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In their News Focus article “Closing the net on common disease genes”(11 May, p. 820), J. Couzin and J. Kaiser present an optimistic appraisal of genome-wide association (GWA) studies. Within the past year, Science has published results from seven GWA studies for obesity, cardiovascular disease, and type II diabetes (1–7). We would like to discuss three aspects of GWA studies.

First, of the seven GWA studies published in Science, four (1–4) reported as significantly associated with the phenotype under study either a single genetic variant or a single cluster of highly correlated genetic variants. The other studies claimed four (5), five (6), and three (7) new genetic associations. The phenotypes studied are all considered “complex”; thus, we would expect multiple genetic factors, environmental factors, and interactions among those factors to be associated with the phenotype. Furthermore, GWA studies are claimed …