A large study of twins has found that genes have a significant say in which people develop Alzheimer's disease.
Scientists from the University of Southern California, Los Angeles found that the heritabliity of the disease is between 58 and 79 per cent following tests on almost 12,000 pairs of twins.
In instances where both identical twins were found to have Alzheimer's there was an average of 3.66 years gap in disease development compared to an 8.12 years difference between dizygotic twins.
These findings, published in the Archives of General Psychiatry, convinced the researchers that genes have a huge role to play in the timing of the disease.
"In the largest twin study to date, we confirmed that heritability for Alzheimer's disease is high and that the same genetic factors are influential for both men and women," the researchers, led by Margaret Gatz, said.
"However, non-genetic risk factors also play an important role and might be the focus for interventions to reduce disease risk or delay disease onset."
Alzheimer's is thought to account for around two-thirds of dementia cases in pensioners.