Alzheimer Disease (AD) is a devastating neurodegenerative disorder and is the most common cause of dementia in the elderly. Much evidence suggests that AD clearly has a measurable genetic component. Many gene-mapping studies have found genes associated with AD but most of them have failed to replicate in follow-up studies. Even the confirmed genetic factors only explain a small amount of AD heritability, leaving most of the AD due to genetic factors unexplained. One reason for this Is that most studies on AD (and other complex diseases) only examine a single genetic variant at a time for association to AD. It Is l^nown, however, that gene-gene and gene-environment Interactions are ubiquitous, and likely play a role in human disease. This has been documented in model organisms, and when investigated properly, has been found to influence disease In humans. Yet most studies do not investigate Interactions among genetic and environmental factors that Influence AD risl
