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What Causes Alzheimer's

By: Miriam Vered - Updated: 4 Dec 2012 | comments*Discuss
 
What Causes Alzheimer's

In every era there have been diseases that wreak havoc in humanity. Throughout history the causes of most such illnesses have been unknown and people generally accepted that.

But we're not used to such ignorance today. Even though we know that there are many illnesses that scientists haven't found cures for yet, we tend to feel profoundly uneasy when even the causes are still shrouded in mystery.

This is the case for Alzheimer's. There are some clues and suspicions, but as yet no clear answers as to the cause. The one thing that's clear beyond a doubt is that increasing age is the main risk factor. Every 5 years beyond age 65 the number of Alzheimer's sufferers doubles.

But no-one really knows why that is, as Alzheimer's is not a part of the normal aging process.

What's Going on Inside the Alzheimer's Brain?

In 1906, Dr Alois Alzheimer, a German doctor noticed changes in the brain tissue of a women who had died after a disease that was then thought unusual. The changes he found looked like clumps and tangles. Nowadays these are called amyloid plaques and neurofibrillary tangles, and they are characteristic of Alzheimer's Disease (AD). In fact, the definitive diagnosis can only be officially made if an autopsy is performed and these plaques and tangles are found in the brain tissue. They consist of abnormal protein deposits combined with degenerating nerve cells.

Levels of the important messenger chemicals called neurotransmitters are also reduced and blood vessels in the brain may be damaged.

Connections between nerve cells are lost and this may be responsible for many of the disease symptoms.

What Causes Alzheimer's?

The Genetic Theory

Genetics probably plays a part in many cases. For example, there is a very rare form of early onset AD that occurs between ages 30-60, which is known to be inherited.

The commoner type is called late onset, where lots of risk factor genes may play a part, but an obvious inheritance pattern is usually not seen.

In any case, sometimes it can be hard to untangle the real causes of diseases that occur more frequently in some families than others. People living together are exposed to the same environment, so it can be hard to tell whether a disease is inherited or caused by an environmental toxin or infection.

So far, the only risk factor gene for late onset Alzheimer’s is a gene for a cholesterol-carrying protein in the blood, called apolipoprotein E (apoE). We all have apoE, but 1 or 2 out of every ten people have the form that increases the risk of Alzheimer's.

There are probably a lot of other genes that increase or decrease the risk of Alzheimer's, but they haven't been identified yet.

Chemical TheoriesSome researchers are studying chemicals in the brain that either promote nerve growth or are toxic to brain cells. They think that changes in the amounts of these chemicals may be connected to Alzheimer's development and progression.

Chemical messengers in the brain are called neurotransmitters. One of these messengers, called acetylcholine (Ach) seems to be reduced in quantity in the Alzheimer's brain, and drugs that lower Ach levels can affect memory. So Ach levels may play a part in causing the disease.

The Autoimmune Theory Some diseases are caused when our body's defenses start to attack us by mistake. Some researchers think that as brain cells age, they may change so much that in some people; the immune system doesn’t recognise them and responds as if they were foreign intruder cells. Antibrain antibodies have been found in some Alzheimer's brains, which may support this theory. But the same antibodies are also found sometimes in aging brains without Alzheimer's, so no-one really knows if they're involved in causing the disease or not.

The Slow Virus TheoryCreutzfeldt-Jakob disease (CJD) is the human form of bovine spongiform encephalopathy or "mad cow disease". Many of the symptoms are very similar to Alzheimer's, and CJD is caused by prions, or "slow viruses". So some scientists think Alzheimer's may have similar causes. But so far there's no evidence one way or the other.

The Blood Vessel TheoryRepeated strokes can cause symptoms similar to Alzheimer's. This is called multi infarct dementia, and strokes occur when fatty deposits narrow arteries in the brain. So blood vessel defects have been studied as a possible cause of Alzheimer's. But so far this line of investigation seems to be a blind alley.

What Does the Future Hold?

A few hundred years ago, seemingly healthy people would often die within hours after developing excruciating pain in the right side of the lower belly. A fever and a cough were often a death sentence. Even the cleverest doctors had not the least idea what caused appendicitis, pneumonia and a host of other diseases. We have come so far in medical knowledge that at some point in the future, as researchers put in place the pieces of the Alzheimer's puzzle, maybe we'll finally solve the Alzheimer's mystery as well.

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