Imagine waiting for a warning light on your car dashboard, only to find the engine is already making strange noises. For people with genetic risk for Parkinson's disease and related conditions, this is exactly what is happening. A review of 121 participants from the Parkinson's Progression Markers Initiative looked at when symptoms appeared versus when biological markers of disease showed up. The study tracked people who had genetic risks but had not yet developed full disease, comparing them to those who had already converted to conditions like Parkinson's, dementia with Lewy bodies, or Alzheimer's.
The results were mixed. Many people who developed symptoms also had the expected biological signs, such as loss of smell or specific protein markers in their spinal fluid. However, the timing did not always match. Some people developed symptoms quickly, while others waited years before their biology caught up. In fact, nearly one-third of those with certain symptoms already had advanced brain changes, while others had preserved smell and no biological evidence yet.
This mismatch is a major hurdle for doctors and patients. It suggests that feeling sick or noticing changes does not automatically mean the disease has biologically started. Some people with genetic risks had high rates of negative biological markers even when they felt symptoms. The study did not report any safety issues because no drugs were tested. Instead, it highlights a gap in our understanding. We must wait for longer follow-up to see if these symptoms eventually lead to full disease or if they are something else entirely.