Clinical correlates of a negative cerebrospinal fluid α-synuclein seed amplification assay result in Parkinson’s disease

Why some Parkinson’s patients puzzle a powerful new test

Doctors now have a highly sensitive lab test that can detect the telltale misfolded protein found in most people with Parkinson’s disease. But a sizeable minority of patients come back negative on this test even though they clearly have Parkinson’s symptoms. This study digs into who these “negative” patients are, whether they are misdiagnosed, and what their stories reveal about different forms of the disease and the future of targeted treatments.

A new window into the hidden biology of Parkinson’s

Parkinson’s disease has long been linked to clumps of a protein called alpha‑synuclein that build up inside brain cells as Lewy bodies. Until recently, these clumps could be confirmed only after death. A newer lab method, called a seed amplification assay, can now pick up tiny traces of misfolded alpha‑synuclein in spinal fluid, effectively offering a living biopsy of Lewy body–type disease. In large studies, about 85–90 percent of people diagnosed with Parkinson’s test positive on this spinal fluid assay, but 10–15 percent do not. The team behind this paper set out to study one of the largest such patient groups to date, asking whether these negative results reflect flawed diagnoses, technical blind spots, or a biologically distinct form of Parkinson’s.

Who was studied and how they were followed

The researchers examined 473 people treated at a German movement disorders center between 2002 and 2024, all diagnosed with Parkinson’s by specialists and all with at least one spinal fluid sample tested. Patients carrying certain genetic mutations known to cause atypical forms of Parkinson’s were removed from the analysis. Everyone underwent detailed exams that captured movement problems, thinking skills, mood, sleep, sense of smell, bowel function and blood‑pressure changes. Many also provided repeat spinal fluid samples over several years, letting the team see whether initially negative tests could later turn positive as the disease progressed.

A distinct pattern in test‑negative patients

About 13 percent of the final group had no detectable alpha‑synuclein seeds in their spinal fluid. These individuals showed a strikingly different balance of symptoms than those who tested positive. On average they had worse “axial” motor problems such as balance and posture issues and were more likely to report repeated falls. At the same time, they were less likely to have several hallmark non‑movement features often tied to classical Lewy body disease: loss of smell, constipation and a sleep problem called REM sleep behavior disorder. Their sense of smell tended to be better, and they reported constipation and dream‑enacting sleep behaviors less often. Some measures hinted at more depression and slightly better thinking skills, though these latter trends were weaker.

Tracking disease course and ruling out other explanations

One obvious concern is that negative tests might simply flag people who never had Parkinson’s in the first place. A small number did later receive different diagnoses such as multiple system atrophy or progressive supranuclear palsy, but most did not. Levels of another spinal fluid marker, neurofilament light chain, which typically run high in rapidly worsening atypical parkinsonian disorders, did not differ between positive and negative groups in the main analyses. Importantly, when the team followed patients over time, both groups showed similar overall worsening of movement and thinking scores and required comparable increases in medication doses. A minority of initially negative patients later converted to positive on repeat spinal fluid testing, suggesting that in some people the detectable misfolded protein may emerge only as disease advances.

What these findings may mean for Parkinson’s subtypes

The results point toward a meaningful subgroup of people with a Parkinson’s‑like illness who lack the usual laboratory signature of misfolded alpha‑synuclein in spinal fluid. They tend to be women, have more trouble with balance and posture, and show fewer problems with smell, sleep and gut function. Their overall rate of decline, however, is not dramatically different from those who test positive. The authors suggest that some of these patients could have a lower or differently distributed burden of Lewy body pathology, or perhaps a distinct form of protein aggregation that current assays miss. As experimental drugs increasingly target alpha‑synuclein itself, this work underscores the importance of using spinal fluid testing to sort patients into biologically defined groups, ensuring that future trials enroll those most likely to benefit while also shedding light on less typical forms of the disease.

Citation: Mastrangelo, A., Wurster, I., Ticca, A. et al. Clinical correlates of a negative cerebrospinal fluid α-synuclein seed amplification assay result in Parkinson’s disease. npj Parkinsons Dis. 12, 97 (2026). https://doi.org/10.1038/s41531-026-01346-3

Keywords: Parkinson’s disease, alpha-synuclein, cerebrospinal fluid, biomarkers, Lewy body pathology