Risky Business: Genes Just Part of the Story

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...

Sometimes, though, a smaller risk can be even more significant.  For example, women who have a sister, mother, or daughter with breast cancer are twice as likely to develop breast cancer themselves.  Since about 12% of women will develop breast cancer in their lifetime, this means the risk is actually 24% or about 1 in 4.

So when investigating these sorts of risks, get both numbers.  You want to know what your increased risk is because a relative has the condition AND what the general risk is.  These two numbers together will give you a better feel for your chances.

An important note here is that these risks are averages.  Your actual chances will depend on the genes you have, how you live your life, etc..  For example, some of the women is the breast cancer example carry certain versions of the BRCA1 or BRCA2 gene.  These women are 5 times more likely to develop breast cancer pushes their risk to around 60%.

This is one of the many reasons why a sitdown with a genetic counselor is so useful.  Your risk depends on your specific situation and not an average risk you find on the internet.  A genetic counselor can take the time to carefully go over your family history and let you know what tests are available so you can better calculate your odds.

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