Washington, Oct 20 (IANS): At least two percent of people over age 40 and five percent of people over 70 have mutations linked to leukaemia and lymphoma in their blood cells, according to research at the Washington University School of Medicine, St. Louis.

Mutations in the body's cells randomly accumulate as part of the ageing process, and most are harmless. For some people, genetic changes in blood cells can develop in genes that play roles in initiating leukaemia and lymphoma - types of blood cancer, the researchers found.

However, the findings, based on blood samples from nearly 3,000 patients, do not mean that people with these genetic mutations are destined to develop a blood cancer, the researchers said.

In fact, the vast majority of them would not as the incidence of blood cancers such as leukaemia or lymphoma is less than 0.1 percent among the elderly.

"We do not yet know whether having one of these mutations causes a higher than normal risk of developing blood cancers," said senior author Li Ding from The Genome Institute at the Washington University.

"But it is quite striking how many people over age 70 have these mutations," Ding added.

The researchers analysed blood samples from people enrolled in The Cancer Genome Atlas project, a massive endeavour funded by the National Cancer Institute and the National Human Genome Research Institute at the National Institutes of Health.

The patients whose blood was analysed for the current study had been diagnosed with cancer but were not known to have leukaemia or lymphoma.

The findings appeared in the journal Nature Medicine.