It usually starts with the bed partner. A punch thrown at three in the morning, a shout, a dive off the mattress at something that was not in the room. REM sleep behaviour disorder is dream enactment: the paralysis that normally holds the body still during dreaming fails, and the dream gets acted out. For most people it is also something else, a signal arriving years early. The protocol paper for the North American Prodromal Synucleinopathy Consortium, published in SLEEP Advances on January 19, 2026, notes that in long term follow up of seniors with isolated RBD, phenoconversion to an overt synucleinopathy (Parkinson's disease, dementia with Lewy bodies, multiple system atrophy) has been reported at rates as high as 73 to 96 percent.
So it is worth being precise about what is listed under Lewy body dementia studies at UCLA. NAPS Stage 2, registered as NCT05826457 and sponsored by Washington University School of Medicine, is an observational study. No drug, no placebo, no treatment arm. The registry record, with status verified in May 2026, gives an actual start date of August 12, 2022, a target of 500 participants, healthy volunteers accepted, estimated primary completion on May 1, 2027 and study completion on May 1, 2028. Its stated purpose is preparation: enrolling people with isolated RBD and controls in anticipation of a future trial of neuroprotective treatment against synucleinopathies.
The protocol describes what that preparation actually looks like. Nine academic centres across North America, over 500 people with polysomnogram confirmed isolated RBD drawn from existing sleep centres, plus 60 control participants matched for age, sex and race. Everyone repeats the same battery annually: motor, cognitive, autonomic, psychiatric, sensory and sleep measures, with biospecimen collection, centralised reading of polysomnography and neuroimaging, and structured diagnostic adjudication rather than each site deciding on its own. Participants who phenoconvert are replaced, keeping the prodromal cohort stocked. The arithmetic behind the 500 is openly stated: assuming roughly 8 percent phenoconvert each year, 5 percent attrition, and 60 percent of Stage 1 participants rolling over, the consortium expects to end with about 300 people available for a trial. As of July 31, 2025, 154 people had enrolled directly into Stage 2, for 535 with isolated RBD across both stages; 396 had completed at least two cycles, 105 had phenoconverted, 14 had died and 34 had withdrawn or been lost.
Why build this rather than simply run a trial? Because the sums are brutal. The large multicentre study led by Ronald Postuma, published in Brain in March 2019, followed 1280 people with isolated RBD: 352 (28 percent) converted during follow up, the median time to conversion was 8.0 years, and the annual rate was 6.25 percent. Its own sample size modelling found that a disease modifying trial recruiting unselected RBD would need about 366 people per group, falling to roughly 200 if enrichment selects those with abnormal quantitative motor testing. A trial that cannot find, characterise and keep that many people does not fail at the drug; it fails before the drug.
The consortium's own baseline paper, in Annals of Clinical and Translational Neurology on February 8, 2023, is a reminder that prodromal does not mean untouched. Among 361 participants (81.7 percent male, mean age 64.9), only 56 were cleanly isolated RBD; 305 already showed at least one abnormality on detailed testing, including global cognition in 38 percent, a motor tap test in 48 percent, smell identification in 57 percent and orthostatic hypotension in 38.8 percent. That is an observation about a research cohort, not a prediction about any individual, and the consortium's aim is to learn which of these measures track progression well enough to serve as trial outcomes.
For a family living with dream enactment now, the honest framing is this: joining a cohort like NAPS is not being treated. Stage 2 is listed as enrolling by invitation, recruiting through established sleep centres, which means the route in runs through a sleep clinician rather than a sign up form. What participants get is careful annual measurement, and a place in the group from which a future trial would be drawn. What the field gets, if it works, is a ready made starting line.