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Conversation with Anna di Rienzo. Part 2

Anna di Rienzo, Professor at the Department of Human Genetics of the University of Chicago.
Why is it so complex? Why are we not much better at making predictions just looking at the genes? Well, with regard to the ability to make a prediction, the main problem is that the disease risk is the result of lots and lots of different genes, each making a very small contribution, meaning that each gene changes your risk by a very small amount. And of all these genes that are underlying a particular disease, we know only of a small minority of that. So that’s a first challenge in terms of taking the genetic data and using it in practice in a clinical setting.
There is also another problem, and that’s certainly the case for many diseases, for example psychiatric or behavioral diseases; and that is that the environment - and by environment, I mean the physical environment, but perhaps more importantly the social and cultural environment, and the economic environment - may have a major contribution, much bigger than the genetics itself. For example, let’s think about type 2 diabetes. Type 2 diabetes is a disease that if you are diagnosed early enough, if you change your lifestyle and diet, you can actually reverse the disease.
So for example, if you’re diagnosed with type 2 diabetes, if you start exercising very regularly and a lot, and you change your diet to have a lower calorie diet, you can actually reverse the disease. So your genotype - your genes - do not change, but if you change your environment, you can change the outcome. And this is very important to remember always, right? That the environment plays a very important role. Another way in which the environment can play a role and can complicate things is in what we refer to as “gene-by-environment interactions”. And this is probably very important in diseases like asthma. What does that mean?
Well it means that you may have a certain genetic variant that increases your probability of developing the disease, only if you’re exposed in a particular environment, but not if you’re not. Now, why is that a challenge? Because it’s very difficult to detect those gene-environment interactions. It’s very difficult, statistically, to distinguish a variant that affects the disease risk only in some conditions. So some people think that that’s part of the reason why we still understand comparatively little about the genetics of asthma even though many genes have already been associated.
Yet another possibility is that instead of having lots and lots of genes, each with variants that are quite common in the populations, and changing your disease risk by a little bit, that there are variants that are very rare in the population, that can affect your risk a great deal. And that is something that a number of people have been working on, and there is a lot of interest in that area. It has been applied very extensively to a number of psychiatric diseases and other diseases. And it is quite clear that this model is important to a different extent for different diseases. So the complexity comes from the fact that the etiology - the causes of the disease - is complex.
They are both genetic and environmental, so there is this complexity, and in addition for both genetics and the environment there is a diversity of possible factors that can increase your risk.

Anna di Rienzo, Professor at the Department of Human Genetics of the University of Chicago.

Her research focuses on the genetic architecture of traits and diseases that vary across human populations; and on understanding the role of natural selection in shaping this architecture.

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