Currently, over 5 million people in the United States have a diagnosis of Alzheimer’s disease, a progressive degenerative brain disorder that robs the individual of memory and critical thinking skills, among many other things. There are two types of Alzheimer’s disease: early (or younger) onset and late onset. Both these types have a genetic component.
In a fact sheet generated by the National Institute on Aging and the National Institutes of Health, early or younger-onset Alzheimer’s disease occurs in individuals prior to the age of 65, and it represents less than 5 percent of all individuals diagnosed with Alzheimer’s disease. Most cases are caused by an inherited change in one of three genes, which results in a type known as familial Alzheimer’s disease or FAD. For others, Alzheimer’s disease develops without any specific known causes. For example, a child whose biological mother or father carries a genetic mutation for early-onset FAD has a 50-50 chance of inheriting that mutation, meaning that the child has a very strong probability of developing the early-onset FAD.
Most individuals with Alzheimer’s disease have the late-onset type of the disease, which occurs after the age of 65. Causes are not yet known for late-onset; however, a combination of genetics, lifestyle and environment likely contribute to the risk of developing the disease.
Researchers have not discovered a specific gene that directly causes late-onset AD. However, one genetic risk factor, one form of the APOE (apoliproprotein E) gene does increase the individual risk. This gene comes in different forms, or alleles, including APOEe2; APOEe3 and APOEe4.
The APOEe4 is called a risk factor gene because it increases the individual’s risk of developing late-onset Alzheimer’s disease.
Researchers know that it is unlikely that genetic testing will ever be able to predict the disease with 100 percent accuracy, as too many other factors influence the disease development and progression. Though a blood test can identify which APOE alleles an individual has, the results cannot predict if the individual will or will not develop the disease. Most researchers confirm that APOE testing is useful for studying the risk of Alzheimer’s disease in large groups of participants and not for determining individual risk.
Alzheimer’s disease genetics research is dependent on volunteers, as the more genetic information researchers can gather and analyze from individuals and families, the more clues they will have for finding additional risk factor genes.
For more information on research, visit nih.gov. For participation in local studies, contact the Institute for Dementia Research and Prevention at Pennington Biomedical Center in Baton Rouge, idrp.pbrc.edu.
Questions about Alzheimer’s disease or a related dementia disorder? Contact Dana Territo, the Memory Whisperer, Director of Services at Alzheimer’s Services of the Capital Area, (225) 334-7494, firstname.lastname@example.org, or visit the organization at 3772 North Blvd., Baton Rouge.