Genome-wide association studies have revealed the large numbers of genes involved in multifactorial disease. Some patterns are emerging that point towards shared pathways, for example in immune-mediated disorders. Sceptics argue that the predictive value of genetic tests is only marginally different from clinical tests, and that some genes appear to protect against one disorder whilst enhancing another, which will hamper preventive or therapeutic interventions. However, more optimistic researchers stress that at least some of the many predisposing genes might be amenable to prophylaxis or therapy.