Early-onset Alzheimer's: When symptoms begin before 65

When Alzheimer's begins in middle age, misdiagnosis may be more likely. Rare disorder affects work, finances and family.
Glenn Smith, Ph.D.
Early-onset Alzheimer's is a rare form of dementia that strikes people younger than age 65. Glenn E. Smith, Ph.D., a neuropsychologist at Mayo Clinic, Rochester, Minn., answers questions about this condition.
How common is early-onset Alzheimer's?
Of all the people with Alzheimer's disease, only 5 percent to 10 percent develop symptoms before age 65. So if 4 million Americans have Alzheimer's, at least 200,000 people have the early-onset form of the disease. Early-onset Alzheimer's has been known to develop between ages 30 and 40, but that's exceedingly rare. It is more common to see someone in their 50s who has the disease.
What causes it?
It often runs in families. Many people with early-onset Alzheimer's have a parent or grandparent who also developed Alzheimer's at a younger age. A significant proportion of early-onset Alzheimer's is linked to three genes.
These three genes are different from the apo E gene, which can increase your risk of Alzheimer's in general. But you can have the apo E gene and never develop Alzheimer's. Conversely, you can have Alzheimer's and not have the apo E gene. The genetic path of inheritance is much stronger in early-onset Alzheimer's. If you have one of those three genes, it would be very unusual for you not to develop Alzheimer's before age 65.
If early-onset Alzheimer's runs in my family, should I get tested for it?
That's a personal decision that only you can make. There are pros and cons to genetic testing. Anyone who's considering it should never proceed without genetic counseling — to examine these pros and cons beforehand.