The Dawn of Evolutionary Epidemiology-Tucson- Sept 14-16

2008 American College of Epidemiology Meeting Program

The Dawn of Evolutionary Epidemiology:
Applying Evolutionary Theory in an Epidemiologic Context

September 14-16, 2008

Early Bird Rates until Sept 9th, register online!

The meeting is at The Westin LaPaloma Resort & Spa
3800 East Sunrise Drive, Tucson, AZ 85718

Full meeting info is at:
http://www.acepidemiology2.org/meetings/2008Tuscon/08Tusconamprogram.html
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What good is fever?

It is pretty obvious that fever is useful. Work by Kluger and others has shown that increased temperatures decrease mortality during infection. Even for lizards! (When infected they crawl to warmer places.)

The mystery has been how fever works. Can higher body temperature alone inhibit pathogen growth? It seems unlikely that changing temperature by just a degree or so would have a major effect. Pathogens are too adaptable.

In a seminar discussion this week, Karl Sperling, from the Institute of Human Genetics, Charité – Universitätsmedizin Berlin, brought up the protective role of heat shock proteins, and how highly conserved they are. This quickly suggested that their original function might have been co-opted to cope with infection.

Sure enough, a quick search revealed (more…)

No genes for schizophrenia? What gives?

Ten years ago, most of us paying attention were exhilarated about the prospects for psychiatric genetics. Heritability is high for many disorders-80% of the variation in vulnerability to bipolar disorder and schizophrenia can be attributed to genetic variations. We thought we would soon find the responsible abnormal genes, and this would quickly reveal the biochemical defects that cause these disorders, and this would quickly lead to ways to cure, or at least dramatically alleviate, these terrible scourges.

Candidate genes were examined by the best researchers using larger and larger samples and sophisticated statistics; a few were identified as prime suspects. Most results could not be replicated, but a few loci were very suspicious based on multiple studies.

Now, in an article by in this month’s American Journal of Psychiatry, Saunders et al. report on 433 SNPs associated with 14 candidate genes that were prime suspects for schizophrenia in about 1900 cases and 2000 controls of European ancestry. The results? Not one of the genes was significantly associated with schizophrenia prevalence. Even a 25% increase would have been detected with high probability.

An editorial by Steven Hamilton tries to put the best possible face on the results by noting that studies of tens of thousands of subjects were required to find genes that contribute to real but small (<25%) increases in risk for Type II diabetes. But that is not the point. Sanders, et al. deserve commendation for stating their conclusion clearly:

Our results suggest that, taken together, common DNA variants in these 14 genes are unlikely to explain a large proportion of the genetic risk for schizophrenia in populations of European ancestry. More robust findings are likely to be discovered using genome-wide association methods and, as our knowledge of the biology of mental illness continues to improve, focused studies of genes based on more precise mechanistic hypotheses. Nevertheless, although larger samples could possibly detect small genetic effects that were missed in this experiment, our findings suggest it is unlikely that true associations exist at the population level for the alleles that have formed the basis for the large candidate gene literature for these 14 postulated schizophrenia candidate genes.

Now what? (more…)

Evolutionary pharmacogenomics

Articles about evolution and medicine are spread so widely over the scientific landscape that no matter how much you read, you know you are missing things. The pleasure on finding them is, however, like finding a diamond in the sand. Such is the case with evolutionary pharmacogenomics (a phrase that turns up not one hit on Goggle!). At our seminar yesterday, Mark Thomas put us onto work by Daniel Nebert. A long-time leader in pharmacogenomics, he has written several papers offering an evolutionary framework for thinking about genes that influence drug metabolism. Suddenly, all kinds of things make sense. (more…)

Ten ways evolution can be applied to medicine

I have always found it somewhat confusing that evolutionary principles can be applied to medicine in so many ways. From the start of my work with George Williams, it has seemed clear that our attempts to ask why natural selection left the body vulnerable to so many diseases are fundamentally different from applications of population genetics or phylogenetic trees. Finally, in preparing an article with Stephen Stearns, we came up with a framework that seems helpful.

First it is essential to be clear about the kind of question:
1. What is the phylogeny of the trait?
2. How has the trait given a selective advantage?

Second, it is important to distinguish five different objects of explanation:
1. Human (or other focus species) phenotypic trait
2. Human (or other focus species) gene
3. Pathogen phenotypic trait
4. Pathogen gene
5. Somatic cell lines such as cancer or immune cells

This fleshes out into a rather nice table that defines ten ways evolutionary biology can be applied to medicine.

The full article is available free from Evolutionary Applications.

Nesse, R. M., & Stearns, S. C. (2008). The great opportunity: Evolutionary applications to medicine and public health. Evolutionary Applications 1(1), 28-48.