Genetics of Alzheimer’s Disease

Abstract

To understand how late-onset, also known as sporadic Alzheimer’s disease, differs from early-onset or familial Alzheimer’s disease, it is important to discuss the genetics of the latter. Genetic research has shown a link between genes on chromosomes 1, 14, and 21 and familial Alzheimer’s. A gene on chromosome 19 called ApoE4 is associated with sporadic Alzheimer’s and is considered a “susceptibility” gene because even when it is inherited from one or both parents, it can only increase the risk for Alzheimer’s, not its certainty. Although sporadic and familial Alzheimer’s has a similar clinical course, the familial type tends to have severe brain atrophy, cognitive impairment around age 45 and patients can develop muscle twitches and spams called myoclonus during the disease. The most important difference between sporadic and familial Alzheimer’s is the specific gene mutation seen in the latter which directly assures that Alzheimer’s will develop. In addition, familial Alzheimer’s will affect individuals at a much earlier age, between 40 and 60 as opposed to over age 65 in most sporadic Alzheimer’s cases. Diagnosis of familial Alzheimer’s can be done by noting family history and neurological symptoms and observing severe brain atrophy on neuroimaging age and genotyping.