The advances in human genetics that have ocurred during the past 20 years have revolutionized our knowledge of the role played by inheritance in health and disase. It is clear that our DNA determines not only the emergence of catastrophic single-gene disorders, which affect millions of persons worldwide, but also interacts with environments to predispose individuals to cancer, allergy, hypertension, heart disease, diabetes, psychiatric disorders and even to some infectious diseases. Overall, the study of longevity and the demonstration of genes favouring a long lifespan suggest that such protective systems exist. In recent years, the study of genetic polymorphisms has made clear that some alleles have beneficial effects. These discoveries can substantially improve our understanding of the interactions between genetics and the environment, between pathogenetic mechanisms and new treatments.