Researchers believe a rare change in a gene called PLD3 can double a person's risk of developing late-onset Alzheimer's disease.
Published in the journal Nature, the study was co-funded by Alzheimer's Research UK and will add growing knowledge of how genes are linked to the cognitive condition.
Currently, there are 21 different genome parts linked to increased rates of Alzheimer's.
However, the team felt that the likelihood of a person being diagnosed with late-onset Alzheimer's – which occurs after the age of 65 – could not be fully explained by the genes links known about thanks to previous studies.
They feel that rate genetic alterations may play a part in heritability, but these changes are often hard to recognise.
In order to explore this theory further, researchers from a number of medical facilities and universities across the UK came together to study 14 families with a history of late-onset Alzheimer's.
DNA sequences were identified in the people affected with the condition before the findings were compared with unaffected family members.
In two of the families, a gene called phospholipase D3 (PLD3) was found. This gene is present in 0.8 per cent of the population and any changes in it increased the chances of Alzheimer's by 200 per cent.
While further studies will need to be completed, the team feel that the gene changes contribute to more protein being produced in the brain, a leading cause of Alzheimer's.
Rebecca Wood, chief executive of Alzheimer’s Research UK, said: "We know that late-onset Alzheimer’s is caused by a complex mix of risk factors, including both genetic and lifestyle.
"Understanding all of these risk factors and how they work together to affect someone’s likelihood of developing Alzheimer’s is incredibly important for developing interventions to slow the onset of the disease."
She added that the charity is very proud to have contributed to the discovery.
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