Cognitive Impairment in Parkinson's Disease: Epidemiology, Clinical Profile, Protective and Risk Factors

Risk of impairment in cognitive instrumental activities of daily living for sexual and gender minority adults with reported Parkinson's disease

Objective: To investigate the risk of impairment in cognitive instrumental activities of daily living (IADL) for people with Parkinson's (PwP) identifying as sexual and/or gender minorities (SGM). Method: Data were obtained from Fox Insight, an online, longitudinal study with self/informant-report questionnaires from PwP and people without Parkinson's. Groups consisted of PwP without cognitive IADL impairment at baseline, identifying as (1) SGM with female sex assigned at birth (SGM-F, n = 75); (2) cisgender, heterosexual with female sex assigned at birth (CH-F, n = 2046); (3) SGM with male sex assigned at birth (SGM-M, n = 84); (4) cisgender, heterosexual with male sex assigned at birth (CH-M, n = 2056). Impairment in cognitive IADL was based on Penn Parkinson's Daily Activities Questionnaire-15 (PDAQ-15). Group differences for PDAQ-15 and impairment likelihood during follow-up were assessed with unadjusted models and adjusting for variables that differed between the groups. Results: SGM-F were the youngest at Parkinson's diagnosis; SGM-M had the lowest PDAQ-15 at baseline (p ≤ .014 for all). Scores declined more for males than females in unadjusted and adjusted models (p < .001 for both). In unadjusted models, SGM-M had a higher impairment risk than PwP identifying as cisgender and heterosexual (p ≤ .018). In adjusted models, females had a lower impairment risk than males (p < .001). Age, education, and discrimination level were significant moderators (p < .001 for all). Conclusions: SGM-M can be at a higher risk for impairment in cognitive IADL, associated with social determinants. Female sex assigned at birth may be associated with a lower level of impairment risk, although this advantage can disappear with social determinants.

Association between loneliness and cognitive function, and brain volume in community-dwelling elderly

Introduction

We investigated the relationship between loneliness, cognitive impairment, and regional brain volume among elderly individuals residing in the Korean community.

Methods

Data from the ARIRANG aging-cognition sub-cohort, collected between 2020 and 2022, were utilized for the present study. Loneliness was assessed using the UCLA-Loneliness Scale (UCLA-LS) questionnaire and the relevant item from Center for Epidemiologic Studies Depression Scale Korean version (CES-D-K). Cognitive impairment was measured through Mini-Mental State Examination (K-MMSE-2) and Seoul Neuropsychological Screening Battery (SNSB-C), with five sub-categories: attention, memory, visuospatial function, language, and executive function. Logistic regression was employed for prevalence ratios related to cognitive impairment, while linear regression was used for regional brain volume including white matter hyperintensity (WMH) and cortical thickness.

Results

Our analysis involved 785 participants (292 men and 493 women). We observed increased cognitive impairment assessed by K-MMSE-2 [UCLA-LS: odds ratio (OR) 3.133, 95% confidence interval (CI) 1.536-6.393; loneliness from CES-D: OR 2.823, 95% CI 1.426-5.590] and SNSB-C total score (UCLA-LS: OR 2.145, 95% CI 1.304-3.529) in the lonely group compared to the non-lonely group. Specifically, the lonely group identified by UCLA-LS showed an association with declined visuospatial (OR 1.591, 95% CI 1.029-2.460) and executive function (OR 1.971, 95% CI 1.036-3.750). The lonely group identified by CES-D-K was associated with impaired memory (OR 1.577, 95% CI 1.009-2.466) and executive function (OR 1.863, 95% CI 1.036-3.350). In the regional brain volume analysis, loneliness was linked to reduced brain volume in frontal white matter (left: -1.24, 95% CI -2.37 ∼-0.12; right: -1.16, 95% CI -2.31 ∼ -0.00), putamen (left: -0.07, 95% CI -0.12 ∼-0.02; right: -0.06, 95% CI -0.11 ∼-0.01), and globus pallidus (-15.53, 95% CI -30.13 ∼-0.93). There was no observed association in WMH and cortical thickness.

Conclusion

Loneliness is associated with cognitive decline and volumetric reduction in the frontal white matter, putamen, and globus pallidus.

Neurocognitive Impairment and Social Cognition in Parkinson's Disease Patients

In addition to motor symptoms, neurocognitive impairment (NCI) affects patients with prodromal Parkinson's disease (PD). NCI in PD ranges from subjective cognitive complaints to dementia. The purpose of this review is to present the available evidence of NCI in PD and highlight the heterogeneity of NCI phenotypes as well as the range of factors that contribute to NCI onset and progression. A review of publications related to NCI in PD up to March 2023 was performed using PubMed/Medline. There is an interconnection between the neurocognitive and motor symptoms of the disease, suggesting a common underlying pathophysiology as well as an interconnection between NCI and non-motor symptoms, such as mood disorders, which may contribute to confounding NCI. Motor and non-motor symptom evaluation could be used prognostically for NCI onset and progression in combination with imaging, laboratory, and genetic data. Additionally, the implications of NCI on the social cognition of afflicted patients warrant its prompt management. The etiology of NCI onset and its progression in PD is multifactorial and its effects are equally grave as the motor effects. This review highlights the importance of the prompt identification of subjective cognitive complaints in PD patients and NCI management.

Novel Findings on CCR1 Receptor in CNS Disorders: A Pathogenic Marker Useful in Controlling Neuroimmune and Neuroinflammatory Mechanisms in Parkinson's Disease

Parkinson's disease (PD) is recognized as the second most common neurodegenerative disease worldwide. Even if PD etiopathogenesis is not yet fully understood, in recent years, it has been advanced that a chronic state of inflammation could play a decisive role in the development of this pathology, establishing the close link between PD and neuroinflammation. In the broad panorama of inflammation and its several signaling pathways, the C-C chemokine receptor type 1 (CCR1) could play a key pathogenic role in PD progression, and could constitute a valuable target for the development of innovative anti-PD therapies. In this study, we probed the neuroprotective properties of the CCR1 antagonist BX471 compound in a mouse model of MPTP-induced nigrostriatal degeneration. BX471 treatments were performed intraperitoneally at a dose of 3 mg/kg, 10 mg/kg, and 30 mg/kg, starting 24 h after the last injection of MPTP and continuing for 7 days. From our data, BX471 treatment strongly blocked CCR1 and, as a result, decreased PD features, also reducing the neuroinflammatory state by regulating glial activation, NF-κB pathway, proinflammatory enzymes, and cytokines overexpression. Moreover, we showed that BX471's antagonistic action on CCR1 reduced the infiltration of immune cells, including mast cells and lymphocyte T activation. In addition, biochemical analyses carried out on serum revealed a considerable increase in circulating levels of CCR1 following MPTP-induced PD. In light of these findings, CCR1 could represent a useful pathological marker of PD, and its targeting could be a worthy candidate for the future development of new immunotherapies against PD.

Association Between Baseline Gait Parameters and Future Fall Risk in Patients With De Novo Parkinson's Disease: Forward Versus Backward Gait

BACKGROUND AND PURPOSE

Falls are not uncommon even in patients with early stages of Parkinson's disease (PD). The aims of this study were to determine the relationships between gait parameters and falls and identify crucial gait parameters for predicting future falls in patients with de novo PD.

METHODS

We prospectively recruited patients with de novo PD, and evaluated their baseline demographics, global cognitive function on the Montreal Cognitive Assessment test, and parkinsonian motor symptoms including their subtypes. Both forward gait (FG) and backward gait (BG) were measured using the GAITRite system. The history of falls in consecutive patients with de novo PD was examined along with 1 year of follow-up data.

RESULTS

Among the 76 patients with de novo PD finally included in the study, 16 (21.1%) were classified as fallers. Fallers had slower gait and shorter stride for FG and BG parameters than did non-fallers, while stride-time variability was greater in fallers but only for BG. Multivariable logistic regression analysis revealed that slow gait was an independent risk factor in BG.

CONCLUSIONS

Among the patients with de novo PD, gait speed and stride length were more impaired for both FG and BG in fallers than in non-fallers. It was particularly notable that slow BG was significantly associated with future fall risk, indicating that BG speed is a potential biomarker for predicting future falls in patients with early-stage PD.

Protective effect of sterubin against neurochemical and behavioral impairments in rotenone-induced Parkinson's disease

This study was conducted to evaluate how sterubin affects rotenone-induced Parkinson's disease (PD) in rats. A total of 24 rats were distributed into 4 equal groups: normal saline control and rotenone control were administered saline or rotenone (ROT), respectively, orally; sterubin 10 received ROT + sterubin 10 mg/kg po; and sterubin alone was administered to the test group (10 mg/kg). Rats of the normal saline and sterubin alone groups received sunflower oil injection (sc) daily, 1 h after receiving the treatments cited above, while rats of the other groups received rotenone injection (0.5 mg/kg, sc). The treatment was continued over the course of 28 days daily. On the 29th day, catalepsy and akinesia were assessed. The rats were then euthanized, and the brain was extracted for estimation of endogenous antioxidants (MDA: malondialdehyde, GSH: reduced glutathione, CAT: catalase, SOD: superoxide dismutase), nitrative (nitrite) stress markers, neuroinflammatory cytokines, and neurotransmitter levels and their metabolites (3,4-dihydroxyphenylacetic acid (DOPAC), dopamine (DA), norepinephrine (NE), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and homovanillic acid (HVA)). Akinesia and catatonia caused by ROT reduced the levels of endogenous antioxidants (GSH, CAT, and SOD), elevated the MDA level, and altered the levels of nitrites, neurotransmitters, and their metabolites. Sterubin restored the neurobehavioral deficits, oxidative stress, and metabolites of altered neurotransmitters caused by ROT. Results demonstrated the anti-Parkinson's activities of sterubin in ROT-treated rats.

Ethnoracial differences for caregiving burden in Parkinson's disease

INTRODUCTION

Caregivers play an important role in Parkinson's disease (PD) treatment, especially as the disease progresses. As the symptom profile and needs of people with PD (PwP) differ across ethnoracial groups, whether caregiving needs also differ for different ethnoracial groups should be investigated.

METHODS

Data were obtained from the Parkinson's Foundation funded Parkinson's Outcomes Project for PwP identifying as Hispanic (n = 495), non-Hispanic Asian (n = 170), non-Hispanic Black (n = 162), or non-Hispanic White (n = 7687). Cross-sectional and longitudinal total Multidimensional Caregiver Strain Index (MCSI) and domain-specific scores for caregiving burden were compared across the ethnoracial groups. Effect of demographics and clinical variables, interaction of these variables with ethnoracial groups for caregiver burden was assessed.

RESULTS

Care partners of PwP identifying as non-Hispanic Asian experienced the most burden. PwP identifying as non-Hispanic White were oldest, yet their care partners experienced the least burden. Care partners of PwP identifying as non-Hispanic Asian experienced more burden in physical and social domains, care partners of PwP identifying as Hispanic experienced more burden in financial and elder demanding/manipulative domains. Over time, burden increased similarly across the ethnoracial groups. Effect of frequency of falls, hospital admission, neuropsychiatric disorder and social support on burden over time differed across the groups.

CONCLUSION

PwP from different ethnoracial groups can experience different levels of caregiving burden. Predictors for caregiving burden, such as social support and falls can have different impacts based on ethnicity and race. Caregiver needs should also be assessed and culturally competent support should be provided to benefit all affected by PD.

Calprotectin in Parkinsonian disease: Anticipation and dedication

Parkinson's disease (PD) is a neurodegenerative disease due to degeneration of dopaminergic neurons (DNs) in the substantia nigra pars compacta (SNpc). PD is characterized by motor and non-motor symptoms. Non-motor symptoms such as constipation and dysfunction of gastrointestinal tract (GIT) motility together with medications used in the management of PD affect gut microbiota. Alterations of gut microbiota with development of gut dyspiosis can induce momentous changes in gut barrier with subsequent systemic inflammation and induction of neuroinflammation. It has been shown that calprotectin which reflect intestinal inflammation and gut barrier injury are augmented in PD. Therefore, this review aims to elucidate the possible role of gut barrier injury and associated dysbiois in PD neuropathology, and how calprotectin reflects gut barrier injury in PD. Benefit of this review was to elucidate that high fecal calprotectin level in PD patients indicated gut dysbiosis and intestinal inflammation. Early increment of fecal calprotectin indicates the development of gut dysbiosis and/or gut-barrier injury which may precede motor symptoms by decades. Thus, fecal calprotectin could be a diagnostic and prognostic biomarker in PD. preclinical and clinical studies are warranted in this regard to emphasize the potential role of fecal calprotectin in PD neuropathology.

Insulin signaling in dopaminergic neurons regulates extended memory formation in Caenorhabditis elegans

Insulin alters several brain functions, and perturbations in insulin levels could be a precipitating factor for Parkinson's disease, a disease associated with the degeneration of dopaminergic neurons. It is unclear whether insulin alters the dopamine signaling pathway and modulates learning and memory. In Caenorhabditis elegans, daf-2 insulin receptor mutants have extended memory when trained for olfactory adaptation. In this study, we show that the absence of daf-2 receptors in dopamine neurons results in this unusual learning behavior. Our results show that insulin function in memory is dopamine-dependent. In the absence of the daf-2 receptor, the calcium influx in dopamine neurons shows an altered pattern resulting in memory recall for an extended period. These results indicate that learning and memory involve insulin-dopamine crosstalk. Imbalances in this pathway result in changes in memory recall.

Genetic variation in the dopamine system is associated with mixed-strategy decision-making in patients with Parkinson's disease

Decision-making during mixed-strategy games requires flexibly adapting choice strategies in response to others' actions and dynamically tracking outcomes. Such decisions involve diverse cognitive processes, including reinforcement learning, which are affected by disruptions to the striatal dopamine system. We therefore investigated how genetic variation in dopamine function affected mixed-strategy decision-making in Parkinson's disease (PD), which involves striatal dopamine pathology. Sixty-six PD patients (ages 49-85, Hoehn and Yahr Stages 1-3) and 22 healthy controls (ages 54-75) competed in a mixed-strategy game where successful performance depended on minimizing choice biases (i.e., flexibly adapting choices trial by trial). Participants also completed a fixed-strategy task that was matched for sensory input, motor outputs and overall reward rate. Factor analyses were used to disentangle cognitive from motor aspects within both tasks. Using a within-subject, multi-centre design, patients were examined on and off dopaminergic therapy, and genetic variation was examined via a multilocus genetic profile score representing the additive effects of three single nucleotide polymorphisms (SNPs) that influence dopamine transmission: rs4680 (COMT Val158 Met), rs6277 (C957T) and rs907094 (encoding DARPP-32). PD and control participants displayed comparable mixed-strategy choice behaviour (overall); however, PD patients with genetic profile scores indicating higher dopamine transmission showed improved performance relative to those with low scores. Exploratory follow-up tests across individual SNPs revealed better performance in individuals with the C957T polymorphism, reflecting higher striatal D2/D3 receptor density. Importantly, genetic variation modulated cognitive aspects of performance, above and beyond motor function, suggesting that genetic variation in dopamine signalling may underlie individual differences in cognitive function in PD.

Associations of Apolipoprotein ε4 Genotypes with Motor and Nonmotor Symptoms in Parkinson's Disease: A Cross-Sectional Study

Background

The apolipoprotein E (APOE) ε4 allele has been associated with cognitive decline in Parkinson's disease (PD), but little is known about its relationship with motor and other nonmotor symptoms and whether APOE ε4 retains an influence on cognition when other factors are considered.

Objective

To investigate the impact of APOE ε4 on motor/nonmotor symptoms and its relationship with other factors affecting cognition in individuals with PD.

Methods

We analyzed data from 7616 individuals, comparing motor/nonmotor symptoms in different APOE genotypes using binary logistic regression. Multivariate logistic regression examined factors associated with cognitive impairments, including APOE ε4, Geriatric Depression Scale (GDS) score, Non-motor Symptom Questionnaire (NMS) score, Movement Disorder Society-Sponsored Revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part II score, and physical activity level.

Results

APOE ε4 heterozygosity was modestly associated with lower cognitive scores (odds ratio [OR], 0.92; 95% confidence interval [CI], 0.87-0.99), whereas no significant association was found for any other nonmotor and motor symptoms. However, in multivariate analysis, cognitive impairment was associated with higher GDS (OR, 1.28; 95% CI, 1.23-1.34), NMS (OR, 1.22; 95% CI, 1.19-1.25), and MDS-UPDRS Part II (OR, 1.07; 95% CI, 1.06-1.09) scores, whereas physical activity was negatively associated (OR, 0.99; 95% CI, 0.98-0.99). APOE ε4 was no longer significant after adjusting for these factors.

Conclusions

There is a link between cognition and APOE ε4 in patients with PD; however, when considering multiple factors, APOE ε4 plays a subordinate role. Other factors, such as depression, physical activity, and other nonmotor symptoms, demonstrate a stronger influence on cognitive impairment.

Everyday technology use among people with Parkinson's disease

OBJECTIVES

To explore the relevance of and ability to use everyday technology (ET) among people with Parkinson's Disease (PD) and to explore associations between ET use and global cognition and motor ability.

MATERIALS AND METHODS

Cross-sectional data was collected from 34 people with PD using the Short Everyday Technology Use Questionnaire+ (S-ETUQ+), the Movement Disorder Society-Unified Parkinson's Disease Rating Scale and the Montreal Cognitive Assessment (MoCA).

RESULTS

Out of 41 ETs in the S-ETUQ+, the mean number perceived as relevant was 27.5 (min-max 19-35, SD 3.6). A good ability to use ET was reported where many ETs had a challenge measure below participants' ability to use them. A strong positive correlation between the ability to use ET and global cognition (MoCA) (r = .676, p = <0.01) was shown.

CONCLUSIONS

ET use has become integrated into everyday life and is important for participation. This study showed a high relevance of and good ability to use ET and a correlation between ET use and global cognition among people with mild-moderate PD. Evaluation and support to use ET in PD are important for maintaining independence and participation, especially among those with cognitive decline.

Recipient Reaction and Composition of Autologous Sural Nerve Tissue Grafts into the Human Brain

Parkinson's disease (PD) is a severe neurological disease for which there is no effective treatment or cure, and therefore it remains an unmet need in medicine. We present data from four participants who received autologous transplantation of small pieces of sural nerve tissue into either the basal forebrain containing the nucleus basalis of Meynert (NBM) or the midbrain substantia nigra (SN). The grafts did not exhibit significant cell death or severe host-tissue reaction up to 55 months post-grafting and contained peripheral cells. Dopaminergic neurites showed active growth in the graft area and into the graft in the SN graft, and cholinergic neurites were abundant near the graft in the NBM. These results provide a histological basis for changes in clinical features after autologous peripheral nerve tissue grafting into the NBM or SN in PD.

Nanowired delivery of antibodies to tau and neuronal nitric oxide synthase together with cerebrolysin attenuates traumatic brain injury induced exacerbation of brain pathology in Parkinson's disease

Concussive head injury (CHI) is one of the major risk factors for developing Parkinson's disease in later life of military personnel affecting lifetime functional and cognitive disturbances. Till date no suitable therapies are available to attenuate CHI or PD induced brain pathology. Thus, further exploration of novel therapeutic agents are highly warranted using nanomedicine in enhancing the quality of life of veterans or service members of US military. Since PD or CHI induces oxidative stress and perturbs neurotrophic factors regulation associated with phosphorylated tau (p-tau) deposition, a possibility exists that nanodelivery of agents that could enhance neurotrophic factors balance and attenuate oxidative stress could be neuroprotective in nature. In this review, nanowired delivery of cerebrolysin-a balanced composition of several neurotrophic factors and active peptide fragments together with monoclonal antibodies to neuronal nitric oxide synthase (nNOS) with p-tau antibodies was examined in PD following CHI in model experiments. Our results suggest that combined administration of nanowired antibodies to nNOS and p-tau together with cerebrolysin significantly attenuated CHI induced exacerbation of PD brain pathology. This combined treatment also has beneficial effects in CHI or PD alone, not reported earlier.

Gene Panel Sequencing Analysis Revealed a Strong Contribution of Rare Coding Variants to the Risk of Parkinson's Disease in Sporadic Moroccan Patients

Parkinson's disease (PD) is a neurodegenerative movement disorder which can be either familial or sporadic. While it is well known that monogenic mutations are not a very common cause of PD, GWAS studies have shown that an additional fraction of the PD heritability could be explained by rare or common variants. To identify the rare variants that could influence the risk of PD in the Moroccan population, a cohort of 94 sporadic PD patients negative for the LRRK2 G2019S mutation was subjected to NGS gene panel sequencing, and gene dosage using the MLPA method. Mean age of onset at enrollment was 51.7 ± 11.51 years, and 60% of patients were men. We identified 70 rare variants under 0.5% of frequency in 16 of the 20 genes analyzed, of which 7 were novel. Biallelic disease-causing variants in genes with recessive inheritance were found in 5 PD cases (5.31%), whereas 13 patients (13.8%) carried likely pathogenic variants in genes with dominant inheritance. Moreover, 8 patients (8.5%) carried a single variant in MAPT or POLG, whereas co-occurrence of rare variants involving more than one gene was observed in 28 patients (30%). PD patients with variants in recessive genes had a younger mean age at onset than patients with dominant ones (33.40 (12.77) vs. 53.15 (6.63), p < 0.001), while their clinical features were similar. However, patients with rare variants in the risk factor genes or in more than one gene tended to have less resting tremor (p < 0.04), but more dystonia (p < 0.006) and dementia (p < 0.002) than those without any rare variants in known PD-associated genes. Our results showed a significant enrichment of rare variants particularly in LRRK2, VPS13C, POLG, and MAPT and underline their impact on the risk of sporadic form of the disease.

The Increase of Theta Power and Decrease of Alpha/Theta Ratio as a Manifestation of Cognitive Impairment in Parkinson's Disease

In this study, we aim to assess and examine cognitive functions in Parkinson's Disease patients using EEG recordings, with a central focus on characteristics associated with a cognitive decline. Based on neuropsychological evaluation using Mini-Mental State Examination, Montreal Cognitive Assessment, and Addenbrooke's Cognitive Examination-III, 98 participants were divided into three cognitive groups. All the particpants of the study underwent EEG recordings with spectral analysis. The results revealed an increase in the absolute theta power in patients with Parkinson's disease dementia (PD-D) compared to cognitively normal status (PD-CogN, p=0.00997) and a decrease in global relative beta power in PD-D compared to PD-CogN (p=0.0413). An increase in theta relative power in the left temporal region (p=0.0262), left occipital region (p=0.0109), and right occipital region (p=0.0221) were observed in PD-D compared to PD-N. The global alpha/theta ratio and global power spectral ratio significantly decreased in PD-D compared to PD-N (p = 0.001). In conclusion, the increase in relative theta power and the decrease in relative beta power are characteristic changes in EEG recordings in PD patients with cognitive impairment. Identifying these changes can be a useful biomarker and a complementary tool in the neuropsychological diagnosis of cognitive impairment in Parkinson's Disease.

Sex and Gender Differences in Parkinson's Disease

The lower prevalence of Parkinson disease (PD) in females is not well understood but may be partially explained by sex differences in nigrostriatal circuitry and possible neuroprotective effects of estrogen. PD motor and nonmotor symptoms differ between sexes, and women experience disparities in care including undertreatment with DBS and less access to caregiving. Our knowledge about PD in gender diverse individuals is limited. Future studies should improve our understanding of the role of hormone replacement therapy in PD, address gender-based inequities in PD care and expand our understanding of PD in SGM and marginalized communities.

Application of novel hybrid machine learning systems and radiomics features for non-motor outcome prediction in Parkinson's disease

Objectives.Parkinson's disease (PD) is a complex neurodegenerative disorder, affecting 2%-3% of the elderly population. Montreal Cognitive Assessment (MoCA), a rapid nonmotor screening test, assesses different cognitive dysfunctionality aspects. Early MoCA prediction may facilitate better temporal therapy and disease control. Radiomics features (RF), in addition to clinical features (CF), are indicated to increase clinical diagnoses, etc, bridging between medical imaging procedures and personalized medicine. We investigate the effect of RFs, CFs, and conventional imaging features (CIF) to enhance prediction performance using hybrid machine learning systems (HMLS).Methods.We selected 210 patients with 981 features (CFs, CIFs, and RFs) from the Parkinson's Progression-Markers-Initiative database. We generated 4 datasets, namely using (i), (ii) year-0 (D1) or year-1 (D2) features, (iii) longitudinal data (D3, putting datasets in years 0 and 1 longitudinally next to each other), and (iv) timeless data (D4, effectively doubling dataset size by listing both datasets from years 0 and 1 separately). First, we directly applied 23 predictor algorithms (PA) to the datasets to predict year-4 MoCA, which PD patients this year have a higher dementia risk. Subsequently, HMLSs, including 14 attribute extraction and 10 feature selection algorithms followed by PAs were employed to enhance prediction performances. 80% of all datapoints were utilized to select the best model based on minimum mean absolute error (MAE) resulting from 5-fold cross-validation. Subsequently, the remaining 20% was used for hold-out testing of the selected models.Results.When applying PAs without ASAs/FEAs to datasets (MoCA outcome range: [11,30]), Adaboost achieved an MAE of 1.74 ± 0.29 on D4 with a hold-out testing performance of 1.71. When employing HMLSs, D4 + Minimum_Redundancy_Maximum_Relevance (MRMR)+K_Nearest_Neighbor Regressor achieved the highest performance of 1.05 ± 0.25 with a hold-out testing performance of 0.57.Conclusion.Our study shows the importance of using larger datasets (timeless), and utilizing optimized HMLSs, for significantly improved prediction of MoCA in PD patients.

Race and Ethnicity in Lewy Body Dementia: A Narrative Review

Lewy body dementia is the third most common and costliest type of dementia. It is an umbrella term for dementia with Lewy bodies and Parkinson's disease dementia, both of which place a substantial burden on the person and society. Recent findings outline ethnoracial differences in dementia risk. Delayed and misdiagnosis across ethnoracial groups contribute to higher levels of burden. In this context, we aimed to summarize current knowledge, gaps, and unmet needs relating to race and ethnicity in Lewy body dementia. In this narrative review, we provide an overview of studies on Lewy body dementia focusing on differences across ethnoracial groups and outline several recommendations for future studies. The majority of the findings comparing different ethnoracial groups were from North American sites. There were no differences in clinical prevalence and progression across ethnoracial groups. Compared to people identifying as non-Hispanic White, co-pathologies were more common and clinical diagnostic accuracy was lower for people identifying as Black. Co-morbidities (e.g., diabetes, hypertension) were more common and medication use rates (e.g., antidepressants, antiparkinsonian agents) were lower for people identifying as Black or Hispanic compared to people identifying as White. More than 90% of clinical trial participants identified as non-Hispanic White. Despite increasing efforts to overcome disparities in Alzheimer's disease and related dementias, inclusion of individuals from minoritized communities in Lewy body dementia studies continues to be limited and the findings are inconclusive. Representation of diverse populations is crucial to improve the diagnostic and therapeutic efforts in Lewy body dementia.

Spontaneous Object Exploration in a Recessive Gene Knockout Model of Parkinson's Disease: Development and Progression of Object Recognition Memory Deficits in Male Pink1-/- Rats

Cognitive impairments appear at or before motor signs in about one third of patients with Parkinson's disease (PD) and have a cumulative prevalence of roughly 80% overall. These deficits exact an unrelenting toll on patients' quality and activities of daily life due in part to a lack of available treatments to ameliorate them. This study used three well-validated novel object recognition-based paradigms to explore the suitability of rats with knockout of the PTEN-induced putative kinase1 gene (Pink1) for investigating factors that induce cognitive decline in PD and for testing new ways to mitigate them. Longitudinal testing of rats from 3-9 months of age revealed significant impairments in male Pink1-/- rats compared to wild type controls in Novel Object Recognition, Novel Object Location and Object-in-Place tasks. Task-specific differences in the progression of object discrimination/memory deficits across age were also seen. Finally, testing using an elevated plus maze, a tapered balance beam and a grip strength gauge showed that in all cases recognition memory deficits preceded potentially confounding impacts of gene knockout on affect or motor function. Taken together, these findings suggest that knockout of the Pink1 gene negatively impacts the brain circuits and/or neurochemical systems that support performance in object recognition tasks. Further investigations using Pink1-/- rats and object recognition memory tasks should provide new insights into the neural underpinnings of the visual recognition memory and visuospatial information processing deficits that are often seen in PD patients and accelerate the pace of discovery of better ways to treat them.

Psychometric properties and construct validity of the Parkinson’s Disease-Cognitive Rating Scale (PD-CRS) in Colombia

Background

Cognitive impairment is frequent among people living with Parkinson’s disease: up to 40% of patients exhibit symptoms of mild cognitive impairment and 25% meet the criteria for dementia. Parkinson’s Disease Cognitive Rating Scale (PD-CRS) is one of the recommended scales by the Movement Disorders Society Task Force for level 1 screening of dementia. However, its psychometric properties have not been studied in the Colombian population.

Methods

A cross-sectional study was conducted on 100 patients with Parkinson’s disease diagnosed by a movement disorders neurologist. Patients were evaluated with PD-CRS and MoCA. Principal component analysis was conducted, and then confirmatory factor analysis was implemented through the maximum-likelihood method. Internal consistency was evaluated using Cronbach α. Convergent and divergent validity were also calculated and concurrent validity with the MoCA was assessed.

Results

62% were males. Their median age was 68 years (IQR 57–74) and the median disease duration was 4 years (IQR 2–9). 77% were classified in early stages (Hoehn and Yahr stage ≤ 2), while the MDS-UPDRS part III score was 25 (IQR 15.5–38). In the principal component factor analysis, the pattern matrix unveiled a mnesic and a non-mnesic domain. Confirmatory factor analysis showed similar explanatory capacity (λ ≥ 0.50) for items other than naming (λ = 0.34). Cronbach’s α for the full 9-items instrument was 0.74. MoCA and PD-CRS total scores were correlated (ρ = 0.71, p = 0.000). Assuming a cut-off score of 62 points, there is an agreement of 89% with the definition of dementia by MoCA for Colombia (κ = 0.59; p = 0.000).

Conclusion

PD-CRS has acceptable psychometric properties for the Colombian population and has significant correlation and agreement with a validated scale (MoCA).

APOE E4 is associated with impaired self-declared cognition but not disease risk or age of onset in Nigerians with Parkinson's disease

The relationship between APOE polymorphisms and Parkinson's disease (PD) in black Africans has not been previously investigated. We evaluated the association between APOE polymorphic variability and self-declared cognition in 1100 Nigerians with PD and 1097 age-matched healthy controls. Cognition in PD was assessed using the single item cognition question (item 1.1) of the MDS-UPDRS. APOE genotype and allele frequencies did not differ between PD and controls (p > 0.05). No allelic or genotypic association was observed between APOE and age at onset of PD. In PD, APOE ε4/ε4 conferred a two-fold risk of cognitive impairment compared to one or no ε4 (HR: 2.09 (95% CI: 1.13-3.89; p = 0.02)), while APOE ε2 was associated with modest protection against cognitive impairment (HR: 0.41 (95% CI 0.19-0.99, p = 0.02)). Of 773 PD with motor phenotype and APOE characterized, tremor-dominant (TD) phenotype predominated significantly in ε2 carriers (87/135, 64.4%) compared to 22.2% in persons with postural instability/gait difficulty (PIGD) (30/135) and 13.3% in indeterminate (ID) (18/135, 13.3%) (p = 0.037). Although the frequency of the TD phenotype was highest in homozygous ε2 carriers (85.7%), the distribution of motor phenotypes across the six genotypes did not differ significantly (p = 0.18). Altogether, our findings support previous studies in other ethnicities, implying a role for APOE ε4 and ε2 as risk and protective factors, respectively, for cognitive impairment in PD.

Alpha-Synuclein: The Spark That Flames Dopaminergic Neurons, In Vitro and In Vivo Evidence

Mitochondria, α-syn fibrils and the endo-lysosomal system are key players in the pathophysiology of Parkinson’s disease. The toxicity of α-syn is amplified by cell-to-cell transmission and aggregation of endogenous species in newly invaded neurons. Toxicity of α-syn PFF was investigated using primary cultures of dopaminergic neurons or on aged mice after infusion in the SNpc and combined with mild inhibition of GBA. In primary dopaminergic neurons, application of α-syn PFF induced a progressive cytotoxicity associated with mitochondrial dysfunction, oxidative stress, and accumulation of lysosomes suggesting that exogenous α-syn reached the lysosome (from the endosome). Counteracting the α-syn endocytosis with a clathrin inhibitor, dopaminergic neuron degeneration was prevented. In vivo, α-syn PFF induced progressive neurodegeneration of dopaminergic neurons associated with motor deficits. Histology revealed progressive aggregation of α-syn and microglial activation and accounted for the seeding role of α-syn, injection of which acted as a spark suggesting a triggering of cell-to-cell toxicity. We showed for the first time that a localized SNpc α-syn administration combined with a slight lysosomal deficiency and aging triggered a progressive lesion. The cellular and animal models described could help in the understanding of the human disease and might contribute to the development of new therapies.

Response times for reflexive saccades correlate with cognition in parkinson's disease, not disease severity or duration

Objective

Dementia is a common and serious non-motor symptom in Parkinson's disease (PD). We aimed to investigate the reflexive saccade in PD patients and explore its potential role as a biomarker for cognitive decline.

Methods

Using an infrared video-based eye tracker, we investigated reflexive saccades in 94 PD patients and 115 healthy controls (HCs). Saccadic parameters were compared between PD patients and HCs, and also among PD subgroups. The correlation of saccadic performance with disease duration, severity and cognition were further investigated.

Results

Compared with healthy controls, PD patients had prolonged and hypometric reflexive saccades even in early disease stage. Univariate and multivariate analysis showed that there was significant inverse relation between prolonged latency and MMSE in PD patients (P &lt; 0.05); tremor dominant PD patients were more likely to have decreased velocity than non-tremor-dominant PD patients (P &lt; 0.05); saccadic accuracy was found to have no significant relation with disease duration, H&amp;Y staging or MMSE.

Conclusion

Reflexive saccadic performance was abnormal in PD and worsened with cognitive decline. The negative correlation between prolonged latency and MMSE scores may make the reflexive saccade a potential predictor for cognitive decline in Parkinson's disease.

Can the prediction model using regression with optimal scale improve the power to predict the Parkinson's dementia?

BACKGROUND

Efficiently detecting Parkinson's disease (PD) with dementia (PDD) as soon as possible is an important issue in geriatric medicine.

AIM

To develop a model for predicting PDD based on various neuropsychological tests using data from a nationwide survey conducted by the Korean Centers for Disease Control and Prevention and to present baseline data for the early detection of PDD.

METHODS

This study comprised 289 patients who were 60 years or older with PD [110 with PDD and 179 Parkinson's Disease-Mild Cognitive Impairment (PD-MCI)]. Regre-ssion with optimal scaling (ROS) was used to identify independent relationships between the neuropsychological test results and PDD.

RESULTS

In the ROS analysis, Korean version of mini mental state ex-amination (MMSE) (KOREAN version of MMSE) (b = -0.52, SE = 0.16) and Hoehn and Yahr staging (b = 0.44, SE = 0.19) were significantly effective models for distinguishing PDD from PD-MCI (P < 0.05), even after adjusting for all of the Parkinson's motor symptom and neuropsychological test results. The optimal number of categories (scaling factors) for KOREAN version of MMSE and Hoehn and Yahr Scale was 10 and 7, respectively.

CONCLUSION

The results of this study suggest that among the various neuropsychological tests conducted, the optimal classification scores for KOREAN version of MMSE and Hoehn and Yahr Scale could be utilized as an effective screening test for the early discrimination of PDD from PD-MCI.

Accelerated long-term forgetting in neurodegenerative disorders: A systematic review of the literature

Accelerated Long-term Forgetting (ALF) is a memory deficit characterised by normal retention up to relatively short intervals (e.g., minutes, hours) with increased forgetting over longer periods (e.g., days, weeks). ALF is often underestimated due to a lack of common memory assessments beyond 30-60 min. The purpose of this review was to provide an overview of ALF occurrence in neurodegenerative disorders, evaluating whether it can be considered a cognitive deficit useful for diagnosing and monitoring patients. We included 19 experimental studies that investigated ALF in neurodegenerative disorders. Most papers were focused on Alzheimer's disease (AD) dementia and related forms of cognitive decline (Mild Cognitive Impairment, Subjective Cognitive decline, Pre-symptomatic subjects at risk of AD dementia). The major finding of the present work concerns the presence of ALF in very early forms of cognitive decline related to AD. These findings, supporting the hypothesis that ALF is a subtle and undetected hallmark of pre-clinical AD, highlights the importance of investigating forgetting over a longer period and devising standardised measures to be included in clinical practice.

The impact of cognitive impairment of individuals with Parkinson’s disease on their caregivers’ mental health: A systematic review protocol

Introduction

Parkinson’s disease is a motor disease, the second most common neurodegenerative disorder with cardinal symptoms including bradykinesia, rigidity, and rest tremor accompanied by cognitive difficulties. The caregivers play a crucial role for individuals with Parkinson’s disease; however, many of them may suffer from high caregiver burden and mental health deterioration. This protocol of a systematic review presents a methodology of the review about the impact of cognitive impairment of individuals with Parkinson’s disease on their caregivers’ mental health.

Material and methods

Research will be identified by combining electronic databases searching and hand searching. The following databases will be included: Medline, PsycInfo, Web of Sciences, Cochrane, CINAHL, Embase and Scopus. The inclusion and exclusion criteria followed to PECOS model. The population of informal caregivers is defined as family members providing care on a patient with Parkinson’s disease. Exposure is linked with the evaluation of a cognitive functioning and outcome is defined as mental health among caregivers of individuals with Parkinson’s disease. We will include two types of studies: observational and intervention. Both, screening and eligibility will be done by two independent reviewers. Study quality will be assessed by two authors independently. Data will be extracted by two reviewers independently and will follow a pre-pilot extraction form. Any discrepancies will be resolved by discussion or/and consultation with another reviewer. The synthesis without meta-analysis (SWiM) guidelines will be used to report on included studies data. The metanalysis with usage the statistical software R version 4.1.2 (2021-11-01) “Bird Hippie” and R metaphor package 3.0–2 of will be conducted if possible.

Discussion

The goal of this systematic review is to present the association between caregivers’ mental health problems and their proteges’ cognitive impairment. It will enable to identify the gaps in literature and its methodology giving the suggestions for further research.

Protocol registration

Protocol registration number in PROSPERO: CRD42022296670

Effects of Pramipexole Combined with Nerve Growth Factor on Cognitive Impairment and Urinary AD7c-NTP Expression in Patients with Parkinson’s Disease

Objective

To explore the effects of pramipexole combined with nerve growth factor (NGF) on cognitive impairment and urinary Alzheimer-associated neural thread protein (AD7c-NTP) expression in patients with Parkinson's disease (PD).

Methods

Fifty patients with PD treated in our hospital from February 2020 to April 2021 were enrolled. The patients were arbitrarily assigned into control group and study group. The former was treated with pramipexole, and the latter was treated with pramipexole combined with NGF. The efficacy, cognitive function, serum inflammatory factors, cortisol levels, serum macrophage migration inhibitory factor (MIF), brain-derived neurotrophic factor (BDNF), urine AD7c-NTP levels, and the incidence of adverse reactions were compared.

Results

First of all, the effective rate in the study group was higher compared to the control group (P < 0.05). After treatment, the cognitive function was enhanced, and the scores of Montreal cognitive assessment (MoCA) in the study group were higher compared to the control group (P < 0.05). The levels of serum IL-6, CRP, and TNF-α decreased after treatment, and the levels of serum IL-6, CRP, and TNF-α in the study group were remarkably lower compared to the control group (P < 0.05). In addition, the levels of serum DA, NE, and 5-HT increased after treatment, and the levels of serum DA, NE, and 5-HT in the study group were remarkably higher compared to the control group (P < 0.05). Then, the levels of serum MIF and urine AD7c-NTP decreased and BDNF increased after treatment, and the level of BDNF in the study group was higher compared to the control group, while the levels of serum MIF and urine AD7c-NTP in the study group were lower compared to the control group (P < 0.05). Finally, the adverse reactions were compared. The incidence of adverse reactions in the study group was lower compared to the control group, and the difference exhibited not statistically significant (16.00% vs. 24.00%, P > 0.05).

Conclusion

Pramipexole combined with NGF therapy not only can effectively strengthen the cognitive impairment of patients with PD and promote clinical efficacy and high safety but also can inhibit inflammatory state, regulate brain neurotransmitters, and reduce urinary AD7c-NTP levels.

Cascaded Deep Learning Frameworks in Contribution to the Detection of Parkinson’s Disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by motor impairment, as well as tremors, stiffness, and rigidity. Besides the typical motor symptomatology, some Parkinsonians experience non-motor symptoms such as hyposmia, constipation, urinary dysfunction, orthostatic hypotension, memory loss, depression, pain, and sleep disturbances. The correct diagnosis of PD cannot be easy since there is no standard objective approach to it. After the incorporation of machine learning (ML) algorithms in medical diagnoses, the accuracy of disease predictions has improved. In this work, we have used three deep-learning-type cascaded neural network models based on the audial voice features of PD patients, called Recurrent Neural Networks (RNN), Multilayer Perception (MLP), and Long Short-Term Memory (LSTM), to estimate the accuracy of PD diagnosis. A performance comparison between the three models was performed on a sample of the subjects’ voice biomarkers. Experimental outcomes suggested that the LSTM model outperforms others with 99% accuracy. This study has also presented loss function curves on the relevance of good-fitting models to the detection of neurodegenerative diseases such as PD.

Remote self-administration of digital cognitive tests using the Brief Assessment of Cognition: Feasibility, reliability, and sensitivity to subjective cognitive decline

Cognitive impairment is a common and pervasive feature of etiologically diverse disorders of the central nervous system, and a target indication for a growing number of symptomatic and disease modifying drugs. Remotely acquired digital endpoints have been recognized for their potential in providing frequent, real-time monitoring of cognition, but their ultimate value will be determined by the reliability and sensitivity of measurement in the populations of interest. To this end, we describe initial validation of remote self-administration of cognitive tests within a regulatorily compliant tablet-based platform. Participants were 61 older adults (age 55+), including 20 individuals with subjective cognitive decline (SCD). To allow comparison between remote (in-home) and site-based testing, participants completed 2 testing sessions 1 week apart. Results for three of four cognitive domains assessed demonstrated equivalence between remote and site-based tests, with high cross-modality ICCs (absolute agreement) for Symbol Coding (ICC = 0.75), Visuospatial Working Memory (ICC = 0.70) and Verbal Fluency (ICC > 0.73). Group differences in these domains were significant and reflected sensitivity to objective cognitive impairment in the SCD group for both remote and site-based testing (p < 0.05). In contrast, performance on tests of verbal episodic memory suggested inflated performance during unmonitored testing and indicate reliable use of remote cognitive assessments may depend on the construct, as well as the population being tested.

Establishing Equivalent Aerobic Exercise Parameters Between Early-Stage Parkinson's Disease and Pink1 Knockout Rats

BACKGROUND

Rodent Parkinson's disease (PD) models are valuable to interrogate neurobiological mechanisms of exercise that mitigate motor impairment. Translating these mechanisms to human PD must account for physical capabilities of the patient.

OBJECTIVE

To establish cardiovascular parameters as a common metric for cross-species translation of aerobic exercise impact.

METHOD

We evaluated aerobic exercise impact on heart rate (HR) in 21 early-stage PD subjects (Hoehn Yahr ≤1.5) exercising in non-contact boxing training for ≥3 months, ≥3x/week. In 4-month-old Pink1 knockout (KO) rats exercising in a progressively-increased treadmill speed regimen, we determined a specific treadmill speed that increased HR to an extent similar in human subjects.

RESULTS

After completing aerobic exercise for ∼30 min, PD subjects had increased HR∼35% above baseline (∼63% maximum HR). Motor and cognitive test results indicated the exercising subjects completed the timed up and go (TUG) and trail-making test (TMT-A) in significantly less time versus exercise-naïve PD subjects. In KO and age-matched wild-type (WT) rats, treadmill speeds of 8-10 m/min increased HR up to 25% above baseline (∼67% maximum HR), with no further increases up to 16 m/min. Exercised KO, but not WT, rats showed increased locomotor activity compared to an age-matched exercise-naïve cohort at 5 months old.

CONCLUSION

These proof-of-concept results indicate HR is a cross-species translation parameter to evaluate aerobic exercise impact on specific motor or cognitive functions in human subjects and rat PD models. Moreover, a moderate intensity exercise regimen is within the physical abilities of early-stage PD patients and is therefore applicable for interrogating neurobiological mechanisms in rat PD models.

Lower Blood Lipid Level Is Associated with the Occurrence of Parkinson's Disease: A Meta-Analysis and Systematic Review

BACKGROUND

The changes of blood lipid levels in patients with Parkinson's disease (PD) and its clinical relevance remain unclear. We aimed to evaluate the potential association of blood lipid and the occurrence of PD, to provide evidence to the clinical treatment and nursing care of PD.

METHODS

We searched PubMed, Medline, Web of Science, Cochrane Library, Wanfang Database, Weipu Database, and China National Knowledge Infrastructure for studies related to the blood lipid levels and PD until November 30, 2021. Two researchers independently screened the literature and extricated the data including the levels of total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C). Newcastle-Ottawa Scale (NOS) was used to evaluate the quality of included studies. RevMan5.3 and Stata 12.0 software were used for statistical processing and analysis.

RESULTS

A total of 15 cohort studies with 9740 participants involving 2032 PD patients and 7708 controls were included. Meta-analysis indicated that TC (SMD = -0.29, 95% CI -0.55∼-0.03, P=0.04), TG (SMD = -16.83, 95% CI -20.71∼-12.95, P < 0.001), HDL-C (SMD = -0.14, 95% CI -0.26∼-0.02, P < 0.001) and LDL-C (SMD = -0.26, 95% CI -0.50∼-0.01, P=0.04) level in the PD patients was significantly lower than that of health controls. Sensitivity analysis indicated that the results were stable. No significant publication bias was found between the synthesized outcomes.

CONCLUSIONS

Lower blood TC, TG, HDL-C, and LDL-C level are associated with the occurrence of PD. Limited by sample size and study population, further high-quality, large-sample clinical trials in different areas are needed to further determine the relationship between blood lipids and PD in the future.

"Accidental, really?" Attributional bias in patients with Parkinson's disease

INTRODUCTION

Among the cognitive domains impaired in Parkinson's disease (PD), social cognition has received particular attention in recent years. Nevertheless, attributional bias, a social-cognitive subdomain, has not yet been studied in this population, despite its potential relationship with neuropsychiatric symptoms, and despite the possibility that deep-brain stimulation of the subthalamic nucleus, an effective treatment for disabling motor symptoms, worsens cognitive impairment. The present study therefore compared the attributional bias of patients with PD (stimulated and nonstimulated subgroups) with that of controls. It also explored the potential correlations between patients' attributional bias and their clinical scores.

METHODS

Thirty-two patients with PD (12 stimulated and 20 nonstimulated) were recruited and matched with 32 healthy controls. Attributional bias was assessed using the Ambiguous Intentions Hostility Questionnaire, which yields three subscores: Hostility Bias, Aggression Bias, and Blame. Depressive symptoms (Hamilton Rating Scale for Depression), paranoid thoughts (Paranoia Scale), global cognition (Montreal Cognitive Assessment), and social functioning (Social Functioning Questionnaire) were also assessed.

RESULTS

Patients exhibited more hostile and aggressive biases than controls, especially in ambiguous situations. Stimulated patients had greater hostility and aggression biases and a higher blame score than controls in accidental situations. No significant differences were observed between stimulated and nonstimulated patients.

CONCLUSION

To our knowledge, this is the first study to have assessed attributional bias in patients with PD and explored the impact of deep-brain stimulation on this particular subdomain of social cognition. Results suggest that patients exhibit attributional bias, and this impairment may be exacerbated in stimulated patients.

Defining (and blocking) neuronal death in Parkinson's disease: Does it matter what we call it?

Parkinson's disease (PD) is the second most common neurodegenerative disease, comprised of both familial and idiopathic forms, behind only Alzheimer's disease (AD). The disease is characterized, regardless of the pathogenesis, primarily by a loss of DA neurons in the ventral midbrain as well as noradrenergic neurons of the locus coeruleus; however, by the time symptoms manifest, considerable neuronal loss in both areas has occurred. Neuroprotective strategies thus have to be paired with more sensitive and specific biomarker assays that can identify early at-risk patients in order to initiate disease-modifying therapies at an earlier stage in the disease. Complicating this is the fact that multiple forms of cell death mediate the neuronal loss; however, with a common underlying element that the cell death is considered a "regulated" form of cell death, in contrast to an un-controlled necrotic cell death process. In this review we focus our discussion on several categories of regulated cell death in the context of PD: apoptosis, necroptosis, pyroptosis, and autophagic cell death. In clinical studies as well as experimental in vivo models of PD, there is evidence for a role of each of these forms of cell death in the loss of midbrain DA neurons, and specific therapeutic strategies have been proposed and tested. What remains unclear however is the relative contributions of these distinct forms of cell death to the overall loss of DA neurons, whether they occur at different stages of the disease, or whether specific sub-regions within the midbrain are more susceptible to specific death triggers and pathways.