Biomarkers in Huntington's and Parkinson's Disease

Dysphagia in Parkinson Disease: Part I - Pathophysiology and Diagnostic Practices

Purpose of Review

Dysphagia affects the majority of individuals with Parkinson disease (PD) and is not typically diagnosed until later in disease progression. This review will cover the current understanding of PD pathophysiology, and provides an overview of dysphagia in PD including diagnostic practices, gaps in knowledge, and future directions.

Recent Findings

Many non-motor and other motor signs of PD appear in the prodrome prior to the manifestation of hall- mark signs and diagnosis. While dysphagia often presents already in the prodrome, it is not routinely addressed in standard neurology examinations.

Summary

Dysphagia in PD can result in compromised efficiency and safety of swallowing, which significantly contributes to malnutrition and dehydration, decrease quality of life, and increase mortality. The heterogeneous clinical presentation of PD complicates diagnostic procedures which often leads to delayed treatment. Research has advanced our knowledge of mechanisms underlying PD, but dysphagia is still largely understudied, especially in the prodromal stage.

Clinical Pharmacology in Drug Development for Rare Diseases in Neurology: Contributions and Opportunities

Several challenges are associated with rare disease drug development in neurology. In this article, we summarize the US Food and Drug Administration's experience with clinical drug development for rare neurological diseases and discuss clinical pharmacology's critical contributions to drug development for rare diseases. We used publicly available information to identify and screen drug products approved for rare neurological indications between 1983 and 2019. We highlighted cases in which clinical pharmacology contributed to the evidence of drug efficacy, dose selection for pivotal clinical trials, dose optimization based on intrinsic and extrinsic factors, pharmacokinetic bridging for formulations, and efficacy bridging across different racial groups. Fifty-one approved drug products were identified since the introduction of the Orphan Drug Act in 1983. Interestingly, the number of approvals in the last few years increased significantly, probably due to advances in genomic research and targeted drug modalities. Evaluation of dose selection in patient populations showed that in 52% of cases, the sponsors did not evaluate efficacy for more than one or two dose levels throughout the development program. Clinical pharmacology studies to evaluate the effect of intrinsic or extrinsic factors were adequately characterized in most of the applications. With the expansion of model informed drug development applications, (e.g., quantitative systems pharmacology and deep learning neural network models), the role and impact of clinical pharmacology is expected to grow exponentially in the next decade and enhance the development of novel treatment modalities for neurological rare diseases.

Cognition, function and awareness of disease impact in early Parkinson's and Huntington's disease

Purpose: Patients with Parkinson's and Huntington's Disease (PD and HD) present impairments in cognitively challenging everyday activities. This study contrasts these two basal ganglia disorders on the ability to perform daily life- like tasks and their level of awareness regarding the disease impact on function.Methods: 19 controls, 10 early-onset PD, 20 early stage PD, and 15 early manifest HD patients were compared in the "EcoKitchen," a virtual reality task with increasing executive load, the "Behavioural Assessment of Dysexecutive Syndrome battery - BADS," and "The Adults and Older Adults Functional Assessment Inventory - IAFAI," a self-report functional questionnaire. The EcoKitchen clinical correlates were investigated.Results: All clinical groups presented slower EcoKitchen performance than controls, however, only HD patients showed decreased accuracy. HD and PD patients exhibited reduced BADS scores compared to the other study participants. Importantly, on the IAFAI, PD patients signalled more physically related incapacities and HD patients indicated more cognitively related incapacities. Accordingly, the EcoKitchen performance was significantly associated with PD motor symptom severity.Conclusions: Our findings suggest differential disease impact on cognition and function across PD and HD patients, with preserved awareness regarding disease- related functional sequelae. These observations have important implications for clinical management, research and rehabilitation.Implications for rehabilitationPatients with early stage Parkinson's and Huntington's disease have diagnosis-specific impairments in the performance of executively demanding everyday activities and, yet, show preserved awareness about the disease impact on their daily life.An active involvement of patients in the rehabilitation process should be encouraged, as their appraisal of the disease effects can help on practical decisions about meaningful targets for intervention, vocational choices, quality-of-life issues and/or specific everyday skills to boost.The EcoKitchen, a non-immersive virtual reality task, can detect and quantify early deficits in everyday-like tasks and is therefore a valuable tool for assessing the effects of rehabilitation strategies on the functional cognition of these patients.Rehabilitation efforts in the mild stages of Parkinson's and Huntington's disease should be aware of greater time needs from the patients in the performance of daily life tasks, target executive skills, and give a more prominent role to patients in symptoms report and management.

The effect of impulsivity and inhibitory control deficits in the saccadic behavior of premanifest Huntington's disease individuals

BACKGROUND

This study aims to test response inhibition in premanifest Huntington's disease individuals (Pre-HD), in the context of a saccadic paradigm with working memory demands and fronto-executive load as a way to measure inhibitory control deficits and impulsive behavior in Huntington's disease (HD).

METHODS

The oculomotor function of 15 Pre-HD and 22 Control individuals was assessed using an experimental paradigm comprising four horizontal saccadic tasks: prosaccade (PS), antisaccade (AS), 1- or 2-back memory prosaccade (MPS), and 1- or 2-back memory antisaccade (MAS). Success rate, latency, directional and timing errors were calculated for each task. A comprehensive battery of neuropsychological tests was also used to assess the overall cognitive functioning of study participants. Statistical correlations between oculomotor, clinical and cognitive measures were computed for the Pre-HD group.

RESULTS

Pre-HD participants showed reduced success rate in the AS task, increased direction errors in the AS and MAS tasks and decreased latency in the MAS task when compared to Controls, despite presenting similar executive and memory scores in the conventional neuropsychological tests applied. Significant associations were identified between specific AS and MAS parameters and disease-related measures, cognitive skills and other oculomotor results of Pre-HD participants.

CONCLUSIONS

Our results show that oculomotor performance in premanifest Huntington's disease deteriorates once inhibitory control, working memory and/or fronto-executive load are added to the task. A more automatic pattern of performance, including a faster response time and directionally erroneous eye movements were detected in the oculomotor behavior of the Pre-HD group-these alterations were significantly correlated with disease stage and cognitive status. Our saccadic paradigm was able to capture impulsivity and inhibitory control deficits in a group of Pre-HD individuals on average far from symptom onset, thus holding the potential to identify the earliest disease-related changes.

A Novel Ecological Approach Reveals Early Executive Function Impairments in Huntington's Disease

Introduction: Impairments in executive functions are common in neurogenetic disorders such as Huntington's disease (HD) and are thought to significantly influence the patient's functional status. Reliable tools with higher ecological validity that can assess and predict the impact of executive dysfunction in daily-life performance are needed. This study aimed to develop and validate a novel non-immersive virtual reality task ("EcoKitchen") created with the purpose of capturing cognitive and functional changes shown by HD carriers without clinical manifestations of the disease (Premanifest HD), in a more realistic setting. Materials and Methods: We designed a virtual reality task with three blocks of increasing executive load. The performance of three groups (Controls, CTRL; Premanifest HD individuals, HP; Early Manifest HD patients, HD) was compared in four main components of the study protocol: the EcoKitchen; a subjective (self-report) measure - "The Adults and Older Adults Functional Assessment Inventory (IAFAI)"; the "Behavioural Assessment of Dysexecutive Syndrome battery (BADS)"; and a conventional neuropsychological test battery. We also examined statistical associations between EcoKitchen and the other executive, functional and clinical measures used. Results: The HD group showed deficits in all the assessment methods used. In contrast, the HP group was only found to be impaired in the EcoKitchen task, particularly in the most cognitively demanding blocks, where they showed a higher number of errors compared to the CTRL group. Statistically significant correlations were identified between the EcoKitchen, measures of the other assessment tools, and HD clinical features. Discussion: The EcoKitchen task, developed as an ecological executive function assessment tool, was found to be sensitive to early deficits in this domain. Critically, in premanifest HD individuals, it identifies dysfunction prior to symptom onset. Further it adds a potential tool for diagnosis and management of the patients' real-life problems.

Modelling the natural history of Huntington's disease progression

BACKGROUND

The lack of reliable biomarkers to track disease progression is a major problem in clinical research of chronic neurological disorders. Using Huntington's disease (HD) as an example, we describe a novel approach to model HD and show that the progression of a neurological disorder can be predicted for individual patients.

METHODS

Starting with an initial cohort of 343 patients with HD that we have followed since 1995, we used data from 68 patients that satisfied our filtering criteria to model disease progression, based on the Unified Huntington's Disease Rating Scale (UHDRS), a measure that is routinely used in HD clinics worldwide.

RESULTS

Our model was validated by: (A) extrapolating our equation to model the age of disease onset, (B) testing it on a second patient data set by loosening our filtering criteria, (C) cross-validating with a repeated random subsampling approach and (D) holdout validating with the latest clinical assessment data from the same cohort of patients. With UHDRS scores from the past four clinical visits (over a minimum span of 2 years), our model predicts disease progression of individual patients over the next 2 years with an accuracy of 89-91%. We have also provided evidence that patients with similar baseline clinical profiles can exhibit very different trajectories of disease progression.

CONCLUSIONS

This new model therefore has important implications for HD research, most obviously in the development of potential disease-modifying therapies. We believe that a similar approach can also be adapted to model disease progression in other chronic neurological disorders.

Cerebrospinal fluid peptides as potential Parkinson disease biomarkers: a staged pipeline for discovery and validation

Finding robust biomarkers for Parkinson disease (PD) is currently hampered by inherent technical limitations associated with imaging or antibody-based protein assays. To circumvent the challenges, we adapted a staged pipeline, starting from our previous proteomic profiling followed by high-throughput targeted mass spectrometry (MS), to identify peptides in human cerebrospinal fluid (CSF) for PD diagnosis and disease severity correlation. In this multicenter study consisting of training and validation sets, a total of 178 subjects were randomly selected from a retrospective cohort, matching age and sex between PD patients, healthy controls, and neurological controls with Alzheimer disease (AD). From ∼14,000 unique peptides displaying differences between PD and healthy control in proteomic investigations, 126 peptides were selected based on relevance and observability in CSF using bioinformatic analysis and MS screening, and then quantified by highly accurate and sensitive selected reaction monitoring (SRM) in the CSF of 30 PD patients versus 30 healthy controls (training set), followed by diagnostic (receiver operating characteristics) and disease severity correlation analyses. The most promising candidates were further tested in an independent cohort of 40 PD patients, 38 AD patients, and 40 healthy controls (validation set). A panel of five peptides (derived from SPP1, LRP1, CSF1R, EPHA4, and TIMP1) was identified to provide an area under curve (AUC) of 0.873 (sensitivity = 76.7%, specificity = 80.0%) for PD versus healthy controls in the training set. The performance was essentially confirmed in the validation set (AUC = 0.853, sensitivity = 82.5%, specificity = 82.5%). Additionally, this panel could also differentiate the PD and AD groups (AUC = 0.990, sensitivity = 95.0%, specificity = 97.4%). Furthermore, a combination of two peptides belonging to proteins TIMP1 and APLP1 significantly correlated with disease severity as determined by the Unified Parkinson's Disease Rating Scale motor scores in both the training (r = 0.381, p = 0.038)j and the validation (r = 0.339, p = 0.032) sets. The novel panel of CSF peptides, if validated in independent cohorts, could be used to assist in clinical diagnosis of PD and has the potential to help monitoring or predicting disease progression.

A novel cognitive-neurophysiological state biomarker in premanifest Huntington's disease validated on longitudinal data

In several neurodegenerative diseases, like Huntington's disease (HD), treatments are still lacking. To determine whether a treatment is effective, sensitive disease progression biomarkers are especially needed for the premanifest phase, since this allows the evaluation of neuroprotective treatments preventing, or delaying disease manifestation. On the basis of a longitudinal study we present a biomarker that was derived by integrating behavioural and neurophysiological data reflecting cognitive processes of action control. The measure identified is sensitive enough to track disease progression over a period of only 6 month. Changes tracked were predictive for a number of clinically relevant parameters and the sensitivity of the measure was higher than that of currently used parameters to track prodromal disease progression. The study provides a biomarker, which could change practice of progression diagnostics in a major basal ganglia disease and which may help to evaluate potential neuroprotective treatments in future clinical trials.

Diffusion tensor imaging in parkinsonian syndromes: a systematic review and meta-analysis

OBJECTIVES

We performed a systematic review to assess alterations in measures of diffusion tensor imaging (DTI) in parkinsonian syndromes, exploring the potential role of DTI in diagnosis and as a candidate biomarker.

METHODS

We searched EMBASE and Medline databases for DTI studies comparing parkinsonian syndromes or related dementias with controls or another defined parkinsonian syndrome. Key details for each study regarding participants, imaging methods, and results were extracted. Estimates were pooled, where appropriate, by random-effects meta-analysis.

RESULTS

Of 333 results, we identified 43 studies suitable for inclusion (958 patients, 764 controls). DTI measures detected alterations in all parkinsonian syndromes, with distribution varying differentially with disease type. Nine studies were included in a meta-analysis of the substantia nigra in Parkinson disease. A notable effect size was found for lowered fractional anisotropy in the substantia nigra for patients with Parkinson disease vs controls (-0.639, 95% confidence interval -0.860 to -0.417, p < 0.0001).

CONCLUSION

DTI may be a promising biomarker in parkinsonian syndromes and have a future role in differential diagnosis. Larger cohort studies are required to investigate some encouraging preliminary findings. Given the complexity of the parkinsonian syndromes, it is likely that any potential DTI biomarker would be used in combination with other relevant biomarkers.

The influence of motor and cognitive impairment upon visually-guided saccades in Parkinson's disease

Studies of saccades in Parkinson's disease (PD) have seldom examined the influence of cognitive status, ranging from normal cognition, through mild cognitive impairment, to dementia. In a large and heterogeneous sample, we examined how motor and cognitive impairment was reflected in the performance of reflexive, visually-guided saccades. We examined 163 people with PD and 47 similar-aged controls. Ninety three of the PD group had normal cognition (PDN), 48 had mild cognitive impairment (PD-MCI), and 22 had dementia (PDD). Pseudo-random targets (amplitudes of 5, 10, 15 and 20 deg and inter-stimulus-intervals ranging from 550 to 1800 ms) were shown in 108 mixed randomised trials, incorporating gap, step, and overlap onset conditions. Analyses were conducted using multi-level regression modeling. Participants were first assessed by continuous measures (Unified PD Rating Scale motor score and the Montreal Cognitive Assessment). Prolonged latency was significantly related to both motor and cognitive impairment, with the cognitive effect being compounded by increasing age. Decreased saccade amplitude, meanwhile, was primarily related to motor impairment. When assessed by discrete cognitive categories, all of the PD groups showed reduced saccadic amplitude relative to controls. Saccadic latencies, meanwhile, were abnormally prolonged only in the PD-MCI and PDD groups (the control and PDN groups were similar to each other). Latency in the overlap task was particularly sensitive to increasing motor and cognitive impairment. We conclude that reflexive saccades in PD are subtly decreased in amplitude even early in the disease process. Prolonged saccade latency, meanwhile, tends to occur later in the disease process, in the presence of more substantial motor and cognitive impairment, and greater age. The progressive impairment of reflexive saccades, and the differential onset of amplitude and latency impairments, may make them a useful objective tool for assessing disease status.

Coenzyme Q10 deficiency in patients with Parkinson's disease

Reactive oxygen species (ROS) are well known to contribute to the pathophysiology of Parkinson's disease (PD). Clinical trials of antioxidants are currently underway in PD patients, however, antioxidant research has been hindered by a lack of peripheral biomarkers.

METHODS

Twenty-two patients with PD elected to have a novel antioxidant assessment (Functional Intracellular Assay (FIA), SpectraCell Lab, Houston, TX) performed between 2004 and 2008. Each PD case was compared to four age- and gender-matched controls (n=88) in four separate, random iterations using laboratory data submitted during the same time period. Logistic regression was used to determine the odds of functional deficiency in antioxidant nutrients (i.e., glutathione, coenzyme Q10, selenium, vitamin E and alpha-lipoic acid) by case-control status. The proportion of cases with functional deficiency was also compared to that for controls by chi(2) test.

RESULTS

Compared to cases, PD patients had a significantly greater odds of deficiency in coenzyme Q10 status (OR: 4.7-5.4; 95% CI: 1.5-17.7; P=0.003-0.009) based on FIA results, but not of vitamin E, selenium, lipoic acid, or glutathione (all P>0.05). The proportion of cases with coenzyme Q10 deficiency was also significantly greater in cases than in controls (32-36% vs. 8-9%; P=0.0012-0.006).

CONCLUSIONS

Deficiency of coenzyme Q10 assessed via FIA should be explored as a potential peripheral biomarker of antioxidant status in PD.

Staging neurodegenerative disorders: structural, regional, biomarker, and functional progressions

The notion of staging in the neurodegenerative disorders is modulated by the constant and progressive loss of several aspects of brain structural integrity, circuitry, and neuronal processes. These destructive processes eventually remove individuals' abilities to perform at sufficient and necessary functional capacity at several levels of disease severity. The classification of (a) patients on the basis of diagnosis, risk prognosis, and intervention outcome, forms the basis of clinical staging, and (b) laboratory animals on the basis of animal model of brain disorder, extent of insult, and dysfunctional expression, provides the components for the clinical staging and preclinical staging, respectively, expressing associated epidemiological, biological, and genetic characteristics. The major focus of clinical staging in the present account stems from the fundamental notions of Braak staging as they describe the course and eventual prognosis for Alzheimer's disease, Lewy Body dementia, and Parkinson's disease. Mild cognitive impairment, which expresses the decline in episodic and semantic memory performance below the age-adjusted normal range without marked loss of global cognition or activities of daily living, and the applications of longitudinal magnetic resonance imaging, major instruments for the monitoring of either disease progression in dementia, present important challenges for staging concepts. Although Braak notions present the essential basis for further developments, current staging conceptualizations seem inadequate to comply with the massive influx of information dealing with neurodegenerative processes in brain, advanced both under clinical realities, and discoveries in the laboratory setting. The contributions of various biomarkers of disease progression, e.g., amyloid precursor protein, and neurotransmitter system imbalances, e.g., dopamine receptor supersensitivity and interactive propensities, await their incorporation into the existing staging models thereby underlining the ongoing, dynamic feature of the staging of brain disorders.

Three-dimensional magnetic resonance spectroscopic imaging in the substantia nigra of healthy controls and patients with Parkinson's disease

OBJECTIVES

To investigate the substantia nigra in patients with Parkinson's disease three-dimensional magnetic resonance spectroscopic imaging with high spatial resolution at 3 Tesla was performed. Regional variations of spectroscopic data between the rostral and caudal regions of the substantia nigra as well as the midbrain tegmentum areas were evaluated in healthy controls and patients with Parkinson's disease.

METHODS

Nine patients with Parkinson's disease and eight age- and gender-matched healthy controls were included in this study. Data were acquired by using three-dimensional magnetic resonance spectroscopic imaging measurements. The ratios between rostral and caudal voxels of the substantia nigra as well as the midbrain tegmentum areas were calculated for the main-metabolites N-acetyl aspartate, creatine, choline, and myo-inositol. Additionally, the metabolite/creatine ratios were calculated.

RESULTS

In all subjects spectra of acceptable quality could be obtained with a nominal voxel size of 0.252 ml. The calculated rostral-to-caudal ratios of the metabolites as well as of the metabolite/creatine ratios showed with exception of choline/creatine ratio significant differences between healthy controls and patients with Parkinson's disease.

CONCLUSIONS

The findings from this study indicate that regional variations in N-acetyl aspartate/creatine ratios in the regions of the substantia nigra may differentiate patients with Parkinson's disease and healthy controls.

Potential of cystamine and cysteamine in the treatment of neurodegenerative diseases

Neurodegenerative disorders are a subset of disabling pathologies characterized, in part, by a progressive and specific loss of certain brain cell populations. Current therapeutic approaches for the treatment of these disorders are mainly designed towards symptom management and do not manifestly block their typified neuronal loss. However, research conducted over the past decade has reflected the increasing interest and need to find disease-modifying molecules. Among the several neuroprotective agents emerging from experimental animal work, cystamine, as well as its reduced form cysteamine, have been identified as potential candidate drugs. Given the significant benefits observed in a Huntington's disease (HD) model, cysteamine has recently leaped to clinical trial. Here, we review the beneficial properties of these compounds as reported in animal studies, their mechanistic underpinnings, and their potential implications for the future treatment of patients suffering from neurodegenerative diseases, and more specifically for HD and Parkinson's disease (PD).

Cerebrospinal fluid biomarkers for Parkinson disease diagnosis and progression

OBJECTIVE

There is a clear need to develop biomarkers for Parkinson disease (PD) diagnosis, differential diagnosis of Parkinsonian disorders, and monitoring disease progression. We and others have demonstrated that a decrease in DJ-1 and/or α-synuclein in the cerebrospinal fluid (CSF) is a potential index for Parkinson disease diagnosis, but not for PD severity.

METHODS

Using highly sensitive and quantitative Luminex assays, we measured total tau, phosphorylated tau, amyloid beta peptide 1-42 (Aβ(1-42)), Flt3 ligand, and fractalkine levels in CSF in a large cohort of PD patients at different stages as well as healthy and diseased controls. The utility of these 5 markers was evaluated for disease diagnosis and severity/progression correlation alone, as well as in combination with DJ-1 and α-synuclein. The major results were further validated in an independent cohort of cross-sectional PD patients as well as in PD cases with CSF samples collected longitudinally.

RESULTS

The results demonstrated that combinations of these biomarkers could differentiate PD patients not only from normal controls but also from patients with Alzheimer disease (AD) and multiple system atrophy. Particularly, with CSF Flt3 ligand, PD could be clearly differentiated from multiple system atrophy, a disease that overlaps with PD clinically, with excellent sensitivity (99%) and specificity (95%). In addition, we identified CSF fractalkine/Aβ(1-42) that positively correlated with PD severity in cross-sectional samples as well as with PD progression in longitudinal samples.

INTERPRETATION

We have demonstrated that this panel of 7 CSF proteins could aid in Parkinson disease diagnosis, differential diagnosis, and correlation with disease severity and progression.

Metallomic profiling and linkage map analysis of early Parkinson's disease: a new insight to aluminum marker for the possible diagnosis

BACKGROUND

Parkinson's disease (PD) is the most common neurodegenerative disorder. The diagnosis of PD is challenging and currently none of the biochemical tests have proven to help in diagnosis. Serum metallomic analysis may suggest the possibility of diagnosis of PD.

METHODOLOGY/RESULTS

The metallomic analysis was targeted on 31 elements obtained from 42 healthy controls and 45 drug naive PD patients using ICP-AES and ICP-MS to determine the concentration variations of elements between PD and normal. The targeted metallomic analysis showed the significant variations in 19 elements of patients compared to healthy control (p<0.04). The partial least squares discriminant analysis (PLS-DA) showed aluminium, copper, iron, manganese and zinc are the key elements, contributes the separation of PD patients from control samples. The correlation coefficient analysis and element-element ratio confirm the imbalance of inter-elements relationship in PD patients' serum. Furthermore, elements linkage map analysis showed aluminium is a key element involved in triggering of phosphorus, which subsequently lead to imbalance of homeostatic in PD serum. The execution of neural network using elements concentrations provides 95% accuracy in detection of disease.

CONCLUSIONS/SIGNIFICANCE

These results suggest that there is a disturbance in the elements homeostasis and inter-elements relationship in PD patients' serum. The analysis of serum elements helps in linking the underlying cellular processes such as oxidative stress, neuronal dysfunction and apoptosis, which are the dominating factors in PD. Also, these results increase the prospect of detection of early PD from serum through neural network algorithm.