The impact of genetic testing on complex diseases

Objective: Wide applications for genetic testing in the clinical care of complex diseases have been discussed. However, it has never been quantified to what extent genetic testing could eventually be useful in the clinical care of common disorders. We aimed to quantify the theoretically possible utilization in common ischemic stroke, an example of a complex disease. Methods: We computed the possible impact of genetic testing on risk assessment, secondary prevention and prognosis of ischemic stroke. This was done for hypothetical genotypes with different frequencies and effects. Results: To apply pharmacogenetic secondary prevention based on a genotype with a frequency of 10% and 33% risk reduction, 204 subjects would have to be screened and 110 given genotype specific treatment for 1 year, in order to prevent one recurrent stroke, compared with standard therapy. The application of genetic testing seems to be less promising in risk assessment and the assessment of prognosis of common ischemic stroke. Conclusions: The highest impact of genetic testing on clinical practice of stroke will be in the areas of secondary prevention. Given the weak effects of reported susceptibility genotypes, it is theoretically unlikely that genetic screening will be used for the assessment of risk or prognosis of a complex disorder, except for Mendelian types of disease.