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EOFAD 101 : Early & Late Onset Alzheimer's Disease
In this article, we compare the rare form of Alzheimer’s disease, early onset familial Alzheimer’s disease (EOFAD), to the more common form of Alzheimer’s disease, late onset Alzheimer’s disease (LOAD).
Introduction
Alzheimer’s disease is commonly divided into two categories based on the age of its onset: late-onset Alzheimer’s disease and early-onset Alzheimer’s disease. However, let’s clarify some terminology before getting into the detailed differences between these two categories. Science and research are constantly evolving as new discoveries are made, and sometimes terminology is slow to catch up to reflect new scientific knowledge. Additionally, people become accustomed to using old terminology. Therefore, you’ll likely see different terms used interchangeably that may or may not refer to the same thing.
A list of terms that have been used for early onset familial Alzheimer’s disease (EOFAD):
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Dominantly Inherited Alzheimer’s disease (DIAD)
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Autosomal dominant Alzheimer’s disease (ADAD)
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Familial Alzheimer’s disease (FAD)
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Early onset Alzheimer’s disease (EOAD)
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Genetic Alzheimer’s disease
A list of other common names used for late onset Alzheimer’s disease (LOAD):
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Alzheimer’s disease
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sporadic Alzheimer’s disease (sAD)
However, it’s important to note that some of these terms can mean different things depending on how they are used. For example, early onset Alzheimer’s disease is used when symptoms of Alzheimer’s disease appear in individuals before the age of 65 - but using this term does not indicate whether a person develops the disease because of an EOFAD mutation (mutations in the APP, PSEN1, or PSEN2 gene). In addition, familial Alzheimer’s disease is used when Alzheimer’s disease runs in a family - but again may or may not refer to Alzheimer’s disease that is caused by the inheritance of an EOFAD mutation.
DIAD and ADAD are terms that scientists use to accurately define individuals with mutations in APP, PSEN1 and PSEN2 that are inherited in an autosomal dominant fashion, however, not everyone knows what dominant or autosomal dominant means.
As you can see, Alzheimer’s disease terminology can be confusing. Here at Youngtimers, we use the term early onset familial Alzheimer’s disease (EOFAD) to refer to the population of individuals and families that are affected by the inheritance of mutations in either PSEN1, PSEN2, or APP.
What are the different types of Alzheimer’s disease? And how do I refer to them correctly?
Both early-onset familial Alzheimer’s disease (EOFAD) and late-onset Alzheimer’s disease (LOAD) are progressive neurodegenerative diseases characterized by the damaging presence of amyloid plaques and tau tangles in the brain. The main differences between the two types of Alzheimer’s disease are the age of onset of the disease and the cause of the disease.
A simplified explanation of the two is below:
Early-onset familial Alzheimer’s disease (EOFAD): EOFAD affects much younger individuals compared to LOAD. It develops in individuals before the age of 65, usually between the ages of 30 – 60 years with an average age of about 45. Unlike LOAD, EOFAD is a rare genetic disorder that is inherited in an autosomal dominant manner. For this reason, many families with EOFAD often see multiple family members over multiple generations affected by the disease. As a rare genetic disease, EOFAD represents less than 1% of all Alzheimer’s disease cases (Bateman et al., 2011), affecting 5.3 out of 100,000 individuals (Campion et al., 1999). It has been estimated that ~45,000 individuals worldwide are affected by EOFAD.
Late-onset Alzheimer’s disease (LOAD): As the name suggests, LOAD tends to affect older individuals, usually after the age of 65. It is a much more common disease (affecting more than 5.8 million people in the US and 24 million globally (Hebert et al., 2013)) and tends to have a less aggressive disease course than EOFAD. Although some risk factors have been identified, we do not know exactly what causes LOAD.