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Disease modification and biomarker development in Parkinson disease: Revision or reconstruction?

ABSTRACT: A fundamental question in advancing Parkinson disease (PD) research is whether it represents one disorder or many. Does each genetic PD inform a common pathobiology or represent a unique entity? Do the similarities between genetic and idiopathic forms of PD outweigh the differences? If aggregates of α-synuclein in Lewy bodies and Lewy neurites are present in most (α-synucleinopathies), are they also etiopathogenically significant in each (α-synuclein pathogenesis)? Does it matter that postmortem studies in PD have demonstrated that mixed protein-aggregate pathology is the rule and pure α-synucleinopathy the exception? Should we continue to pursue convergent biomarkers that are representative of the diverse whole of PD or subtype-specific, divergent biomarkers, present in some but absent in most? Have clinical trials that failed to demonstrate efficacy of putative disease-modifying interventions been true failures (shortcomings of the hypotheses, which should be rejected) or false failures (shortcomings of the trials; hypotheses should be preserved)? Each of these questions reflects a nosologic struggle between the lumper's clinicopathologic model that embraces heterogeneity of one disease and the splitter's focus on a pathobiology-specific set of diseases. Most important, even if PD is not a single disorder, can advances in biomarkers and disease modification be revised to concentrate on pathologic commonalities in large, clinically defined populations? Or should our efforts be reconstructed to focus on smaller subgroups of patients, distinguished by well-defined molecular characteristics, regardless of their phenotypic classification? Will our clinical trial constructs be revised to target larger and earlier, possibly even prodromal, cohorts? Or should our trials efforts be reconstructed to target smaller but molecularly defined presymptomatic or postsymptomatic cohorts? At the Krembil Knowledge Gaps in Parkinson's Disease Symposium, the tentative answers to these questions were discussed, informed by the failures and successes of the fields of breast cancer and cystic fibrosis.

SUBMITTER: Espay AJ

PROVIDER: S-EPMC7220234 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Deposition of the pathological α-synuclein (αSynP) in the brain is the hallmark of synucleinopathies, including Parkinson disease (PD), Lewy body dementia (LBD), and multiple system atrophy (MSA). Whether real-time quaking-induced conversion (RT-QuIC) and protein misfolding cyclic amplification (PMCA) assays can sensitively detect skin biomarkers for PD and non-PD synucleinopathies remains unknown. To develop sensitive and specific skin biomarkers for antemortem diagnosis of PD and other synucleinopathies. This retrospective and prospective diagnostic study evaluated autopsy and biopsy skin samples from neuropathologically and clinically diagnosed patients with PD and controls without PD. Autopsy skin samples were obtained at 3 medical centers from August 2016 to September 2019, and biopsy samples were collected from 3 institutions from August 2018 to November 2019. Based on neuropathological and clinical diagnoses, 57 cadavers with synucleinopathies and 73 cadavers with nonsynucleinopathies as well as 20 living patients with PD and 21 living controls without PD were included. Specifically, cadavers and participants had PD, LBD, MSA, Alzheimer disease, progressive supranuclear palsy, or corticobasal degeneration or were nonneurodegenerative controls (NNCs). A total of 8 approached biopsy participants either refused to participate in or were excluded from this study due to uncertain clinical diagnosis. Data were analyzed from September 2019 to April 2020. Skin αSynP seeding activity was analyzed by RT-QuIC and PMCA assays. A total of 160 autopsied skin specimens from 140 cadavers (85 male cadavers [60.7%]; mean [SD] age at death, 76.8 [10.1] years) and 41 antemortem skin biopsies (27 male participants [66%]; mean [SD] age at time of biopsy, 65.3 [9.2] years) were analyzed. RT-QuIC analysis of αSynP seeding activity in autopsy abdominal skin samples from 47 PD cadavers and 43 NNCs revealed 94% sensitivity (95% CI, 85-99) and 98% specificity (95% CI, 89-100). As groups, RT-QuIC also yielded 93% sensitivity (95% CI, 85-97) and 93% specificity (95% CI, 83-97) among 57 cadavers with synucleinopathies (PD, LBD, and MSA) and 73 cadavers without synucleinopathies (Alzheimer disease, progressive supranuclear palsy, corticobasal degeneration, and NNCs). PMCA showed 82% sensitivity (95% CI, 76-88) and 96% specificity (95% CI, 85-100) with autopsy abdominal skin samples from PD cadavers. From posterior cervical and leg skin biopsy tissues from patients with PD and controls without PD, the sensitivity and specificity were 95% (95% CI, 77-100) and 100% (95% CI, 84-100), respectively, for RT-QuIC and 80% (95% CI, 49-96) and 90% (95% CI, 60-100) for PMCA. This study provides proof-of-concept that skin αSynP seeding activity may serve as a novel biomarker for antemortem diagnoses of PD and other synucleinopathies.

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Disease modification and biomarker development in Parkinson disease: Revision or reconstruction?

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