Via the New York Times, it looks like the home genotyping company 23andMe is getting the go-ahead from the US Food and Drug Administration to give customers medical information linked to their personal genetics. But not just any medical information:
The new health-related information 23andMe will provide is called carrier status. That relates to whether people have genetic mutations that could lead to a disease in their offspring, presuming the other parent has a mutation in the same gene and the child inherits both mutated genes. There will be information on 36 diseases, including cystic fibrosis, sickle cell anemia and Tay-Sachs.
That’s interesting, and not surprising, because those diseases all have very simple genetic bases — if I’m not mistaken, the ones listed are all caused by mutations at single genes, and the effects of those mutations are so strong that people who inherit those mutations from both their parents almost always come down with the disease. Before the FDA told 23andMe to cut it out, the company was providing estimates of genetic risk for dozens of conditions from heart disease to Alzheimer’s. But those are much more complex diseases, with (likely) many genes involved, each contributing just a bit to the risk.
As I wrote for The Molecular Ecologist back around the time the FDA stepped in, understanding the results of genetic tests for multi-gene traits isn’t straightforward, even for trained geneticists.
… many [genome-wide association] studies of disease are not designed to categorize the people in the study samples in the binary terms I sketched out above—do they or do they not have the disease?—but instead look for associations with risk of disease. One of the broad findings to come out of all the GWA work is that many diseases are affected by multiple parts of the genome, so that each individual genetic variant elevates the risk of disease just a bit. These subtler effects are harder to identify with statistical certainty, and they mean that learning you carry a SNP variant associated with Type II diabetes is not at all the same thing as receiving the results of a blood test that shows your blood sugar regulation is out of whack.
It is possible to carry genetic markers associated with elevated risk for such diseases without ever developing the disease. Genes found by GWA may also have different effects in different environments, or in people with different genetic ancestry. It’ll be interesting to see if there’s a workable solution for this. Maybe the FDA will come up with industry-standard educational material that can help make sure people put the results of consumer-genetics tests for complex traits in proper perspective.
Meanwhile, 23andMe customers can download their raw genetic data and find a lot of the complicated, uncertain stuff that the FDA doesn’t want the genotyping company to present, in online sources like SNPedia.