Alzheimer's disease affects 4 million Americans today, and by the middle of the next century, that number may double or triple. It is the 4th or 5th leading cause of death in the United States in people over 65. Alzheimer's disease costs the U.S. more than $90 billion each year in medical and nursing care, lost productivity, home care, and premature deaths.

Developing a useful animal model to learn about the pathology of Alzheimer's disease and then to test potential treatments for it is critical. Fortunately, mice can be bred that carry many of the abnormal genes that cause the various problems associated with Alzheimer's disease. These mice, called transgenic mice, have been bred to manifest the signs and symptoms of Alzheimer's disease. These include age-related memory and learning impairment, loss of brain cells, deposition of protein called amyloid in the brain, and tangles of nerve fibers composed of a protein called tau (the latter two are among the hallmarks of the human autopsy findings in Alzheimer's disease).

One line of transgenic mouse has been bred to carry mutant genes for a protein called amyloid precursor protein (APP). The mice develop deposits of amyloid protein in their brains. Other mice have mutations in genes for a protein called presenilin (found in humans with the disease), but they do not get deposits of amyloid protein unless they also have the mutant APP genes. Other strains of transgenic mice carry the genes that produce ApoE4, another protein found in humans, and tau protein. Work is underway to cross these various strains until mice are produced that carry as many of the known genes that cause the damage of Alzheimer's disease as possible. A mouse model that closely mimics the human pathology will enable scientists to not only understand the disease better but to test treatments with greater hope of applicability to humans.