ABSTRACT
The risk of developing Alzheimer’s disease probably depends on the number and impact of the contributing genes and risk factors rather than on the presence or absence of any single mutation, polymorphism, or risk factor. Risk factors are antecedents that are considered to be a component of the disease pathway. Biological gradient or “dose-response” implies that as the degree of exposure increased to a putative risk factor or as the number of genes or “gene dose” increases, the risk of disease will be greater. In epidemiological studies two or more groups are usually compared for the frequency of exposure to putative risk factor or factors. The model of the classical disease pathway offers a way of conceptualizing how and when risk factors act in the process of disease. An estimation of relative risks, under the rare disease assumption, is possible, but Alzheimer’s disease may not be a rare disease in the age group over 65.
