What Is Alzheimer's Disease
Alzheimer's disease (AD) is a slow-evolving disease of the brain that is characterized by loss of memory and eventually by disturbances in reasoning, planning, language, and perception. Many scientists believe that Alzheimer's disease results from an increase in the production or accumulation of a specific protein (beta-amyloid protein) in the brain that leads to nerve cell death.
The chances of having Alzheimer's disease increase after the age of 70 and may affect around 50% of persons over the age of 85. However, Alzheimer's disease is not a normal part of aging and is not something that inevitably happens in later life. Some people may live to over 100 years of age and never develop Alzheimer's disease.
Who develops Alzheimer's disease?
The main risk factor for Alzheimer's disease is increased age. As people age, the frequency of Alzheimer's disease continues to increase. Ten percent of people over 65 years old and 50% of those over 85 years old may have Alzheimer's disease. Unless new treatments are developed to decrease the possibility of developing Alzheimer's disease, the number of individuals with Alzheimer's disease in the United States is expected to be 14 million by the year 2050.
Genes and heredity are also risk factors for Alzheimer's disease. Most patients develop Alzheimer's disease after age 70. However, 2%-5% of patients develop the disease in the fourth or fifth decade of life (40s or 50s). At least half of these early onset patients have inherited gene mutations associated with their Alzheimer's disease. Moreover, the children of a patient with early onset Alzheimer's disease who has one of these gene mutations has a 50% risk of developing Alzheimer's disease.
There is also a genetic risk for late onset cases. In the majority of Alzheimer's disease cases, however, no specific genetic risks have yet been identified. A relatively common form of a gene located on chromosome 19 is associated with late onset Alzheimer's disease.
Other risk factors for Alzheimer's disease include high blood pressure (hypertension), diabetes, coronary artery disease, and possibly elevated blood cholesterol. Individuals who have completed less than eight years of education also have an increased risk for Alzheimer's disease. These factors increase the risk of Alzheimer's disease, but by no means do they mean that Alzheimer's disease is inevitable in persons with these factors.
Down syndrome may also develop the brain changes of Alzheimer's disease by 40 years of age. This fact was also a clue to the "amyloid hypothesis of Alzheimer's disease" (see section later in this article).