A test for Alzheimer's can predict a person's risk of developing the disease 10 years before its onset, scientists have claimed.

Researchers with the CSIC Institute of Biomedical Research of Barcelona said they had identified the earliest known biomarker known to be associated with Alzheimer's.

They said the biomarker was present in cerebral spinal fluid at least 10 years before first signs of dementia set in.

Ramon Trullas, lead author of the study, said their research would "change the way we think about the causes of Alzheimer's disease".

"This discovery may enable us to search for more effective treatments that can be administered during the preclinical stage," he said.

The research team found that a decrease in the content of mitochondrial DNA (mtDNA) in the cerebral spinal fluid may indicate Alzheimer's and could also play a role in cause the disease.

Triggers death

They believed that decreased mtDNA (the structures within cells that convert the chemical energy from food into a form that cells can use) shows a decreased ability of the mitochondria to power the brain's neurons, which triggers their death.

The decrease precedes other biomarkers of Alzheimer's and may be the earliest known predictor for the disease, said the team. They said that the detection of the biomarker was not hindered by technical difficulties associated with other protein detection.

According to the Alzheimer's Society, there are 800,000 people living with dementia in the UK. By 2021, this figure is expected to reach over a million.

Trullas said that other laboratories and hospitals had to successfully replicate his results to confirm that reduced mtDNA levels should be investigated as a possible cause of the disease.