Changes to the serotonin system of the brain could act as a crucial early warning signal for Parkinson’s disease and may lead to the development of new screening tools for the chronic condition.

While Parkinson’s has traditionally been thought to occur due to damage to the brain’s dopamine system, a group of researchers from King’s Cross London (KCL) has discovered that changes to the brain’s serotonin system come first. These changes take place many years before patients begin to show the movement and cognitive problems characteristic of the disease.

KCL head of neurodegeneration imaging Marios Politis said: “Our results suggest that early detection of changes in the serotonin system could open doors to the development of new therapies to slow, and ultimately prevent, progression of Parkinson’s disease.”

People with Parkinson’s have a build-up of the protein α-synuclein in their brains. While most cases do not have a clear cause, a minority of cases can be tied to genetic causes.

Mutations to the SNCA gene that regulates α-synuclein are extremely rare, but those who do have it are almost certain to develop Parkinson’s disease.

The research team identified 14 people with the SNCA mutation, half of whom had yet to show any symptoms of Parkinson’s, as well as 65 patients with non-genetic Parkinson’s and 25 healthy volunteers. Using PET scans, the team found that the serotonin system starts to malfunction in people with Parkinson’s well before symptoms affecting movement occur, and before the first changes in the dopamine system.

KCL research associate Heather Wilson said: “We found that serotonin function was an excellent marker for how advanced Parkinson’s disease has become. Crucially, we found detectable changes to the serotonin system among patients who were not yet diagnosed.

“Therefore, brain imaging of the serotonin system could become a valuable tool to detect individuals at risk for Parkinson’s disease, monitor their progression and help with the development of new treatments.”

PET scans are expensive and difficult to carry out, so further work will be required to develop an affordable and straightforward scanning device as a screening tool. Studying the early stages of the disease means treatments could be developed to slow or halt its progress.