Thursday, September 9, 2010

Genetics Extra

From past posts you would know that though I believe in genetic predisposition to disease, I do NOT believe that is what people in general should be focusing on. Instead, I think that a genetic predispositions for some diseases is a big flashing neon sign urging that individual to make as many healthy choices in their day to day life as possible. To be fair, there are diseases that are 100% genetic, but they are rare.

It is more likely that a disease has both a genetic and environmental cause - an interaction often takes place between the two. I am currently refreshing my basic genetic knowledge for the epidemiology class for which I am an assistant. We are having a genetics student as a speaker in a few weeks. One of our suggested themes for the class is HER response to direct to consumer advertising of the genetic tests and the GAOs response to them. This was the topic of a past blog post.

I wanted to share a few things from the reading, beyond what I have just said. First is that twin studies are pretty close to the best scientists can hope for to study genetic links. However, the twins have to be identical or monozygotic because those pairs are from the same ovum and share 100% genes. Fraternal or dizygotic twins are the same as non twin siblings in the gene sense. So look for that if you are reviewing a twin study. Further, know that the twins of either type are very likely to also share the same environment and thus be influenced by it.

Adoption studies are better but not perfect as any time we are out in the community there will be factors that we cannot control or even know sometimes that may have an influence.

The other thing I wanted to explain with regard to twin studies are the terms concordant and discordant. Consider this sentence, "The twins were concordant for breast cancer." My immediately deduction is that the twins BOTH had cancer. Only part of that is right as the other is unknown from the sentence. Whatever the outcome, the result is concordant - the same. Both twins either have it or don't. If I said instead, "The twins were discordant for breast cancer." I would mean that one had it and one did not. This would lead us to think that genes were NOT involved. It is not whether they have the disease or not, but if both identical twins have the same disease status then they are concordant.

Last thing - what geneticists find in many instances is that the younger the age of onset of disease in one monozygotic twin the more likely it is to be concordant. In other words, both twins will get the disease and it is thus more often linked to genetics. If in identical twin girls, one gets a cancer at 13 say, the other twin is also likely to have it or get it soon. IF the twin gets the cancer in her 50s, there is much less of a chance that her sibling will get it - from her genes - it is more likely to be some environmental cause.

Ok lesson over :)

Check out the widget I added to the blog home page - under the text of the posts. It is from my favorite Go Slow Whoa initative from the NHLBI -

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