Imagine if Alzheimer’s disease could be spotted in its earliest stages, long before memory loss sets in, with a simple urine test. Researchers think it might be possible after discovering that mice with Alzheimer's disease have a unique odour to their urine.

While the work is still in the early “proof-of-concept” stage, the researchers say it’s possible that identifying a distinctive odour signature of early Alzheimer's could one day lead to a test that would spot the disease in humans too.

For their study, researchers with the U.S. Department of Agriculture studied three mouse models known as APP mice, or amyloid precursor protein mice.

To create the mice, scientists insert human genes associated with mutations of a certain gene called amyloid precursor protein gene into mice genomes. They then activate those genes with drugs.

AAP mice then develop the same buildup of amyloid brain plaques seen in human Alzheimer’s and begin showing similar dementia symptoms.

The researchers found that each strain of APP mice produced urinary “odour profiles” that could be distinguished from the urine odour of control mice.

It’s not that APP mice’s urine contained new chemical compounds; instead, the difference reflected a shift of existing urinary compound concentrations.

Interestingly, the researchers could spot the odour differences before any of the APP mice experienced amyloid buildup. That suggests the odour is related more to the presence of the genes rather than to the development of the brain disease itself.

The researchers conducted further blind studies and found they could correctly identify APP mice versus control mice just by studying their odour profiles.

Researcher Bruce Kimball, a chemical ecologist with the USDA National Wildlife Research Center, says the study means it’s possible there could be ways to identify other brain diseases using urine smell.

“Now we have evidence that urinary odour signatures can be altered by changes in the brain characteristic of Alzheimer's disease," he said in a statement. "This finding may also have implications for other neurologic diseases."

They add though that “extensive studies” are still needed to characterize Alzheimer's-related urine odour in humans.

The study appears in the journal Scientific Reports.