Would you want to know early on, even though there is no cure? Or would you prefer to remain ignorant and let nature takes it's course? I think there are valid arguments on both sides and ultimately it is really a personal choice. What I find interesting about this breakthrough (and others like it) is that by identifying early stage patients, the science community is able to conduct studies with them and learn. Those studies could lead to developing a cure in the future. There is a huge lack of data to work with today. I would volunteer to be part of a study that could potentially help future generations find a cure to such a horrible disease.

In addition to Jeff's excellent reply ... Current methods for "diagnosing" Alzheimer's are very laborious, involve all sorts of expensive testing, and in the end, the best we can do is say "probable" Alzheimer's.  The disease cannot be positively diagnosed unless and until a brain biopsy is done at autopsy.  There are dozens upon dozens of disorders that can cause dementia symptoms, most of which can be treated and many of which can be cured.  It is extremely important to develop reliable, inexpensive methods for ruling out Alzheimer's as well as diagnosing it.  And while there is no cure for Alzheimer's, there are medicines and medical foods that can help delay the progression of symptoms so that you and/or your loved one can enjoy a better quality of life for a longer time.