They found that the gene, known to be present in many Alzheimer's disease cases, affects the insulin pathway. Disruption of this pathway is a hallmark of diabetes.

They team says its finding, which appears in this month's issue of the journal Genetics. could point to a therapeutic target for both diseases.

"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," Prof. Chris Li said in a statement.

Although the cause of Alzheimer's is still unclear, one criterion for diagnosis of the disease after death is the presence of sticky plaques of amyloid protein in decimated portions of patients' brains.

In the study, Li and her colleagues scrutinized a protein called APL-1, made by a gene in the worm Caenorhabditis elegans which they say happens to be a perfect stand-in for the human Alzheimer's disease gene.

"What we found was that mutations in the worm-equivalent of the APP gene slowed their development, which suggested that some metabolic pathway was disrupted," Li said.

This suggested that the human version of the gene likely plays a role in both Alzheimer's disease and diabetes.

They also found that additional mutations in the insulin pathway reversed the defects of the APP mutation. This helped explain how these genes are functionally linked.

"This is an important discovery, especially as it comes on the heels of the U.S. government's new commitment to treat and prevent Alzheimer's disease by 2025," said Dr. Mark Johnston, editor-in-chief of "Genetics." "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 both diseases."