What Causes Alzheimer's Disease?
The cause of Alzheimer's disease---why these neurofibrillary tangles develop in some people and not in others---remains a mystery. Modern methods of analyzing brain tissue have revealed that the neurofibrillary tangles are deposits or plaques of abnormal proteins, the most common of which is beta amyloid. An Alzheimer's brain is also deficient in several neurotransmitters (chemicals that allow nerves in different parts of the brain to send messages to each other), the best known of which is acetylcholine. Although replenishing these neurotransmitters has no real impact on dementia, doing so sometimes alleviates symptoms.
There are several interesting theories about the cause of Alzheimer's. One suggests that the culprit is an as yet unidentified virus. Or perhaps the brain may be deficient in nerve growth factor (NGF), a substance that stimulates the formation of new nerve connections (synapses). When the brain is lacking in NGF and can't make enough synapses, memory and intellectual function become impaired. When NGF is administered to rats, new connections form in those areas of the brain that are concerned with memory. Although these and other observations hold out the promise that Alzheimer's will one day be cured, don't hold your breath---at least for the moment.
How do you know if you're especially susceptible to Alzheimer's? There are no absolute risk factors, but there are some statistical correlations.
Age: Full-blown Alzheimer's affects about 4 million Americans, virtually all of whom are older than sixty; the majority are beyond eighty-five. At least half the current residents of nursing homes in this country have Alzheimer's disease; most of the others are there because they have brain damage from recurrent small strokes, Parkinson's disease, and other less common neurological disorders.
Family History: The risk of getting Alzheimer's in your lifetime is slightly more if any of your close relatives, such as a parent, sibling, or child is, or was, affected. However, the more such relatives you have, the greater your risk. (In-laws don't count.)
Genetics: A specific gene called ApoE, usually situated on chromosome #19, is a marker of susceptibility to Alzheimer's in about 15 percent of the population. However, if you happen to carry it, don't panic. Most persons who do never develop Alzheimer's, and vice versa. More recently, another gene, this one located on the #12 chromosome, has been found in up to 15 percent of late-onset Alzheimer's (appearing at or beyond age 80). Again, its presence merely indicates that, in combination with certain environmental factors, you may be predisposed to Alzheimer's but are by no means certain to develop it. Although genetic testing is important in the research of Alzheimer's disease, it is not yet precise enough to warrant its routine use. It is not clear why Hispanics and Blacks without these specific genes are at two and four times the risk, respectively, of developing Alzheimer's disease. Some other as yet unidentified gene or genes, or perhaps environmental factors such as diet, occupation, and exposure to toxic substances, may be responsible.
Other possible causes of Alzheimer's that have been suggested but remain unproved include underactivity of the thyroid gland (hypothyroidism) and chronic alcohol excess.
Symptoms of Alzheimer's
Full-blown Alzheimer's impairs virtually every function of the brain: memory, behavior, abstract thinking, personality, judgment, language, movement, and coordination. It's interesting that patients with Alzheimer's lose these abilities in the reverse sequence in which we develop them during childhood. For example, the very first thing babies can do is swallow; then they recognize and respond to the mother or other caregiver; next they begin to repeat words; then they walk; next in the sequence are bladder and bowel control; finally they begin to converse, to exercise their memory, and to demonstrate judgment. In Alzheimer's, the higher thought processes are the first to go. The earliest symptoms are impaired learning and an inability to retain new information, lack of reasoning power, trouble performing complex tasks, a distinctive subtle change in personality, confusion, and a lack of orientation. These are followed by loss of bladder and bowel control, and walking is progressively more difficult. As motor skills become impaired, the Alzheimer's patient cannot walk unassisted, is unable to swallow normally, and often dies from pneumonia due to aspiration of fluid or liquid into the lung.
From Live Now Age Later: Proven Ways to Slow Down the Clock,by Isadore Rosenfeld. © June 1999, Isadore Rosenfeld. Used with permission.
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