No doctor will say with absolute certainty that someone has Parkinson's. They might be eighty, ninety, even 99 per cent sure, but not until someone has died and they can look inside the brain can a diagnosis finally be confirmed.
We've been struggling for decades to find the answer - a definitive diagnostic test for Parkinson's. So far brain scans, blood tests and urine samples haven't come up with the goods. As a result there's often doubt, and even error, in Parkinson's diagnosis, particularly in the early stages.
A new initiative linking UK and Israeli scientists could change this, and - bizarrely - they think the answer might be in the patient's breath.
Professor Roger Barker, a researcher we're funding at the University of Cambridge, and Professor Hossam Haick, an engineer in Tel Aviv have joined forces, and with a joint grant from Parkinson's UK and the British Council, are embarking on a study to see if they can develop a simple breath test to accurately detect Parkinson's.
Once the breath testing equipment has been shipped to Cambridge from Tel Aviv Professor Barker will study around 200 people - with and without Parkinson's - to see if just by looking at their breath they can determine which have the condition.
It might sound far-fetched but there's evidence that breath has real potential to reveal secrets of the brain. They've already shown in a study of 57 people that breath alone could differentiate people with Parkinson's and healthy individuals. And it's not a completely new idea - breath tests have been used to diagnose cancer, with dogs even being able to sniff out the disease.
When I spoke to Professor Barker he told me he is looking beyond the scope of breath as purely a diagnostic tool. He's hoping it will not only improve diagnosis, but also that it will tell us more about how Parkinson's develops. His dream is that the molecules he finds in the breath of people with Parkinson's will lead him to the discovery of new drugs.
This is just the kind of 'out there' research we need to be funding, to have a chance of tackling what is arguably one of the most challenging conditions in modern medicine. Parkinson's can leave people struggling to walk, speak and sleep, and yet we still don't even know some of the basics like what causes the condition.
There are 127,000 people in the UK with Parkinson's, and up to 7.5 million worldwide. There's no time to waste. To help us fund more research, visit parkinsons.org.uk/research