Margarita, in answer to your question, Dad got a diagnosis of Alzheimers about 6 almost 7 yrs ago now, which was later slightly changed to dementia of the alzheimers type.
With regards to euthanasia, one thing I will add to the discussion is that how does one really judge 'quality of life'. Does a person in prison have quality of life, does a child suffering from a life of disease in Africa have quality of life, does a person born with brain damage have quality of life. The problem with euthanasia is that this is such a personal question, what is quality of life for you, may be different for me, or for him or her. No doubt generally family members will have a fair idea of what quality of life means to their loved one, but that too is presupposing that the family member is truly a 'loved' one, that there is no personal bias, that the family member truly 'knows' their loved one (I continue to wonder how well I knew my father, and at the same time I know there were sides to Dad that my Mum didn't know either). A family member can of course tell family before they get to the point where the euthanasia issue arises how they feel about it, and in my opinion this would be the best way to do things, but then one also has to bear in mind that one never really knows how one will feel in a situation until one is actually in the situation. I might think I wouldn't want to live Dad's life now, but once I'm there, who really knows?
The home where Dad lives doesn't try to keep him alive so they can get more money, I get the impression that they think my family and I are crazy and cruel for trying to fight this disease, and they frustrate us because they think its wrong to keep him walking, (he appears to enjoy it by the way), they want to give him mush foods and probably would be keen for him to just be on a drip (yet he has no problems eating non-mush or swallowing unthickened drinks). They think we are cruel, while we're terrified they will kill Dad before his time is truly up, in the name of kindness. Before one makes a call on quality of life, please please be certain that you are qualified to judge that. Ask a depressed person who could have every bodily function working well except the chemicals in their brain, could be a millionaire, could have a loving family and they will tell you that they have no quality of life. I personally think its too vague a reason to give for justifying euthanasia. I have no answers though because I am all too aware that I will be most probably faced with these questions in the future. My plan at this point is not to justify my decision with 'I wanted to release him from a life where there was no quality' but instead say 'I just didn't believe he was still spiritually in his body'.
I do believe he will let go when he is ready, and if he is never ready then either the state will decide that, my mother or sister will decide (as they have POA) or my lot in life will be to have a father on a machine for decades. Coming from a background where I know intimately of cultures where members can die just because they believe they are fated to and where my own grandfather who lived on a machine for years (emphasema) who on the day he said he was giving up died just hours later, this is where I personally have decided to stand on the fence.
I understand that others have different views.