Monday, January 08, 2007

Alzheimer's disease and herpes virus
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A gene known to be a major risk factor for Alzheimer's disease puts out the welcome mat for the virus that causes cold sores, allowing the virus to be more active in the brain compared to other forms of the gene. The new findings, published online in the journal Neurobiology of Aging, add some scientific heft to the idea, long suspected by some scientists, that herpes somehow plays a role in bringing about Alzheimer's disease.

The work links a form of the ApoE gene known as ApoE-4, which after advanced age is the leading known risk factor for getting Alzheimer's disease, with the form of herpes - herpes simplex 1 or HSV - that infects more than 80 percent of Americans and causes cold sores around the mouth. The findings from a group at the University of Rochester Medical Center show that the particular form of the gene that puts people at risk also creates a fertile environment for herpes in the brain, allowing the virus to be more active than other forms of the ApoE gene permit.

Scientists have known for more than 15 years that the ApoE-4 gene is a player in Alzheimer's disease, but the idea that it works in concert with the herpes virus is new.

The team is exploring different ways that herpes might affect the development of Alzheimer's disease. In one study the team looking at the role of Nectin-1, a cell adhesion molecule that herpes uses as one route to infect a cell. Nectin-1 plays a crucial role in forming synapses, the structures between brain cells that move information and signals from one cell to the next. The team is studying whether herpes somehow disturbs the receptor, possibly altering the structure and function of the synapse. Damage to synapses is one of the earliest signs of Alzheimer's disease.

Another possibility is that the body's immune response against herpes somehow damages the brain, and that such damage is worse in people with the ApoE-4 copy of the gene. Earlier this year Federoff's team published a study that showed inflammation is the earliest change that could be detected in a brain affected by Alzheimer's disease, before any of the hallmark plaques or tangles and certainly long before any behavioral changes are seen. Such inflammation often is a byproduct when the immune system fights an infection.

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