Pop quiz: What does Alzheimer’s disease smell like?

 If you said urine, then a winner is you. It used to be that Alzheimer’s disease (AD) came first, and then the urine followed – as in you forget where the bathroom is and end up wetting your pants and having to wear male adult diapers or female incontinence underwear, depending on your gender. However, researchers from the Monell Chemical Senses Center, the U.S. Department of Agriculture, and other institutions have found that a distinct urine smell may help predict the onset of this mental illness.

Sure, the urine odor was discovered in mouse models of Alzheimer’s disease – which, come to think of it, is probably why Pinky kept asking what they were going to do tonight – but “while this research is at the proof-of-concept stage, the identification of distinctive odor signatures may someday point the way to human biomarkers to identify Alzheimer's at early stages,” neuroscientist at the Case Western Reserve University School of Medicine and study author Daniel Wesson, PhD, said.

“Previous research from the USDA and Monell has focused on body odor changes due to exogenous sources such as viruses or vaccines. Now we have evidence that urinary odor signatures can be altered by changes in the brain characteristic of Alzheimer's disease,” Bruce Kimball, researcher at the USDA National Wildlife Research Center said. “Now we have evidence that urinary odour signatures can be altered by changes in the brain characteristic of Alzheimer's disease. This finding may also have implications for other neurologic diseases.” Kimball said.

The scientists monitored three mouse models labeled ‘APP mice’ which carry the brain pathology of AD. The mice were made to develop a build-up of amyloid plaques in the brain – a common indicator of AD. “Urinary odor signatures can be altered by metabolic processes associated with precursors to Alzheimer's disease,” Kimball said. Behavioral and chemical analyses showed that each sample produced highly distinct urine from the control mice. The changes in odor occurred before a build-up of plaque deposits was detected. The research suggests that the urine smell is related to an existing gene as opposed to the development of new brain pathological changes.

Since there is no cure for Alzheimer’s disease, early detection is essential for caregivers to keep up with the progress of the condition in their loved ones. “Establishing additional biomarkers in screening populations for AD will provide enhanced diagnostic specificity and will be critical in evaluating disease-modifying therapies,” the authors wrote. Nevertheless, they also pointed out that more research is needed in order to identify and characterize Alzheimer’s disease-related odor signatures in humans.

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