Monday, June 14, 2010

The Sweeping Assumptions of GWAS

As a graduate student a few years ago, I learned about (and in some cases witnessed) the various phases, fads, and revolutions in the field of human genetics. The mid to late 90's saw a shift from family-based linkage analysis to a plethora of small candidate gene studies. The early 2000's saw the completion of the human genome project, the development of the HapMap project, and the birth of genome-wide association studies. And very shortly, I believe we will transition to either partial or whole-genome sequencing as the study design of choice. Lots of factors motivate these shifts, including cost-effectiveness, sample availability, pressure to innovate, and simply the "bandwagon" effect.

It often seems, however, that the last factor to be considered is the hypothesis of the underlying disease model. Much like choosing a statistical test, each study design is coupled with a specific hypothesis and corresponding assumptions that are tested. Linkage (co-segregation of a genomic region with disease), candidate gene (association of a specific allele within a gene of interest), GWAS (association of common variants), and sequencing (identification of low frequency alleles) carry with them a null hypothesis that can be rejected when the study is sufficiently powered.

In 2000, when the march toward GWAS began, Terwilliger and Göring presented arguments against the common disease/common variant hypothesis, and they recently published an updated perspective on this argument.

Terwilliger JD, Göring HH. Update to Terwilliger and Göring's "Gene mapping in the 20th and 21st centuries" (2000): gene mapping when rare variants are common and common variants are rare. Hum Biol. 2009 Dec;81(5-6):729-33.

I have to admit that GWAS bashing is always a fun read, and the authors go the extra mile by citing references to all those who are now suddenly adopting their view in light of new sequencing technologies. I would however like to point out that the authors could easily find themselves cited in a future publication that denotes the folly of whole-genome sequencing… After all, there are so many possible explanations for the missing heritability of common diseases – why should we expect the multiple rare-variant/common disease hypothesis to be the holy grail?

Besides, EVERYONE knows its all due to methylation. :)


  1. I don't think they are advocating for whole genome sequencing (except the benefit it may have in elucidating Mendelian disorders). Rather, they are saying "assume you have the whole genome--because eventually you will--and then ask yourself if you could figure out the genetics of the disease in question."

    As they say, the most important aspect of a project researchers have control over is the study design. If that is flawed, then the study may be worthless.

  2. It's not methylation that is the answer. Of course it has to be RNAi!!

  3. Of course... RNAi! Something we can sequence! Brian I just looked at your blog and I noticed that you study plant breeding -- I'm a hobby gardener and I'd love to play with plant genetics. Any tips on how to get started?


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