The causes of Alzheimer's disease are not yet well understood, especially as the disease seems to have a number of disparate roots. However, a number of genetic problems have been shown to contribute to the development of Alzheimer's, and these are discussed in the context of other theories.
Types
Even though no cause of Alzheimer's has ever been fully described, inheritance has been linked to two major forms of the disease. Early-onset Alzheimer's, which affects only about 5 percent of people suffering from the disease, according to the National Institute on Aging (NIA), has been linked to mutations on the first, 14th and 21st chromosomes. This leads to an increased production of beta-amyloid, a component of the plaques associated with the disease. Children of a parent with one of these mutations have a 50/50 chance of developing Alzheimer's. Genetic links to late-onset Alzheimer's are less certain, although the presence of a gene for APOE (apolipoprotein E) ε4, which is found on chromosome 19, mark a risk factor for developing the disease. According to the NIA, this gene may influence the age at which the disease develops, but its mere presence does not always mean that the disease will develop.
Identification
Methods of diagnosing Alzheimer's have not heretofore generally involved genetic testing, and currently include, according to the Alzheimer's Association, tests for dementia, a review of the patient's medical history, a mini-mental state exam (MMSE, in which the patient is asked a number of questions and to identify a number of objects and facts), as well as physical and neurological tests (MRI, fMRI, CT). However, in the August 2007 issue of Lancet Neurology, Bruno Dubois makes recommendations for revising criteria based on the presence of biomarkers (sections of genetic code that might indicate the possibility for a trait).
Effects
Alzheimer's is a disease whose effects are both irreversible and incurable. Two distinct brain malformations occur in Alzheimer's: plaques and tangles. According to the Alzheimer's Association, plaques are buildups of beta-amyloid between neurons (brain cells), while tangles, twisted as their name suggests, are composed of a protein called tau. These malformations contribute to Alzheimer's dementia, memory loss, confusion and the other symptoms of the disease. Genetic links have been made in some cases to the development of plaques and tangles.
Theories/Speculation
In the February 2009 issue of Nature, Anatoly Nikolaev suggests that the beta-amyloid component of Alzheimer's disease might be a breakdown of natural regulatory processes that is a natural result of aging. Other research has suggested that Herpes simplex 1 might play a role in triggering the disease.
Potential
Based on recommendations of researchers such as Dubois, it may become standard in the future, with increased quality of testing and understanding of genetic components of the disease, to use genetic testing to both screen for Alzheimer's and to diagnose it. Future research may help doctors and scientists understand better why APOE ε4 influences Alzheimer's in late-onset patients and to see if there are other associated genetic factors.
Tags: Alzheimer disease, Alzheimer Association, been linked, beta-amyloid component, Genetic links, genetic testing, have been