Signs of Parkinson’s disease could be detected in the nose years before people develop more obvious symptoms of the condition.

The finding could lead to the development of a nasal swab test for the disorder, similar to ones used for coronavirus testing, and may shed light on its causes, says Werner Poewe at the Medical University of Innsbruck in Austria.

Parkinson’s disease is a condition involving tremors and difficulties in moving that usually starts in later life. It is caused by the death of brain cells that make a signalling molecule called dopamine. These cells die because of the build-up of a faulty version of a protein called synuclein. When some molecules of synuclein become wrongly folded, this spreads to others, like a row of dominoes toppling.

In the past few years there has been growing evidence that, in some cases, synuclein starts becoming misfolded in the gut and this spreads up to the brain through long nerve fibres. But a nasal origin has also been suspected, because many people with Parkinson’s disease have a reduced sense of smell, which often begins years before their movement problems.

Poewe’s team looked for misfolded synuclein in the noses of 63 people who had another early sign of Parkinson’s, a sleep disorder where people start acting out their dreams, which is caused by the loss of the usual brain mechanism that keeps us motionless during sleep. The researchers took samples of the cells at the top of people’s nasal cavities with a swab.

Read more: Parkinson’s disease may start in the gut and travel to the brain

They found that 44 per cent of people with the sleep disorder had misfolded synuclein in their noses. This compared with 46 per cent in another group of 41 people with confirmed Parkinson’s disease and 10 per cent of 59 people of a similar age who didn’t have the condition. Those who tested positive in this latter group could also be in the early stages of Parkinson’s disease, says Poewe.

People with the sleep disorder who tested positive through the nose swab also had more severe loss of smell, suggesting faulty synuclein problems are indeed the cause of this symptom.

One idea is that synuclein starts becoming wrongly folded in the nose in some people and in the gut in others, and then spreads to the brain, says Poewe. Alternatively, synuclein could start misfolding in multiple sites all over the nervous system.

Several medicines aimed at stopping misfolded synuclein from spreading to other nerve cells are in development. If they prove effective, a nasal swab would be an easier test than the current way of checking for faulty synuclein, which is to take a sample of cerebrospinal fluid from the spine, says Poewe. “This is the least invasive obtainable tissue to test.”

“Early diagnosis is going to be important in the future when we have better drugs,” says Alfonso De Simone at Imperial College London. “The later you get diagnosed, the more damage you will have to your neurons.”

Creutzfeldt-Jakob disease, another brain disorder caused by protein misfolding, although one that is much rarer, can also be diagnosed by collecting nerve cells from the top of the nasal cavity.

Journal reference: Brain, DOI: 10.1093/brain/awab005