How to Use an Article About Genetic Association

In the first article of this series, we reviewed the basic genetics concepts necessary to understand genetic association studies. In this second article, we enumerate the major issues in judging the validity of these studies, framed as critical appraisal questions. Was the disease phenotype properly defined and accurately recorded by someone blind to the genetic information? Have any potential differences between disease and nondisease groups, particularly ethnicity, been properly addressed? In genetic studies, one potential cause of spurious associations is differences between cases and controls in ethnicity, a situation termed population stratification. Was measurement of the genetic variantsunbiasedandaccurate?MethodsfordeterminingDNAsequencevariation are not perfect and may have some measurement error. Do the genotype proportions observe Hardy-Weinberg equilibrium? This simple mathematic rule about the distribution of genetic groups may be one way to check for errors in reading DNA information. Have the investigators adjusted their inferencesformultiplecomparisons?Giventhethousandsofgeneticmarkerstested in genome-wide association studies, the potential for false-positive and falsenegative results is much higher than in traditional medical studies, and it is particularly important to look for replication of results.