LRRK2 and GBA mutations differentially affect the initial presentation of Parkinson disease

The modifying effect of mutant LRRK2 on mutant GBA1-associated Parkinson disease

Parkinson disease (PD) is the second most common neurodegenerative disease. While most cases are sporadic, in ~ 5%-10% of PD patients the disease is caused by mutations in several genes, among them GBA1 (glucocerebrosidase beta 1) and LRRK2 (leucine-rich repeat kinase 2), both prevalent among the Ashkenazi Jewish population. LRRK2-associated PD tends to be milder than GBA1-associated PD. Several recent clinical studies have suggested that carriers of both GBA1 and LRRK2 mutations develop milder PD compared to that observed among GBA1 carriers. These findings strongly suggested an interplay between the two genes in the development and progression of PD. In the present study Drosophila was employed as a model to investigate the impact of mutations in the LRRK2 gene on mutant GBA1-associated PD. Our results strongly indicated that flies expressing both mutant genes exhibited milder parkinsonian signs compared to the disease developed in flies expressing only a GBA1 mutation. This was corroborated by a decrease in the ER stress response, increase in the number of dopaminergic cells, elevated levels of tyrosine hydroxylase, reduced neuroinflammation, improved locomotion and extended survival. Furthermore, a significant decrease in the steady-state levels of mutant GBA1-encoded GCase was observed in the presence of mutant LRRK2, strongly implying a role for mutant LRRK2 in degradation of mutant GCase.

Radiological markers of CSF α-synuclein aggregation in Parkinson's disease patients

Alpha-synuclein (αS) aggregation is a widely regarded hallmark of Parkinson's disease (PD) and can be detected through synuclein amplification assays (SAA). This study investigated the association between cerebrospinal fluid (CSF) radiological measures in 41 PD patients (14 iPD, 14 GBA1-PD, 13 LRRK2-PD) and 14 age-and-sex-matched healthy controls. Quantitative measures including striatal binding ratios (SBR), whole-brain and deep gray matter volumes, neuromelanin-MRI (NM-MRI), functional connectivity (FC), and white matter (WM) diffusion-tensor imaging (DTI) were calculated. Nine LRRK2-PD patients were SAA-negative (PD-SAA-). PD-SAA+ patients showed lower whole-brain gray matter, putamenal, brainstem, and substantia nigra volumes, reduced FC in the left caudate, and lower fractional anisotropy in the left fronto-occipital fasciculus compared to PD-SAA-. Taken together, αS aggregation was observed in iPD, GBA1-PD, and 38% of LRRK2-PD patients, and this was associated with reduced regional brain volumes, altered caudal FC, and SBRs. These changes were less pronounced in PD-SAA-, possibly suggesting a milder neurodegenerative process.

Levodopa-carbidopa intestinal gel for advanced Parkinson's disease: Impact of LRRK2 and GBA1 mutations

BACKGROUND

Advanced Parkinson's disease (PD) can be treated with Levodopa-Carbidopa Intestinal Gel (LCIG).

OBJECTIVE

To compare descriptive data of LCIG treatment in GBA1-PD and LRRK2-PD.

METHODS

This multicenter retrospective study compared clinical data obtained from electronic medical records of PD patients treated with LCIG. Patients were grouped based on their genetic status.

RESULTS

Fifty-two iPD, 15 LRRK2-PD and 23 GBA1-PD were included in this study. No difference in daily dose of LCIG or levodopa equivalent daily dose were detected. GBA1-PD had significantly shorter disease duration at LCIG initiation (p = 0.01) and experienced more hallucinations (p = 0.03) compared with LRRK2-PD and iPD. LRRK2-PD and iPD had significantly longer duration of LCIG treatment compared with GBA1-PD (p < 0.01).

CONCLUSION

Overall, LCIG treatment was well tolerated in LRRK2-PD and GBA1-PD. GBA1-PD required LCIG earlier in their course of their disease and had higher frequencies of hallucinations during treatment, attesting to a more severe disease course.

Transcriptomic changes in oligodendrocytes and precursor cells associate with clinical outcomes of Parkinson's disease

Several prior studies have proposed the involvement of various brain regions and cell types in Parkinson's disease (PD) pathology. Here, we performed snRNA-seq on the prefrontal cortex and anterior cingulate regions from a small cohort of post-mortem control and PD brain tissue. We found a significant association of oligodendrocytes (ODCs) and oligodendrocyte precursor cells (OPCs) with PD-linked risk loci and report several dysregulated genes and pathways, including regulation of tau-protein kinase activity, regulation of inclusion body assembly and protein processing involved in protein targeting to mitochondria. In an independent PD cohort with clinical measures (681 cases and 549 controls), polygenic risk scores derived from the dysregulated genes significantly predicted Montreal Cognitive Assessment (MoCA)-, and Beck Depression Inventory-II (BDI-II)-scores but not motor impairment (UPDRS-III). We extended our analysis of clinical outcome prediction by incorporating differentially expressed genes from three separate datasets that were previously published by different laboratories. In the first dataset from the anterior cingulate cortex, we identified an association between ODCs and BDI-II. In the second dataset obtained from the substantia nigra (SN), OPCs displayed an association with UPDRS-III. In the third dataset from the SN region, a distinct subtype of OPCs, labeled OPC_ADM, exhibited an association with UPDRS-III. Intriguingly, the OPC_ADM cluster also demonstrated a significant increase in PD samples. These results suggest that by expanding our focus to glial cells, we can uncover region-specific molecular pathways associated with PD symptoms.

GBA1-Associated Parkinson's Disease Is a Distinct Entity

GBA1-associated Parkinson's disease (GBA1-PD) is increasingly recognized as a distinct entity within the spectrum of parkinsonian disorders. This review explores the unique pathophysiological features, clinical progression, and genetic underpinnings that differentiate GBA1-PD from idiopathic Parkinson's disease (iPD). GBA1-PD typically presents with earlier onset and more rapid progression, with a poor response to standard PD medications. It is marked by pronounced cognitive impairment and a higher burden of non-motor symptoms compared to iPD. Additionally, patients with GBA1-PD often exhibit a broader distribution of Lewy bodies within the brain, accentuating neurodegenerative processes. The pathogenesis of GBA1-PD is closely associated with mutations in the GBA1 gene, which encodes the lysosomal enzyme beta-glucocerebrosidase (GCase). In this review, we discuss two mechanisms by which GBA1 mutations contribute to disease development: 'haploinsufficiency,' where a single functional gene copy fails to produce a sufficient amount of GCase, and 'gain of function,' where the mutated GCase acquires harmful properties that directly impact cellular mechanisms for alpha-synuclein degradation, leading to alpha-synuclein aggregation and neuronal cell damage. Continued research is advancing our understanding of how these mechanisms contribute to the development and progression of GBA1-PD, with the 'gain of function' mechanism appearing to be the most plausible. This review also explores the implications of GBA1 mutations for therapeutic strategies, highlighting the need for early diagnosis and targeted interventions. Currently, small molecular chaperones have shown the most promising clinical results compared to other agents. This synthesis of clinical, pathological, and molecular aspects underscores the assertion that GBA1-PD is a distinct clinical and pathobiological PD phenotype, necessitating specific management and research approaches to better understand and treat this debilitating condition.

Mild cognitive impairment among LRRK2 and GBA1 patients with Parkinson's disease

BACKGROUND

Mild cognitive impairment (MCI) is common in Parkinson's disease (PD). We aimed to assess the incidence of MCI among patients with PD, carriers of mutations in LRRK2 and GBA1 genes, based on the movement disorder society (MDS) criteria for the diagnosis of MCI in early-stage PD.

METHODS

Patients with PD were included if they scored ≤2 on the Hoehn and Yahr and ≤6 years since motor symptom onset. A group of age and gender matched healthy adults served as controls. A neuropsychological cognitive battery was used covering five cognitive domains (executive functions, working memory, memory, visuospatial and language). MCI was explored while applying two methods (level I and II). Frequency of MCI was assessed in comparison between groups.

RESULTS

70 patients with idiopathic PD (iPD) (68 % males), 42 patients with LRRK2-PD (61 % males), 83 patients with GBA1-PD (63 % males) and 132 age and gender matched controls (61 % males), participated in this study. PD groups were similar in clinical characteristics. Level I criteria were positive in 57.5 % of iPD, 43 % of LRRK2-PD and 63.4 % of the GBA1-PD (p = 0.071). Level II criteria was met by 39 % of iPD, 14 % LRRK2-PD and 41 % of GBA1-PD (p < 0.001), when using a 2 standard-deviation (SD) threshold. GBA1-PD and iPD showed impairments on multiple domains even in the more conservative 2 SD, reflecting MCI.

CONCLUSIONS

The majority of our PD cohort was classified as MCI when assessed with strict criteria. GBA1-PD and iPD showed a more widespread pattern of MCI compared with LRRK2-PD.

Association between sex and Huntington's disease: an updated review on symptomatology and prognosis of neurodegenerative disorders

Huntington's disease is a rare autosomal dominant disorder presenting with chorea, rigidity, hypo-/akinesia, cognitive decline, and psychiatric disturbances. Numerous risk factors have been defined in the onset of this disease. However, the number of CAG repeats in the genes are the most crucial factor rendering patients susceptible to the disease. Studies have shown significant differences in onset and disease presentation among the sexes, which prompts analysis of the impact of different sexes on disease etiology and progression. This article therefore discusses the evidence-based role of sex in aspects of symptomatology, pathogenesis, biomarkers, progression, and prognosis of Huntington's disease, with a secondary review of sex-linked differences in Alzheimer's and Parkinson's disease.

Transcriptomic changes in oligodendrocytes and precursor cells predicts clinical outcomes of Parkinson's disease

Several prior studies have proposed the involvement of various brain regions and cell types in Parkinson's disease (PD) pathology. Here, we performed snRNA-seq on the prefrontal cortex and anterior cingulate regions from post-mortem control and PD brain tissue. We found a significant association of oligodendrocytes (ODCs) and oligodendrocyte precursor cells (OPCs) with PD-linked risk loci and report several dysregulated genes and pathways, including regulation of tau-protein kinase activity, regulation of inclusion body assembly and protein processing involved in protein targeting to mitochondria. In an independent PD cohort with clinical measures (681 cases and 549 controls), polygenic risk scores derived from the dysregulated genes significantly predicted Montreal Cognitive Assessment (MoCA)-, and Beck Depression Inventory-II (BDI-II)-scores but not motor impairment (UPDRS-III). We extended our analysis of clinical outcome prediction by incorporating three separate datasets that were previously published by different laboratories. In the first dataset from the anterior cingulate cortex, we identified a correlation between ODCs and BDI-II. In the second dataset obtained from the substantia nigra (SN), OPCs displayed notable predictive ability for UPDRS-III. In the third dataset from the SN region, a distinct subtype of OPCs, labeled OPC_ADM, exhibited predictive ability for UPDRS-III. Intriguingly, the OPC_ADM cluster also demonstrated a significant increase in PD samples. These results suggest that by expanding our focus to glial cells, we can uncover region-specific molecular pathways associated with PD symptoms.

Differences in EEG Event-Related Potentials during Dual Task in Parkinson's Disease Carriers and Non-Carriers of the G2019S-LRRK2 Mutation

BACKGROUND

The G2019S-LRRK2 gene mutation is a common cause of hereditary Parkinson's disease (PD), associated with a higher frequency of the postural instability gait difficulty (PIGD) motor phenotype yet with preserved cognition. This study investigated neurophysiological changes during motor and cognitive tasks in PD patients with and without the G2019S-LRRK2 mutation.

METHODS

33 iPD patients and 22 LRRK2-PD patients performed the visual Go/NoGo task (VGNG) during sitting (single-task) and walking (dual-task) while wearing a 64-channel EEG cap. Event-related potentials (ERP) from Fz and Pz, specifically N200 and P300, were extracted and analyzed to quantify brain activity patterns.

RESULTS

The LRRK2-PD group performed better in the VGNG than the iPD group (group*task; p = 0.05). During Go, the iPD group showed reduced N2 amplitude and prolonged N2 latency during walking, whereas the LRRK2-PD group showed only shorter latency (group*task p = 0.027). During NoGo, opposite patterns emerged; the iPD group showed reduced N2 and increased P3 amplitudes during walking while the LRRK2-PD group demonstrated increased N2 and reduced P3 (N2: group*task, p = 0.010, P3: group*task, p = 0.012).

CONCLUSIONS

The LRRK2-PD group showed efficient early cognitive processes, reflected by N2, resulting in greater neural synchronization and prominent ERPs. These processes are possibly the underlying mechanisms for the observed better cognitive performance as compared to the iPD group. As such, future applications of intelligent medical sensing should be capable of capturing these electrophysiological patterns in order to enhance motor-cognitive functions.

Sex differences in alpha-synucleinopathies: a systematic review

Background

Past research indicates a higher prevalence, incidence, and severe clinical manifestations of alpha-synucleinopathies in men, leading to a suggestion of neuroprotective properties of female sex hormones (especially estrogen). The potential pathomechanisms of any such effect on alpha-synucleinopathies, however, are far from understood. With that aim, we undertook to systematically review, and to critically assess, contemporary evidence on sex and gender differences in alpha-synucleinopathies using a bench-to-bedside approach.

Methods

In this systematic review, studies investigating sex and gender differences in alpha-synucleinopathies (Rapid Eye Movement (REM) Behavior Disorder (RBD), Parkinson's Disease (PD), Dementia with Lewy Bodies (DLB), Multiple System Atrophy (MSA)) from 2012 to 2022 were identified using electronic database searches of PubMed, Embase and Ovid.

Results

One hundred sixty-two studies were included; 5 RBD, 6 MSA, 20 DLB and 131 PD studies. Overall, there is conclusive evidence to suggest sex-and gender-specific manifestation in demographics, biomarkers, genetics, clinical features, interventions, and quality of life in alpha-synucleinopathies. Only limited data exists on the effects of distinct sex hormones, with majority of studies concentrating on estrogen and its speculated neuroprotective effects.

Conclusion

Future studies disentangling the underlying sex-specific mechanisms of alpha-synucleinopathies are urgently needed in order to enable novel sex-specific therapeutics.

The Influence of GBA and LRRK2 on Mood Disorders in Parkinson's Disease

Background

Mood disorders have emerged as major non-motor comorbidities in Parkinson's disease (PD) even at the prodromal stage of the disease. Mutations in the LRRK2 and GBA genes are common among Ashkenazi Jews, with more severe phenotype reported for GBA-PD.

Objective

To explore the association between genetic status and mood related disorders before and after diagnosis of PD and the association between mood-related medications, phenotype, and genetic status.

Methods

Participants were genotyped for mutations in the LRRK2 and GBA genes. State of depression, anxiety and non-motor features were evaluated using validated questionnaires. History of mood disorders prior to diagnosis of PD and use of mood-related medications were assessed.

Results

The study included 105 idiopathic PD (iPD), 55 LRRK2-PD and 94 GBA-PD. Scores on mood related questionnaires and frequency of depression and anxiety before diagnosis were similar between the groups (p>0.05). However, more GBA-PD patients used mood related medications before PD diagnosis than LRRK2-PD and iPD (16.5% vs 7.1% and 8.2%, p=0.044). LRRK2-PD and GBA-PD receiving mood-related medications at time of assessment had worse motor and non-motor phenotype compared to those that did not (p<0.05). LRRK2-PD receiving mood related-medications at time of assessment, scored higher on mood-related questionnaires compared to LRRK2-PD not receiving such medications (p<0.04).

Conclusions

Prodromal GBA-PD are more frequently treated with mood related-medications despite equal rates of reported mood-related disorders, while LRRK2-PD with mood-related disorders experience high rates of anxiety and depression despite treatment, attesting to the need of more precise assessment and treatment of these genetic subgroups.

Genetic Evidence for Endolysosomal Dysfunction in Parkinson’s Disease: A Critical Overview

Parkinson’s disease (PD) is the second most common neurodegenerative disorder in the aging population, and no disease-modifying therapy has been approved to date. The pathogenesis of PD has been related to many dysfunctional cellular mechanisms, however, most of its monogenic forms are caused by pathogenic variants in genes involved in endolysosomal function (LRRK2, VPS35, VPS13C, and ATP13A2) and synaptic vesicle trafficking (SNCA, RAB39B, SYNJ1, and DNAJC6). Moreover, an extensive search for PD risk variants revealed strong risk variants in several lysosomal genes (e.g., GBA1, SMPD1, TMEM175, and SCARB2) highlighting the key role of lysosomal dysfunction in PD pathogenesis. Furthermore, large genetic studies revealed that PD status is associated with the overall “lysosomal genetic burden”, namely the cumulative effect of strong and weak risk variants affecting lysosomal genes. In this context, understanding the complex mechanisms of impaired vesicular trafficking and dysfunctional endolysosomes in dopaminergic neurons of PD patients is a fundamental step to identifying precise therapeutic targets and developing effective drugs to modify the neurodegenerative process in PD.

Deep brain stimulation in Early Onset Parkinson's disease

INTRODUCTION

Subthalamic Deep Brain Stimulation (STN-DBS) is a safe and well-established therapy for the management of motor symptoms refractory to best medical treatment in patients with Parkinson's disease (PD). Early intervention is discussed especially for Early-onset PD (EOPD) patients that present with an age of onset ≤ 45-50 years and see themselves often confronted with high psychosocial demands.

METHODS

We retrospectively assessed the effect of STN-DBS at 12 months follow-up (12-MFU) in 46 EOPD-patients. Effects of stimulation were evaluated by comparison of disease-specific scores for motor and non-motor symptoms including impulsiveness, apathy, mood, quality of life (QoL), cognition before surgery and in the stimulation ON-state without medication. Further, change in levodopa equivalent dosage (LEDD) after surgery, DBS parameter, lead localization, adverse and serious adverse events as well as and possible additional clinical features were assessed.

RESULTS

PD-associated gene mutations were found in 15% of our EOPD-cohort. At 12-MFU, mean motor scores had improved by 52.4 ± 17.6% in the STIM-ON/MED-OFF state compared to the MED-OFF state at baseline (p = 0.00; n = 42). These improvements were accompanied by a significant 59% LEDD reduction (p < 0.001), a significant 6.6 ± 16.1 points reduction of impulsivity (p = 0.02; n = 35) and a significant 30 ± 50% improvement of QoL (p = 0.01). At 12-MFU, 9 patients still worked full- and 6 part-time. Additionally documented motor and/or neuropsychiatric features decreased from n = 41 at baseline to n = 14 at 12-MFU.

CONCLUSION

The present study-results demonstrate that EOPD patients with and without known genetic background benefit from STN-DBS with significant improvement in motor as well as non-motor symptoms. In line with this, patients experienced a meaningful reduction of additional neuropsychiatric features. Physicians as well as patients have an utmost interest in possible predictors for the putative DBS outcome in a cohort with such a highly complex clinical profile. Longitudinal monitoring of DBS-EOPD-patients over long-term intervals with standardized comprehensive clinical assessment, accurate phenotypic characterization and documentation of clinical outcomes might help to gain insights into disease etiology, to contextualize genomic information and to identify predictors of optimal DBS candidates as well as those in danger of deterioration and/or non-response in the future.

Early motor response to dopamine replacement therapy in Parkinson's disease patients carrying GBA variants

BACKGROUND

Mutations in the glucocerebrosidase (GBA) gene represent the most common genetic risk factor for Parkinson's Disease (PD) and are associated with a more aggressive motor phenotype at late stages. However, the motor response at early stages of disease remains understudied.

METHODS

Retrospective study of PD patients that underwent next-generation sequencing panel tests for PD-related genes. We extracted demographic data and the MDS-UPDRS III response to an acute levodopa challenge (LDC), the best ON score, and the levodopa equivalent daily dose (LEDD) during the first six months after the LDC and initiation of DRT. We compared the response of GBA-PD patients to that of patients without pathogenic variants or rearrangements in other PD related genes (sporadic PD).

RESULTS

13 GBA-PD and 48 sporadic PD patients were identified. Baseline MDS-UPDRS III score (24.6 ± 9.6 vs. 21.8 ± 9.3. p = 0.4), response to LDC (39.2% ± 7.9% vs. 32.7% ± 13.4%; p = 0.1), best ON score (36.9% ± 39.5% vs. 41.6% ± 20.8%; p = 0.6) and LEDD (188 mg ± 100 mg vs. 261.8 mg ± 164.8 mg; p = 0.2) during the first six months after initiation of DRT were not different between GBA-PD and sporadic PD patients.

CONCLUSIONS

At early disease stages of GBA-PD, the motor response to acute levodopa challenge test and the initial response to DRT are similar to that of patients with sporadic PD. Although limited by small sample size, these preliminary findings should be confirmed by future prospective larger studies.

Cumulative additional information does not improve the neuromuscular control during postural responses to perturbations in postural instability/gait disorders subtype of Parkinson's disease

BACKGROUND

Postural response impairments in postural instability and gait disorders (PIGD) subtype patients may be attributed to Parkinson's disease (PD)-deterioration in central-set (programing/modulating of central outputs during motor responses). Although additional information improves some PD motor impairments, an unanswered question is whether additional information can benefit postural response in PIGD subtype.

OBJECTIVE

To analyze the effect of cumulative additional information on postural responses after perturbation in PIGD and neurologically healthy older adults (CG).

METHODS

Perturbations were applied in 16 PIGD and 19 CG by the support-base translation. Participants performed 3 blocks of 5 trials without additional information (B1-B3, Day 1) and 5 trials of each cumulative additional information (C1-C4, Day 2): information about perturbation (C1), visual (C2), verbal (C3), and somatosensory information (C4). Electromyography and center of pressure (CoP) parameters were analyzed by ANOVAs with Group (PIGD × CG) and Block (B1 × B2 × B3) and with Group (PIGD × CG) and Condition (B3 × C1 × C2 × C3 × C4).

RESULTS

PIGD decreased the range of CoP in B3 while CG decreased both range of CoP and the integral of antagonist's muscle activity (iEMG) in B2. Also, PIGD decreased the recovery time in C4 while CG increased the iEMG of agonist's muscle in C2 and antagonist's muscle in all conditions except C2.

CONCLUSION

Additional information provided before postural control assessment influences the postural response in PIGD and CG differently. PIGD demonstrated inflexibility of central-set in modulating the neuromuscular control regardless of additional information. CG presents a flexible system evidenced by the increase of agonist muscle iEMG when provided visual information.

Prevalence of ten LRRK2 variants in Parkinson's disease: A comprehensive review

INTRODUCTION

Variants in the leucine-rich repeat kinase 2 gene (LRRK2) are risk factors for Parkinson's disease (PD), but their prevalence varies geographically, reflecting the locations of founder events and dispersion of founders' descendants.

METHODS

A comprehensive literature review was conducted to identify studies providing prevalence estimates for any of ten variants in LRRK2 (G2019S, R1441C, R1441G, R1441H, I2020T, N1437H, Y1699C, S1761R, G2385R, R1628P) among individuals with PD globally. We calculated crude country-specific variant prevalence estimates and, when possible, adjusted estimates for ethno-racial composition. For clinic-based studies, probands were used over other familial cases, whereas for population-based studies, all PD cases were used.

RESULTS

The analysis included 161 articles from 52 countries yielding 581 prevalence estimates across the ten variants. G2019S was the most common variant, exceeding 1.0% in 26 of 51 countries with estimates. The other variants were far less common. G2385R and R1628P were observed almost exclusively in East Asian countries, where they were found in ∼5-10% of cases. All prevalence estimates adjusted for ethno-racial composition were lower than their unadjusted counterparts, although data permitting this adjustment was only available for six countries.

CONCLUSIONS

Except for G2019S, the LRRK2 variants covered in this review were uncommon in most countries studied. However, there were countries with higher prevalence for some variants, reflecting the uneven geographic distribution of LRRK2 variants. The fact that ethno-racial group‒adjusted estimates were lower than crude estimates suggests that estimates derived largely from clinic-based studies may overstate the true prevalence of some LRRK2 variants in PD.

Redefining the hypotheses driving Parkinson's diseases research

Parkinson’s disease (PD) research has largely focused on the disease as a single entity centred on the development of neuronal pathology within the central nervous system. However, there is growing recognition that PD is not a single entity but instead reflects multiple diseases, in which different combinations of environmental, genetic and potential comorbid factors interact to direct individual disease trajectories. Moreover, an increasing body of recent research implicates peripheral tissues and non-neuronal cell types in the development of PD. These observations are consistent with the hypothesis that the initial causative changes for PD development need not occur in the central nervous system. Here, we discuss how the use of neuronal pathology as a shared, qualitative phenotype minimises insights into the possibility of multiple origins and aetiologies of PD. Furthermore, we discuss how considering PD as a single entity potentially impairs our understanding of the causative molecular mechanisms, approaches for patient stratification, identification of biomarkers, and the development of therapeutic approaches to PD. The clear consequence of there being distinct diseases that collectively form PD, is that there is no single biomarker or treatment for PD development or progression. We propose that diagnosis should shift away from the clinical definitions, towards biologically defined diseases that collectively form PD, to enable informative patient stratification. N-of-one type, clinical designs offer an unbiased, and agnostic approach to re-defining PD in terms of a group of many individual diseases.

DRD2 Taq1A Polymorphism-Related Brain Volume Changes in Parkinson's Disease: Voxel-Based Morphometry

Taq1A polymorphism is a DRD2 gene variant located in an exon of the ANKK1 gene and has an important role in the brain's dopaminergic functions. Some studies have indicated that A1 carriers have an increased risk of developing Parkinson's disease (PD) and show poorer clinical performance than A2 homo carriers. Previous studies have suggested that A1 carriers had fewer dopamine D2 receptors in the caudate and increased cortical activity as a compensatory mechanism. However, there is little information about morphological changes associated with this polymorphism in patients with PD. The study's aim was to investigate the relationship between brain volume and Taq1A polymorphism in PD using voxel-based morphometry (VBM). Based on Taq1A polymorphism, 103 patients with PD were divided into two groups: A1 carriers (A1/A1 and A1/A2) and A2 homo carriers (A2/A2). The volume of the left prefrontal cortex (PFC) was significantly decreased in A2 homo carriers compared to A1 carriers. This finding supports the association between Taq1A polymorphism and brain volume in PD and may explain the compensation of cortical function in A1 carriers with PD.

GBA Variants and Parkinson Disease: Mechanisms and Treatments

The GBA gene encodes for the lysosomal enzyme glucocerebrosidase (GCase), which maintains glycosphingolipid homeostasis. Approximately 5–15% of PD patients have mutations in the GBA gene, making it numerically the most important genetic risk factor for Parkinson disease (PD). Clinically, GBA-associated PD is identical to sporadic PD, aside from the earlier age at onset (AAO), more frequent cognitive impairment and more rapid progression. Mutations in GBA can be associated with loss- and gain-of-function mechanisms. A key hallmark of PD is the presence of intraneuronal proteinaceous inclusions named Lewy bodies, which are made up primarily of alpha-synuclein. Mutations in the GBA gene may lead to loss of GCase activity and lysosomal dysfunction, which may impair alpha-synuclein metabolism. Models of GCase deficiency demonstrate dysfunction of the autophagic-lysosomal pathway and subsequent accumulation of alpha-synuclein. This dysfunction can also lead to aberrant lipid metabolism, including the accumulation of glycosphingolipids, glucosylceramide and glucosylsphingosine. Certain mutations cause GCase to be misfolded and retained in the endoplasmic reticulum (ER), activating stress responses including the unfolded protein response (UPR), which may contribute to neurodegeneration. In addition to these mechanisms, a GCase deficiency has also been associated with mitochondrial dysfunction and neuroinflammation, which have been implicated in the pathogenesis of PD. This review discusses the pathways associated with GBA-PD and highlights potential treatments which may act to target GCase and prevent neurodegeneration.

Glucocerebrosidase Mutations Cause Mitochondrial and Lysosomal Dysfunction in Parkinson’s Disease: Pathogenesis and Therapeutic Implications

Parkinson’s disease (PD) is the second most common neurodegenerative disease and is characterized by multiple motor and non-motor symptoms. Mutations in the glucocerebrosidase (GBA) gene, which encodes the lysosomal enzyme glucocerebrosidase (GCase), which hydrolyzes glucosylceramide (GlcCer) to glucose and ceramide, are the most important and common genetic PD risk factors discovered to date. Homozygous GBA mutations result in the most common lysosomal storage disorder, Gaucher’s disease (GD), which is classified according to the presence (neuronopathic types, type 2 and 3 GD) or absence (non-neuronopathic type, type 1 GD) of neurological symptoms. The clinical manifestations of PD in patients with GBA mutations are indistinguishable from those of sporadic PD at the individual level. However, accumulating data have indicated that GBA-associated PD patients exhibit a younger age of onset and a greater risk for cognitive impairment and psychiatric symptoms. The mechanisms underlying the increased risk of developing PD in GBA mutant carriers are currently unclear. Contributors to GBA-PD pathogenesis may include mitochondrial dysfunction, autophagy-lysosomal dysfunction, altered lipid homeostasis and enhanced α-synuclein aggregation. Therapeutic strategies for PD and GD targeting mutant GCase mainly include enzyme replacement, substrate reduction, gene and pharmacological small-molecule chaperones. Emerging clinical, genetic and pathogenic studies on GBA mutations and PD are making significant contributions to our understanding of PD-associated pathogenetic pathways, and further elucidating the interactions between GCase activity and neurodegeneration may improve therapeutic approaches for slowing PD progression.

Mutations in GBA and LRRK2 Are Not Associated with Increased Inflammatory Markers

Background:

Inflammation is an integral part of neurodegeneration including in Parkinson’s disease (PD). Ashkenazi Jews have high rates of genetic PD with divergent phenotypes among GBA-PD and LRRK2-PD. The role of inflammation in the prodromal phase of PD and the association with disease phenotype has yet to be elucidated.

Objective:

To assess central and peripheral cytokines among PD patients with mutations in the LRRK2 and GBA genes and among non-manifesting carriers (NMC) of these mutations in order to determine the role of inflammation in genetic PD.

Methods:

The following cytokines were assessed from peripheral blood and cerebrospinal fluid (CSF): TNF-α, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10 and INF- γ. A comprehensive intake including general medical conditions, use of anti-inflammatory treatments, motor and cognitive assessments and additional laboratory measures were recorded, enabling the construction of the MDS probable prodromal score.

Results:

Data from 362 participants was collected: 31 idiopathic PD (iPD), 30 LRRK2-PD, 77 GBA-PD, 3 homozygote GBA-PD, 3 GBA-LRRK2-PD, 67 LRRK2-NMC, 105 GBA-NMC, 14 LRRK2-GBA-NMC, and 32 healthy controls. No between-group differences in peripheral or CSF cytokines were detected. No correlation between disease characteristics or risk for prodromal PD could be associated with any inflammatory measure.

Conclusion:

In this study, we could not detect any evidence on dysregulated immune response among GBA and LRRK2 PD patients and non-manifesting mutation carriers.

The Quebec Parkinson Network: A Researcher-Patient Matching Platform and Multimodal Biorepository

BACKGROUND

Genetic, biologic and clinical data suggest that Parkinson's disease (PD) is an umbrella for multiple disorders with clinical and pathological overlap, yet with different underlying mechanisms. To better understand these and to move towards neuroprotective treatment, we have established the Quebec Parkinson Network (QPN), an open-access patient registry, and data and bio-samples repository.

OBJECTIVE

To present the QPN and to perform preliminary analysis of the QPN data.

METHODS

A total of 1,070 consecutively recruited PD patients were included in the analysis. Demographic and clinical data were analyzed, including comparisons between males and females, PD patients with and without RBD, and stratified analyses comparing early and late-onset PD and different age groups.

RESULTS

QPN patients exhibit a male:female ratio of 1.8:1, an average age-at-onset of 58.6 years, an age-at-diagnosis of 60.4 years, and average disease duration of 8.9 years. REM-sleep behavior disorder (RBD) was more common among men, and RBD was associated with other motor and non-motor symptoms including dyskinesia, fluctuations, postural hypotension and hallucinations. Older patients had significantly higher rates of constipation and cognitive impairment, and longer disease duration was associated with higher rates of dyskinesia, fluctuations, freezing of gait, falls, hallucinations and cognitive impairment. Since QPN's creation, over 60 studies and 30 publications have included patients and data from the QPN.

CONCLUSIONS

The QPN cohort displays typical PD demographics and clinical features. These data are open-access upon application (http://rpq-qpn.ca/en/), and will soon include genetic, imaging and bio-samples. We encourage clinicians and researchers to perform studies using these resources.

Biochemical markers for severity and risk in GBA and LRRK2 Parkinson's disease

BACKGROUND

The phenotype of Parkinson's disease (PD) is variable with mutations in genes such as LRRK2 and GBA explaining part of this heterogeneity. Additional genetic and environmental factors contribute to disease variability.

OBJECTIVE

To assess the association between biochemical markers, PD severity and probability score for prodromal PD, among GBA and LRRK2 mutation carriers.

METHODS

Levels of uric acid, vitamin D, C-reactive protein, microalbumin/creatinine ratio (ACR), white blood count (WBC), hemoglobin, platelets, neutrophil/lymphocyte ratio and estimated glomerular filtration rate (eGFR) were assessed from patients with PD and non-manifesting carriers (NMC) of mutations in GBA and LRRK2, together with disease related questionnaires enabling the construction of the MDS prodromal probability score.

RESULT

A total of 241 patients with PD: 105 idiopathic PD (iPD), 49 LRRK2-PD and 87 GBA-PD and 412 non-manifesting subjects; 74 LRRK2-NMC, 118 GBA-NMC and 220 non-manifesting non-carriers (NMNC), participated in this study. No significant differences in biochemical measures were detected among patients with PD or non-manifesting carriers. Among GBA-PD patients, worse motor performance was associated with ACR (B = 4.68, 95% CI (1.779-7.559); p = 0.002). The probability score for prodromal PD among all non-manifesting participants was associated with eGFR; NMNC (B = - 0.531 95% CI (- 0.879 to - 0.182); p < 0.001, LRRK2-NMC (B = - 1.014 95% CI (- 1.663 to - 0.366); p < 0.001) and GBA-NMC (B = - 0.686 95% CI (1.300 to - 0.071); p = 0.029).

CONCLUSION

Sub-clinical renal impairment is associated with increased likelihood for prodromal PD regardless of genetic status. While the mechanism behind this finding needs further elucidation, it suggests that kidney function might play a role in PD pathogenesis.

Current and emerging therapeutic targets for Parkinson's disease

Parkinson's disease (PD) is characterized by gradual neurodegeneration and forfeiture of dopamine neurons in substantia nigra pars compacta which ultimately leads to depletion of dopamine levels. PD patients not only display motor features such as rigidity, tremor, and bradykinesia but also non-motor features such as depression, anxiety, etc. Various treatments are available for PD patients such as dopamine replacement are well established but it is only partially or transiently effective. As these therapies not able to restore dopaminergic neurons and delay the development of Parkinson's disease, therefore, the need for an effective therapeutic approach is crucial. The present review discusses a comprehensive overview of current novel targets for PD which includes molecular chaperone, neuroinflammation, mitochondrial dysfunction, neuromelanin, Ubiquitin-proteasome system, protein Abelson, Synaptic vesicle glycoprotein 2C, and Cocaine-amphetamine-regulated transcript, etc. These approaches will help to identify new targets for the treatment of disease and may provide a ray of hope for PD patient treatment. Graphical abstract.

Association of GBA Genotype With Motor and Functional Decline in Patients With Newly Diagnosed Parkinson Disease

Objective

To establish the significance of glucocerebrosidase gene (GBA) carrier status on motor impairment in a large cohort of patients with incident Parkinson disease (PD).

Methods

Three European population-based studies followed 528 patients with PD from diagnosis. A total of 440 with genomic DNA from baseline were assessed for GBA variants. We evaluated motor and functional impairment annually using the Unified Parkinson’s Disease Rating Scale (UPDRS) motor and activities of daily living (ADL) sections. Differential effects of classes of GBA variants on disease progression were evaluated using mixed random and fixed effects models.

Results

A total of 387 patients with idiopathic disease (age at baseline 70.3 ± 9.5 years; 60.2% male) and 53 GBA carriers (age at baseline 66.8 ± 10.1 years; 64.2% male) were included. The motor profile of the groups was clinically indistinguishable at diagnosis. GBA carriers showed faster annual increase in UPDRS scores measuring ADL (1.5 point per year, 95% confidence interval [CI] 1.1–2.0) and motor symptoms (2.2 points per year, 95% CI 1.3–3.1) compared to noncarriers (ADL, 1.0 point per year, 95% CI 0.9–1.1, p = 0.003; motor, 1.3 point per year, 95% CI 1.1–1.6, p = 0.007). Simulations of clinical trial designs showed that recruiting only GBA carriers can reduce trial size by up to 65% compared to a trial recruiting all patients with PD.

Conclusion

GBA variants are linked to a more aggressive motor disease course over 7 years from diagnosis in patients with PD. A better understanding of PD progression in genetic subpopulations may improve disease management and has direct implications for improving the design of clinical trials.

Sex differences in movement disorders

A number of studies reported the possible differences between men and women in movement disorders. Evidence shows that estrogens may have a neuroprotective effect and may modulate the neurodevelopment of the different brain structures. Movement disorders including Parkinson's disease, dementia with Lewy body, Huntington's disease, Tourette's syndrome, and dystonia among others display significant clinical differences between sexes, with structural differences in the dopaminergic pathways between men and women. Here we summarize the most relevant clinical aspects of some of the most common movement disorders, highlighting the differences in disease onset, clinical presentation, therapy, and outcomes. Increased recognition of these differences may help physicians better understand the pathophysiology of these conditions and provide a tailored therapeutic approach.

A Possible Modifying Effect of the G2019S Mutation in the LRRK2 Gene on GBA Parkinson's Disease

BACKGROUND

The phenotype of Parkinson's disease (PD) is milder among patients with LRRK2-PD and more severe among patients with GBA-PD; however, whether an additive phenotypical effect occurs among dual-mutation carriers requires validation.

OBJECTIVE

The objective of this study was to explore the phenotypic expression of patients with PD who carry mutations in both genes compared with a single-mutation presentation.

METHODS

Patients with PD were genotyped for the G2019S-LRRK2 mutation and 9 mutations in the GBA gene. Subjects were classified into 5 groups: idiopathic PD, mild GBA-PD, severe GBA-PD, LRRK2-PD, and LRRK2+GBA-PD. Clinical symptoms were evaluated using performance-based measures.

RESULTS

A total of 1090 patients with idiopathic PD, 155 patients with LRRK2-PD, 155 patients with mild GBA-PD, 56 patients with severe GBA-PD, and 27 patients with LRRK2+GBA-PD participated in this study. The patients with LRRK2-PD and LRRK2+GBA-PD exhibited lower scores on total Unified Parkinson's Disease Rating Scale (P < 0.01) and better olfaction (P < 0.01) compared with GBA-PD.

CONCLUSIONS

Patients with LRRK2+GBA-PD were symptomatically similar to patients with LRRK2-PD, suggesting a dominant effect of LRRK2 over GBA in the phenotypic presentation. © 2020 International Parkinson and Movement Disorder Society.

Glucocerebrosidase Defects as a Major Risk Factor for Parkinson's Disease

Heterozygous mutations of the GBA1 gene, encoding for lysosomal enzyme glucocerebrosidase (GCase), occur in a considerable percentage of all patients with sporadic Parkinson's disease (PD), varying between 8% and 12% across the world. Genome wide association studies have confirmed the strong correlation between PD and GBA1 mutations, pointing to this element as a major risk factor for PD, possibly the most important one after age. The pathobiological mechanisms underlying the link between a defective function of GCase and the development of PD are still unknown and are currently the focus of intense investigation in the community of pre-clinical and clinical researchers in the PD field. A major controversy regards the fact that, despite the unequivocal correlation between the presence of GBA1 mutations and the risk of developing PD, only a minority of asymptomatic carriers with GBA1 mutations convert to PD in their lifetime. GBA1 mutations reduce the enzymatic function of GCase, impairing lysosomal efficiency and the cellular ability to dispose of pathological alpha-synuclein. Changes in the cellular lipidic content resulting from the accumulation of glycosphingolipids, triggered by lysosomal dysfunction, may contribute to the pathological modification of alpha-synuclein, due to its ability to interact with cell membrane lipids. Mutant GCase can impair mitochondrial function and cause endoplasmic reticulum stress, thereby impacting on cellular energy production and proteostasis. Importantly, reduced GCase activity is associated with clear activation of microglia, a major mediator of neuroinflammatory response within the brain parenchyma, which points to neuroinflammation as a major consequence of GCase dysfunction. In this present review article, we summarize the current knowledge on the role of GBA1 mutations in PD development and their phenotypic correlations. We also discuss the potential role of the GCase pathway in the search for PD biomarkers that may enable the development of disease modifying therapies. Answering these questions will aid clinicians in offering more appropriate counseling to the patients and their caregivers and provide future directions for PD preclinical research.

GBA1-associated parkinsonism: new insights and therapeutic opportunities

PURPOSE OF REVIEW

GBA1 mutations, which result in the lysosomal disorder Gaucher disease, are the most common known genetic risk factor for Parkinson disease and Dementia with Lewy Bodies (DLB). The pathogenesis of this association is not fully understood, but further elucidation of this link could lead to new therapeutic options.

RECENT FINDINGS

The characteristic clinical phenotype of GBA1-PD resembles sporadic Parkinson disease, but with an earlier onset and more severe course. Many different GBA1 mutations increase the risk of Parkinson disease, some primarily detected in specific populations. Glucocerebrosidase deficiency appears to be associated with increased α-synuclein aggregation and accumulation, mitochondrial dysfunction because of impaired autophagy, and increased endoplasmic reticulum stress.

SUMMARY

As our understanding of GBA1-associated Parkinson disease increases, new treatment opportunities emerge. MicroRNA profiles are providing examples of both up-regulated and down-regulated proteins related to GBA1 and may provide new therapeutic targets. Chaperone therapy, directed at either misfolded glucocerebrosidase or α-synuclein aggregation, is currently under development and there are several early clinical trials ongoing. Substrate reduction therapy, aimed at lowering the accumulation of metabolic by-products, especially glucosylsphingosine, is also being explored. Basic science insights from the rare disorder Gaucher disease are serving to catapult drug discovery for parkinsonism.

Clinical and Dopamine Transporter Imaging Characteristics of Leucine Rich Repeat Kinase 2 (LRRK2) and Glucosylceramidase Beta (GBA) Parkinson's Disease Participants in the Parkinson's Progression Markers Initiative: A Cross-Sectional Study

BACKGROUND

There are limited data on the phenotypic and dopamine transporter (DAT) imaging characterization of the Parkinson's disease (PD) patients with leucine rich kinase 2 (LRRK2) and glucosylceramidase beta (GBA) mutations.

OBJECTIVE

The objective of this study was to examine baseline clinical and DAT imaging characteristics in GBA and LRRK2 mutation carriers with early PD compared with sporadic PD.

METHODS

The Parkinson's Progression Markers Initiative is an ongoing observational longitudinal study that enrolled participants with sporadic PD, LRRK2 and GBA PD carriers from 33 sites worldwide. All participants are assessed annually with a battery of motor and nonmotor scales, 123-I Ioflupane DAT imaging, and biologic variables.

RESULTS

We assessed 158 LRRK2 (89% G2019S), 80 GBA (89 %N370S), and 361 sporadic PD participants with the mean (standard deviation) disease duration of 2.9 (1.9), 3.1 (2.0), and 2.6 (0.6) years, respectively. When compared with sporadic PD, the GBA PD patients had no difference in any motor, cognitive, or autonomic features. The LRRK2 PD patients had less motor disability and lower rapid eye movement behavior disorder questionnaire scores, but no meaningful difference in cognitive or autonomic features. Both genetic cohorts had a higher score on the impulse control disorders scale when compared with sporadic PD, but no difference in other psychiatric features. Both genetic PD cohorts had less loss of dopamine transporter on DAT imaging when compared with sporadic PD.

CONCLUSIONS

We confirm previous reports of milder phenotype associated with LRRK2-PD. A previously reported more aggressive phenotype in GBA-PD is not evident early in the disease in N370s carriers. This observation identifies a window for potential disease-modifying interventions. Longitudinal data will be essential to define the slope of progression for both genetic cohorts.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT01141023). © 2020 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Organoid and pluripotent stem cells in Parkinson's disease modeling: an expert view on their value to drug discovery

Introduction: Parkinson's disease is a devastating neurodegenerative disorder preferentially involving loss of dopaminergic neurons in the substantia nigra, leading to typical motor symptoms. While there are still no therapeutics to modify disease course, recent work using induced pluripotent stem cell (iPSC) and 3D brain organoid models have provided further insight into Parkinson's disease pathogenesis and potential therapeutic targets.Areas covered: This review highlights the generation of iPSC neurons and neural organoids as models for studying Parkinson's disease. It further discusses the recent work using patient-derived neurons from both familial and sporadic forms of Parkinson's to study disease pathogenic phenotypes and pathways. It additionally provides an evaluation of iPSC neurons and organoid models for therapeutic development in Parkinson's.Expert opinion: The use of Parkinson's disease patient-derived neurons and organoids provides us with the exciting opportunity to directly investigate pathogenic mechanisms and test drug compounds in human neurons. Future studies will involve generating more sophisticated models of brain organoids, studying neuronal pathways using larger patient cohorts, and routinely assessing therapeutics in these models.

Sex differences in movement disorders

In a range of neurological conditions, including movement disorders, sex-related differences are emerging not only in brain anatomy and function, but also in pathogenesis, clinical features and response to treatment. In Parkinson disease (PD), for example, oestrogens can influence the severity of motor symptoms, whereas elevation of androgens can exacerbate tic disorders. Nevertheless, the real impact of sex differences in movement disorders remains under-recognized. In this article, we provide an up-to-date review of sex-related differences in PD and the most common hyperkinetic movement disorders, namely, essential tremor, dystonia, Huntington disease and other chorea syndromes, and Tourette syndrome and other chronic tic disorders. We highlight the most relevant clinical aspects of movement disorders that differ between men and women. Increased recognition of these differences and their impact on patient care could aid the development of tailored approaches to the management of movement disorders and enable the optimization of preclinical research and clinical studies.

Postural Instability in Parkinson's Disease: A Review

Parkinson’s disease (PD) is a heterogeneous progressive neurodegenerative disorder, which typically affects older adults; it is predicted that by 2030 about 3% of the world population above 65 years of age is likely to be affected. At present, the diagnosis of PD is clinical, subjective, nonspecific, and often inadequate. There is a need to quantify the PD factors for an objective disease assessment. Among the various factors, postural instability (PI) is unresponsive to the existing treatment strategies resulting in morbidity. In this work, we review the physiology and pathophysiology of postural balance that is essential to treat PI among PD patients. Specifically, we discuss some of the reported factors for an early PI diagnosis, including age, nervous system lesions, genetic mutations, abnormal proprioception, impaired reflexes, and altered biomechanics. Though the contributing factors to PI have been identified, how their quantification to grade PI severity in a patient can help in treatment is not fully understood. By contextualizing the contributing factors, we aim to assist the future research efforts that underpin posturographical and histopathological studies to measure PI in PD. Once the pathology of PI is established, effective diagnostic tools and treatment strategies could be developed to curtail patient falls.

Glucocerebrosidase mutations and synucleinopathies: Toward a model of precision medicine

Glucocerebrosidase is a lysosomal enzyme. The characterization of a direct link between mutations in the gene coding for glucocerebrosidase (GBA1) with the development of Parkinson's disease and dementia with Lewy bodies has heightened interest in this enzyme. Although the mechanisms through which glucocerebrosidase regulates the homeostasis of α-synuclein remains poorly understood, the identification of reduced glucocerebrosidase activity in the brains of patients with PD and dementia with Lewy bodies has paved the way for the development of novel therapeutic strategies directed at enhancing glucocerebrosidase activity and reducing α-synuclein burden, thereby slowing down or even preventing neuronal death. Here we reviewed the current literature relating to the mechanisms underlying the cross talk between glucocerebrosidase and α-synuclein, the GBA1 mutation-associated clinical phenotypes, and ongoing therapeutic approaches targeting glucocerebrosidase. © 2018 International Parkinson and Movement Disorder Society.

Carriers of both GBA and LRRK2 mutations, compared to carriers of either, in Parkinson's disease: Risk estimates and genotype-phenotype correlations

INTRODUCTION

The clinical characteristics of Parkinson's disease (PD) associated with both the LRRK2 p.G2019S mutation and a GBA variant (LRRK2-GBA-PD) have not yet been determined.

METHODS

In this retrospective observational study of Ashkenazi-Jewish (AJ) PD patients, we describe the clinical course and characteristics of LRRK2-GBA-PD and estimate the risk to develop PD for the double mutation carriers. Odds ratios (OR) were estimated using published data on frequencies of GBA and LRRK2 mutations. Demographic and clinical data was retrieved from medical records and from rating at last visit.

RESULTS

Our analysis included 236 PD patients, divided into four groups: LRRK2-PD (n = 66), GBA-PD (n = 78), GBA-LRRK2-PD (n = 12) and mutation-negative PD (MNPD, n = 80 randomly selected). The estimated ORs in different models for GBA-LRRK2 PD were 15-28 (95% CI 6.7-72.0, p < 0.0001), compared to AJ controls. Using logistic regression (while controlling for sex, age at onset and PD duration), we found that probable REM-sleep behavior disorder (RBD) was significantly more common for GBA-PD than for LRRK2-PD, while none of the GBA-LRRK2-PD patients reported RBD. Dementia was significantly more common for GBA-PD than for the LRRK2-PD and MNPD. Psychosis was the most common for GBA-PD and least common for LRRK2-GBA-PD.

CONCLUSIONS

While GBA-PD is characterized by higher rates of dementia, probable RBD and psychosis, it seems that compared to the other groups, these features are less common for LRRK2-GBA-PD. This may imply to a possible protective effect of LRRK2 p.G2019S mutation among GBA variant carriers.

Neurological effects of glucocerebrosidase gene mutations

The association between Gaucher disease (GD) and Parkinson disease (PD) has been described for almost two decades. In the biallelic state (homozygous or compound heterozygous) mutations in the glucocerebrosidase gene (GBA) may cause GD, in which glucosylceramide, the sphingolipid substrate of the glucocerebrosidase enzyme (GCase), accumulates in visceral organs leading to a number of clinical phenotypes. In the biallelic or heterozygous state, GBA mutations increase the risk for PD. Mutations of the GBA allele are the most significant genetic risk factor for idiopathic PD, found in 5%–20% of idiopathic PD cases depending on ethnicity. The neurological consequences of GBA mutations are reviewed and the proposition that GBA mutations result in a disparate but connected range of clinically and pathologically related neurological features is discussed. The literature relating to the clinical, biochemical and genetic basis of GBA PD, type 1 GD and neuronopathic GD is considered highlighting commonalities and distinctions between them. The evidence for a unifying disease mechanism is considered.

Survival rates among Parkinson's disease patients who carry mutations in the LRRK2 and GBA genes

BACKGROUND

The G2019S mutation in the LRRK2 gene generates a milder PD phenotype compared with GBA-PD; however, genetic based survival studies are lacking.

OBJECTIVES

To compare mortality rates between LRRK2-PD, GBA-PD, and idiopathic PD patients (iPD).

METHODS

Patients were screened for the G2019S mutation in the LRRK2 gene and the seven common GBA mutations among Ashkenazi Jews, classified as mild and severe (mGBA, sGBA). Motor symptoms onset and date of death were ascertained, with mortality rates calculated for each group of patients.

RESULTS

Overall, 380 of 1,086 idiopathic PD patients, 49 of 159 LRRK2-PD, 56 of 148 mGBA-PD, and 13 of 49 sGBA-PD participants died by the time of analysis. LRRK2-PD tended to have longer survival compared to idiopathic PD whereas GBA status did not affect mortality. Genetic status did not predict mortality in a multivariate analysis.

CONCLUSION

Survival of patients with PD does not seem to be related to GBA status, whereas LRRK2 might confer higher survival rates.

Parkinson's disease phenotype is influenced by the severity of the mutations in the GBA gene

OBJECTIVE

Mutations in the glucocerebrosidase (GBA) gene are divided into mild and severe (mGBA, sGBA) based on their contribution to the phenotype of Gaucher disease (GD) among homozygotes. We conducted a longitudinal analysis of Parkinson's disease (PD) patients carrying mutations in the GBA gene to better characterize genotype-phenotype correlations.

METHODS

Patients underwent a comprehensive assessment of medical, neurological, cognitive and non-motor functions. Data from these patients was explored to evaluate differences in disease phenotype based on genotype.

RESULTS

A total of 355 PD patients participated in this study; 152 idiopathic PD patients, 139 mGBA, 48 sGBA and 16 GD-PD. Groups were similar in age, sex, years of education and age of onset. Both sGBA and GD-PD had higher Unified Parkinson Disease Rating Scale (UPDRS) scores (p = 0.041), higher frequencies of REM sleep behavior disorder (RBD) (p = 0.022) and hallucinations (p < 0.0001) compared to the other groups of patients. sGBA experienced more non-motor symptoms (p < 0.0001), depression (p < 0.001) and worse hyposmia (p = 0.010). Trail making test was significantly longer in GD-PD followed by sGBA, mGBA and iPD (p = 0.005).

DISCUSSION

Motor, cognitive, olfactory and psychiatric symptoms are more severe in sGBA and GD-PD compared to mGBA and iPD, reinforcing the notion that the severity of the PD phenotype is related to the severity of the mutation in the GBA gene.

Glucocerebrosidase Mutations in Parkinson Disease

Following the discovery of a higher than expected incidence of Parkinson Disease (PD) in Gaucher disease, a lysosomal storage disorder, mutations in the glucocerebrocidase (GBA) gene, which encodes a lysosomal enzyme involved in sphingolipid degradation were explored in the context of idiopathic PD. GBA mutations are now known to be the single largest risk factor for development of idiopathic PD. Clinically, on imaging and pharmacologically, GBA PD is almost identical to idiopathic PD, other than certain features that can be identified in the specialist research setting but not in routine clinical practice. In patients with a known GBA mutation, it is possible to monitor for prodromal signs of PD. The clinical similarity with idiopathic PD and the chance to identify PD at a pre-clinical stage provides a unique opportunity to research therapeutic options for early PD, before major irreversible neurodegeneration occurs. However, to date, the molecular mechanisms which lead to this increased PD risk in GBA mutation carriers are not fully elucidated. Experimental models to define the molecular mechanisms and test therapeutic options include cell culture, transgenic mice and other in vivo models amenable to genetic manipulation, such as drosophilia. Some key pathological pathways of interest in the context of GBA mutations include alpha synuclein aggregation, lysosomal-autophagy axis changes and endoplasmic reticulum stress. Therapeutic agents that exploit these pathways are being developed and include the small molecule chaperone Ambroxol. This review aims to summarise the main features of GBA-PD and provide insights into the pathological relevance of GBA mutations on molecular pathways and the therapeutic implications for PD resulting from investigation of the role of GBA in PD.

A novel p.L216I mutation in the glucocerebrosidase gene is associated with Parkinson's disease in Han Chinese patients

OBJECTIVES

Pathogenic mutations in the glucocerebrosidase (GBA) gene are associated with Parkinson's disease (PD), of which L444P and N370S are the most frequently observed in patients with PD. The aim of this study was to systematically explore variations in the coding regions of GBA in Han Chinese patients with PD, as well as to expand the GBA mutation spectrum.

MATERIAL AND METHODS

A total of 213 Han Chinese patients with PD and 348 controls were enrolled in the study. Whole coding regions of GBA were captured and sequenced by target region sequencing. Sanger sequencing was also used to confirm the identified variants.

RESULTS

We identified a novel variant (c. C646A; p.L216I; NM_001171811.1) of GBA in two unrelated patients, which was not observed in the controls. Both patients had early-onset PD and neither exhibited any motor-related symptoms. However, we did not find an L444P or N370S mutations in our patients.

CONCLUSIONS

The p.L216I mutation is a novel GBA mutation, which we identified in two Han Chinese patients with PD. The patients exhibited similar characteristics, which differed from those seen in patients with other GBA mutations. Future work is needed to investigate this mutation further, as well as larger cohort studies to explore other GBA mutations associated with PD in the Han Chinese and in other populations.

Glucocerebrosidase and Parkinson Disease: Molecular, Clinical, and Therapeutic Implications

Parkinson disease (PD) is a complex neurodegenerative disease characterised by multiple motor and non-motor symptoms. In the last 20 years, more than 20 genes have been identified as causes of parkinsonism. Following the observation of higher risk of PD in patients affected by Gaucher disease, a lysosomal disorder caused by mutations in the glucocerebrosidase (GBA) gene, it was discovered that mutations in this gene constitute the single largest risk factor for development of idiopathic PD. Patients with PD and GBA mutations are clinically indistinguishable from patients with idiopathic PD, although some characteristics emerge depending on the specific mutation, such as slightly earlier onset. The molecular mechanisms which lead to this increased PD risk in GBA mutation carriers are multiple and not yet fully elucidated, they include alpha-synuclein aggregation, lysosomal-autophagy dysfunction and endoplasmic reticulum stress. Moreover, dysfunction of glucocerebrosidase has also been demonstrated in non-GBA PD, suggesting its interaction with other pathogenic mechanisms. Therefore, GBA enzyme function represents an interesting pharmacological target for PD. Cell and animal models suggest that increasing GBA enzyme activity can reduce alpha-synuclein levels. Clinical trials of ambroxol, a glucocerebrosidase chaperone, are currently ongoing in PD and PD dementia, as is a trial of substrate reduction therapy. The aim of this review is to summarise the main features of GBA-PD and discuss the implications of glucocerebrosidase modulation on PD pathogenesis.

Sleep disorders and Parkinson disease; lessons from genetics

Parkinson disease is a common, age-related neurodegenerative disorder, projected to afflict millions of individuals in the near future. Understanding its etiology and identifying clinical, genetic or biological markers for Parkinson disease onset and progression is therefore of major importance. Various sleep-related disorders are the most common group of non-motor symptoms in advanced Parkinson disease, but they can also occur during its prodromal phase. However, with the exception of REM sleep behavior disorder, it is unclear whether they are part of the early pathological process of Parkinson disease, or if they develop as Parkinson disease advances because of treatments and neurodegeneration progression. The advancements in genetic studies in the past two decades have generated a wealth of information, and recent genetic studies offer new insight on the association of sleep-related disorders with Parkinson disease. More specifically, comparing genetic data between Parkinson disease and sleep-related disorders can clarify their association, which may assist in determining whether they can serve as clinical markers for Parkinson disease risk or progression. In this review, we discuss the current knowledge on the genetics of sleep-related disorders in Parkinson disease context, and the potential implications on research, diagnosis, counseling and treatment.

α-Synuclein accumulation and GBA deficiency due to L444P GBA mutation contributes to MPTP-induced parkinsonism

Background

Mutations in glucocerebrosidase (GBA) cause Gaucher disease (GD) and increase the risk of developing Parkinson’s disease (PD) and Dementia with Lewy Bodies (DLB). Since both genetic and environmental factors contribute to the pathogenesis of sporadic PD, we investigated the susceptibility of nigrostriatal dopamine (DA) neurons in L444P GBA heterozygous knock-in (GBA^+/L444P) mice to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a selective dopaminergic mitochondrial neurotoxin.

Method

We used GBA^+/L444P mice, α-synuclein knockout (SNCA^−/−) mice at 8 months of age, and adeno-associated virus (AAV)-human GBA overexpression to investigate the rescue effect of DA neuronal loss and susceptibility by MPTP. Mitochondrial morphology and functional assay were used to identify mitochondrial defects in GBA^+/L444P mice. Motor behavioral test, immunohistochemistry, and HPLC were performed to measure dopaminergic degeneration by MPTP and investigate the relationship between GBA mutation and α-synuclein. Mitochondrial immunostaining, qPCR, and Western blot were also used to study the effects of α-synuclein knockout or GBA overexpression on MPTP-induced mitochondrial defects and susceptibility.

Results

L444P GBA heterozygous mutation reduced GBA protein levels, enzymatic activity and a concomitant accumulation of α-synuclein in the midbrain of GBA^+/L444P mice. Furthermore, the deficiency resulted in defects in mitochondria of cortical neurons cultured from GBA^+/L444P mice. Notably, treatment with MPTP resulted in a significant loss of dopaminergic neurons and striatal dopaminergic fibers in GBA^+/L444P mice compared to wild type (WT) mice. Levels of striatal DA and its metabolites were more depleted in the striatum of GBA^+/L444P mice. Behavioral deficits, neuroinflammation, and mitochondrial defects were more exacerbated in GBA^+/L444P mice after MPTP treatment. Importantly, MPTP induced PD-like symptoms were significantly improved by knockout of α-synuclein or augmentation of GBA via AAV5-hGBA injection in both WT and GBA^+/L444P mice. Intriguingly, the degree of reduction in MPTP induced PD-like symptoms in GBA^+/L444Pα-synuclein (SNCA)^−/− mice was nearly equal to that in SNCA^−/− mice after MPTP treatment.

Conclusion

Our results suggest that GBA deficiency due to L444P GBA heterozygous mutation and the accompanying accumulation of α-synuclein render DA neurons more susceptible to MPTP intoxication. Thus, GBA and α-synuclein play dual physiological roles in the survival of DA neurons in response to the mitochondrial dopaminergic neurotoxin, MPTP.

Electronic supplementary material

The online version of this article (10.1186/s13024-017-0233-5) contains supplementary material, which is available to authorized users.

Clinical profiles associated with LRRK2 and GBA mutations in Brazilians with Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder characterized by remarkable phenotypic variability. Accumulated evidence points that the manifestation of PD clinical signs might be differentially modified by genetic factors, as mutations in LRRK2 and GBA genes. In this sense, the clarification of the genotype-phenotype correlations in PD has important implications in predicting prognosis and can contribute to the development of specific therapeutic approaches.

METHODS

Here, we conducted the first comparative analysis of motor and non-motor features in 17 LRRK2 and 22 GBA mutation carriers and 93 non-carriers unrelated PD patients from Brazil, a highly admixed population.

RESULTS

Significant differences were found between the three groups. LRRK2 PD patients presented more occurrence of familiar history. Resting tremor was observed in a lower frequency in GBA mutation carries. In contrast, gait freezing and dysautonomia was present in lower frequencies in LRRK2 carriers. Besides that, LRRK2 and GBA mutation carriers showed a higher incidence of depressive symptoms and a younger age at onset, when compared to non-carriers.

CONCLUSION

Our results suggest that specific mutations in GBA and LRRK2 influence the clinical signs of the disease, with significant implications for handling of specific patient groups.

Neuropsychiatric characteristics of GBA-associated Parkinson disease

Mutations in GBA1 are a well-established risk factor for Parkinson disease (PD). GBA-associated PD (GBA-PD) may have a higher burden of nonmotor symptoms than idiopathic PD (IPD). We sought to characterize the relationship between GBA-PD and neuropsychiatric symptoms. Subjects were screened for common GBA1 mutations. GBA-PD (n=31) and non-carrier (IPD; n=55) scores were compared on the Unified Parkinson Disease Rating Scale (UPDRS), Montreal Cognitive Assessment (MoCA), Beck Depression Inventory (BDI), and the State-Trait Anxiety Index (STAI). In univariate comparisons, GBA-PD had a greater prevalence of depression (33.3%) versus IPD (13.2%) (p<0.05). In regression models controlling for age, sex, disease duration, motor disability, and MoCA score, GBA-PD had an increased odds of depression (OR 3.66, 95% CI 1.13-11.8) (p=0.03). Post-hoc analysis stratified by sex showed that, among men, GBA-PD had a higher burden of trait anxiety and depression than IPD; this finding was sustained in multivariate models. Among women, GBA-PD did not confer greater psychiatric morbidity than IPD. These results suggest that GBA1 mutations confer greater risk of neuropsychiatric morbidity in PD, and that sex may affect this association.

A cognitive fMRI study in non-manifesting LRRK2 and GBA carriers

Mutations in the GBA and LRRK2 genes account for one-third of the prevalence of Parkinson's disease (PD) in Ashkenazi Jews. Non-manifesting carriers (NMC) of these mutations represent a population at risk for future development of PD. PD patient who carry mutations in the GBA gene demonstrates more significant cognitive decline compared to idiopathic PD patients. We assessed cognitive domains using fMRI among NMC of both LRRK2 and GBA mutations to better understand pre-motor cognitive functions in these populations. Twenty-one LRRK2-NMC, 10 GBA-NMC, and 22 non-manifesting non-carriers (NMNC) who participated in this study were evaluated using the standard questionnaires and scanned while performing two separate cognitive tasks; a Stroop interference task and an N-Back working memory task. Cerebral activation patterns were assessed using both whole brain and predefined region of interest (ROI) analysis. Subjects were well matched in all demographic and clinical characteristics. On the Stroop task, in spite of similar behavior, GBA-NMC demonstrated increased task-related activity in the right medial frontal gyrus and reduced task-related activity in the left lingual gyrus compared to both LRRK2-NMC and NMNC. In addition, GBA-NMC had higher activation patterns in the incongruent task compared to NMNC in the left medial frontal gyrus and bilateral precentral gyrus. No whole-brain differences were noted between groups on the N-Back task. Paired cognitive and task-related performance between GBA-NMC, LRRK2-NMC, and NMNC could indicate that the higher activation patterns in the incongruent Stroop condition among GBA-NMC compared to LRRK2-NMC and NMNC may represent a compensatory mechanism that enables adequate cognitive performance.

Effect of a Leucine-rich Repeat Kinase 2 Variant on Motor and Non-motor Symptoms in Chinese Parkinson's Disease Patients

The G2385R variant of the leucine-rich repeat kinase 2 (LRRK2) is strongly associated with Parkinson's disease (PD) in Asian populations. However, it is still unclear whether the clinical phenotype of PD patients with the G2385R variant can be distinguished from that of patients with idiopathic PD. In this study, we investigated motor and non-motor symptoms of LRRK2 G2385R variant carriers in a Chinese population. We genotyped 1031 Chinese PD patients for the G2385R variant of the LRRK2 gene, and examined the demographic and clinical characteristics of LRRK2 G2385R variant carrier and non-carrier PD patients. LRRK2 G2385R variant carriers were more likely to present the postural instability and gait difficulty dominant (PIGD) phenotype. This variant was also significantly associated with motor fluctuations and the levodopa equivalent dose (LED). G2385R variant carriers had higher REM sleep behavior disorder (RBD) screening questionnaire (RBDSQ) score and more RBD symptoms compared with non-carriers. We concluded that the G2385R variant could be a risk factor for the PIGD phenotype, motor fluctuations, LED values and RBD symptoms.

Genetic and Clinical Predictors of Deep Brain Stimulation in Young-Onset Parkinson's Disease

OBJECTIVE

In a cohort of patients with young-onset Parkinson's disease (PD), the authors assessed (1) the prevalence of genetic mutations in those who enrolled in deep brain stimulation (DBS) programs compared with those who did not enroll DBS programs and (2) specific genetic and clinical predictors of DBS enrollment.

METHODS

Subjects were participants from 3 sites (Columbia University, Rush University, and the University of Pennsylvania) in the Consortium on Risk for Early Onset Parkinson's Disease (CORE-PD) who had an age at onset < 51 years. The analyses presented here focus on glucocerebrosidase (GBA), leucine-rich repeat kinase 2 (LRRK2), and parkin (PRKN) mutation carriers. Mutation carrier status, demographic data, and disease characteristics in individuals who did and did not enroll in DBS were analyzed. The association between mutation status and DBS placement was assessed in logistic regression models.

RESULTS

Patients who had PD with either GBA, LRRK2, or PRKN mutations were more common in the DBS group (n = 99) compared with the non-DBS group (n = 684; 26.5% vs. 16.8%, respectively; P = 0.02). In a multivariate logistic regression model, GBA mutation status (odds ratio, 2.1; 95% confidence interval, 1.0-4.3; P = 0.05) was associated with DBS surgery enrollment. However, when dyskinesia was included in the multivariate logistic regression model, dyskinesia had a strong association with DBS placement (odds ratio, 3.8; 95% confidence interval, 1.9-7.3; P < 0.0001), whereas the association between GBA mutation status and DBS placement did not persist (P = 0.25).

CONCLUSIONS

DBS populations are enriched with genetic mutation carriers. The effect of genetic mutation carriers on DBS outcomes warrants further exploration.