Classification of Parkinson's Disease and Delineating Progression Markers from the Sebum Volatilome

Parkinsons Disease (PD) has been associated with a distinct odour, which emanates from the skin and is strongest in sebum-rich areas. In this study, sebum was sampled from participants using cotton gauze and the volatile components emanating from these swabs were analysed directly with thermal desorption gas chromatography - mass spectrometry (TD GC-MS). We analysed subjects with clinically established PD (n=46) along with healthy controls (n=28) sampled from two sites. The volatilome profiles obtained for PD and control cohorts were compared with the profile of participants (n=9) with isolated REM sleep behaviour disorder (iRBD) to investigate metabolite changes in probable prodromal PD. We also compared PD participants sampled at yearly intervals for a total of three years. Volatile compounds from TD GC-MS analysis were found in different quantities between PD, control and iRBD subjects. We found 55 significant features where abundance in samples from individuals with iRBD was intermediate between that found for PD and control samples. Significant features were found to be alkanes and fatty acid methyl esters (FAMEs), with other metabolites identified as an aldehyde, purine and tropinone. In olfactory analysis of the iRBD samples three out of nine were classified PD, and on clinical follow up two of these showed PD symptoms. Further, when analysing the volatilome from longitudinal PD sampling, almost two-thirds of the significant features showed differential regulation over the three visits. Our findings support the use of sebum as an accessible biofluid rich with measurable volatile compounds which alter in abundance in individuals with PD and iRBD, as the disease progresses.