Diana, Princess of Wales once said that there was a third person in her marriage. There is a third entity in our marriage, too. Not another woman, but Alzheimer’s Disease (AD).

Once I recovered from the shock of the diagnosis I decided to learn as much as I could about this disease that was stealing my husband’s identity, and robbing me of a beloved partner, bit by bit.

On World Alzheimer’s Day, let me share with you what I, as a caregiver and a member of the Board of Overseers of The Alzheimer’s Drug Discovery Foundation (ADDF), have learned. You might want to check some sources for yourself and I recommend the websites of The Alzheimer’s Association, The Alzheimer’s Society Toronto, The National Institute on Aging, and The Alzheimer’s Drug Discovery Foundation.

First, what is it? Dementia is defined as a weakening of memory and cognitive function. There are several types of dementia, but Alzheimer’s is the most common and it is a progressive, fatal, neurodegenerative disease. If you think that it is only recently that we have started to hear so much about AD, you are correct. It acquired a name in 1906, when a German physician, Dr. Alois Alzheimer performed an autopsy on a patient who had died after several years of memory loss and confusion. The autopsy revealed the plaques and tangles that are now considered the definitive diagnosis of AD.

But, although Alzheimer’s had acquired a name, it was not until the 1970s that the medical profession formally recognized it as a disease, and not just a normal part of aging. And even then, it was diagnosed only when the patient was in the last, very visible stage of dementia and confirmed by an autopsy. Over the past quarter of a century, the medical and scientific worlds gradually determined that there are three progressive stages through Alzheimer’s — a) the preclinical, b) mild cognitive impairment, and c) dementia. The increase in numbers with AD is partly the result of diagnosis now taking place earlier in the progression, and partly because, as a generation, we are living longer.

It is now known that Alzheimer’s takes root in the brain a decade or more before any symptoms are present. There are two types: early onset, and late onset. Early onset strikes people in their 40s and 50s. I can only imagine the heartbreak that these families endure, watching a loved one lose self before life is even lived.

Fatal? Yes. Like many people, before I became part of the Alzheimer’s world, I thought that Alzheimer’s did not kill. It does. Death by Alzheimer’s: the body forgets how to function. Millions are diagnosed with AD — their average life span after diagnosis is seven years. None will survive. None.

What causes it? Most scientists agree that there are many factors that may contribute to or trigger AD. The list includes age, family history and genetics, presence of type two adult diabetes, mild cognitive impairment, environment, head injury and lifestyle.

Alzheimer’s is not an inevitable result of aging, but the chances of occurrence do increase with age. The statistics are scary: One person in eight over the age of 65, one in three over the age of 80.

Dr. Howard Fillit, the Executive Director of The Alzheimer’s Drug Discovery Foundation, (ADDF) lists the presence of ApoE as the “most significant genetic risk factor for late-onset AD. A certain type of ApoE (ApoE E4) increases the risk before 75 up to 20 fold.” Although testing for this gene is not part of a routine blood analysis, genetic testing can be requested, and could provide valuable information to those with a family history of AD. Dr. Fillit points out, “The odds of getting AD increase four-fold if one of your parents has it; probably at least double that, if both do.”

The brain is part of the body, so protecting it means observing the rules set out for general good health. Just as an unhealthy lifestyle may make you vulnerable to other diseases, so it may also make you a candidate for Alzheimer’s. But the right choices in diet, exercise, intellectual stimulation, do not necessarily inoculate you.

Ronald Reagan had a supportive family, interesting work, the best medical care available, and was physically fit, but he died of Alzheimer’s. My husband also lived a healthy and happy life that included tennis, fly fishing, sailing, engaging work, and family and friends who cared for him. At 70 he could still get into the white tie and tails he wore when he was a Princeton undergraduate. Still, he will die from complications of Alzheimer’s.

How is it diagnosed? In most instances, the family physician, consulted by the patient or a concerned family member, will make the diagnosis. The primary care doctor might then recommend a visit to a geriatric specialist or a neurologist. Diagnostic testing will probably include such challenges as memorizing a list of names, word association, drawing a clock, counting backwards. An MRI or a CT may be suggested. These do not diagnose Alzheimer’s but they rule out other possible causes.

ADDF provided critical seed funding for one of the most exciting new developments in diagnostic tools which, earlier this year, was approved by the FDA for use in the United States. A radioactive dye called Amyvid developed by Avid Pharmaceuticals and now part of the Eli Lilly and Company portfolio makes possible for the first time, a PET scan that will estimate beta-amyloid neuritic plaque density in adults experiencing some cognitive loss.

A negative scan would suggest that those problems are not the result of Alzheimer’s, but some other factor. A positive scan does not necessarily mean that the patient has AD, but combined with other diagnostic tools, it can help arrive at a more accurate assessment. That’s only a start, but it is more, much more, than we have had.