Emergence of breath testing as a new non-invasive diagnostic modality for neurodegenerative diseases.

Neurodegenerative diseases (NDDs) are incapacitating disorders that result in progressive motor and cognitive impairment. These diseases include Alzheimer's disease, the most common cause of dementia, frontotemporal dementia, amyotrophic lateral sclerosis, dementia with Lewy bodies, Parkinson's, Huntington's, Friedreich's ataxia, and prion disease. Dementia causing NDDs impose a high social and economic burden on communities around the world. Rapid growth in knowledge regarding the pathogenic mechanisms and disease-associated biomarkers of these diseases in the past few decades have accelerated the development of new diagnostic methods and therapeutic opportunities. Continuous effort is being applied to the development of more advanced, easy-to-apply and reliable methods of diagnosis, that are able to identify disease manifestation at its earliest stages and before clinical symptoms become apparent. Development of these diagnostic tools are essential in aiding effective disease management through accurate monitoring of disease progression, timely application of therapeutics and evaluation of treatment efficacy. Recently, several studies have identified novel biomarkers based on compounds in exhaled breath associated with specific NDDs. The use of breath testing, as a means of monitoring neurodegenerative disease onset and progression, has the potential to have a significant impact on augmenting the diagnosis of NDDs as the approach is non-invasive, relatively cost effective and straight forward to implement. This review highlights key features of current diagnostic methods utilised to identify NDDs, and describes the potential application and limitations associated with the use of breath analysis for disease diagnosis and progression monitoring.