CAP TODAY Pathology/Laboratory Medicine/Laboratory Management
Editors: Donna E. Hansel, MD, PhD, division head of pathology and laboratory medicine, MD Anderson Cancer Center, Houston; James Solomon, MD, PhD, assistant professor, Department of Pathology and Laboratory Medicine, Weill Cornell Medicine, New York; Erica Reinig, MD, assistant professor and medical director of molecular diagnostics, University of Wisconsin-Madison; Marcela Riveros Angel, MD, molecular genetic pathology fellow, Department of Pathology, OHSU; Andrés G. Madrigal, MD, PhD, assistant professor, clinical, Ohio State University Wexner Medical Center, Columbus; Maedeh Mohebnasab, MD, assistant professor of pathology, University of Pittsburgh; and Alicia Dillard, MD, clinical pathology chief resident, New York-Presbyterian/Weill Cornell Medical Center.
A novel assay for Parkinson disease and other synucleinopathies
September 2023—Neurodegenerative diseases are a broad group of disorders characterized by progressive loss of nerve cells in the central or peripheral nervous system. These diseases are often chronic and incurable, with symptoms ranging from cognitive decline to motor or sensory dysfunction. There are many types of neurodegenerative diseases, with various underlying etiologies. One group of diseases, the synucleinopathies, are associated with the misfolding and aggregation of the protein α-synuclein. This group includes disease entities such as Parkinson disease, dementia with Lewy bodies, and multiple-system atrophy. It is thought that, in the pathogenesis of synucleinopathies, small α-synuclein aggregates known as fibrils recruit soluble monomers to propagate their growth in a mechanism analogous to crystallization seeding. Once large enough, the aggregates deposit in neural tissues, forming lesions, such as Lewy bodies, that are visible under the microscope. How these α-synuclein fibril seeds spread through the nervous system is unclear, but they have been detected in the cerebrospinal fluid, skin, salivary gland, and olfactory mucosa of affected patients. Therefore, it is hypothesized that the pathogenesis of synucleionopathies may involve the spread of α-synuclein fibril seeds through blood. To detect α-synuclein seeds in serum, the authors developed an immunoprecipitation-based real-time quaking-induced conversion (IP/RT-QuIC) assay and evaluated its clinical sensitivity. The assay works based on α-synuclein fibrils seeding the growth of larger aggregates. In the assay, the patient’s serum is incubated with an anti-α-synuclein antibody bound to magnetic beads, which isolates the α-synuclein seeds from the serum. The isolated seeds are then mixed with recombinant α-synuclein monomers and a fluorescent reporter dye. The mixture undergoes periodic agitation, and as the seeds recruit α-synuclein monomers and form larger fibrils and aggregates, the fluorescence signal increases. Serum with higher concentrations of α-synuclein seeds undergo more rapid fibril formation, allowing for a quantitative output. The assay was tested on sera from a cohort of 270 patients with synucleinopathy, which was compared with sera from 128 controls and 72 patients with nonsynucleinopathy neurodegenerative diseases. The assay was highly accurate for distinguishing patients with Parkinson disease from controls, with a sensitivity of 94.6 percent, specificity of 92.1 percent, and area under the receiver operating characteristic curve (AUC) of 0.96. The AUC for distinguishing patients with multiple-system atrophy from controls was 0.64, and it was 0.90 for distinguishing patients with dementia with Lewy bodies from controls. The rate at which the aggregates formed in the assay correlated with the Unified Parkinson’s Disease Rating Scale part three and disease duration. In an analysis with a blinded external cohort, the assay was able to distinguish patients with Parkinson disease and patients with multiple-system atrophy from controls with AUCs of 0.86 and 0.80, respectively. The authors demonstrated that the amplified α-synuclein seeds formed in the IP/RT-QuIC assay retained their disease-specific structural characteristics and pathogenic properties. They concluded that this study details a potential novel clinical assay for identifying patients with synucleinopathies using blood samples.
Okuzumi A, Hatano T, Matsumoto G, et al. Propagative α-synuclein seeds as serum biomarkers for synucleinopathies. Nat Med. 2023;29(6):1448–1455.
Correspondence: Dr. Nobutaka Hattori at nhattori@juntendo.ac.jp