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    Mayo Clinic Minute: Is Alzheimer’s Type 3 diabetes?

Are some cases of Alzheimer's disease triggered by a form of diabetes in the brain? Perhaps they are, according to researchers. Mayo Clinic's campuses in Rochester, Minnesota, and Jacksonville, Florida, recently participated in a multi-institution clinical study, testing whether a new insulin nasal spray can improve Alzheimer’s symptoms.

“This study has furthered our understanding of the gene that is the strongest genetic risk factor known for Alzheimer’s disease,” says Dr. Guojun Bu, a Mayo Clinic neuroscientist. "About 20 percent of the human population carries this riskier form of [the gene] APOE, called the E4," says Dr. Bu. It's believed that more than 50 percent of Alzheimer’s cases can be linked to APOE4, according to the study, which was published in Neuron.

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It's an accepted fact that people with Type 2 diabetes have a higher risk of Alzheimer's disease. One reason may be reduced blood flow to the brain because of damaged blood vessels, Dr. Bu explains. "And, therefore, the supply of essential nutrients to the brain is also impaired."     

Dr. Bu has found genetics may also be to blame. A variant of the so-called Alzheimer’s gene, APOE4, seems to interfere with brain cells' ability to use insulin, which may eventually cause the cells to starve and die. Unofficially, it's called Type 3 diabetes. "What it refers [to] is that their brain's insulin utilization or signaling is not functioning. Their risk of developing Alzheimer’s disease is about 10 to 15 times higher."

Researchers wondered if it is diabetes of the brain, could insulin delivered in an intranasal mist help patients? The results of a phase 2 clinical trial have raised hope. "The outcome is very positive. The patient's cognitive decline is slowed, if not improved." The multicenter research study will now expand into a broader phase 3 trial, with the backing of the National Institutes of Health.