Early onset Alzheimer's disease could be detected through a change in the smell of a person's urine, researchers have said.
Studies in mice found that the degenerative disease leaves a particular odour in urine, which occurs before the condition has significantly developed.
Researchers believe that the discovery of this early biomarker for Alzheimer's could allow doctors to spot the condition in patients before mental deterioration begins.
This, they said, would pave the way for upcoming treatments and help slow early progression of the irreversible disease.
Study author Bruce Kimball, who is a chemical ecologist with the USDA National Wildlife Research Center (NWRC) and based at the Monell Center, 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."
It is estimated that there are 500,000 people living with Alzheimer's in the UK.
Researchers from the US-based Monell Center and the US Department of Agriculture (USDA) analysed three separate mouse models, known as APP mice, which mimic Alzheimer's-related brain pathology.
They found that each strain of APP mice produced urinary odour profiles that could be distinguished from those of control mice.
According to researchers, these odour changes were reflective of a shift of concentrations of existing urinary compounds, rather than new chemical compounds.
The odour differences between APP and control mice were mostly independent of age and preceded detectable amounts of plaque build-up in the brains of the APP mice.
Scientists believe the presence of the odour is caused by an underlying gene rather than pathological changes in the brain.
Daniel Wesson, co-author of the study and a neuroscientist at the Case Western Reserve University School of Medicine, 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."
The study was published in the online journal Scientific Reports.