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 a few questions about this condition.

Of all the people who have Alzheimer's, only 6 percent to 8 percent develop symptoms before age 65. So if 4 million Americans have Alzheimer's, around 300,000 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. The risk increases with age.

It runs in families. Often someone with early-onset Alzheimer's has 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.

No. If you have apo-E, it just increases your risk of Alzheimer's. But you can have the gene and never develop Alzheimer's. Conversely, you can have Alzheimer's and not have the 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.

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.

There's a perception that it does, but it's not really backed up by hard data. It depends on what endpoint you're using in your measurement. If you use admission to a nursing home, that may occur earlier for the early-onset group — but only because their spouses have so many other things on their plates.

People who have early-onset Alzheimer's often still have children at home. They or their spouses may have elderly parents that need care, too. That generation often is sandwiched between caring for their ailing parents and caring for their teen-age children at the same time. Adding in a spouse with Alzheimer's can simply be too much to handle.

Alzheimer's disease has a tremendous impact at any age. But we don't expect to see dementia at a young age, so problems emerging at work or home may be mistakenly ascribed to lack of motivation or diligence, or possible psychiatric problems. People with early-onset Alzheimer's may lose relationships or be fired instead of being identified as medically ill or disabled.

The loss of intimacy is something that comes up a lot with early-onset Alzheimer's. Many people who develop late-onset Alzheimer's have already been widowed. But couples in their 40s or 50s often are in the middle of their married lives. Spouses face the possibility of spending the next many years of their lives without an active partner. Losing the romantic component and changing to a caregiver status complicates the relationship.

People with early-onset Alzheimer's often have to quit work, and this loss of income is a serious concern. Finances get even tighter if their spouses also quit their jobs to become full-time caregivers. Some medical benefits and many social-support programs will not provide assistance unless the person with Alzheimer's is over age 65. Younger people often require special waivers to get into such programs.

Accurate diagnosis is critical so that you can explain your condition to your employer and perhaps arrange a lighter workload or more convenient schedule. For family reasons it is even more crucial. The diagnosis is fundamental in helping the family react with appropriate understanding and compassion. In addition, a complete evaluation will rule out reversible forms of dementia that might improve with treatment.

The key treatments in Alzheimer's are education and support. This is especially true given the special social challenges of early-onset Alzheimer's. Getting connected to services such as support groups can help you identify resources, gain a deeper understanding and learn ways to adapt to the situation.