Research sheds light on Alzheimer’s disease
In 1906, Dr. Alois Alzheimer examined the brain tissue of a German woman who had shown signs of dementia. Given the common belief that dementia was a symptom of old age, this case was unusual because the woman was only 51. The autopsy results were also surprising. Using a newly developed technique for tissue analysis, Alzheimer discovered unusual clumps of protein and tangled fibers – now called amyloid plaques and neurofibrillary tangles – in and around the nerve cells of the woman’s brain. When these findings were published, the basis for a diagnosis of Alzheimer’s disease was established.
More than one hundred years later, Alzheimer’s disease is the most common form of dementia. It affects more than 4 million Americans, including an estimated one in 10 people older than 65 and perhaps nearly half of those older than 85. Moreover, even though the disease is not a normal part of the aging process, advancing age is the strongest risk factor so it will become more prevalent as the average lifespan increases.
Since 1984, the National Institute on Aging has promoted research to understand, treat and prevent this devastating disease by funding Alzheimer’s Disease Research Centers at major academic medical institutions, including the University of Washington. As a result of this coordinated scientific effort, our knowledge of what happens in the brain before and after disease symptoms appear has increased greatly.
The human brain consists of billions of specialized nerve cells, called neurons, that transmit messages through an electrochemical process. When functioning normally, each neuron has an axon that transmits messages to other neurons and dendrites that receive messages from other nerve cells.
Dementia occurs when large numbers of neurons stop functioning, lose connections with other neurons and die. People with dementia have significantly impaired mental functioning that interferes with normal activities and relationships. They also can lose their ability to solve problems and maintain emotional control, and they may experience personality changes and behavioral problems such as agitation, delusions and hallucinations.
In Alzheimer’s disease, severe dementia is linked to an increase in the number of amyloid plaques and neurofibrillary tangles. In brief, amyloid plaques are formed when a protein fragment, called amyloid-beta, mixes with other molecules, neurons and non-nerve cells. In addition to releasing toxic substances that harm nerve cells directly, these plaques may cause a change in another protein, called tau, resulting in tangles within nerve fibers. When this happens, the neuron’s internal structure for transmitting messages is disrupted and cell death may occur.
Still, many questions remain to be answered by basic research and clinical trials. One of the most important is to determine whether the amyloid plaques and neurofibrillary tangles that define Alzheimer’s disease are its direct causes or side effects of the disease process. Other key areas of inquiry include the use of sophisticated brain scans, such as PET (positron emission tomography) and MRI (magnetic resonance imaging) to diagnose the disease earlier, the search for genetic risk factors to identify new targets for drug therapy, and the evaluation of drug and immunization therapies that may be able to block or reverse the formation of amyloid plaques.
Protecting against dementia
While new therapies for preventing or delaying Alzheimer’s disease continue to be tested, a recent investigation at Harborview Medical Center reveals that the second leading cause of dementia in older adults may already be treatable and preventable. For this investigation, the research team analyzed brain tissue from organ donors who were enrolled in a long-range study run by Dr. Eric Larson at the Group Health Cooperative Center for Health Studies. While Alzheimer’s disease, as expected, accounted for the largest number of dementia cases, a surprising discovery was that small-vessel damage from multiple small and unnoticeable strokes was the cause of dementia for nearly one-third of the study group.
The good news is that high blood pressure and diabetes, the risk factors for these small strokes, are generally preventable and treatable. As a result, a likely way to reduce the risk of dementia is to follow recommendations for good cardiovascular health: don’t smoke, control your weight, monitor your cholesterol levels and exercise regularly.
Finally, a number of studies have demonstrated the benefits of staying mentally active. Whether your pastime is chess or crossword puzzles, playing a musical instrument, or being socially involved, intellectually stimulating activities can help to maintain thinking skills and the ability to perform basic tasks, such as shopping, cooking and handling finances.