is inherited as a Mendelian dominant trait, while the more common form of the disease is a complex trait with a significant environmental component. Thus, any genetic analysis of Alzheimer's disease that did not include age of onset as a component of the disease definition would suffer greatly from the shortcoming known to epidemiologists as misclassification bias. A linkage or association analysis of Alzheimer's disease using only the pathological definition of the disease and ignoring the age of onset would be mixing cases with two distinct genetic etiologies. This could result in a severe loss of power to detect a disease predisposing variant of a gene.
