Alzheimer's Disease Risk Factors
The risk for Alzheimer's disease increases with each decade of adult life. People with a family history of Alzheimer's have a greater risk, implying that a genetic factor is involved in the development of the disease. A clear inherited pattern of AD exists in less than 10 percent of cases.
Some inherited patterns involve a mutation of the gene for the protein APP, which is found on chromosome 21. Nearly all people with Down's syndrome (trisomy 21) who live into their 40s develop the disease. Other patterns involve a defect on chromosome 14. The gene for the protein Apo E, found on chromosome 19, is a risk factor that may be involved in modifying the age of onset for Alzheimer's disease.
Untreated chronic high blood pressure (hypertension) and high cholesterol (hypercholesterolemia) in middle age have been identified as risk factors for loss of mental function in older people. Treatment for these conditions may reduce the Alzheimer's risk. Adults who have had head injuries are three times more likely to develop Alzheimer's disease. Studies also have shown that diabetes may increase the risk for Alzheimer's and other forms of dementia.
It is thought that gender plays a role because several studies suggest that women are afflicted with Alzheimer's disease more often than men. However, the evidence is inconsistent, and some studies report that the disease is more prevalent in men. Therefore, more research is needed to obtain conclusive evidence regarding prevalence in gender.
Alzheimer's Disease Causes
Genetic factors are known to play a role in some cases of Alzheimer's. The APP gene found on chromosome 21 is implicated in the occurrence of AD in Down's syndrome patients who survive beyond 40 years. Some families with a history of early-onset AD have a mutation on the APP gene and others have a mutation in the presenilin-1 gene (PS-1) found on chromosome 14. Another gene, the Apo E gene on chromosome 19, also has been implicated in the disease. Apo E is a protein found with beta amyloid in neuritic plaques.
It is not known whether the characteristic neuritic plaques and neurofibrillary tangles are the cause or the result of the disease process.