The breast cancer gene that Angelina Jolie found she carries may hold the key to beating Alzheimer's disease, scientists say.

They have revealed that men and women who have died from the most common form of dementia have lower than usual amounts of a protein known as BRCA1 in their brains.

This protein - and the gene that makes it - is more usually associated with breast and ovarian cancers.

Women who, like Hollywood A-lister Jolie, carry a flawed version of the gene struggle to make enough of the protein.

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This leaves them much more likely than usual to develop the cancers. Jolie, 40, chose to have both breasts removed after she discovered that her DNA meant she had an 87 per cent chance of developing breast cancer - eight times the average for a woman.

Now research in America has linked low levels of the BRCA1 protein with dementia. This suggests that the protein helps to keep the brain healthy - and that a drug which restores its levels to normal could halt, and even prevent, Alzheimer's.

Existing drugs provide only temporary relief. The condition soon takes its devastating course, robbing people of their speech, memory and dignity.

When scientists at the Gladstone Institute of Neurological Disease in San Francisco examined the brains of people who had died with Alzheimer's, they found levels of the BRCA1 protein were up to 75 per cent lower than normal.

They also showed that amyloid beta, a compound known to clog up the brain in Alzheimer's sufferers, seemed to be behind the drop. Their series of experiments in mice confirmed its importance to brain health.

When the mice were low in the protein, their brain cells, or neurons, shrank.

Memory and learning games carried out afterwards proved to be more difficult than before.

The scientists are now looking at whether raising BRCA1 levels in mice can reverse or even prevent such problems.

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Dr Lennart Mucke, the study's senior author, said: "Therapeutic manipulation of repair factors such as BRCA1 may ultimately be used to prevent neuronal damage and cognitive decline in patients with Alzheimer's disease or in people at risk for the disease.

"By normalising the levels or function of BRCA1, it may be possible to protect neurons from excessive DNA damage and prevent the many detrimental processes it can set in motion."

- Daily Mail