Claiming diagnostic tests for diabetes genes is misleading, say experts

Predictive genetic testing for type 2 diabetes BMJ Volume 333 pp 509-10

Claims that the discovery of a gene could help prevent diabetes may raise unrealistic expectations, warn doctors in this week's BMJ.

Earlier this year, scientists discovered that a variant of the TCF7L2 gene was associated with type 2 diabetes. In subsequent media coverage, they claimed this could lead to a diagnostic test to identify people who carry the variant gene and that people who knew of their extra risk would then be motivated to avoid the lifestyle habits that lead to diabetes.

Undeniably this discovery is noteworthy, write Cecile Janssens and colleagues. Type 2 diabetes is a leading cause of illness and death in the developed world and is increasing in prevalence worldwide. The association is robust - the investigators replicated their finding in three large, independent study populations - and it offers potential new insight into the pathobiology of diabetes.

Yet the claim that this knowledge will lead to a diagnostic test and hence to disease prevention now routine for such genetic discoveries may not be true and, above all, misleads the public.

Even if this discovery led to a 100% effective intervention that specifically targeted the effects of the genetic variant, 45% of the general population would need to receive this intervention to prevent 21% of diabetes cases, they explain. An intervention that specifically targets the effects of TCF7L2 variants would therefore need to be cheap, harmless, and burdenless to warrant such substantial overtreatment.

Alternatively, the genetic test could identify people at high risk who would benefit from appropriate advice on diet and physical activity. But many carriers would find their risk increased from 33% to only 38%. Would these figures provide enough incentive for them to change their lifestyles, they ask?

Ultimately, genetic discoveries may lead to better understanding of the disease process and to better therapeutic and preventive interventions, say the authors. In the meantime, scientists and the media are responsible for accurately and carefully interpreting the implications of studies of genetic associations for the benefit of the general public.

"Raising unrealistic expectations even inadvertently could distract attention from what can be done by applying what we already know to prevent diabetes and its complications," they conclude.

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Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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