It has been known for some time that people with diabetes have a much higher risk of developing Alzheimer's, but not why this is so.
Now, in experiments on worms, researchers from the City College of New York found that a known Alzheimer's gene also plays a role in the way insulin is processed.
A key indication of Alzheimer's, which can only be seen after death, is the presence of sticky plaques of amyloid protein in decimated portions of patients' brains. It's known that mutations in a gene involved in the processing of amyloid protein in Alzheimer's which run in families.
Now, the researchers who looked at a similar gene in the nematode worms (C-elegans) found the gene also affected their insulin pathway -- the chemical reactions involved in its production and processing.
"People with type 2 diabetes have an increased risk of dementia. The insulin pathways are involved in many metabolic processes, including helping to keep the nervous system healthy," lead study author Prof Chris Li was quoted as saying by the BBC News.
However, she stressed that more work was needed to probe this potential link and its effects further.
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Mark Johnston, editor-in-chief of the journal Genetics, which published the study, said it was an important discovery.
"We know there's a link between Alzheimer's and diabetes, but until now it was somewhat of a mystery. This finding could open new doors for treating and preventing the disease."
Dr Marie Janson, director of development at Alzheimer's Research UK, said: "This early-stage study may provide an interesting clue to help scientists unravel how diabetes and Alzheimer's are linked, but questions still remain to be answered.
"As this research looked at the effects of a gene in worms, studies are now needed to discover whether the equivalent gene in people has the same effect, and exactly what mechanisms may be involved."