Alzheimer's gene testing not necessary

DEAR DR. GOTT: My father has Alzheimer’s disease. Should I be tested for the APOE 4 allele? I would like to know what I’m facing.

DEAR READER: Your short note has a complex answer. I must start by asking some questions.

How old is your father? At what age was he diagnosed? What are his symptoms? Is there any doubt of the diagnosis? Is he under the care of a neurologist or other physician familiar with Alzheimer’s disease? Does anyone else in your family have Alzheimer’s or other neurological conditions? How old are you? Are you displaying any symptoms or early-warning signs?

The more information readers and patients provide, the more accurate the answers they will receive. Given that I don’t know these things, I can only provide a general overview.

There are several types of dementia. These include Lewy body dementia, Parkinson’s dementia, normal pressure hydrocephalus and more; however, the most common form is Alzheimer’s, of which there are two forms — early-onset and late-onset. AD affects about 4.5 million Americans.

Early-onset AD is rare. It occurs in people between the ages of 30 and 60 and accounts for only about 5 percent of all cases. If one parent is affected, a child has a 50-percent chance of inheriting one of the gene mutations that almost always lead to the development of AD.

Late-onset AD develops in those over the age of 60 and accounts for the remaining 95 percent of AD sufferers. No specific gene has been found to cause AD, but there is a predisposing genetic factor that increases the risk of developing the condition. It is known as the apolipoprotein E (APOE) gene. There are several forms of this gene, but APOE 2, 3 and 4 occur most frequently.

APOE 2 appears to be somewhat rare but may provide some protection against AD. Those with this type who do develop Alzheimer’s typically do so later than others.

APOE 3 is the most common form. It is thought to play a neutral role, neither increasing nor decreasing risk.

APOE 4 is found in about 40 percent of all late-onset AD sufferers but occurs in about 25 percent to 30 percent of the population. Having this gene does not mean a person will develop Alzheimer’s, but it does increase the risk.

There is no known way to determine who will develop AD and who will not. Most researchers believe that APOE testing is beneficial only for studying AD risk in large groups of people, not for defining a single person’s specific risk.

There is no great advantage to undergoing the test. You would be better served by learning as much about the condition as you can and by watching for signs and symptoms. In the meantime, eat properly, exercise regularly and engage in brain-stimulating activities that keep your brain active and functioning at its highest possible level.

Peter Gott practiced medicine in Lakeville for 40 years.