The Role of METhanogens in the PROgression Of Parkinson's Disease and Related Neurological Conditions

Eligibility criteria

Inclusion Criteria:
People with PD:
* 55 years of age or above;
* MDS criteria for Idiopathic PD;
* H\&Y\<3.
People at high risk of developing PD (people with REM Sleep behaviour disorders):
* 55 years of age or above;
* RBD diagnosis confirmed by polysomnography.
Other conditions affecting cognition (e.g. dementia, mild cognitive impairment):
* 55 years of age or above;
* Diagnosis of non-PD dementia or MCI, or, MoCA score ≤25
Healthy Controls:
* 55 years of age or above
* MoCA total score ≥26.
Exclusion Criteria:
* Presence of other neurological disorder, chronic inflammatory/autoimmune disorder, active cancer, active metabolic disease, diabetes type I and II, and active or latent infection;
* Use of immunosuppressive drugs within the preceding 12 months;
* Use of oral/intravenous steroids within the preceding 3 months;
* Regular use (more than twice per week) of non-steroidal anti-inflammatory drugs (e.g. ibuprofen, naproxen, diclofenac, meloxicam) or over 75mg aspirin;
* Participation in other interventional studies, within the preceding 3 months;
* Consumption of laxatives, stool softeners, stool bulking agents, motility agents, iron supplements and probiotics within the preceding 3 months;
* Current smoker
* Inability to understand or speak English fluently.
For participants in Component 2 of the study (Experimental Medicine Study), additional exclusion criteria will be in place, namely, known allergy to any of the probiotic's ingredients: Bulking agent (isomalt), sweetener (xylitol), L. reuteri DSM 17938, strawberry flavouring and flavour enhancer (citric acid).

The sponsor's own eligibility wording, lightly reformatted. The study team makes the final eligibility decision — worth discussing with your doctor.

Eligibility criteria as of 2026-08-25