Cognitive and Antipsychotic Medication Use in Monoallelic GBA-Related Parkinson Disease

Quetiapine, Clozapine, and Pimavanserin Treatment Response in Monogenic Parkinson's Disease Psychosis: A Systematic Review

Psychotic symptoms frequently occur in idiopathic Parkinson's disease (PD) and often require treatment with antipsychotic therapy. Most antipsychotics have the potential to worsen the motor symptoms of PD; quetiapine, clozapine, and pimavanserin are commonly used for the treatment of idiopathic PD because these medications tend to be comparatively well tolerated. Although psychotic symptoms may also occur in monogenic forms of PD, no reviews have focused on the use of antipsychotic medications in this context. The objective of the present systematic review was to characterize the effectiveness and tolerability of quetiapine, clozapine, and pimavanserin in monogenic PD-associated psychosis. A literature search was performed with PubMed, Scopus, and Embase. The search yielded 24 eligible articles describing 30 individuals, although treatment response with respect to psychotic symptoms was described in only 11 cases; of these, six individuals experienced symptomatic improvement or remission (four with clozapine and two with quetiapine), two exhibited a poor therapeutic response (one to clozapine and one to quetiapine), and the other three responded initially to antipsychotic therapy before experiencing a recurrence of symptoms. The use of quetiapine and clozapine in GBA variant-associated PD is briefly reviewed separately. Notably, no reports of pimavanserin therapy were identified. In keeping with the idiopathic PD literature, relatively low doses of medication were used in most cases. Lastly, side effects were rarely reported. Although quetiapine and particularly clozapine may be effective and well tolerated in the treatment of monogenic PD psychosis, this review highlights the paucity of available evidence to guide clinical decision making in this context.

GBA-associated PD: chances and obstacles for targeted treatment strategies

Given the clear role of GBA in the pathogenesis of Parkinson’s disease (PD) and its impact on phenotypical characteristics, this review provides an overview of the current knowledge of GBA-associated PD with a special focus on clinical trajectories and the underlying pathological mechanisms. Importantly, differences and characteristics based on mutation severity are recognized, and current as well as potential future treatment options are discussed. These findings will inform future strategies for patient stratification and cohort enrichment as well as suitable outcome measures when designing clinical trials.

Exploring the Genotype-Phenotype Correlation in GBA-Parkinson Disease: Clinical Aspects, Biomarkers, and Potential Modifiers

Variants in the glucocerebrosidase (GBA) gene are the most common genetic risk factor for Parkinson disease (PD). These include pathogenic variants causing Gaucher disease (GD) (divided into “severe,” “mild,” or “complex”—resulting from recombinant alleles—based on the phenotypic effects in GD) and “risk” variants, which are not associated with GD but nevertheless confer increased risk of PD. As a group, GBA-PD patients have more severe motor and nonmotor symptoms, faster disease progression, and reduced survival compared with noncarriers. However, different GBA variants impact variably on clinical phenotype. In the heterozygous state, “complex” and “severe” variants are associated with a more aggressive and rapidly progressive disease. Conversely, “mild” and “risk” variants portend a more benign course. Homozygous or compound heterozygous carriers usually display severe phenotypes, akin to heterozygous “complex” or “severe” variants carriers. This article reviews genotype–phenotype correlations in GBA-PD, focusing on clinical and nonclinical aspects (neuroimaging and biochemical markers), and explores other disease modifiers that deserve consideration in the characterization of these patients.

GBA-Associated Synucleinopathies: Prime Candidates for Alpha-Synuclein Targeting Compounds

With disease-modifying compounds targeting alpha-synuclein available in clinical trials, patient stratification according to alpha-synuclein-specific enrichment strategies is a much-needed prerequisite. Such a scenario will be exemplified for GBA, one major genetic risk factor that is specifically associated with the alpha-synucleinopathies: Parkinson's disease and dementia with Lewy bodies.

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.

Nosology and Phenomenology of Psychosis in Movement Disorders

BACKGROUND

Psychotic symptoms, such as delusions and hallucinations, are part of the clinical picture of several conditions presenting movement disorders. Phenomenology and epidemiology of psychosis in Parkinson's disease have received wide attention; however, the presence of psychosis in other movement disorders is, comparatively, less well known.

OBJECTIVES

To review psychotic symptoms present in different movement disorders.

METHODS

A comprehensive and structured literature search was performed to identify and analyze data on patients with movement disorders and comorbid psychosis.

RESULTS

In monogenic parkinsonisms, such as PARK-GBA, PARK-LRRK2, and PARK-SNCA, visual hallucinations related to dopamine replacement therapy are frequent as well as are delusions in PARK-LRRK2 and PARK-SNCA, but not in PARK-GBA. Different types of delusions and hallucinations are found in Huntington's disease and other choreic disorders. In Tourette's syndrome, paranoid delusions as well as visual, olfactory, and auditory hallucinations have been described, which usually develop after an average of 10 years of disease. Delusions in ataxias are more frequent in ATX-TBP, ATX-ATN1, and ATX-ATXN3, whereas it is rare in Friedreich's ataxia. Psychosis is also a prominent and frequent clinical feature in Fahr's disease, Wilson's disease, neurodegeneration with brain iron accumulation, and some lysosomal storage disorders, whereas it is uncommon in atypical parkinsonisms and dystonia. Psychosis usually occurs at late disease stages, but may appear as onset symptoms of the disease, especially in Wilson's disease, Huntington's disease, late-onset Tays-Sachs, and Niemann-Pick.

CONCLUSION

Psychosis is a frequent comorbidity in most hyper- and hypokinetic movement disorders. Appropriate recognition is relevant both in the early and late disease stages.

GBA1 mutations: Prospects for exosomal biomarkers in α-synuclein pathologies

The discovery that patients with Gaucher Disease (GD), a rare lysosomal storage disorder, were developing symptoms similar to Parkinson's disease (PD) led to investigation of the relationship between the two seemingly unrelated pathologies. GD, an autosomal recessive disorder, is the result of a biallelic mutation in the gene GBA1, which encodes for the enzyme glucocerebrosidase (GCase). Since the observation of its relation to PD, GBA1 mutations have become recognized as the most common genetic risk factor for development of synucleinopathies such as PD and dementia with Lewy bodies. Although the exact mechanism by which GBA1 mutations promote PD is unknown, current understanding suggests that impaired GCase inhibits lysosomal activity and decreases the overall ability of the cell to degrade proteins, specifically the neuronal protein α-synuclein. Decreased elimination of α-synuclein can lead to its abnormal accumulation and aggregation, an important component of PD development. Further understanding of how decreased GCase activity increases risk for α-synuclein pathology can assist with the development of clinical biomarkers for early detection of synucleinopathies, as well as promote novel treatments tailored for people with a GBA1 mutation. Historically, α-synuclein has not been a reliable biomarker for PD. However, recent research on α-synuclein content within exosomes, which are small vesicles released by cells that carry specific cellular cargo, has yielded encouraging results. Moreover, decreased GCase activity has been shown to influence exosomal contents. Exosomes have emerged as a promising new avenue for the identification of novel biomarkers and therapeutic targets aimed at improving neuronal GCase function and limiting the development of synucleinopathies.

Association of Subthalamic Deep Brain Stimulation With Motor, Functional, and Pharmacologic Outcomes in Patients With Monogenic Parkinson Disease: A Systematic Review and Meta-analysis

IMPORTANCE

Comparative outcomes among different monogenic forms of Parkinson disease after subthalamic nucleus deep brain stimulation (STN DBS) remain unclear.

OBJECTIVE

To compare clinical outcomes in patients with the most common monogenic forms of Parkinson disease treated with STN DBS.

DESIGN, SETTING, AND PARTICIPANTS

Systematic review and meta-analysis in which a PubMed search of interventional and noninterventional studies of Parkinson disease with LRRK2, GBA, or PRKN gene mutations published between January 1, 1990, and May 1, 2018, was conducted. Among the inclusion criteria were articles that reported the Motor subscale of the Unified Parkinson's Disease Rating Scale Part III (UPDRS-III) before and after STN DBS treatment, that involved human participants, and that were published in the English language. Studies that used aggregated data from patients with different genetic mutations were excluded, and so were studies with assumed but not confirmed genetic data or incomplete follow-up data.

MAIN OUTCOMES AND MEASURES

Changes in UPDRS-III scores and levodopa equivalent daily dose (LEDD) were analyzed for each monogenic form of Parkinson disease. Additional end points included activities of daily living (UPDRS-II), motor complications (UPDRS-IV), and cognitive function.

RESULTS

Of the 611 eligible studies, 17 (2.8%) met the full inclusion criteria; these 17 studies consisted of 8 cohort studies (47.1%), 3 case series (17.6%), and 6 case reports (35.3%), and they involved a total of 518 patients. The UPDRS-III score improved by 46% in LRRK2 (mean change, 23.0 points; 95% CI, 15.2-30.8; P < .001), 49% in GBA (20.0 points; 95% CI, 4.5-35.5; P = .01), 43% in PRKN (24.1 points; 95% CI, 12.4-35.9; P < .001), and 53% in idiopathic Parkinson disease (25.2 points; 95% CI, 21.3-29.2; P < .001). The LEDD was reduced by 61% in LRRK2 (mean change, 711.9 mg/d; 95% CI, 491.8-932.0; P < .001), 22% in GBA (269.2 mg/d; 95% CI, 226.8-311.5; P < .001), 61% in PRKN (494.8 mg/d; 95% CI, -18.1 to -1007.8; P = .06), and 55% in idiopathic Parkinson disease (681.8 mg/d; 95% CI, 544.4-819.1; P < .001). Carriers of the PRKN mutations showed sustained improvements in UPDRS-II and UPDRS-IV, whereas LRRK2 mutation carriers sustained improvements only in UPDRS-IV. Carriers of the GBA mutation showed worse postsurgical cognitive and functional performance.

CONCLUSIONS AND RELEVANCE

Treatment with STN DBS for patients with Parkinson disease with LRRK2, GBA, or PRKN mutations appears to be associated with similar motor outcomes but different changes in dopaminergic dose, activities of daily living, motor complications, and cognitive functions.

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.

[The clinical features of Parkinson's disease in patients with mutations and polymorphic variants of GBA gene]

BACKGROUND

Mutations in the glucocerebrosidase gene (GBA) increase the risk of Parkinson's disease (PD) by 6-10 times in all populations and are associated with the early-onset of PD, development of cognitive impairment and presence of psychotic disorders. At the same time, polymorphic variants associated with the twofold increase in the risk of PD were also described in the GBA gene.

AIM

To estimate the clinical features of PD in patients with mutations and polymorphic variants of the GBA gene.

MATERIAL AND METHODS

Evaluation of motor, cognitive, emotional, psychotic and autonomic dysfunctions in patients with mutations (N370S, L444P) and polymorphic variants (E326K, T369M) in the GBA gene was performed using clinical scales.

RESULTS

Patients with mutations (mGBA-PD), and with polymorphic variants (pGBA-PD) in the GBA gene were compared with the group of patients with sporadic PD (sPD). Compared to sPD, affective disorders (depression and anxiety) were more expressed in the mGBA-PD group (p=0.001) and the general GBA-PD group (p=0.001) assessed with Sheehan anxiety rating scale, in the pGBA-PD group (p=0.012) and the general GBA-PD group (p=0.05) assessed with the NPI, in the mGBA-PD (p=0.003), pGBA-PD (p=0.022), and general GBA-PD groups (p=0.001) assessed with the Hospital Anxiety and Depression scale (HADS 'A'), and in the pGBA-PD group (p=0.005) assessed with the HADS 'D'. Non-motor symptoms assessed with the PD-NMS were more expressed in the pGBA-PD patients (p=0.007) and in the total group with GBA-PD (p=0,014) compared to sPD. Cognitive impairment measured with MMSE was more marked in mGBA-PD patients (p=0.022). Differences in motor and non-motor clinical symptoms between pGBA-PD and mGBA-PD groups were not found.

CONCLUSION

Thus, clinical features of non-motor symptoms were described both in carriers of GBA mutations and polymorphisms. Identification of the specific clinical phenotype of PD in carriers of GBA polymorphic variants is important due to their relatively high prevalence in PD patients.

Cognitive and motor functioning in elderly glucocerebrosidase mutation carriers

Mutations in the glucocerebrosidase (GBA) gene are a strong genetic risk factor for the development of Parkinson's disease and dementia with Lewy Bodies. However the penetrance of GBA mutations is low for these diseases in heterozygous carriers. The aim of this study was to examine the relationship between mutation status and cognitive and motor functioning in a sample of community-dwelling older adults. Using linear mixed effects models, we examined the effect of heterozygous mutation status on 736 community-dwelling older adults (≥70 years) without dementia or Parkinson's disease assessed over an average of 6 years, 28 of whom had a single GBA mutation (primarily N370S). Verbal memory was measured using the picture version of the Free and Cued Selective Reminding Test, and carriers showed significantly (p < 0.05) greater decline in verbal memory over time. There was no difference in motor function or any other cognitive domain. Taken together, these results suggest an effect, but an overall limited burden, of harboring a single GBA mutation in aging mutation carriers.

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.

Advances in GBA-associated Parkinson's disease--Pathology, presentation and therapies

GBA mutations are to date the most common genetic risk factor for Parkinson's disease. The GBA gene encodes the lysomal hydrolase glucocerebrosidase. Whilst bi-allelic GBA mutations cause Gaucher disease, both mono- and bi-allelic mutations confer risk for Parkinson's disease. Clinically, Parkinson's disease patients with GBA mutations resemble idiopathic Parkinson's disease patients. However, these patients have a modest reduction in age-of-onset of disease and a greater incidence of cognitive decline. In some cases, GBA mutations are also responsible for familial Parkinson's disease. The accumulation of α-synuclein into Lewy bodies is the central neuropathological hallmark of Parkinson's disease. Pathologic GBA mutations reduce enzymatic function. A reduction in glucocerebrosidase function increases α-synuclein levels and propagation, which in turn inhibits glucocerebrosidase in a feed-forward cascade. This cascade is central to the neuropathology of GBA-associated Parkinson's disease. The lysosomal integral membrane protein type-2 is necessary for normal glucocerebrosidase function. Glucocerebrosidase dysfunction also increases in the accumulation of β-amyloid and amyloid-precursor protein, oxidative stress, neuronal susceptibility to metal ions, microglial and immune activation. These factors contribute to neuronal death. The Mendelian Parkinson's disease genes, Parkin and ATP13A2, intersect with glucocerebrosidase. These factors sketch a complex circuit of GBA-associated neuropathology. To clinically interfere with this circuit, central glucocerebrosidase function must be improved. Strategies based on reducing breakdown of mutant glucocerebrosidase and increasing the fraction that reaches the lysosome has shown promise. Breakdown can be reduced by interfering with the ability of heat-shock proteins to recognize mutant glucocerebrosidase. This underlies the therapeutic efficacy of certain pharmacological chaperones and histone deacetylase inhibitors. These therapies are promising for Parkinson's disease, regardless of mutation status. Recently, there has been a boom in studies investigating the role of glucocerebrosidase in the pathology of Parkinson's disease. This merits a comprehensive review of the current cell biological processes and pathological pictures involving Parkinson's disease associated with GBA mutations.