Toronto, Dec 12 (IANS): The colour of our eyes or the straightness of our hair is linked to our DNA, but the development of Alzheimer's disease isn't exclusively linked to genetics, suggest new research.

In the first study published about Alzheimer's disease among identical triplets, researchers found that despite sharing the same DNA, two of the triplets developed Alzheimer's while one did not.

The two triplets that developed Alzheimer's were diagnosed in their mid-70s, said the paper published in the journal Brain.

"These findings show that your genetic code doesn't dictate whether you are guaranteed to develop Alzheimer's," said Dr Morris Freedman, head of neurology at Baycrest Centre for Geriatric Care.

"There is hope for people who have a strong family history of dementia since there are other factors, whether it's the environment or lifestyle, we don't know what it is, which could either protect against or accelerate dementia."

All three, 85-year-old siblings had hypertension, but the two with Alzheimer's had long-standing, obsessive-compulsive behaviour.

The research team analyzed the gene sequence and the biological age of the body's cells from blood that was taken from each of the triplets, as well as the children of one of the triplet's with Alzheimer's.

Among the children, one developed early onset Alzheimer's disease at age 50 and the other did not report signs of dementia.

The research team also discovered that although the triplets were octogenarians at the time of the study, the biological age of their cells was six to ten years younger than their chronological age.

In contrast, one of the triplet's children, who developed early onset Alzheimer's, had a biological age that was nine years older than the chronological age.

The other child, who did not have dementia, of the same triplet showed a biological age that was close to their actual age.

"The latest genetics research is finding that the DNA we die with isn't necessarily what we received as a baby, which could relate to why two of the triplets developed Alzheimer's and one didn't," says Dr. Ekaterina Rogaeva, senior author on the paper and researcher at the University of Toronto's Tanz Centre for Research in Neurodegenerative Diseases.

"As we age, our DNA ages with us and as a result, some cells could mutate and change over time".

With additional funding, researchers could further explore the interaction between genetics and environment in the development of Alzheimer's disease and the impact of environmental factors in delaying the onset of this disorder.