Bridging molecular genetics and biomarkers in lewy body and related disorders

A proteomic signature for dementia with Lewy bodies

INTRODUCTION

We sought to determine if a proteomic profile approach developed to detect Alzheimer's disease would distinguish patients with Lewy body disease from normal controls, and if it would distinguish dementia with Lewy bodies (DLB) from Parkinson's disease (PD).

METHODS

Stored plasma samples were obtained from 145 patients (DLB n = 57, PD without dementia n = 32, normal controls n = 56) enrolled from patients seen in the Behavioral Neurology or Movement Disorders clinics at the Mayo Clinic, Florida. Proteomic assays were conducted and analyzed as per our previously published protocols.

RESULTS

In the first step, the proteomic profile distinguished the DLB-PD group from controls with a diagnostic accuracy of 0.97, sensitivity of 0.91, and specificity of 0.86. In the second step, the proteomic profile distinguished the DLB from PD groups with a diagnostic accuracy of 0.92, sensitivity of 0.94, and specificity of 0.88.

DISCUSSION

These data provide evidence of the potential utility of a multitiered blood-based proteomic screening method for detecting DLB and distinguishing DLB from PD.

Blood-Based Biomarker Screening with Agnostic Biological Definitions for an Accurate Diagnosis Within the Dimensional Spectrum of Neurodegenerative Diseases

The discovery, development, and validation of novel candidate biomarkers in Alzheimer's disease (AD) and other neurodegenerative diseases (NDs) are increasingly gaining momentum. As a result, evolving diagnostic research criteria of NDs are beginning to integrate biofluid and neuroimaging indicators of pathophysiological mechanisms. More than 10% of people aged over 65 suffer from NDs. There is an urgent need for a refined two-stage diagnostic model to first initiate an early, sensitive, and noninvasive process in primary care settings. Individuals that meet detection criteria will then be channeled to more specific, costly (positron-emission tomography), and invasive (cerebrospinal fluid) assessment methods for confirmatory biological characterization and diagnosis.A reliable and sensitive blood test for AD and other NDs is not yet established; however, it would provide the golden screening gate for an efficient primary care management. A limitation to the development of a large-scale blood-screening biomarker-based test is the traditional application of clinically descriptive criteria for the categorization of single late-stage ND constructs. These are genetically and biologically heterogeneous, reflected in multiple pathophysiological mechanisms and subsequent pathologies throughout a dimensional continuum. Evidence suggests that a shared, "open-source" integrated multilevel categorization of NDs that clusters individuals based on descriptive clinical phenotypes and pathophysiological biomarker signatures will provide the next incremental step toward an improved diagnostic process of NDs. This intermediate objective toward unbiased biomarker-guided early detection of individuals at risk for NDs is currently carried out by the international pilot Alzheimer Precision Medicine Initiative Cohort Program (APMI-CP).

Biomarkers in biological fluids for dementia with Lewy bodies

Dementia with Lewy bodies (DLB) has become the second most common neurodegenerative dementia due to demographic ageing. Differential diagnosis is still troublesome especially in early stages of the disease, since there is a great clinical and neuropathological overlap primarily with Alzheimer's disease and Parkinson's disease. Therefore, more specific biomarkers, not only for scientific reasons but also for clinical therapeutic decision-making, are urgently needed. In this review, we summarize the knowledge on fluid biomarkers for DLB, derived predominantly from cerebrospinal fluid. We discuss the value of well-defined markers (β-amyloid, (phosphorylated) tau, α-synuclein) as well as some promising 'upcoming' substances, which still have to be further evaluated.

Biomarkers in Parkinson's disease (recent update)

Parkinson's disease (PD) is the second most common neurodegenerative disorder mostly affecting the aging population over sixty. Cardinal symptoms including, tremors, muscle rigidity, drooping posture, drooling, walking difficulty, and autonomic symptoms appear when a significant number of nigrostriatal dopaminergic neurons are already destroyed. Hence we need early, sensitive, specific, and economical peripheral and/or central biomarker(s) for the differential diagnosis, prognosis, and treatment of PD. These can be classified as clinical, biochemical, genetic, proteomic, and neuroimaging biomarkers. Novel discoveries of genetic as well as nongenetic biomarkers may be utilized for the personalized treatment of PD during preclinical (premotor) and clinical (motor) stages. Premotor biomarkers including hyper-echogenicity of substantia nigra, olfactory and autonomic dysfunction, depression, hyposmia, deafness, REM sleep disorder, and impulsive behavior may be noticed during preclinical stage. Neuroimaging biomarkers (PET, SPECT, MRI), and neuropsychological deficits can facilitate differential diagnosis. Single-cell profiling of dopaminergic neurons has identified pyridoxal kinase and lysosomal ATPase as biomarker genes for PD prognosis. Promising biomarkers include: fluid biomarkers, neuromelanin antibodies, pathological forms of α-Syn, DJ-1, amyloid β and tau in the CSF, patterns of gene expression, metabolomics, urate, as well as protein profiling in the blood and CSF samples. Reduced brain regional N-acetyl-aspartate is a biomarker for the in vivo assessment of neuronal loss using magnetic resonance spectroscopy and T2 relaxation time with MRI. To confirm PD diagnosis, the PET biomarkers include [(18)F]-DOPA for estimating dopaminergic neurotransmission, [(18)F]dG for mitochondrial bioenergetics, [(18)F]BMS for mitochondrial complex-1, [(11)C](R)-PK11195 for microglial activation, SPECT imaging with (123)Iflupane and βCIT for dopamine transporter, and urinary salsolinol and 8-hydroxy, 2-deoxyguanosine for neuronal loss. This brief review describes the merits and limitations of recently discovered biomarkers and proposes coenzyme Q10, mitochondrial ubiquinone-NADH oxidoreductase, melatonin, α-synculein index, Charnoly body, and metallothioneins as novel biomarkers to confirm PD diagnosis for early and effective treatment of PD.

The role of α-synuclein in neurodegeneration — An update

Genetic, neuropathological and biochemical evidence implicates α-synuclein, a 140 amino acid presynaptic neuronal protein, in the pathogenesis of Parkinson’s disease and other neurodegenerative disorders. The aggregated protein inclusions mainly containing aberrant α-synuclein are widely accepted as morphological hallmarks of α-synucleinopathies, but their composition and location vary between disorders along with neuronal networks affected. α-Synuclein exists physiologically in both soluble and membran-bound states, in unstructured and α-helical conformations, respectively, while posttranslational modifications due to proteostatic deficits are involved in β-pleated aggregation resulting in formation of typical inclusions. The physiological function of α-synuclein and its role linked to neurodegeneration, however, are incompletely understood. Soluble oligomeric, not fully fibrillar α-synuclein is thought to be neurotoxic, main targets might be the synapse, axons and glia. The effects of aberrant α-synuclein include alterations of calcium homeostasis, mitochondrial dysfunction, oxidative and nitric injuries, cytoskeletal effects, and neuroinflammation. Proteasomal dysfunction might be a common mechanism in the pathogenesis of neuronal degeneration in α-synucleinopathies. However, how α-synuclein induces neurodegeneration remains elusive as its physiological function. Genome wide association studies demonstrated the important role for genetic variants of the SNCA gene encoding α-synuclein in the etiology of Parkinson’s disease, possibly through effects on oxidation, mitochondria, autophagy, and lysosomal function. The neuropathology of synucleinopathies and the role of α-synuclein as a potential biomarker are briefly summarized. Although animal models provided new insights into the pathogenesis of Parkinson disease and multiple system atrophy, most of them do not adequately reproduce the cardinal features of these disorders. Emerging evidence, in addition to synergistic interactions of α-synuclein with various pathogenic proteins, suggests that prionlike induction and seeding of α-synuclein could lead to the spread of the pathology and disease progression. Intervention in the early aggregation pathway, aberrant cellular effects, or secretion of α-synuclein might be targets for neuroprotection and disease-modifying therapy.