Towards a diagnostic test for Parkinson’s disease

Parkinson’s disease (PD) is a chronic neurological disorder affecting one in 100 people over the age of 60, with estimates suggesting that approximately 5 million people are suffering from the condition worldwide. PD develops when the dopamine-producing neurons of the substantia nigra part of the brain are lost over time. Dopamine is needed for the coordination of movement, the loss of which is therefore responsible for the appearance of the main PD symptoms of stiffness, tremor and slowness. There is no cure for PD and treatment is aimed at managing symptoms, with medication being effective only in the short term. Currently there is no clinical test for PD, but diagnosis is based on medical history and assessment of simple physical tasks. Additionally, most instances of PD are idiopathic, with the risks from genetic and/or environmental causes being very low, except in certain rare cases. Hence, diagnosis, particularly in the early stages of symptoms, can be difficult and inconclusive. Additionally, as with many of the neurodegenerative conditions, physical symptoms only become apparent late in the development of the condition – after the loss of 80% of dopamine. However, the help of a woman with a remarkable sense of smell is bringing the creation of a definitive clinical test for PD closer. Joy Milne is a retired nurse from Perth, Scotland, whose husband Les, a consultant anesthetist, was diagnosed with PD at the age of 45 and died at 65. Approximately 10 years before the diagnosis, Joy realized that Les had developed a different, slightly muskier smell. After meeting other people with PD, Joy found that they all had the same unusual aroma. Joy’s ability to detect PD by smell was confirmed in tests conducted by scientists at the University of Edinburgh and she is now working with Dr Perdita Barran at the University of Manchester to isolate the specific compounds that create the distinctive PD aroma. So far, a handful of compounds have been identified. Currently, a definitive clinical test would allow a conclusive diagnosis for patients suffering from the varied and vague early symptoms of PD. In the future, however, given the lack of identifiable risk factors and the fact that the changes responsible for PD as well as the development of the unusual PD aroma happen up to a decade before external physical symptoms appear, for any medication that will cure or at least prevent disease progression to have any real chance of success, screening of the apparently healthy, asymptomatic population will have to be carried out.