Scientists have found a genetic risk factor for late onset Alzheimer's disease which is only carried by women.
The discovery is the first evidence to suggest that genetics may partly explain why more women than men tend to develop the disease.
The key variant was found in a gene on the X chromosome, of which females have two copies, but males only one.
The study, by the Mayo Clinic College of Medicine, features in the journal Nature Genetics.
The Mayo team carried out a detailed genetic analysis of patients with Alzheimer's diease.
They identified a particular variant of a gene called PCDH11X which appeared to be closely linked to a higher risk of the disease.
However, further analysis showed that the association was almost entirely restricted to women.
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