I'm sorry to ask but - who are you?

Can you imagine or have you already experienced the feeling when a close friend or a family member of yours doesn't recognize you anymore? After years of ups and downs with that person, I will never understand how they can simply forget people those who are closest to them.

The Alzheimer disease: What is it? How does it evolve? How does it end? How can I avoid getting this disease?

The illness commonly known as Alzheimer's is actually just one of many forms dementia can take, but it's the most spread one.
You start to forget things occasionally, misplace items, virtually lose your short-term memory and of course don't admit that you forgot to do something because you forgot about it. You are becoming more and more absent-minded, already forget important appointments and are often confused. That's  the advanced stage of the disease but not yet the final one.
You continue by having real difficulties remembering anything recently learned, speaking gets harder and harder and you repeat the same stories, sentences and words over and over again. You become either more aggressive or apathetic, depending on the character of the person, lose your self-awareness and forget about the existence of even your closest friends and family members.
Eventually, patients don't die because of the illness itself, but because of external factors they are prone to when confused and not being themselves actually.

But now to the most important question: How can I avoid getting this disease?
Doing sports, reading, learning languages, playing musical instruments, solving puzzles, regular social interaction and a balanced diet contribute to your mind's and body's well-being and therefore also help you to stay healthy. People who smoke tend to contract Alzheimer's more likely than those who don't. However, drinking alcohol in a moderate amount as well as beverages containing caffeine or cocoa is said to reduce the risk of getting this disease. High blood pressure and a high cholesterol level should be treated as soon as possible in order to avoid unwanted effects on the brain.

Unfortunately, there is no guarantee that avoiding Alzheimer's through keeping a healthy lifestyle works out. Therefore, scientists and medics currently work on a vaccination but unfortunately they are still far away from a breakthrough.

The main problem with Alzheimer's is that the patient's relatives and friends suffer when trying to look after him/her. That's why I hope that there is going to be a reliable way of avoiding the disease or at least alleviate Alzheimer's. 

Everyone who suffers this disease has "light moments", though. A relative of mine was already in the terminal stage, remembering nothing at all, not any person close to her, actually she just awaited death. But on Christmas Eve just one month before she eventually died, she suddenly started to sing "Silent Night, Holy Night", all three stanzas, word by word. You know, I am not a religious person at all, but that was pretty awesome, just thinking that her brain was actually totally destroyed but somehow the part where she saved the lyrics of this song remained healthy.

Sources: http://www.alz.org/
http://en.wikipedia.org/wiki/Alzheimer%27s_disease
my own