GBA Mutations Are Associated With Earlier Onset and Male Sex in Dementia With Lewy Bodies

A review of type 3 Gaucher disease: unique neurological manifestations and advances in treatment

Gaucher disease (GD) is a rare lysosomal storage disease that is caused by mutations in the GBA gene. It is classified into three main phenotypes according to the patient's clinical presentation. Of these, chronic neuronopathic GD (GD3) is characterized by progressive neurological damage. Understanding the unique neurological manifestations of GD3 has important diagnostic and therapeutic implications. Our article summarizes the neurological symptoms specific to GD3 and related therapeutic advances, and it highlights the relevance of the gene to clinical symptoms, so as to provide a reference for the diagnosis and treatment of GD3.

Increased glucosylsphingosine levels and Gaucher disease in GBA1-associated Parkinson's disease

INTRODUCTION

Gaucher's disease (GD) is caused by biallelic mutations in the GBA1 gene, leading to reduced glucocerebrosidase (GCase) activity and substrate (glucosylceramide and glucosylsphingosine, GlcSph) accumulation. GBA1 variant carriers are at risk of Parkinson's disease (PD), but only those with biallelic mutations cross the threshold of GCase reduction, leading to substrate accumulation and GD. The link between GBA1 mutations, GD and PD is not fully understood. Here we aimed at reporting the results of a large PD population screening with dried blood spot tests for GD.

METHODS

We measured GCase activity and GlcSph levels in 1344 PD patients with dried blood spot tests, and performed GBA1 genetic sequencing.

RESULTS

While the GCase activity was reduced in GBA1-PD carriers compared to wild type PD, GlcSph was increased in GBA1-PD compared to GBA1-controls, regardless of the underlying type of GBA1 variant. 13.6 % and 0.4 % of PD patients had mono- or biallelic GBA1 mutations respectively. GCase deficiency, lipid accumulation and clinical manifestations of GD was detected in five PD patients with biallelic GBA1 mutations, of whom four had a risk combined with a GD causing variant.

CONCLUSIONS

GlcSph appearing higher in PD may represent a reliable biomarker of the disease and deserves to be further investigated. This study highlights the importance of screening PD patients for possible underlying GD, which is a treatable condition that should not be missed. We diagnosed GD cases carrying a "risk" variant in one allele, which is an unprecedented finding deserving further investigation.

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.

Parkinson's disease in a patient with GBA and LRRK2 covariants after acute hypoxic insult: a case report

BACKGROUND

The glucocerebrosidase (GBA) and leucine-rich repeat kinase 2 (LRRK2) genes are associated with the risk of sporadic Parkinson's disease (PD). As an environmental factor, hypoxic insults may impair dopamine neurons in the substantia nigra and exacerbate PD symptoms. However, covariants of GBA and LRRK2 combined with hypoxic insults in clinical cases of Parkinsonism have not yet been reported.

CASE PRESENTATION

A 69-year-old male patient with PD and his relatives were clinically characterized and sequenced using the whole-exome technique. A novel covariant, c.1448 T > C (p. L483P, rs421016) on GBA and c.691 T > C (p. S231P, rs201332859) on LRRK2 were identified in this patient who first developed bradykinesia and rigidity in the neck at one month after an acute hypoxic insult during mountaineering. The patient presented with a mask-like face, festinating gait, asymmetric bradykinesia, and moderate rigidity. These symptoms were treated with levodopa and pramipexole, resulting in a 65% improvement in the Unified Parkinson's Disease Rating Scale (UPDRS) motor score. These parkinsonian symptoms persisted and developed with hallucinations, constipation, and rapid eye movement sleep behavior disorder. After 4 years, the patient exhibited a wearing-off phenomenon and died from pulmonary infection 8 years after disease onset. His parents, wife, and siblings were not diagnosed with PD, and his son carried p. L483P without Parkinsonism-like symptoms.

CONCLUSIONS

This is a case report of PD after hypoxic insult in a patient carrying a covariant of GBA and LRRK2. This study may help us understand the interaction between genetic and environmental factors in clinical PD.

Sex differences in dementia with Lewy bodies: Focused review of available evidence and future directions

In this review, we summarize the current knowledge on sex differences in dementia with Lewy bodies (DLB) relating to epidemiology, clinical features, neuropathology, biomarkers, disease progression, and caregiving. While many studies show a higher DLB prevalence in men, this finding is inconsistent and varies by study approach. Visual hallucinations may be more common and occur earlier in women with DLB, whereas REM sleep behavior disorder may be more common and occur earlier in men. Several studies report a higher frequency of parkinsonism in men with DLB, while the frequency of fluctuations appears similar between sexes. Women tend to be older, have greater cognitive impairment at their initial visit, and are delayed in meeting DLB criteria compared to men. Women are also more likely to have Lewy body disease with co-existing AD-related pathology than so-called "pure" Lewy body disease, while men may present with either. Research is mixed regarding the impact of sex on DLB progression. Biomarker and treatment research assessing for sex differences is lacking. Women provide the majority of caregiving in DLB but how this affects the caregiving experience is uncertain. Gaining a better understanding of sex differences will be instrumental in aiding future development of sex-specific strategies in DLB for early diagnosis, care, and drug development.

GBA1 Gene Mutations in α-Synucleinopathies-Molecular Mechanisms Underlying Pathology and Their Clinical Significance

α-Synucleinopathies comprise a group of neurodegenerative diseases characterized by altered accumulation of a protein called α-synuclein inside neurons and glial cells. This aggregation leads to the formation of intraneuronal inclusions, Lewy bodies, that constitute the hallmark of α-synuclein pathology. The most prevalent α-synucleinopathies are Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). To date, only symptomatic treatment is available for these disorders, hence new approaches to their therapy are needed. It has been observed that GBA1 mutations are one of the most impactful risk factors for developing α-synucleinopathies such as PD and DLB. Mutations in the GBA1 gene, which encodes a lysosomal hydrolase β-glucocerebrosidase (GCase), cause a reduction in GCase activity and impaired α-synuclein metabolism. The most abundant GBA1 gene mutations are N370S or N409S, L444P/L483P and E326K/E365K. The mechanisms by which GCase impacts α-synuclein aggregation are poorly understood and need to be further investigated. Here, we discuss some of the potential interactions between α-synuclein and GCase and show how GBA1 mutations may impact the course of the most prevalent α-synucleinopathies.

Differences in Sex-Specific Frequency of Glucocerebrosidase Variant Carriers and Familial Parkinsonism

BACKGROUND

Although men and women with the LRRK2 G2019S variant appear to be equally likely to have Parkinson's disease (PD), the sex-distribution among glucocerebrosidase (GBA) variant carriers with PD, including limited to specific variant severities of GBA, is not well understood. Further, the sex-specific genetic contribution to PD without a known genetic variant is controversial.

OBJECTIVES

To better understand sex differences in genetic contribution to PD, especially sex-specific frequencies among GBA variant carriers with PD (GBA PD) and LRRK2-G2019S variant carriers with PD (LRRK2 PD).

METHODS

We assess differences in the sex-specific frequency in GBA PD, including in subsets of GBA variant severity, LRRK2 PD, and idiopathic PD in an Ashkenazi Jewish cohort with PD. Further, we expand prior work evaluating differences in family history of parkinsonism.

RESULTS

Both idiopathic PD (267/420 men, 63.6%) (P < 0.001) and GBA PD overall (64/107, 59.8%) (P = 0.042) were more likely to be men, whereas no difference was seen in LRRK2 PD (50/99, 50.5%) and LRRK2/GBA PD (5/10, 50%). However, among GBA PD probands, severe variant carriers were more likely to be women (15/19 women, 79.0%) (P = 0.005), whereas mild variant carriers (44/70 men, 62.9%) (P = 0.039) and risk-variant carriers (15/17 men, 88.2%) (P = 0.001) were more likely to be men.

CONCLUSIONS

Our study demonstrates that the male-sex predominance present in GBA PD overall was not consistent across GBA variant severities, and a female-sex predominance was present among severe GBA variant carriers. Therefore, research and trial designs for PD should consider sex-specific differences, including across GBA variant severities. © 2022 International Parkinson and Movement Disorder Society.

Exploring the link between GBA1 mutations and Dementia with Lewy bodies, A mini-review

IMPORTANCE

Dementia with Lewy bodies (DLB) is a neurodegenerative disease linked to abnormal accumulation of phosphorylated α-synuclein. GBA1 is the gene encoding the lysosomal enzyme glucocerebrosidase (GCase), whose mutations are a risk factor of DLB.

OBJECTIVE

To report all available data exploring the association between GBA1 mutations and DLB.

EVIDENCE REVIEW

All publications focused on GCase and DLB in humans between 2003 and 2022 were identified on PubMed, Cochrane and ClinicalTrials.gov.

FINDINGS

29 studies were included and confirmed the strong association between GBA1 mutations and DLB (Odds Ratio [OR]: 8.28). GBA1 mutation carriers presented a more malignant phenotype, with earlier symptom onset, more severe motor and cognitive dysfunctions, more visual hallucinations and rapid eye movement sleep disorder. GBA1 mutations were associated with "purer" neuropathological DLB. No therapeutic recommendations exist and clinical trials targeting GCase are just starting in DLB patients.

CONCLUSIONS AND RELEVANCE

This review reports a link between GBA1 mutations and the DLB phenotype with limited evidence due to the small number of studies.

Predictors of RBD progression and conversion to synucleinopathies

Purpose of review

Rapid eye movement (REM) sleep behaviour disorder (RBD) is considered the expression of the initial neurodegenerative process underlying synucleinopathies and constitutes the most important marker of their prodromal phase. This article reviews recent research from longitudinal research studies in isolated RBD (iRBD) aiming to describe the most promising progression biomarkers of iRBD and to delineate the current knowledge on the level of prediction of future outcome in iRBD patients at diagnosis.

Recent findings

Longitudinal studies revealed the potential value of a variety of biomarkers, including clinical markers of motor, autonomic, cognitive, and olfactory symptoms, neurophysiological markers such as REM sleep without atonia and electroencephalography, genetic and epigenetic markers, cerebrospinal fluid and serum markers, and neuroimaging markers to track the progression and predict phenoconversion. To-date the most promising neuroimaging biomarker in iRBD to aid the prediction of phenoconversion is striatal presynaptic striatal dopaminergic dysfunction.

Summary

There is a variety of potential biomarkers for monitoring disease progression and predicting iRBD conversion into synucleinopathies. A combined multimodal biomarker model could offer a more sensitive and specific tool. Further longitudinal studies are warranted to iRBD as a high-risk population for early neuroprotective interventions and disease-modifying therapies.

Monogenetic Forms of Parkinson’s Disease – Bridging the Gap Between Genetics and Biomarkers

The therapy of neurodegenerative diseases such as Parkinson’s disease (PD) is still limited to the treatment of symptoms and primarily aimed at compensating for dopaminergic hypofunction. Numerous disease-modifying therapies currently in the pipeline attempt to modify the underlying pathomechanisms. In recent decades, the results of molecular genetics and biomarker research have raised hopes of earlier diagnosis and new neuroprotective therapeutic approaches. As the disease-causing processes in monogenetic forms of PD are better understood than in sporadic PD, these disease subsets are likely to benefit first from disease-modifying therapies. Recent studies have suggested that disease-relevant changes found in genetically linked forms of PD (i.e., PARK-LRRK2, PARK-GBA) can also be reproduced in patients in whom no genetic cause can be found, i.e., those with sporadic PD. It can, therefore, be assumed that as soon as the first causal therapy for genetic forms of PD is approved, more patients with PD will undergo genetic testing and counseling. Regarding future neuroprotective trials in neurodegenerative diseases and objective parameters such as biomarkers with high sensitivity and specificity for the diagnosis and course of the disease are needed. These biomarkers will also serve to monitor treatment success in clinical trials. Promising examples in PD, such as alpha-synuclein species, lysosomal enzymes, markers of amyloid and tau pathology, and neurofilament light chain, are under investigation in blood and CSF. This paper provides an overview of the opportunities and current limitations of monogenetic diagnostic and biomarker research in PD and aims to build a bridge between current knowledge and association with PD genetics and biomarkers.

Phenotypic Heterogeneity among GBA p.R202X Carriers in Lewy Body Spectrum Disorders

We describe the clinical and neuropathologic features of patients with Lewy body spectrum disorder (LBSD) carrying a nonsense variant, c.604C>T; p.R202X, in the glucocerebrosidase 1 (GBA) gene. While this GBA variant is causative for Gaucher's disease, the pathogenic role of this mutation in LBSD is unclear. Detailed neuropathologic evaluation was performed for one index case and a structured literature review of other GBA p.R202X carriers was conducted. Through the systematic literature search, we identified three additional reported subjects carrying the same GBA mutation, including one Parkinson's disease (PD) patient with early disease onset, one case with neuropathologically-verified LBSD, and one unaffected relative of a Gaucher's disease patient. Among the affected subjects carrying the GBA p.R202X, all males were diagnosed with Lewy body dementia, while the two females presented as PD. The clinical penetrance of GBA p.R202X in LBSD patients and families argues strongly for a pathogenic role for this variant, although presenting with a striking phenotypic heterogeneity of clinical and pathological features.

Glucocerebrosidase mutations: A paradigm for neurodegeneration pathways

Biallelic (homozygous or compound heterozygous) glucocerebrosidase gene (GBA) mutations cause Gaucher disease, whereas heterozygous mutations are numerically the most important genetic risk factor for Parkinson disease (PD) and are associated with the development of other synucleinopathies, notably Dementia with Lewy Bodies. This phenomenon is not limited to GBA, with converging evidence highlighting further examples of autosomal recessive disease genes increasing neurodegeneration risk in heterozygous mutation carriers. Nevertheless, despite extensive research, the cellular mechanisms by which mutations in GBA, encoding lysosomal enzyme β-glucocerebrosidase (GCase), predispose to neurodegeneration remain incompletely understood. Alpha-synuclein (A-SYN) accumulation, autophagic lysosomal dysfunction, mitochondrial abnormalities, ER stress and neuroinflammation have been proposed as candidate pathogenic pathways in GBA-linked PD. The observation of GCase and A-SYN interactions in PD initiated the development and evaluation of GCase-targeted therapeutics in PD clinical trials.

Sex differences for phenotype in pathologically defined dementia with Lewy bodies

INTRODUCTION

Sex differences in dementia with Lewy bodies (DLB) have been reported in clinically defined cohorts; however, clinical diagnostic accuracy in DLB is suboptimal and phenotypic differences have not been assessed in pathologically confirmed participants.

METHODS

Core DLB features were compared across 55 women and 156 men with pathologically defined DLB in the National Alzheimer's Coordinating Center. These analyses were repeated for 55 women and 55 men matched for age, education and tau burden.

RESULTS

In the total sample, women died older, had fewer years of education, had higher tau burden but were less likely to be diagnosed with dementia and clinical DLB. In the matched sample, visual hallucinations continued to be less common in women, and fewer women met clinical DLB criteria.

DISCUSSION

Sex impacts clinical manifestations of underlying pathologies in DLB. Despite similar underlying Lewy body pathology, women are less likely to manifest core DLB features and may be clinically underdiagnosed.

Family History is Associated with Phenotype in Dementia with Lewy Bodies

It is currently unknown whether patients with dementia with Lewy bodies (DLB) with relatives with dementia or Parkinson’s disease (familial DLB patients) have a different phenotype than sporadic DLB patients. In this study, we aimed to examine disease onset, rate of cognitive decline, survival, and Alzheimer’s disease (AD) biomarkers in patients with familial DLB (n = 154) and sporadic DLB (n = 137), using linear mixed model analysis and Cox regression analysis, among others. Familial patients had a shorter survival (8.0 years) and more often elevated cerebrospinal fluid AD biomarkers (47%) than sporadic patients (9.0 years; p≤0.001; 30%, p = 0.037). Our findings suggest that genetic factors are important in DLB and that the identification of new genetic factors will probably improve the prediction of prognosis.

The complex relationship between genotype, pathology and phenotype in familial dementia

Causative genes involved in familial forms of dementias, including Alzheimer's disease (AD), frontotemporal lobar degeneration (FTLD) and dementia with Lewy bodies (DLB), as well as amyotrophic lateral sclerosis and prion diseases where dementia is present as a significant clinical feature, are associated with distinct proteinopathies. This review summarizes the relationship between known genetic determinants of these dementia syndromes and variations in key neuropathological proteins in terms of three types of heterogeneity: (i) Locus Heterogeneity, whereby mutations in different genes cause a similar proteinopathy, as exemplified by mutations in APP, PSEN1 and PSEN2 leading to AD neuropathology; (ii) Allelic Heterogeneity, whereby different mutations in the same gene lead to different proteinopathies or neuropathological severity, as exemplified by different mutations in MAPT and PRNP giving rise to protein species that differ in their biochemistry and affected cell types; and (iii) Phenotypic Heterogeneity, where identical gene mutations lead to different proteinopathies, as exemplified by LRRK2 p.G2019S being associated with variable Lewy body presence and alternative AD neuropathology or FTLD-tau. Of note, the perceived homogeneity in histologic phenotypes may arise from laboratory-specific assessment protocols which can differ in the panel of proteins screened. Finally, the understanding of the complex relationship between genotype and phenotype in dementia families is highly relevant in terms of therapeutic strategies which range from targeting specific genes, to a broader strategy of targeting a downstream, common biochemical problem that leads to the histopathology.

Genetic architecture of common non-Alzheimer's disease dementias

Frontotemporal dementia (FTD), dementia with Lewy bodies (DLB) and vascular dementia (VaD) are the most common forms of dementia after Alzheimer's disease (AD). The heterogeneity of these disorders and/or the clinical overlap with other diseases hinder the study of their genetic components. Even though Mendelian dementias are rare, the study of these forms of disease can have a significant impact in the lives of patients and families and have successfully brought to the fore many of the genes currently known to be involved in FTD and VaD, starting to give us a glimpse of the molecular mechanisms underlying these phenotypes. More recently, genome-wide association studies have also pointed to disease risk-associated loci. This has been particularly important for DLB where familial forms of disease are very rarely described. In this review we systematically describe the Mendelian and risk genes involved in these non-AD dementias in an effort to contribute to a better understanding of their genetic architecture, find differences and commonalities between different dementia phenotypes, and uncover areas that would benefit from more intense research endeavors.

Epigenetics in Lewy Body Diseases: Impact on Gene Expression, Utility as a Biomarker, and Possibilities for Therapy

Lewy body disorders (LBD) include Parkinson's disease (PD) and dementia with Lewy bodies (DLB). They are synucleinopathies with a heterogeneous clinical manifestation. As a cause of neuropathological overlap with other neurodegenerative diseases, the establishment of a correct clinical diagnosis is still challenging, and clinical management may be difficult. The combination of genetic variation and epigenetic changes comprising gene expression-modulating DNA methylation and histone alterations modifies the phenotype, disease course, and susceptibility to disease. In this review, we summarize the results achieved in the deciphering of the LBD epigenome. To provide an appropriate context, first LBD genetics is briefly outlined. Afterwards, a detailed review of epigenetic modifications identified for LBD in human cells, postmortem, and peripheral tissues is provided. We also focus on the difficulty of identifying epigenome-related biomarker candidates and discuss the results obtained so far. Additionally, epigenetic changes as therapeutic targets, as well as different epigenome-based treatments, are revised. The number of studies focusing on PD is relatively limited and practically inexistent for DLB. There is a lack of replication studies, and some results are even contradictory, probably due to differences in sample collection and analytical techniques. In summary, we show the current achievements and directions for future research.

Pathological Influences on Clinical Heterogeneity in Lewy Body Diseases

PD, PD with dementia, and dementia with Lewy bodies are clinical syndromes characterized by the neuropathological accumulation of alpha-synuclein in the CNS that represent a clinicopathological spectrum known as Lewy body disorders. These clinical entities have marked heterogeneity of motor and nonmotor symptoms with highly variable disease progression. The biological basis for this clinical heterogeneity remains poorly understood. Previous attempts to subtype patients within the spectrum of Lewy body disorders have centered on clinical features, but converging evidence from studies of neuropathology and ante mortem biomarkers, including CSF, neuroimaging, and genetic studies, suggest that Alzheimer's disease beta-amyloid and tau copathology strongly influence clinical heterogeneity and prognosis in Lewy body disorders. Here, we review previous clinical biomarker and autopsy studies of Lewy body disorders and propose that Alzheimer's disease copathology is one of several likely pathological contributors to clinical heterogeneity of Lewy body disorders, and that such pathology can be assessed in vivo. Future work integrating harmonized assessments and genetics in PD, PD with dementia, and dementia with Lewy bodies patients followed to autopsy will be critical to further refine the classification of Lewy body disorders into biologically distinct endophenotypes. This approach will help facilitate clinical trial design for both symptomatic and disease-modifying therapies to target more homogenous subsets of Lewy body disorders patients with similar prognosis and underlying biology. © 2019 International Parkinson and Movement Disorder Society.

Lipids as Trans-Acting Effectors for α-Synuclein in the Pathogenesis of Parkinson's Disease

Aggregation of α-synuclein (αSyn) plays a central role in the pathogenesis of Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). Lewy bodies (LBs) and Lewy neurites, which consist mainly of aggregated αSyn, are widely observed in the affected regions of patient brains. Except for some familial forms of PD/DLB, most sporadic PD/DLB patients express the wild-type (WT) αSyn protein without any mutations, and the mechanisms as to how WT αSyn gains the propensity to pathologically aggregate still remains unclear. Furthermore, the mechanisms by which the same αSyn protein can cause different synucleinopathies with distinct phenotypes and pathologies, such as PD, DLB, and multiple system atrophy (MSA), still remain largely unknown. Recently, mutations in the GBA1 gene (encoding glucocerebrosidase), which are responsible for the lysosomal storage disorder Gaucher disease (GD), have been reported to be the strongest risk factor for developing sporadic PD/DLB. We previously demonstrated that glucosylceramide accumulated by GBA1 deficiency promotes the conversion of αSyn into a proteinase K-resistant conformation. Furthermore, decreased glucocerebrosidase activity has also been reported in the brains of patients with sporadic PD/DLB. Moreover, αSyn pathology has also been shown in the brains of lysosomal storage disorder patients, which show glycosphingolipid accumulation. These observations suggest the possibility that altered lipid metabolism and lipid accumulation play roles in αSyn aggregation and PD/DLB pathogenesis. Indeed, several previous studies have demonstrated that lipid interactions affect the conformation of αSyn and induces its oligomerization and aggregation. In this review, we will give an overview of the association between αSyn aggregation and lipid interactions from the viewpoints of the etiology, pathology, and genetics of PD/DLB. We also discuss the distinct species of αSyn aggregates and their association with specific types of synucleinopathies, and introduce our hypothesis that lipid interactions play a role as trans-acting effectors in producing distinct strains of αSyn fibrils.

GBA, Gaucher Disease, and Parkinson's Disease: From Genetic to Clinic to New Therapeutic Approaches

Parkinson’s disease (PD) is the second most common degenerative disorder. Although the disease was described more than 200 years ago, its pathogenetic mechanisms have not yet been fully described. In recent years, the discovery of the association between mutations of the GBA gene (encoding for the lysosomal enzyme glucocerebrosidase) and PD facilitated a better understating of this disorder. GBA mutations are the most common genetic risk factor of the disease. However, mutations of this gene can be found in different phenotypes, such as Gaucher’s disease (GD), PD, dementia with Lewy bodies (DLB) and rapid eye movements (REM) sleep behavior disorders (RBDs). Understanding the pathogenic role of this mutation and its different manifestations is crucial for geneticists and scientists to guide their research and to select proper cohorts of patients. Moreover, knowing the implications of the GBA mutation in the context of PD and the other associated phenotypes is also important for clinicians to properly counsel their patients and to implement their care. With the present review we aim to describe the genetic, clinical, and therapeutic features related to the mutation of the GBA gene.

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.

The Genetics of Dementia with Lewy Bodies: Current Understanding and Future Directions

PURPOSE OF REVIEW

Dementia with Lewy bodies (DLB) is a neurodegenerative disease that can be clinically and pathologically similar to Parkinson's disease (PD) and Alzheimer's disease (AD). Current understanding of DLB genetics is insufficient and has been limited by sample size and difficulty in diagnosis. The first genome-wide association study (GWAS) in DLB was performed in 2017; a time at which the post-GWAS era has been reached in many diseases.

RECENT FINDINGS

DLB shares risk loci with AD, in the APOE E4 allele, and with PD, in variation at GBA and SNCA. Interestingly, the GWAS suggested that DLB may also have genetic risk factors that are distinct from those in AD and PD. Although off to a slow start, recent studies have reinvigorated the field of DLB genetics and these results enable us to start to have a more complete understanding of the genetic architecture of this disease.

Characterization of Brain Lysosomal Activities in GBA-Related and Sporadic Parkinson's Disease and Dementia with Lewy Bodies

Mutations in the GBA gene, encoding the lysosomal hydrolase glucocerebrosidase (GCase), are the most common known genetic risk factor for Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). The present study aims to gain more insight into changes in lysosomal activity in different brain regions of sporadic PD and DLB patients, screened for GBA variants. Enzymatic activities of GCase, β-hexosaminidase, and cathepsin D were measured in the frontal cortex, putamen, and substantia nigra (SN) of a cohort of patients with advanced PD and DLB as well as age-matched non-demented controls (n = 15/group) using fluorometric assays. Decreased activity of GCase (− 21%) and of cathepsin D (− 15%) was found in the SN and frontal cortex of patients with PD and DLB compared to controls, respectively. Population stratification was applied based on GBA genotype, showing substantially lower GCase activity (~ − 40%) in GBA variant carriers in all regions. GCase activity was further significantly decreased in the SN of PD and DLB patients without GBA variants in comparison to controls without GBA variants. Our results show decreased GCase activity in brains of PD and DLB patients with and without GBA variants, most pronounced in the SN. The results of our study confirm findings from previous studies, suggesting a role for GCase in GBA-associated as well as sporadic PD and DLB.

Glucocerebrosidase gene variants are accumulated in idiopathic REM sleep behavior disorder

INTRODUCTION

Glucocerebrosidase (GBA) gene variants are associated with the development of the Lewy body disorders (LBD) Parkinson disease (PD) and dementia with Lewy bodies (DLB). Idiopathic REM sleep behavior disorder (IRBD) represents prodromal LBD in most instances. We investigated whether GBA variants are overrepresented in IRBD and if their presence shortens the time to conversion to clinically-defined LBD.

METHODS

All GBA coding exons from 69 polysomnography-confirmed IRBD patients and 84 matched controls were sequenced by the Sanger method.

RESULTS

Seven missense variants (E326K, L444P, A446T, A318G, R329C, T369M, N370S) were identified in eight (11.6%) IRBD patients and in one (1.2%) control (P = 0.026). After a mean follow-up of 8.9 ± 3.8 years from IRBD diagnosis, five subjects with GBA variants developed LBD (3 DLB and 2 PD) and three remained disease-free. The risk of developing a LBD was similar in IRBD subjects with GBA variants than in those without variants (log rank test, p = 0.935).

CONCLUSIONS

In IRBD, GBA variants are 1) more frequent when compared to controls, 2) associated with impending PD and DLB but 3) not indicative of a short-term risk for LBD after IRBD diagnosis. IRBD patients carrying GBA variants could be studied with disease-modifying interventions aiming to restore the GBA metabolic pathway.

Whole genome sequence analyses of brain imaging measures in the Framingham Study

Objective

We sought to identify rare variants influencing brain imaging phenotypes in the Framingham Heart Study by performing whole genome sequence association analyses within the Trans-Omics for Precision Medicine Program.

Methods

We performed association analyses of cerebral and hippocampal volumes and white matter hyperintensity (WMH) in up to 2,180 individuals by testing the association of rank-normalized residuals from mixed-effect linear regression models adjusted for sex, age, and total intracranial volume with individual variants while accounting for familial relatedness. We conducted gene-based tests for rare variants using (1) a sliding-window approach, (2) a selection of functional exonic variants, or (3) all variants.

Results

We detected new loci in 1p21 for cerebral volume (minor allele frequency [MAF] 0.005, p = 10⁻⁸) and in 16q23 for hippocampal volume (MAF 0.05, p = 2.7 × 10⁻⁸). Previously identified associations in 12q24 for hippocampal volume (rs7294919, p = 4.4 × 10⁻⁴) and in 17q25 for WMH (rs7214628, p = 2.0 × 10⁻³) were confirmed. Gene-based tests detected associations (p ≤ 2.3 × 10⁻⁶) in new loci for cerebral (5q13, 8p12, 9q31, 13q12-q13, 15q24, 17q12, 19q13) and hippocampal volumes (2p12) and WMH (3q13, 4p15) including Alzheimer disease– (UNC5D) and Parkinson disease–associated genes (GBA). Pathway analyses evidenced enrichment of associated genes in immunity, inflammation, and Alzheimer disease and Parkinson disease pathways.

Conclusions

Whole genome sequence–wide search reveals intriguing new loci associated with brain measures. Replication of novel loci is needed to confirm these findings.

GBA Variants Influence Motor and Non-Motor Features of Parkinson's Disease

The presence of mutations in glucocerebrosidase (GBA) gene is a known factor increasing the risk of developing Parkinson’s disease (PD). Mutations carriers have earlier disease onset and are more likely to develop neuropsychiatric symptoms than other sporadic PD cases. These symptoms have primarily been observed in Parkinson’s patients carrying the most common pathogenic mutations L444P and N370S. However, recent findings suggest that other variants across the gene may have a different impact on the phenotype as well as on the disease progression. We aimed to explore the influence of variants across GBA gene on the clinical features and treatment related complications in PD. In this study, we screened the GBA gene in a cohort of 532 well-characterised PD patients and 542 controls from southern Spain. The potential pathogeniticy of the identified variants was assessed using in-silico analysis and subsequently classified as benign or deleterious. As a result, we observed a higher frequency of GBA variants in PD patients (12.2% vs. 7.9% in controls, p = 0.021), earlier mean age at disease onset in GBA variant carriers (50.6 vs. 56.6 years; p = 0.013), as well as more prevalent motor and non-motor symptoms in patients carrying deleterious variants. In addition, we found that dopaminergic motor complications are influenced by both benign and deleterious variants. Our results highlight the fact that the impact on the phenotype highly depends on the potential pathogenicity of the carried variants. Therefore, the course of motor and non-motor symptoms as well as treatment-related motor complications could be influenced by GBA variants.

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.

The Genetic Basis of Cognitive Impairment and Dementia in Parkinson's Disease

Cognitive dysfunction is a common feature of Parkinson's disease (PD) with mild cognitive impairment affecting around a quarter of patients in the early stages of their disease, and approximately half developing dementia by 10 years from diagnosis. However, the pattern of cognitive impairments and their speed of evolution vary markedly between individuals. While some of this variability may relate to extrinsic factors and comorbidities, inherited genetic heterogeneity is also known to play an important role. A number of common genetic variants have been identified, which contribute to cognitive function in PD, including variants in catechol-O-methyltransferase, microtubule-associated protein tau, and apolipoprotein E. Furthermore, rarer mutations in glucocerebrosidase and α-synuclein and are strongly associated with dementia risk in PD. This review explores the functional impact of these variants on cognition in PD and discusses how such genotype-phenotype associations provide a window into the mechanistic basis of cognitive heterogeneity in this disorder. This has consequent implications for the development of much more targeted therapeutic strategies for cognitive symptoms in PD.