Smelling Alzheimer's: Unique urine odour discovered at early stages of disease

A unique smell in the urine of mice with Alzheimer's disease has been discovered, possibly providing a way of diagnosing the disease before cognitive decline. Scientists found a uniquely identifiable odour signature that appears before significant development of the disease in mouse models, and say extensive studies are now required to find and characterise Alzheimer's-related odour signatures in humans.

The team led by scientists at the Philadelphia's Monell Center and the US Department of Agriculture (USDA) looked at three mouse models of Alzheimer's looking at behavioural and chemical analysis. The found each strain of the Alzheimer's led to urine odour profiles that were different from those in the control mice.

Publishing their findings in the journal Scientific Reports, they said the change in odours was the result of a shift in the concentrations of existing urine compounds. They preceded detectable amounts of plaque build-up in the brains (a hallmark of Alzheimer's). The team argues that the odour is related to the presence of an underlying gene rather than changes to the brain.

"In conclusion, our findings in mouse models of AD [Alzheimer's disease] suggest that volatile odour signatures are also likely to be observed in human AD populations and may be informative early indicators of AD during prodromal disease states," they wrote.

Study author Bruce Kimball said: "Previous research from the USDA and Monell has focused on body odour changes due to exogenous sources such as viruses or vaccines. 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."

Daniel Wesson, another author of the study, added: "While this research is at the proof-of-concept stage, the identification of distinctive odour signatures may someday point the way to human biomarkers to identify Alzheimer's at early stages."

While the team says extensive studies will be required to find similar results in humans, the findings could one day lead to a non-invasive way to diagnose Alzheimer's in the early stages – meaning treatments currently being developed to slow the progression of the disease could be utilised before cognitive deterioration takes place.

Commenting on the study, Doug Brown, Director of Research at Alzheimer's Society, said: "The findings of this study are interesting, but it is too early to tell if they can help us to develop ways to identify people with Alzheimer's disease before memory symptoms appear. The test was carried out on genetically altered mice, which do not fully replicate several of the important changes seen in the brains of people with dementia, so we cannot yet predict that we will see the same urine changes in people.

"Dementia is the biggest health challenge facing us today, and timely diagnosis is critical to providing the best treatment and care. Although this is an interesting approach to the problem of identifying Alzheimer's before memory symptoms appear, it is too early to tell whether this could be a valid way to diagnose the condition in people."