Mood and cognition in leucine-rich repeat kinase 2 G2019S Parkinson's disease

Human-Induced Pluripotent Stem Cell (iPSC)-Derived GABAergic Neuron Differentiation in Bipolar Disorder

Bipolar disorder (BP) is a recurring psychiatric condition characterized by alternating episodes of low energy (depressions) followed by manias (high energy). Cortical network activity produced by GABAergic interneurons may be critical in maintaining the balance in excitatory/inhibitory activity in the brain during development. Initially, GABAergic signaling is excitatory; with maturation, these cells undergo a functional switch that converts GABAA channels from depolarizing (excitatory) to hyperpolarizing (inhibitory), which is controlled by the intracellular concentration of two chloride transporters. The earliest, NKCC1, promotes chloride entry into the cell and depolarization, while the second (KCC2) stimulates movement of chloride from the neuron, hyperpolarizing it. Perturbations in the timing or expression of NKCC1/KCC2 may affect essential morphogenetic events including cell proliferation, migration, synaptogenesis and plasticity, and thereby the structure and function of the cortex. We derived induced pluripotent stem cells (iPSC) from BP patients and undiagnosed control (C) individuals, then modified a differentiation protocol to form GABAergic interneurons, harvesting cells at sequential stages of differentiation. qRT-PCR and RNA sequencing indicated that after six weeks of differentiation, controls transiently expressed high levels of NKCC1. Using multi-electrode array (MEA) analysis, we observed that BP neurons exhibit increased firing, network bursting and decreased synchrony compared to C. Understanding GABA signaling in differentiation may identify novel approaches and new targets for treatment of neuropsychiatric disorders such as BP.

Emerging perspectives on precision therapy for Parkinson's disease: multidimensional evidence leading to a new breakthrough in personalized medicine

PD is a prevalent and progressive neurodegenerative disorder characterized by both motor and non-motor symptoms. Genes play a significant role in the onset and progression of the disease. While the complexity and pleiotropy of gene expression networks have posed challenges for gene-targeted therapies, numerous pathways of gene variant expression show promise as therapeutic targets in preclinical studies, with some already in clinical trials. With the recognition of the numerous genes and complex pathways that can influence PD, it may be possible to take a novel approach to choose a treatment for the condition. This approach would be based on the symptoms, genomics, and underlying mechanisms of the disease. We discuss the utilization of emerging genetic and pathological knowledge of PD patients to categorize the disease into subgroups. Our long-term objective is to generate new insights for the therapeutic approach to the disease, aiming to delay and treat it more effectively, and ultimately reduce the burden on individuals and society.

Parkinson's LRRK2-G2019S risk gene mutation drives sex-specific behavioral and cellular adaptations to chronic variable stress

Anxiety is a psychiatric non-motor symptom of Parkinson's that can appear in the prodromal period, prior to significant loss of brainstem dopamine neurons and motor symptoms. Parkinson's-related anxiety affects females more than males, despite the greater prevalence of Parkinson's in males. How stress, anxiety and Parkinson's are related and the basis for a sex-specific impact of stress in Parkinson's are not clear. We addressed this using young adult male and female mice carrying a G2019S knockin mutation of leucine-rich repeat kinase 2 ( Lrrk2 G2019S ) and Lrrk2 WT control mice. In humans, LRRK2 G2019S significantly elevates the risk of late-onset Parkinson's. To assess within-sex differences between Lrrk2 G2019S and control mice in stress-induced anxiety-like behaviors in young adulthood, we used a within-subject design whereby Lrrk2 G2019S and Lrrk2 WT control mice underwent tests of anxiety-like behaviors before (baseline) and following a 28 day (d) variable stress paradigm. There were no differences in behavioral measures between genotypes in males or females at baseline, indicating that the mutation alone does not produce anxiety-like responses. Following chronic stress, male Lrrk2 G2019S mice were affected similarly to male wildtypes except for novelty-suppressed feeding, where stress had no impact on Lrrk2 G2019S mice while significantly increasing latency to feed in Lrrk2 WT control mice. Female Lrrk2 G2019S mice were impacted by chronic stress similarly to wildtype females across all behavioral measures. Subsequent post-stress analyses compared cFos immunolabeling-based cellular activity patterns across several stress-relevant brain regions. The density of cFos-activated neurons across brain regions in both male and female Lrrk2 G2019S mice was generally lower compared to stressed Lrrk2 WT mice, except for the nucleus accumbens of male Lrrk2 G2019S mice, where cFos-labeled cell density was significantly higher than all other groups. Together, these data suggest that the Lrrk2 G2019S mutation differentially impacts anxiety-like behavioral responses to chronic stress in males and females that may reflect sex-specific adaptations observed in circuit activation patterns in stress-related brain regions.

Proxy-analysis of the genetics of cognitive decline in Parkinson's disease through polygenic scores

Cognitive decline is common in Parkinson's disease (PD) and its genetic risk factors are not well known to date, besides variants in the GBA and APOE genes. However, variation in complex traits is caused by numerous variants and is usually studied with genome-wide association studies (GWAS), requiring a large sample size, which is difficult to achieve for outcome measures in PD. Taking an alternative approach, we computed 100 polygenic scores (PGS) related to cognitive, dementia, stroke, and brain anatomical phenotypes and investigated their association with cognitive decline in six longitudinal cohorts. The analysis was adjusted for age, sex, genetic ancestry, follow-up duration, GBA and APOE status. Then, we meta-analyzed five of these cohorts, comprising a total of 1702 PD participants with 6156 visits, using the Montreal Cognitive Assessment as a cognitive outcome measure. After correction for multiple comparisons, we found four PGS significantly associated with cognitive decline: intelligence (p = 5.26e-13), cognitive performance (p = 1.46e-12), educational attainment (p = 8.52e-10), and reasoning (p = 3.58e-5). Survival analyses highlighted an offset of several years between the first and last quartiles of PGS, with significant differences for the PGS of cognitive performance (5 years) and educational attainment (7 years). In conclusion, we found four PGS associated with cognitive decline in PD, all associated with general cognitive phenotypes. This study highlights the common genetic factors between cognitive decline in PD and the general population, and the importance of the participant's cognitive reserve for cognitive outcome in PD.

Possible association between the lrrk2 gene and anxiety behavior: a systematic literature review

Alterations to the LRRK2 gene have been associated with Parkinson's disease and alcohol consumption in animals and humans. Furthermore, these disorders are strongly related to anxiety disorders (ADs). Thus, we investigated how the LRRK2 gene might influence anxiety in humans and mice. We elaborated a systematic review based on the PRISMA Statement of studies that investigated levels of anxiety in animal or human models with alterations in the LRRK2 gene. The search was conducted in the PubMed, Scopus, and Web of Science databases, and in reference lists with descriptors related to ADs and the LRRK2. From the 62 articles assessed for eligibility, 16 were included: 11 conducted in humans and seven, in mice. Lrrk2 KO mice and the LRRK2 G2019S, LRRK2 R1441G, and LRRK2 R1441C variants were addressed. Five articles reported an increase in anxiety levels concerning the LRRK2 variants. Decreased anxiety levels were observed in two articles, one focusing on the LRRK2 G2019S and the other, on the Lrrk2 KO mice. Eight other articles reported no differences in anxiety levels in individuals with Lrrk2 alterations compared to their healthy controls. This study discusses a possible influence between the LRRK2 gene and anxiety, adding information to the existing knowledge respecting the influence of genetics on anxiety.

Genetics of cognitive dysfunction in Parkinson's disease

Presentation and progression of cognitive symptoms in Parkinson's disease are highly variable. PD is a genetically complex disorder with multiple genetic risk factors and understanding the role that genes play in cognitive outcomes is important for patient counseling and treatment. Currently, there are seven well-described genes that increase the risk for PD, with variable levels of penetrance: SNCA, LRRK2, VPS35, PRKN, PINK1, DJ1 and GBA. In addition, large, genome-wide association studies have identified multiple loci in our DNA which increase PD risk. In this chapter, we summarize what is currently known about each of the seven strongly-associated PD genes and select PD risk variants, including PITX3, TMEM106B, SNCA Rep1, APOɛ4, COMT and MAPT H1/H1, along with their respective relationships to cognition.

Cognitive Impairment in Genetic Parkinson's Disease

Cognitive impairment is common in idiopathic Parkinson's disease (PD). Knowledge of the contribution of genetics to cognition in PD is increasing in the last decades. Monogenic forms of genetic PD show distinct cognitive profiles and rate of cognitive decline progression. Cognitive impairment is higher in GBA- and SNCA-associated PD, lower in Parkin- and PINK1-PD, and possibly milder in LRRK2-PD. In this review, we summarize data regarding cognitive function on clinical studies, neuroimaging, and biological markers of cognitive decline in autosomal dominant PD linked to mutations in LRRK2 and SNCA, autosomal recessive PD linked to Parkin and PINK1, and also PD linked to GBA mutations.

A More Homogeneous Phenotype in Parkinson's Disease Related to R1441G Mutation in the LRRK2 Gene

Parkinson's disease (PD) is characterized by a great clinical heterogeneity. Nevertheless, the biological drivers of this heterogeneity have not been completely elucidated and are likely to be complex, arising from interactions between genetic, epigenetic, and environmental factors. Despite this heterogeneity, the clinical patterns of monogenic forms of PD have usually maintained a good clinical correlation with each mutation once a sufficient number of patients have been studied. Mutations in LRRK2 are the most commonly known genetic cause of autosomal dominant PD known to date. Furthermore, recent genome-wide association studies have revealed variations in LRRK2 as significant risk factors also for the development of sporadic PD. The LRRK2-R1441G mutation is especially frequent in the population of Basque ascent based on a possible founder effect, being responsible for almost 50% of cases of familial PD in our region, with a high penetrance. Curiously, Lewy bodies, considered the neuropathological hallmark of PD, are absent in a significant subset of LRRK2-PD cases. Indeed, these cases appear to be associated with a less aggressive primarily pure motor phenotype. The aim of our research is to examine the clinical phenotype of R1441G-PD patients, more homogeneous when we compare it with sporadic PD patients or with patients carrying other LRRK2 mutations, and reflect on the value of the observed correlation in the genetic forms of PD. The clinical heterogeneity of PD leads us to think that there may be as many different diseases as the number of people affected. Undoubtedly, genetics constitutes a relevant key player, as it may significantly influence the phenotype, with differences according to the mutation within the same gene, and not only in familial PD but also in sporadic forms. Thus, extending our knowledge regarding genetic forms of PD implies an expansion of knowledge regarding sporadic forms, and this may be relevant due to the future therapeutic implications of all forms of PD.

Systematic review of genetic variants associated with cognitive impairment and depressive symptoms in Parkinson's disease

OBJECTIVE

Cognitive impairment and depression are among the most prevalent and most disabling non-motor symptoms in Parkinson's disease (PD). The genetic factors that are associated with these symptoms remain uncertain. This systematic review aims to summarise the prevailing evidence from all genetic association studies investigating the genetic variants associated with cognitive impairment and depressive symptoms in people with PD.

METHOD

A systematic review using five online databases: PubMed, PsycINFO, CINAHL, EMBASE and OpenGrey (PROSPERO protocol: CRD42017067431). We completed the quality assessment using the Q-Genie tool.

RESULTS

2353 articles were screened, and 43 articles were found to be eligible to be included. A meta-analysis of studies investigating LRRK2 rs34637584 confirmed that the minor allele carriers had significantly less cognitive impairment (p = 0.015). Further meta-analyses showed that GBA variants rs76763715 (p < 0.001) and rs421016 (p = 0.001) were significantly associated with more cognitive impairment in people with PD. Minor alleles of GBA variants rs76763715, rs421016, rs387906315 and rs80356773 were associated with more depressive symptoms in PD. Moreover, APOE ε4 allele has been associated with more cognitive impairment in PD. BDNF (rs6265) and CRY1 (rs2287161) variants have been associated with more depressive symptoms in people with PD.

CONCLUSIONS

PD carriers of GBA variants are at high risk for cognitive decline and depression. Screening for these variants may facilitate early identification and effective management of these non-motor symptoms. The molecular mechanisms underlying favourable cognitive functioning in LRRK2 rs34637584 variant carriers warrant further investigation.

Clinical Heterogeneity Among LRRK2 Variants in Parkinson's Disease: A Meta-Analysis

Background: Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Variants in the LRRK2 gene have been shown to be associated with PD. However, the clinical characteristics of LRRK2-related PD are heterogeneous. In our study, we performed a comprehensive pooled analysis of the association between specific LRRK2 variants and clinical features of PD.

Methods: Articles from the Medline, Embase, and Cochrane databases were included in the meta-analysis. Strict inclusion criteria were applied, and detailed information was extracted from the final original articles included. Revman 5.3 software was used for publication biases and pooled and sensitivity analyses.

Results: In all, 66 studies having the clinical manifestations of PD patients with G2019S, G2385R, R1628P, and R1441G were included for the final analysis. The prominent clinical features of LRRK2-G2019S-related PD patients were female sex, higher rates of early-onset PD (EOPD), and family history (OR: 0.77 [male], 1.37, 2.62; p < 0.00001, 0.02, < 0.00001). PD patients with G2019S were more likely to have high scores of Schwab & England (MD: 1.49; p < 0.00001), low GDS scores, high UPSIT scores (MD: 0.43, 4.70; p = 0.01, < 0.00001), and good response to L-dopa (OR: 2.33; p < 0.0001). Further, G2019S carriers had higher LEDD (MD: 115.20; p < 0.00001) and were more likely to develop motor complications, such as dyskinesia and motor fluctuations (OR: 2.18, 2.02; p < 0.00001, 0.04) than non-carriers. G2385R carriers were more likely to have family history (OR: 2.10; p = 0.007) than non-G2385R carriers and lower H-Y and higher MMSE scores (MD: −0.13, 1.02; p = 0.02, 0.0007). G2385R carriers had higher LEDD and tended to develop motor complications, such as motor fluctuations (MD: 53.22, OR: 3.17; p = 0.01, < 0.00001) than non-carriers. Other clinical presentations did not feature G2019S or G2385R. We observed no distinct clinical features for R1628P or R1441G. Our subgroup analyses in different ethnic group for specific variant also presented with relevant clinical characteristics of PD patients.

Conclusions: Clinical heterogeneity was observed among LRRK2-associated PD in different variants in total and in different ethnic groups, especially for G2019S and G2385R.

Motor and non-motor features of Parkinson's disease in LRRK2 G2019S carriers versus matched controls

INTRODUCTION

LRRK2 G2019S mutation carriers with Parkinson's disease (PD) have been generally indistinguishable from those with idiopathic PD, with the exception of variable differences in some motor and non-motor domains, including cognition, gait, and balance. LRRK2 G2019S is amongst the most common genetic etiologies for PD, particularly in Ashkenazi Jewish (AJ) populations.

METHODS

This cross-sectional data collection study sought to clarify the phenotype of LRRK2 G2019S mutation carriers with PD. Primary endpoints were the Movement Disorder Society Unified Parkinson Disease Rating Scale (MDS-UPDRS) and Montreal Cognitive Assessment (MoCA). Other motor and non-motor data were also assessed. The Mann-Whitney U Test was utilized to compare LRRK2 G2019S carriers with PD (LRRK2+) with non-carrier PD controls who were matched for age, gender, education, and PD duration. Survival analyses and log rank tests were utilized to compare interval from onset of PD to development of motor and non-motor complications.

RESULTS

We screened 251 subjects and 231 completed the study, of whom 9 were LRRK2+, including 7 AJ subjects. 22.73% of AJ subjects with a family history of PD (FH) and 12.96% of AJ subjects without a FH were LRRK2+. There were no significant differences between the 9 LRRK2+ subjects and 19 matched PD controls in MDS-UPDRS, MoCA, or other motor and non-motor endpoints.

CONCLUSION

Prevalence of the LRRK2 G2019S mutation in AJ and non-AJ subjects in our study population in Cleveland, Ohio was comparable to other clinical studies. There were no significant motor or non-motor differences between LRRK2+ PD and matched PD controls.

Are dementia with Lewy bodies and Parkinson's disease dementia the same disease?

BACKGROUND

Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD), which share many clinical, neurochemical, and morphological features, have been incorporated into DSM-5 as two separate entities of major neurocognitive disorders with Lewy bodies. Despite clinical overlap, their diagnosis is based on an arbitrary distinction concerning the time of onset of motor and cognitive symptoms, namely as early cognitive impairment in DLB and later onset following that of motor symptoms in PDD. Their morphological hallmarks - cortical and subcortical α-synuclein/Lewy body plus β-amyloid and tau pathologies - are similar, but clinical differences at onset suggest some dissimilar profiles. Based on recent publications, including the fourth consensus report of the DLB Consortium, a critical overview is provided herein.

DISCUSSION

The clinical constellations of DLB and PDD include cognitive impairment, parkinsonism, visual hallucinations, and fluctuating attention. Intravitam PET and postmortem studies have revealed a more pronounced cortical atrophy, elevated cortical and limbic Lewy body pathologies, higher Aβ and tau loads in cortex and striatum in DLB compared to PDD, and earlier cognitive defects in DLB. Conversely, multitracer PET studies have shown no differences in cortical and striatal cholinergic and dopaminergic deficits. Clinical management of both DLB and PDD includes cholinesterase inhibitors and other pharmacologic and non-drug strategies, yet with only mild symptomatic effects. Currently, no disease-modifying therapies are available.

CONCLUSION

DLB and PDD are important dementia syndromes that overlap in many clinical features, genetics, neuropathology, and management. They are currently considered as subtypes of an α-synuclein-associated disease spectrum (Lewy body diseases), from incidental Lewy body disease and non-demented Parkinson's disease to PDD, DLB, and DLB with Alzheimer's disease at the most severe end. Cognitive impairment in these disorders is induced not only by α-synuclein-related neurodegeneration but by multiple regional pathological scores. Both DLB and PDD show heterogeneous pathology and neurochemistry, suggesting that they share important common underlying molecular pathogenesis with Alzheimer's disease and other proteinopathies. While we prefer to view DLB and PDD as extremes on a continuum, there remains a pressing need to more clearly differentiate these syndromes and to understand the synucleinopathy processes leading to either one.

The impact of murine LRRK2 G2019S transgene overexpression on acute responses to inflammatory challenge

The most common Parkinson's disease (PD) mutation is the gain-of-function LRRK2 G2019S variant, which has also been linked to inflammatory disease states. Yet, little is known of the role of G2019S in PD related complex behavioral or immune/hormonal processes in response to inflammatory/toxicant challenges. Hence, we characterized the behavioral, neuroendocrine-immune and central monoaminergic responses in G2019S overexpressing mutants following systemic interferon-gamma (IFN-γ) or lipopolysaccharide (LPS) administration. Although LPS markedly (and IFN-γ modestly in some cases) increased cytokine and corticosterone levels, while inducing pronounced sickness and home-cage activity deficits, the G2019S mutation had no effect on these parameters. No differences were observed with regards to brain microglia with the acute LPS injection, regardless of genotype. Nor did the G2019S mutation influence neurotransmitter levels within the medial prefrontal cortex or paraventricular nucleus of the hypothalamus. However, the LRRK2 G2019S transgenic mice did have altered monoamine levels within the striatum and hippocampus. Indeed, G2019S mice had altered basal levels and turnover of dopamine within the striatum, along with changes in hippocampal serotonin and norepinephrine activity in response to LPS and IFN-γ. The present findings suggest the importance of murine G2019S in hippocampal and striatal neurotransmission, but that the transgene didn't appear to be involved in functional behavioral and stress-like hormonal and cytokine changes provoked by inflammatory insults.

A review of psychiatric co-morbidity described in genetic and immune mediated movement disorders

Psychiatric symptoms are an increasingly recognised feature of movement disorders. Recent identification of causative genes and autoantibodies has allowed detailed analysis of aetiologically homogenous subgroups, thereby enabling determination of the spectrum of psychiatric symptoms in these disorders. This review evaluates the incidence and type of psychiatric symptoms encountered in patients with movement disorders. A broad spectrum of psychiatric symptoms was identified across all subtypes of movement disorder, with depression, generalised anxiety disorder and obsessive-compulsive disorder being most common. Psychosis, schizophrenia and attention deficit hyperactivity disorder were also identified, with the psychiatric symptoms often predating onset of the motor disorder. The high incidence of psychiatric symptoms across such a wide range of movement disorders suggests a degree of common or overlapping pathogenic mechanisms. Our review demonstrates the need for increased clinical awareness of such co-morbidities, which should facilitate early neuropsychiatric intervention and allied specialist treatment for patients.

Psychosis in parkinsonism: an unorthodox approach

Psychosis in Parkinson's disease (PD) is currently considered as the occurrence of hallucinations and delusions. The historical meaning of the term psychosis was, however, broader, encompassing a disorganization of both consciousness and personality, including behavior abnormalities, such as impulsive overactivity and catatonia, in complete definitions by the International Classification of Diseases-10 (ICD-10) and the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). Our review is aimed at reminding that complex psychotic symptoms, including impulsive overactivity and somatoform disorders (the last being a recent controversial entity in PD), were carefully described in postencephalitic parkinsonism (PEP), many decades before dopaminergic treatment era, and are now described in other parkinsonisms than PD. Eminent neuropsychiatrists of the past century speculated that studying psychosis in PEP might highlight its mechanisms in other conditions. Yet, functional assessments were unavailable at the time. Therefore, the second part of our article reviews the studies of neural correlates of psychosis in parkinsonisms, by taking into account both theories on the narrative functions of the default mode network (DMN) and hypotheses on DMN modulation.

The Monoamine Brainstem Reticular Formation as a Paradigm for Re-Defining Various Phenotypes of Parkinson's Disease Owing Genetic and Anatomical Specificity

The functional anatomy of the reticular formation (RF) encompasses a constellation of brain regions which are reciprocally connected to sub-serve a variety of functions. Recent evidence indicates that neuronal degeneration within one of these regions spreads synaptically along brainstem circuitries. This is exemplified by the recruitment of various brainstem reticular nuclei in specific Parkinson’s disease (PD) phenotypes, and by retrospective analysis of lethargic post-encephalitic parkinsonism. In fact, the spreading to various monoamine reticular nuclei can be associated with occurrence of specific motor and non-motor symptoms (NMS). This led to re-consider PD as a brainstem monoamine disorder (BMD). This definition surpasses the anatomy of meso-striatal motor control to include a variety of non-motor domains. This concept clearly emerges from the quite specific clinical-anatomical correlation which can be drawn in specific paradigms of PD genotypes. Therefore, this review article focuses on the genetics and neuroanatomy of three PD genotypes/phenotypes which can be selected as prototype paradigms for a differential recruitment of the RF leading to differential occurrence of NMS: (i) Parkin-PD, where NMS are rarely reported; (ii) LRRK2-PD and slight SNC point mutations, where the prevalence of NMS resembles idiopathic PD; (iii) Severe SNCA point mutations and multiplications, where NMS are highly represented.

Cognitive decline in Parkinson disease

Dementia is a frequent problem encountered in advanced stages of Parkinson disease (PD). In recent years, research has focused on the pre-dementia stages of cognitive impairment in PD, including mild cognitive impairment (MCI). Several longitudinal studies have shown that MCI is a harbinger of dementia in PD, although the course is variable, and stabilization of cognition - or even reversal to normal cognition - is not uncommon. In addition to limbic and cortical spread of Lewy pathology, several other mechanisms are likely to contribute to cognitive decline in PD, and a variety of biomarker studies, some using novel structural and functional imaging techniques, have documented in vivo brain changes associated with cognitive impairment. The evidence consistently suggests that low cerebrospinal fluid levels of amyloid-β₄₂, a marker of comorbid Alzheimer disease (AD), predict future cognitive decline and dementia in PD. Emerging genetic evidence indicates that in addition to the APOE*ε4 allele (an established risk factor for AD), GBA mutations and SCNA mutations and triplications are associated with cognitive decline in PD, whereas the findings are mixed for MAPT polymorphisms. Cognitive enhancing medications have some effect in PD dementia, but no convincing evidence that progression from MCI to dementia can be delayed or prevented is available, although cognitive training has shown promising results.

Clinical Features of LRRK2 Carriers with Parkinson's Disease

LRRK2 mutations are present in 1% of all sporadic Parkinson's disease (PD) cases and 5% of all familial PD cases. Several mutations in the LRRK2 gene are associated with PD, the most common of which is the Gly2019Ser mutation. In the following review, we summarize the demographics and motor and non-motor symptoms of LRRK2 carriers with PD, as well as symptoms in non-manifesting carriers. The clinical features of LRRK2-associated PD are often indistinguishable from those of idiopathic PD on an individual basis. However, LRRK2 PD patients are likely to have less non-motor symptoms compared to idiopathic PD patients, including less olfactory and cognitive impairment. LRRK2-associated PD patients are less likely to report REM sleep behavior disorder (RBD) than noncarriers. In addition, it is possible that carriers are more prone to cancer than noncarriers with PD, but larger studies are required to confirm this observation. Development of more sensitive biomarkers to identify mutation carriers at risk of developing PD, as well as biomarkers of disease progression among LRRK2 carriers with PD, is required. Such biomarkers would help evaluate interventions, which may prevent PD among non-manifesting carriers, or slow down disease progression among carriers with PD.

Pathology of behavior in PD: What is known and what is not?

Abnormal behavior in Parkinson's disease (PD) stems from a complex orchestration of impaired neural networks that result from PD-related neurodegeneration across multiple levels. Typically, cellular and tissue abnormalities generate neurochemical changes and disrupt specific regions of the brain, in turn creating impaired neural circuits and dysfunctional global networks. The objective of this chapter is to provide an overview of the array of pathological changes that have been linked to different behavioral symptoms of PD such as depression, anxiety, apathy, fatigue, impulse control disorders, psychosis, sleep disorders and dementia.

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.

Genetics of long-term treatment outcome in bipolar disorder

Bipolar disorder (BD) shows one of the strongest genetic predispositions among psychiatric disorders and the identification of reliable genetic predictors of treatment response could significantly improve the prognosis of the disease. The present study investigated genetic predictors of long-term treatment-outcome in 723 patients with BD type I from the STEP-BD (Systematic Treatment Enhancement Program for Bipolar Disorder) genome-wide dataset. BD I patients with >6months of follow-up and without any treatment restriction (reflecting a natural setting scenario) were included. Phenotypes were the total and depressive episode rates and the occurrence of one or more (hypo)manic/mixed episodes during follow-up. Quality control of genome-wide data was performed according to standard criteria and linear/logistic regression models were used as appropriate under an additive hypothesis. Top genes were further analyzed through a pathway analysis. Genes previously involved in the susceptibility to BD (DFNB31, SORCS2, NRXN1, CNTNAP2, GRIN2A, GRM4, GRIN2B), antidepressant action (DEPTOR, CHRNA7, NRXN1), and mood stabilizer or antipsychotic action (NTRK2, CHRNA7, NRXN1) may affect long-term treatment outcome of BD. Promising findings without previous strong evidence were TRAF3IP2-AS1, NFYC, RNLS, KCNJ2, RASGRF1, NTF3 genes. Pathway analysis supported particularly the involvement of molecules mediating the positive regulation of MAPK cascade and learning/memory processes. Further studies focused on the outlined genes may be helpful to provide validated markers of BD treatment outcome.

The Parkinson's Disease-Associated Mutation LRRK2-G2019S Impairs Synaptic Plasticity in Mouse Hippocampus

Parkinson's disease (PD) is a major movement disorder characterized by the loss of dopamine neurons and formation of Lewy bodies. Clinical and pathological evidence indicates that multiple brain regions are affected in PD in a spatiotemporal manner and are associated with a variety of motor and nonmotor symptoms, including disturbances in mood, executive function, and memory. The common PD-associated gene for leucine-rich repeat kinase, leucine-rich repeat kinase 2 (LRRK2), is highly expressed in brain regions that are involved with nonmotor functions, including the neocortex and hippocampus, but whether mutant LRRK2 contributes to neuronal dysfunction in these regions is unknown. Here, we use bacterial artificial chromosome transgenic mouse models of LRRK2 to explore potential nonmotor mechanisms of PD. Through electrophysiological analysis of the Schaffer collateral-CA1 synapse in dorsal hippocampus, we find that overexpression of LRRK2-G2019S increases basal synaptic efficiency through a postsynaptic mechanism, and disrupts long-term depression. Furthermore, these effects of the G2019S mutation are age dependent and can be normalized by acute inhibition of LRRK2 kinase activity. In contrast, overexpression of wild-type LRRK2 has no effect under the same conditions, suggesting a specific phenotype for the G2019S mutation. These results identify a pathogenic function of LRRK2 in the hippocampus that may contribute to nonmotor symptoms of PD.

SIGNIFICANCE STATEMENT

Parkinson's disease (PD) is among the most common neurological diseases and is best known for its adverse effects on brain regions that control motor function, resulting in tremor, rigidity, and gait abnormalities. Less well appreciated are the psychiatric symptoms experienced by many PD patients, including depression and memory loss, which do not respond well to currently available treatments for PD. Here, we describe functional effects of a common PD-linked mutation of leucine-rich repeat kinase 2 in the mouse hippocampus, an area of the brain that is responsible for encoding and retaining memories. By providing a potential mechanism for some of the cognitive symptoms produced by this mutation, our findings may lead to novel approaches for the treatment of nonmotor symptoms of PD.

Disclosure of research results in genetic studies of Parkinson's disease caused by LRRK2 mutations

With the advent of large genetic studies examining both symptomatic and asymptomatic individuals, whether and how to disclose genetic research results have become pressing questions. The need is particularly acute in the case of LRRK2 research: Movement centers worldwide are recruiting cohorts of individuals with Parkinson's disease (PD) and their family members, including asymptomatic carriers. Clinical features and treatment are complex and evolving, and disclosure policies vary at different sites and have been modified during the course of some studies. We present the major ethical principles of autonomy, beneficence, nonmaleficence, and honesty that should guide disclosure policies in studies of families with LRRK2 mutations. We make recommendations regarding genetic counseling, policies of either active or passive disclosure, responsibilities of funders to budget for genetic counseling, clinical genetic testing where locally required for disclosure, and aspects of study design to avoid mandatory disclosure whenever feasible. © 2015 International Parkinson and Movement Disorder Society.

Cognitive profile of LRRK2-related Parkinson's disease

BACKGROUND

Increasing evidence suggests that genetic factors play a role in the variability associated with cognitive performance in Parkinson's disease (PD). Mutations in the LRRK2 gene are the most common cause of monogenic PD; however, the cognitive profile of LRRK2-related PD is not well-characterized.

METHODS

A cohort of 1,447 PD patients enrolled in the PD Cognitive Genetics Consortium was screened for LRRK2 mutations and completed detailed cognitive testing. Associations between mutation carrier status and cognitive test scores were assessed using linear regression models.

RESULTS

LRRK2 mutation carriers (n = 29) demonstrated better performance on the Mini Mental State Examination (P = 0.03) and the Letter-Number Sequencing Test (P = 0.005). A smaller proportion of LRRK2 carriers were demented (P = 0.03).

CONCLUSIONS

Our cross-sectional study demonstrates better performance on certain cognitive tests, as well as lower rates of dementia in LRRK2-related PD. Future longitudinal studies are needed to determine whether LRRK2 mutation carriers exhibit slower cognitive decline. © 2015 International Parkinson and Movement Disorder Society.

The neurobiological basis of cognitive impairment in Parkinson's disease

The recent formalization of clinical criteria for Parkinson's disease with dementia (PDD) codifies many studies on this topic, including those assessing biological correlates. These studies show that the emergence of PDD occurs on the background of severe dopamine deficits with, the main pathological drivers of cognitive decline being a synergistic effect between alpha-synuclein and Alzheimer's disease pathology. The presence of these pathologies correlates with a marked loss of limbic and cortically projecting dopamine, noradrenaline, serotonin, and acetylcholine neurons, although the exact timing of these relationships remains to be determined. Genetic factors, such as triplications in the α-synuclein gene, lead to a clear increased risk of PDD, whereas others, such as parkin mutations, are associated with a reduced risk of PDD. The very recent formalization of clinical criteria for PD with mild cognitive impairment (PD-MCI) allows only speculation on its biological and genetic bases. Critical assessment of animal models shows that chronic low-dose MPTP treatment in primates recapitulates PD-MCI over time, enhancing the current biological concept of PD-MCI as having enhanced dopamine deficiency in frontostriatal pathways as well as involvement of other neurotransmitter systems. Data from other animal models support multiple transmitter involvement in cognitive impairment in PD. Whereas dopamine dysfunction has been highlighted because of its obvious role in PD, the role of the other neurotransmitter systems, neurodegenerative pathologies, and genetic factors in PD-MCI remains to be fully elucidated.

Neuropsychological performance in LRRK2 G2019S carriers with Parkinson's disease

BACKGROUND

Ashkenazi Jewish (AJ) LRRK2 carriers are more likely to manifest the postural instability gait difficulty (PIGD) motor phenotype than non-carriers but perform similarly to non-carriers on cognitive screening tests.

OBJECTIVE

To compare the cognitive profiles of AJ with Parkinson's disease (PD) with and without LRRK2 G2019S mutations using a comprehensive neuropsychological battery.

METHODS

We administered a neuropsychological battery to PD participants in the Michael J. Fox Foundation AJ consortium. Participants (n = 236) from Beth Israel Medical Center, NY, Columbia University Medical Center, NY and Tel Aviv Medical Center, Israel included 116 LRRK2 G2019S carriers and 120 non-carriers. Glucocerbrosidase mutation carriers were excluded. We compared performance on each neuropsychological test between carriers and non-carriers. Participants in New York (n = 112) were evaluated with the entire battery. Tel Aviv participants (n = 124) were evaluated on attention, executive function and psychomotor speed tasks. The association between G2019S mutation status (predictor) and each neuropsychological test (outcome) was assessed using linear regression models adjusted for PIGD motor phenotype, site, sex, age, disease duration, education, Unified Parkinson's Disease Rating Scale (UPDRS) Part III, levodopa equivalent dose, and Geriatric Depression Score (GDS).

RESULTS

Carriers had longer disease duration (p < 0.001) and were more likely to manifest the PIGD phenotype (p = 0.024). In adjusted regression models, carriers performed better than non-carriers in Stroop Word Reading (p < 0.001), Stroop Interference (p = 0.011) and Category Fluency (p = 0.026).

CONCLUSION

In AJ-PD, G2019S mutation status is associated with better attention (Stroop Word Reading), executive function (Stroop Interference) and language (Category Fluency) after adjustment for PIGD motor phenotype.

The role of the LRRK2 gene in Parkinsonism

Parkinson’s disease (PD), like many common age-related conditions, has been recognized to have a substantial genetic component. Multiple lines of evidence suggest that Leucine-rich repeat kinase 2 (LRRK2) is a crucial factor to understanding the etiology of PD. LRRK2 is a large, widely expressed, multi-domain and multifunctional protein. LRRK2 mutations are the major cause to inherited and sporadic PD. In this review, we discuss the pathology and clinical features which show diversity and variability of LRRK2-associated PD. In addition, we do a thorough literature review and provide theoretical data for gene counseling. Further, we present the evidence linking LRRK2 to various possible pathogenic mechanism of PD such as α-synuclein, tau, inflammatory response, oxidative stress, mitochondrial dysfunction, synaptic dysfunction as well as autophagy-lysosomal system. Based on the above work, we investigate activities both within GTPase and outside enzymatic regions in order to obtain a potential therapeutic approach to solve the LRRK2 problem.

Cognitive dysfunction in Parkinson's disease related to the R1441G mutation in LRRK2

OBJECTIVE

The neuropsychological characteristics of patients with Parkinson's Disease (PD) associated with R1441G mutation in the LRRK2 gene (R1441G-PD) are not well known. The aim of this study was to examine the cognitive status and mood of R1441G-PD patients.

METHODS

Thirty patients with R1441G-PD were compared with thirty idiopathic PD (i-PD) patients who were matched by age, sex, education, disease onset age and duration, using a comprehensive battery of neuropsychological test, and considering the Movement Disorder Society (MDS) criteria for the diagnosis of Mild Cognitive Impairment (PD-MCI) and dementia (PD-Dementia).

RESULTS

The mean scores in the depression and anxiety scales were similar in the two groups. Depressive symptoms were detected in 31.8% of R1441G-PD and 25% of i-PD patients and anxiety symptoms were evident in 4.5% and 15%, respectively, but the differences were not significant. The only neuropsychological test on which there was a significantly worse performance in the R1441G-PD group was the Boston naming test but the difference became not significant when Bonferroni's correction was applied. The prevalence of PD-MCI was 30% in both R1441G-PD and i-PD, with no differences in the number and type of domains altered given that executive function, memory and attention were mainly affected. PD-Dementia was diagnosed in 13.3% (n = 4) of R1441G-PD and 26.7% (n = 8) of i-PD patients (difference was not significant).

CONCLUSION

In conclusion, significant differences were not detected between R1441G-PD and i-PD in cognitive, depression and anxiety scales, or PD-MCI and PD-Dementia prevalence, and the cognitive profile was identical in the two groups.

Comparative study of Parkinson's disease and leucine-rich repeat kinase 2 p.G2019S parkinsonism

Parkinson disease is a progressive neurodegenerative disease for which leucine-rich repeat kinase 2 (LRRK2 carriers) p.G2019S confers substantial genotypic and population attributable risk. With informed consent, we have recruited clinical data from 778 patients from Tunisia (of which 266 have LRRK2 parkinsonism) and 580 unaffected subjects. Motor, autonomic, and cognitive assessments in idiopathic Parkinson disease and LRRK2 patients were compared with regression models. The age-associated cumulative incidence of LRRK2 parkinsonism was also estimated using case-control and family-based designs. LRRK2 parkinsonism patients had slightly less gastrointestinal dysfunction and rapid eye movement sleep disorder. Overall, disease penetrance in LRRK2 carriers was 80% by 70 years but women become affected a median 5 years younger than men. Idiopathic Parkinson disease patients with younger age at diagnosis have slower disease progression. However, age at diagnoses does not predict progression in LRRK2 parkinsonism. LRRK2 p.G2019S mutation is a useful aid to diagnosis and modifiers of disease in LRRK2 parkinsonism may aid in developing therapeutic targets.

LRRK2: cause, risk, and mechanism

In 2004 it was first shown that mutations in LRRK2 can cause Parkinson's disease. This initial discovery was quickly followed by the observation that a single particular mutation is a relatively common cause of Parkinson's disease across varied populations. Further genetic investigation has revealed a variety of genetic ties to Parkinson's disease across this gene. These include common alleles with quite broad effects on risk, likely through both alterations at the protein sequence level, and in the context of expression. A great deal of functional characterization of LRRK2 and disease-causing mutations in this protein has occurred over the last 9 years, and considerable progress has been made. Particular attention has been paid to the kinase activity of LRRK2 as a therapeutic target, and while it is no means certain that this is viable target it is likely that this hypothesis will be tested in clinical trials sooner rather than later. We believe that the future goals for LRRK2 research are, while challenging, relatively clear and that the next 10 years of research promises to be perhaps more exciting than the last.