The recent failure of an Eli Lilly clinical trial to test a promising drug highlights our lack of understanding about the cause of Alzheimer’s disease (see New York Times article).

The Amyloid beta hypothesis, which is the prevalent idea today, states in its simplest form that the accumulation of Amyloid beta protein in the brain causes brain cells to die and, therefore, leads to symptoms of Alzheimer’s disease.

The Amyloid beta hypothesis is based on the observation that an extraordinary accumulation of Amyloid beta protein is seen in the brains of known Alzheimer’s disease patients. The problem is that this is a correlation and does not necessarily point to a cause.

There are a number of other possible interpretations for Amyloid beta accumulation including possibly a response by the body to protect the brain from the ravages of Alzheimer’s disease.

Perhaps Amyloid beta accumulation in the brain is similar to the scab that forms after we scrape our skin? The scab doesn’t cause the skin damage but is formed by the body to help repair and protect the skin.

Amyloid beta may or may not be important in the cause of Alzheimer’s disease but we must keep in mind that at this time we only know correlations. We do not know the cause.