Tuesday, April 21, 2009


Is knowing the genetic mutations that lurk at certain locations of our DNA really useful in terms of assessing our risks with respect to diseases like diabetes or stroke?

Some specialists have lately voiced their doubts about this, countering the idea – which has been dogma these last years – that each common disease is the product of a few common genetic variants. This assumption has motivated dozens of so-called “genome-wide studies”, where geneticists set out to hunt down disease-causing genes through the detection of sets of point mutations – the famous SNPs – that would be frequently present in sick people but not in healthy people.

The problem with this approach is that such a simple situation is actually the exception, says David Goldstein, a geneticist at Duke University, who a few days ago commented on the subject in the New England Journal of Medicine. On the contrary, according to him, the most likely is that in their great majority, common diseases are caused by a myriad of rare mutations that, in a given person combine, as in a genetic lottery, to produce a specific disease.

If that is correct, getting a personal genetic test done by firms such as 23andme – which I did myself – or others is practically useless in terms of finding out our disease risks. The tests those businesses offer are merely a reading of half a million (sometimes a bit more) locations in the DNA molecule near which it has been inferred, from genome-wide studies, that one of those common disease-causing mutations may lie. This means that, in most cases, the results will never let us see the big picture. Better, then, to trust our family history of disease to tell us what to expect – the good, old “clinical history”, so dear to physicians a century ago.

According to Steve Jones, a well-known geneticist at University College London, writing today in the Daily Telegraph, those who order commercial genetic tests are simply throwing their money out the window. Goldstein, for his part, also argues that, if we really want to dig out the true and complex roots of human disease, rather than decoding many little bits of DNA from many people it might be better, from the point of view of medical research, to read the whole DNA sequences – the whole two times three billion letters – of a smaller number of individuals.

But not all the news is bad: up to now, nobody has questioned commercial personal genetic tests from the perspective of genealogy – and by the way, Goldstein is a big experts in that field. In fact, as I see it, that part is much more fun and exciting; I never doubted it and I intend to keep digging.

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