Causes of Alzheimer's Disease

Other Genetic Factors in Late-Onset Alzheimer's. Most people with late-onset Alzheimer's disease do not carry the ApoE4 gene. Increasingly, researchers believe that many cases of late-onset Alzheimer's are a result of a collaboration of genetic factors that participate in the process of producing or degrading beta amyloid. Some under investigation are the following:

• Researchers are now targeting chromosomes 9, 10, and 12 as possible locations for genetic factors involved with Alzheimer's disease. (The ApoE4 gene is on chromosome 19.) In 2005, researchers announced that mutations linked to the ubiquilin 1 (UBQLN1) gene, located on chromosome 9, might be associated with increased risk for late-onset Alzheimer's disease.
• Researchers have detected mutations in the proteins amyloid precursor protein (APP) and ubiquitin-B (Ubi-B), which may account for some cases of late- and early-onset Alzheimer's. Such mutations are not inherited, however, but appear to be genetic mistakes that occur during transcription, the coding process in which DNA establishes the pattern for the production of its proteins and other molecules.

Genetic Factors for Early-Onset Alzheimer's. Scientists are coming closer to identifying defective genes responsible for early-onset Alzheimer's, an uncommon, but extremely aggressive form of the disease.

• Mutations in genes known as presenilin-1 (PS1) and presenilin-2 (PS2) account for most cases of early-onset inherited Alzheimer's disease. The defective genes appear to accelerate beta amyloid plaque formation and apoptosis, a natural process by which cells self-destruct.
• Genetic mutations in the genes that control amyloid precursor protein (APP) are also being targeted as causes of early-onset Alzheimer's. The genetic disease Down syndrome, for example, overproduces beta-amyloid precursor protein (APP), the source of beta amyloid, and almost always leads to early Alzheimer's. Other APP mutations are being identified.

Environmental Factors

Researchers are also investigating environmental factors (infections, metals, industrial and other toxins) that may trigger oxidation, inflammation, and the disease process, particularly in people with a genetic susceptibility to Alzheimer's.

Infectious Organisms. Slow, infectious viruses cause a number of other degenerative neurologic diseases, such as kuru and Creutzfeldt-Jakob disease.