genes are involved and then give them some links to some reliable websites on the topic. I always try to emphasize that for a lot of diseases, genes are just one part of the story and that speaking with a genetic counselor in person might be a good idea. I also warn them to look very carefully at the risk numbers.
Very often risks are given in how much more likely someone is to get a disease compared to the general public. So, for example, if you have a brother or sister with schizophrenia, then you can be up to 9 times more likely to end up with the disease too. Sounds like a scary number! But it may not be...
If the general risk is 1 in a million, then 9 times is pretty insignificant. It means that your risk is 1 in 110,000 or so. This is worse than the chances of dating a supermodel (1 in 87,000) or of winning the lottery if you buy 50 tickets (1 in 77,000). So if this were the case, a 9 fold increase means you still probably aren't getting the disease.
For schizophrenia, the general risk is 1 in 100. This means that if you have a parent or sibling with the disease, your chances go up to about 1 in 11. Unfortunately 9 times more likely looks pretty significant here...