Some age-related and other diseases with formal definitions based on symptoms and late stage mechanisms are likely several distinct conditions that happen to converge on a similar end result. This is particularly true of conditions of the brain and the immune system, where there is a great deal of biochemistry yet to map and fully understand. While Parkinson’s disease in the late stages uniformly involves α-synuclein aggregation and loss of dopaminergenic neurons, the research community has in recent years gathered the data needed to make a clear distinction between cases that start in the brain and cases that start in the intestines. Thus Parkinson’s disease is in fact two distinct diseases that will likely require different approaches to prevention and early stage diagnosis and treatment.

Researchers around the world have been puzzled by the different symptoms and varied disease pathways of Parkinson’s patients. A major study has now identified that there are actually two types of the disease. Although the name may suggest otherwise, Parkinson’s disease is not one but two diseases, starting either in the brain or in the intestines, which explains why patients with Parkinson’s describe widely differing symptoms. “With the help of advanced scanning techniques, we’ve shown that Parkinson’s disease can be divided into two variants, which start in different places in the body. For some patients, the disease starts in the intestines and spreads from there to the brain through neural connections. For others, the disease starts in the brain and spreads to the intestines and other organs such as the heart.”

Parkinson’s disease is characterised by slow deterioration of the brain due to accumulated alpha-synuclein, a protein that damages nerve cells. This leads to the slow, stiff movements which many people associate with the disease. In the study, the researchers have used advanced PET and MRI imaging techniques to examine people with Parkinson’s disease. People who have not yet been diagnosed but have a high risk of developing the disease are also included in the study. The study showed that some patients had damage to the brain’s dopamine system before damage in the intestines and heart occurred. In other patients, scans revealed damage to the nervous systems of the intestines and heart before the damage in the brain’s dopamine system was visible.

“It has long since been demonstrated that Parkinson’s patients have a different microbiome in the intestines than healthy people, without us truly understanding the significance of this. Now that we’re able to identify the two types of Parkinson’s disease, we can examine the risk factors and possible genetic factors that may be different for the two types. The next step is to examine whether, for example, body-first Parkinson’s disease can be treated by treating the intestines with fecal microbiota transplantation or in other ways that affect the microbiome. The discovery of brain-first Parkinson’s is a bigger challenge. This variant of the disease is probably relatively symptom-free until the movement disorder symptoms appear and the patient is diagnosed with Parkinson’s. By then the patient has already lost more than half of the dopamine system, and it will therefore be more difficult to find patients early enough to be able to slow the disease.”