(iStock)

Scientists have long sought to explain why Alzheimer’s Disease strikes women so much more often than men.

Among the 5.2 million Americans 65 and over who have the devastating brain disease, nearly two thirds are women. A common explanation is that women live longer and therefore have more time to come down with the illness, which largely afflicts older people.

But it may be that fewer men are being accurately diagnosed and that more attention should be paid to younger patients, according to new data presented Tuesday at the annual Alzheimer’s Association International Conference in Toronto.

Looking at the State of Florida’s brain bank, researchers at the Mayo Clinic found Alzheimer’s in 1,625 of 2,809 people who had donated their brains for autopsies. The donors were almost equally divided: 51 percent men and 49 percent women. But contrary to what has been seen in the general population, the Alzheimer’s cases in the brain bank were much more evenly divided: 54 percent of cases were women and 46 percent were men.

The researchers believe some crucial differences in the cases may help explain the difference, and illuminate why women receive so many more diagnoses than men.

The women in the study were older when the disease hit and had more typical symptoms, such as memory loss. The men were younger when they got Alzheimer’s, had a shorter disease duration, and more commonly had atypical symptoms.

It is hard to diagnose the disease in people under 70, according to Melissa Murray, an assistant professor at the Mayo Clinic’s department of neuroscience, who presented the study.

Rather than suffering from memory loss, younger patients often present with behavior, motor, or language problems, which can lead to misdiagnoses and inappropriate treatment.

“If you don’t know what the disease is then you can’t give even the modicum of treatment that we have available,” Murray said, noting that symptoms in men are often mistaken for cortico-basal syndrome, frontotemporal dementia, or other conditions.

The study also found that the disease attacks different areas of the brain in men and women. In men, it spreads more quickly and more commonly attacks the cortex, which is responsible for behavior, language, and motor skills. In women, the spread is slower and the disease more typically attacks the hippocampus, leading to memory problems – a classic sign of Alzheimer’s.

The researchers plan to further investigate how hormonal differences, lifestyle risk factors, and women’s longevity, or “survivor bias,” may affect the course of the disease in men and women.

“Men may lack protective factors for Alzheimer’s Disease, so they may get it at younger ages,” Murray said.

Heather Snyder, the Alzheimer’s Association’s senior director of medical and scientific operations, said the study offered an interesting perspective on understanding the reasons for the sex disparity in diagnoses. Comparing Alzheimer’s detection to the prevention of heart attacks, which can have different symptoms in women than in men, she added, “Is it biology, is it genetics, or are there difference in care that we need to be aware of?”

Conference participants also presented updates on research suggesting that clinicians will soon be able to use simple smell and eye tests to detect cognitive impairment and Alzheimer’s.

It is currently only possible to clinically detect Alzheimer’s after significant brain damage has already taken place. Brain imaging and spinal taps that can show the amyloid buildup associated with Alzheimer’s in pre-symptomatic people are costly and invasive.

But research increasingly shows that difficulty with identifying odors in a simple and inexpensive scratch-and-sniff test may be a reliable predictor of cognitive decline.

In a study of 397 older people presented at the conference on Tuesday, researchers at the Columbia University Medical Center found that those with low odor identification scores were more than three times more likely to have memory decline than those with high scores.

Changes in and around the eye may also be predictors of the disease, according to a study out of the NIHR Biomedical Research Centre, Moorfields Eye Hospital and UCL Institute of Ophthalmology in London. Using a bank of 33,000 United Kingdom residents registered with the National Health Service, researchers found that those with retinal nerve fiber layer thinning were significantly more likely to experience poor cognitive function.

Another study, out of the University of Waterloo in Ontario, showed that amyloid deposits in human and dog retinas could be detected with an inexpensive and noninvasive polarized light test that did as well as more invasive imaging.

The findings support earlier studies showing correlation between smell and eye tests and cognitive decline.