Archive for the 'Background' Category

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How well can a screening test predict disease risk?

We can usually be pretty confident that if our genotyping results say we carry a certain genetic variant, we really do carry that variant.  So why doesn’t that necessarily equate to a confident prediction about disease risk?  As Caroline outlined in her previous post on the risks and benefits of population screening, the results of screening tests (genetic or otherwise) may not provide a definitive diagnosis.  Test results often just categorise people as being at high or low risk of disease.  In this post, we’ll look at some of the ways we assess the predictive ability of a diagnostic test, and why the results we get from them are usually probabilistic.

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How to read a genome-wide association study

As any avid follower of genomics or medical genetics knows, genome-wide association studies (GWAS) have been the dominant tool used by complex disease genetics researchers in the last five years. There’s a very active debate in the field about whether GWAS have revolutionized our understanding of disease genetics or whether they were a waste of money for little tangible gain. No matter where you fall in that spectrum, however, you need only to browse the table of contents of any recent issue of Nature Genetics to see how ubiquitous they are. Since GWAS provide so much of the fodder for unzipping your genome, and in order to help you cut through the hype in the mainstream press coverage of GWAS, I’ve put together a quick primer on how to go straight to the original paper and decide for yourself whether it’s a landmark finding or a dud.

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Risks and benefits of population screening

The concept of screening is bandied around quite a bit these days, particularly associated with genetics and genome profiling for both common and rare diseases. But the term is often used without due consideration or understanding of the issues associated with screening itself. If we are to critically assess the potential for personal genomics to prevent disease in individuals and populations, we need to understand some underlying public health principles.

So what is screening? Most importantly, medical screening generally involves testing (apparently) healthy people, rather than individuals with a particular clinical problem. This simple statement comes with quite a bit of baggage – if you go around telling healthy people that they have (or are likely to develop) some hideously awful disease, and need some rather unpleasant treatments to stop it, you really want to be sure that you’re right! Which means being certain that the test used is strongly predictive of the disease in question, rather than just being mildly associated with it, and that it can be used to reliably discriminate between those who have or will get the disease and those who don’t and won’t.

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