The Different Types of Alzheimer's

Alzheimer's disease is associated with dementia, a loss of short term memory, and an inability to carry out once routine daily tasks. Alzheimer's afflicts approximately 5 million individuals in the United States, a number that is expected to be on the rise as the baby boomer generation gets older. There are two major types of Alzheimer's disease: late-onset Alzheimer's and familial early-onset Alzheimer's disease. These two types of Alzheimer's differ in the age of onset and genetic predisposition. However, they are generally not thought to differ in disease course severity.

Late-onset Alzheimer's disease is characterized by its development at or after the age of 65. The most significant risk factor for late-onset Alzheimer's disease is age, as the risk for Alzheimer's doubles every 5 years once the age of 65 is reached. Further demonstrating the link of age to Alzheimer's is the estimation that 1 in 3 individuals over the age of 85 will develop the disease. However, this is not to say that genetic predisposition does not play a role, as the concordance rate of Alzheimer's disease is higher in identical twins than in non-identical twin siblings. Also, a specific allele of the APOE gene is a candidate for increased risk of late-onset Alzheimer's development.

Another form of Alzheimer's is known as familial early-onset Alzheimer's. This rarer form is Alzheimer's has a stronger genetic link and accounts for less than 10% of all Alzheimer's cases. Disease manifestation occurs before the age of 65, hence the moniker early-onset Alzheimer's. Three genes have been identified to increase the risk of this type of Alzheimer's: presenilin-1, presenilin-2, and amyloid precursor protein. These genes are thought to lead to the formation of plaques in the brain that cause cellular damage and neuronal death. This damage leads to eventual cognitive impairment and memory dysfunction.

Warning signs for Alzheimer's include forgetfulness, repeating oneself repeatedly, becoming lost and disorientated in familiar places, and the loss of the ability to perform once routine tasks. Clinicians will perform a mini-mental exam to assess a patient's progression and also rule out other forms of dementia before Alzheimer's is suggested. There is no cure for Alzheimer's disease but treating it early both pharmacologically and emotionally, by joining a support group, may help improve the patient's quality of life and that of their family. For additional information on Alzheimer's care consult your primary care provider or local pharmacist.

References and Statistical Sources:

Bertram, L., and Tanzi, RE. Thirty years of Alzheimer's disease genetics: the implications of systematic meta-analyses. Nature Reviews Neuro. 2008: 2008 Oct;9(10):768-78.

Mayo Clinic Staff. Early-onset Alzheimer's: When symptoms begin before 65. http://www.mayoclinic.com/health/alzheimers/AZ00009. Accessed 3/8/2010.

Querfurth,HW; LaFerla, FM. Alzheimer's Disease. New England Journal of Medicine. 2010; 362:329-344.

Williamson J, Goldman J, Marder KS. Genetic aspects of Alzheimer disease. Neurologist. 2009 Mar;15(2):80-6.