This proof of principle study provides the first description of the skin volatilome in Parkinson’s disease compared to controls. Additional larger scale research combining chemical analyses with the noses of human and canine smellers may help to establish a panel of volatile biomarkers for the disorder that could open new avenues for stratification and facilitate earlier detection of the disease as well as furthering understandings of disease mechanisms.
While odor is not routinely used in modern society to detect disease, a number of disorders are associated with unique smells, but there is little evidence for odors as symptoms of neurodegenerative disorders.
Joy Milne has demonstrated an extremely sensitive sense of smell that enables her to detect odors not typically detected. Identification and quantification of compounds associated with Parkinson’s disease odor may enable early screening and provide insights into molecular changes that occur as the disease progresses.
Swabs taken from various parts of the body in initial testing suggests the odor is present on parts of the skin that produce high levels of sebum. Characteristic odors are result of the olfactory system detecting substances in the air including VOCs, thermal desorption gas chromatography mass spectrometry can be used to measure these VOCs. This technique uses an enclosed test sample which is heated to release volatile components, the headspace is then captured and analyzed in an approach that is suitable for the use in identifying metabolites that gives rise to the distinct scent of PD.
Thermal desorption gas chromatography mass spectrometry was used to identify volatile compounds in sebum swabbed from the upper backs of 30 Parkinson’s disease patients and matched to controls. Initial testing was followed by a second round of testing on samples from a completely separate group of 31 Parkinson’s disease patients and controls.
Eicosane, octadecanal, and hippuric acid were among the VOCs found at greater concentrations in the sebum from Parkinson’s disease participants when compared to controls, which indicates altered levels of neurotransmitters; levels of perillic aldehyde were lower in PD samples, and there were no significant differences between participants on medication and drug naive PD patients.
Hooking an odor port to the instrument allowed Milne to offer her opinion on the testing; she reported when any smell was present and when she detected the distinctive strong musky smell of Parkinson’s disease. Milne’s olfactogram results corresponded well with that of GC-MS detection, having significant overlap between regions containing up-regulated compounds and regions in which a smell similar or identical to that of PD scent was present. Milne was also able to confirm the smell of PD when presented with samples that contained lab prepared mixtures of the compounds at different concentrations.
9 biomarkers were identified that were changed in the sebum of Parkinson’s disease by combining the data. While the combination of nine compounds may not be solely responsible for the unique smell, they do at least contribute to it according to the researchers, who note larger studies are needed with extended olfactory data from human and canine smellers in addition to headspace analyses for the next phase in further characterising the PD sebum volatilome.
