The entire DNA sequence of a woman who lived to 115 has been pieced together by scientists.

The woman, who was the oldest in the world at the time of her death, had the mind of someone decades younger and no signs of dementia, say Dutch experts.

The study, reported at a scientific conference in Canada, suggests she had genes that protected against dementia.

Further work could give clues to why some people are born with genes for a long life, says a UK scientist.

It is more than 10 years since the first draft of the human genetic code was revealed.

The woman, whose identity is being kept secret, and is known only as W115, is the oldest person to have her genes mapped.

She donated her body to medical science, allowing doctors to study her brain and other organs, as well as her entire genetic code....