There are two types of Alzheimer's disease: early-onset and late-onset. The diagnosis of these types of Alzheimer's is based on age and an individual's genes. Though the symptoms of the disease remain the same with both types, there are different implications depending on which type of Alzheimer's an individual has:
Early-onset is much less common than late-onset Alzheimer's. With early-onset Alzheimer's, symptoms begin appearing before an individual reaches the age of 60. Unfortunately, the disease tends to progress very quickly with early-onset Alzheimer's. Because early-onset Alzheimer's can run in families, scientists have been able to identify several genes associated with this type of the disease.
Late-onset is the more common form of Alzheimer's disease. This type of the disease occurs in individuals who are age 60 or older. The progression of the disease can vary from person to person with late-onset Alzheimer's. This form of the disease may also run in families, but the link between genes is not as clear. Scientists have identified a gene called ApoE which is linked to late-onset Alzheimer's. However, the presence of this gene does not guarantee that a person will develop late-onset Alzheimer's, and those who lack the gene can develop it as well.