Penetrance of LRRK2 G2385R and R1628P is modified by common PD-associated genetic variants

An overview of the worldwide distribution of LRRK2 mutations in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder with significant genetic influence. The LRRK2 gene is a major genetic contributor, particularly the Gly2019Ser mutation. This focused review investigates the global distribution of LRRK2 mutations, with emphasis on Gly2019Ser and other pathogenic variants. Prevalence rates of Gly2019Ser are highest in North Africa and the Ashkenazi-Jewish population, indicating a potential common ancestor and founder effect. Other LRRK2 mutations, including Asn1437His, Arg1441Gly/Cys/His, Tyr1699Cys and Ile2020Thr, exhibit varying global prevalences. Understanding these distributions enhances our knowledge of PD genetics and aids personalized medicine. Further research is crucial to unravel clinical implications and develop targeted therapies for LRRK2 mutation carriers.

Escherichia coli triggers α-synuclein pathology in the LRRK2 transgenic mouse model of PD

Alpha-synuclein (α-syn) pathology is the hallmark of Parkinson's disease (PD). The leucine-rich repeat kinase 2 (LRRK2) gene is a major-effect risk gene for sporadic PD (sPD). However, what environmental factors may trigger the formation of α-syn pathology in carriers of LRRK2 risk variants are still unknown. Here, we report that a markedly increased abundance of Escherichia coli (E. coli) in the intestinal microbiota was detected in LRRK2 risk variant(R1628P or G2385R) carriers with sPD compared with carriers without sPD. Animal experiments showed that E. coli administration triggered pathological α-syn accumulation in the colon and spread to the brain via the gut-brain axis in Lrrk2 R1628P mice, due to the co-occurrence of Lrrk2 variant-induced inhibition of α-syn autophagic degradation and increased phosphorylation of α-syn caused by curli in E. coli-derived extracellular vesicles. Fecal microbiota transplantation (FMT) effectively ameliorated motor deficits and α-syn pathology in Lrrk2 R1628P mice. Our findings elaborate on the mechanism that E. coli triggers α-syn pathology in Lrrk2 R1628P mice, and highlight a novel gene-environment interaction pattern in LRRK2 risk variants. Even more importantly, the findings reveal the interplay between the specific risk gene and the matched environmental factors triggers the initiation of α-syn pathology in sPD.

Applications of Machine Learning to Diagnosis of Parkinson's Disease

BACKGROUND

Accurate diagnosis of Parkinson's disease (PD) is challenging due to its diverse manifestations. Machine learning (ML) algorithms can improve diagnostic precision, but their generalizability across medical centers in China is underexplored.

OBJECTIVE

To assess the accuracy of an ML algorithm for PD diagnosis, trained and tested on data from different medical centers in China.

METHODS

A total of 1656 participants were included, with 1028 from Beijing (training set) and 628 from Fuzhou (external validation set). Models were trained using the least absolute shrinkage and selection operator-logistic regression (LASSO-LR), decision tree (DT), random forest (RF), eXtreme gradient boosting (XGboost), support vector machine (SVM), and k-nearest neighbor (KNN) techniques. Hyperparameters were optimized using five-fold cross-validation and grid search techniques. Model performance was evaluated using the area under the curve (AUC) of the receiver operating characteristic (ROC) curve, accuracy, sensitivity (recall), specificity, precision, and F1 score. Variable importance was assessed for all models.

RESULTS

SVM demonstrated the best differentiation between healthy controls (HCs) and PD patients (AUC: 0.928, 95% CI: 0.908-0.947; accuracy: 0.844, 95% CI: 0.814-0.871; sensitivity: 0.826, 95% CI: 0.786-0.866; specificity: 0.861, 95% CI: 0.820-0.898; precision: 0.849, 95% CI: 0.807-0.891; F1 score: 0.837, 95% CI: 0.803-0.868) in the validation set. Constipation, olfactory decline, and daytime somnolence significantly influenced predictability.

CONCLUSION

We identified multiple pivotal variables and SVM as a precise and clinician-friendly ML algorithm for prediction of PD in Chinese patients.

LRRK2: Genetic mechanisms vs genetic subtypes

In 2004, the identification of pathogenic variants in the LRRK2 gene across several families with autosomal dominant late-onset Parkinson's disease (PD) revolutionized our understanding of the role of genetics in PD. Previous beliefs that genetics in PD was limited to rare early-onset or familial forms of the disease were quickly dispelled. Currently, we recognize LRRK2 p.G2019S as the most common genetic cause of both sporadic and familial PD, with more than 100,000 affected carriers across the globe. The frequency of LRRK2 p.G2019S is also highly variable across populations, with some regions of Asian or Latin America reporting close to 0%, contrasting to Ashkenazi Jews or North African Berbers reporting up to 13% and 40%, respectively. Patients with LRRK2 pathogenic variants are clinically and pathologically heterogeneous, highlighting the age-related variable penetrance that also characterizes LRRK2-related disease. Indeed, the majority of patients with LRRK2-related disease are characterized by a relatively mild Parkinsonism with less motor symptoms with variable presence of α-synuclein and/or tau aggregates, with pathologic pleomorphism widely described. At a functional cellular level, it is likely that pathogenic variants mediate a toxic gain-of-function of the LRRK2 protein resulting in increased kinase activity perhaps in a cell-specific manner; by contrast, some LRRK2 variants appear to be protective reducing PD risk by decreasing the kinase activity. Therefore, employing this information to define appropriate patient populations for clinical trials of targeted kinase LRRK2 inhibition strategies is very promising and demonstrates a potential future application for PD using precision medicine.

Association of Olfactory Performance With Motor Decline and Age at Onset in People With Parkinson Disease and the LRRK2 G2019S Variant

BACKGROUND AND OBJECTIVES

There is clinical and phenotypic heterogeneity in LRRK2 G2019S Parkinson disease (PD), including loss of smell. Olfactory scores have defined subgroups of LRRK2 PD at baseline. We now extend this work longitudinally to better determine features associated with olfactory classes and to gain further insight into this heterogeneity.

METHODS

Evaluation of 162 patients with LRRK2 PD and 198 patients with idiopathic PD (IPD) from the LRRK2 Ashkenazi Jewish Consortium was performed, with follow-up available for 92 patients with LRRK2 PD and 74 patients with IPD. Olfaction (University of Pennsylvania Smell Identification Test [UPSIT]), motor function (Unified Parkinson Disease Rating Scale), and cognition (Montreal Cognitive Assessment), as well as sleep, nonmotor, and mood, were measured. Gaussian mixture models were applied on the UPSIT percentile score to determine subgroups based on olfactory performance. Linear mixed effects models, using PD duration as the time scale, assessed the relationship between UPSIT subgroup membership and motor/cognitive change.

RESULTS

Baseline olfaction was better in LRRK2 PD compared with IPD (mean UPSIT ± SD: 24.2 ± 8.8 vs 18.9 ± 7.6), with higher mean percentile scores (difference: 15.3 ± 11.6) (p < 0.001) and less frequent hyposmia (55.6% vs 85.4%; p < 0.001). Analysis suggested 3 classes among LRRK2 PD. Age at onset in LRRK2 PD was earlier in the worst olfaction group (group 1), compared with groups 2 and 3 (54.5 ± 11.1 vs 61.7 ± 9.3) (p = 0.012), and separately in the hyposmic group overall (55.0 ± 11.3 vs 61.7 ± 9.1) (p < 0.001). Longitudinal motor deterioration in LRRK2 PD was also significantly faster in the worst UPSIT group than the best UPSIT group (group 3 vs group 1: B = 0.31, SE = 0.35 vs B = 0.96, SE = 0.28) (rate difference = -0.65, SE = 0.29) (p = 0.03). However, olfactory group membership was not significantly associated with cognitive decline.

DISCUSSION

In this large LRRK2 cohort with longitudinal analysis, we extend prior work demonstrating subgroups defined by olfaction in LRRK2 G2019S PD and show that the worst olfaction group has earlier age at PD onset and more rapid motor decline. This supports a subgroup of LRRK2 PD that might show more rapid change in a clinical trial of LRRK2-related agents and highlights the need to integrate careful phenotyping into allocation schema in clinical trials of LRRK2-related agents.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that worse olfactory scores were associated with an earlier age at symptomatic onset and a faster rate of motor deterioration in patients with LRRK2 PD.

A 10-Year Community-Based Study of Leucine-Rich Repeat Kinase 2 G2385R Carriers' Conversion to Parkinson's Disease

BACKGROUND

The G2385R variant of leucine-rich repeat kinase 2 (LRRK2) is mainly associated with Parkinson's disease(PD) in Asian populations.

OBJECTIVE

The aim of this study was to investigate the PD conversion rate and clinical characteristics of LRRK2 G2385R nonmanifesting carriers.

METHODS

All participants were from the community-based longitudinal cohort of Shanghai Ruijin Hospital. The G2385R carriers and noncarriers were screened by Sanger sequencing and received face-to-face interviews at baseline and follow-up assessments. The Kaplan-Meier method was used to compare the conversion rate of PD. Cox regression models were used to estimate the risk of G2385R variant for PD.

RESULTS

In the combined cohort, 26 (7.9%) people developed PD in 329 carriers versus 9 (2.6%) in 345 noncarriers (P = 0.0016). Cox regression model confirmed that the G2385R variant was a strong risk factor for PD in a Chinese population older than 50 years (hazard ratio, 3.314; 95% confidence interval, 1.551-7.078; P = 0.002). No difference was found in clinical symptoms between carriers and noncarriers.

CONCLUSIONS

We confirmed an increased conversion of PD in leucine-rich repeat kinase 2 G2385R carriers during a 10-year follow-up. © 2022 International Parkinson and Movement Disorder Society.

Penetrance of Parkinson disease LRRK2 G2385R-associated variant in the Chinese population

BACKGROUND AND PURPOSE

Penetrance estimates of the leucine-rich repeat kinase 2 (LRRK2) variants for Parkinson disease (PD) vary widely. G2385R is one of the most common LRRK2 variants in Asian populations, and its penetrance is currently unknown. We aimed to estimate the penetrance of G2385R in the Chinese population.

METHODS

The G2385R variant was tested by Sanger sequencing in 6386 participants older than 50 years, all from the community cohort established by Shanghai Ruijin Hospital in 2009-2011. G2385R carriers and matched noncarriers underwent a brief questionnaire survey (including sex, current age, PD diagnosis, and age at onset) and face-to-face PD assessment during 2020-2021. The penetrance of PD was estimated by the Kaplan-Meier method.

RESULTS

A total of 396 G2385R carriers and 415 noncarriers were included, after excluding those with a baseline diagnosis of PD or unwilling to participate. In G2385R carriers, the penetrance of PD was 1.64% at 70 years, 10.26% at 80 years, and 18.49% at 90 years, and reached 25.90% at 95 years. The penetrance of PD in G2385R carriers was higher than in noncarriers (p = 0.0071). In noncarriers, only 0%, 3.72%, and 9.66% developed parkinsonism by 70, 80, and 90 years of age. Among carriers and noncarriers, there were no statistically significant differences in penetrance comparisons between males and females, or between urban and rural.

CONCLUSIONS

The lifetime penetrance of LRRK2 G2385R in the Chinese population was 25.9%. The penetrance modifier of G2385R in our study was age-related. Further investigation of genetic and environmental modifiers affecting G2385R penetrance is warranted.

What have we learned from genome-wide association studies (GWAS) in Parkinson's disease?

After fifteen years of genome-wide association studies (GWAS) in Parkinson's disease (PD), what have we learned? Addressing this question will help catalogue the progress made towards elucidating disease mechanisms, improving the clinical utility of the identified loci, and envisioning how we can harness the strides to develop translational GWAS strategies. Here we review the advances of PD GWAS made to date while critically addressing the challenges and opportunities for next-generation GWAS. Thus, deciphering the missing heritability in underrepresented populations is currently at the reach of hand for a truly comprehensive understanding of the genetics of PD across the different ethnicities. Moreover, state-of-the-art GWAS designs hold a true potential for enhancing the clinical applicability of genetic findings, for instance, by improving disease prediction (PD risk and progression). Lastly, advanced PD GWAS findings, alone or in combination with clinical and environmental parameters, are expected to have the capacity for defining patient enriched cohorts stratified by genetic risk profiles and readily available for neuroprotective clinical trials. Overall, envisioning future strategies for advanced GWAS is currently timely and can be instrumental in providing novel genetic readouts essential for a true clinical translatability of PD genetic findings.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Exploring the focal role of LRRK2 kinase in Parkinson's disease

The major breakthroughs in our knowledge of how biology plays a role in Parkinson's disease (PD) have opened up fresh avenues designed to know the pathogenesis of disease and identify possible therapeutic targets. Mitochondrial abnormal functioning is a key cellular feature in the pathogenesis of PD. An enzyme, leucine-rich repeat kinase 2 (LRRK2), involved in both the idiopathic and familial PD risk, is a therapeutic target. LRRK2 has a link to the endolysosomal activity. Enhanced activity of the LRRK2 kinase, endolysosomal abnormalities and aggregation of autophagic vesicles with imperfectly depleted substrates, such as α-synuclein, are all seen in the substantia nigra dopaminergic neurons in PD. Despite the fact that LRRK2 is involved in endolysosomal and autophagic activity, it is undefined if inhibiting LRRK2 kinase activity will prevent endolysosomal dysfunction or minimise the degeneration of dopaminergic neurons. The inhibitor's capability of LRRK2 kinase to inhibit endolysosomal and neuropathological alterations in human PD indicates that LRRK2 inhibitors could have significant therapeutic usefulness in PD. G2019S is perhaps the maximum common mutation in PD subjects. Even though LRRK2's well-defined structure has still not been established, numerous LRRK2 inhibitors have been discovered. This review summarises the role of LRRK2 kinase in Parkinson's disease.

Genomewide Association Studies of LRRK2 Modifiers of Parkinson's Disease

Objective

The aim of this study was to search for genes/variants that modify the effect of LRRK2 mutations in terms of penetrance and age‐at‐onset of Parkinson's disease.

Methods

We performed the first genomewide association study of penetrance and age‐at‐onset of Parkinson's disease in LRRK2 mutation carriers (776 cases and 1,103 non‐cases at their last evaluation). Cox proportional hazard models and linear mixed models were used to identify modifiers of penetrance and age‐at‐onset of LRRK2 mutations, respectively. We also investigated whether a polygenic risk score derived from a published genomewide association study of Parkinson's disease was able to explain variability in penetrance and age‐at‐onset in LRRK2 mutation carriers.

Results

A variant located in the intronic region of CORO1C on chromosome 12 (rs77395454; p value = 2.5E‐08, beta = 1.27, SE = 0.23, risk allele: C) met genomewide significance for the penetrance model. Co‐immunoprecipitation analyses of LRRK2 and CORO1C supported an interaction between these 2 proteins. A region on chromosome 3, within a previously reported linkage peak for Parkinson's disease susceptibility, showed suggestive associations in both models (penetrance top variant: p value = 1.1E‐07; age‐at‐onset top variant: p value = 9.3E‐07). A polygenic risk score derived from publicly available Parkinson's disease summary statistics was a significant predictor of penetrance, but not of age‐at‐onset.

Interpretation

This study suggests that variants within or near CORO1C may modify the penetrance of LRRK2 mutations. In addition, common Parkinson's disease associated variants collectively increase the penetrance of LRRK2 mutations. ANN NEUROL 2021;90:82–94

Sex effects on clinical features in LRRK2 G2385R carriers and non-carriers in Parkinson's disease

BACKGROUND

Differences of genotypes between male and female have been studied in Parkinson's disease (PD), but limited research has focused on the comparison between sexes with LRRK2 G2385 variant.

OBJECTIVE

The aim of this study was to explore sex effects in the same genetic subtype and role of leucine-rich repeat kinase 2 (LRRK2) G2385R variants in the same sex in PD.

METHODS

613 PD patients were recruited from the Movement Disorders Clinic in Ruijin Hospital. We did not include healthy controls in this study. The data collected includes demographic information, disease history, scores of motor and non-motor symptoms scales, midbrain transcranial sonography and DNA. Binary logistic regression analysis was performed to evaluate the association between clinical features and sex in LRRK2 G2385R carriers and non-carriers, as well as the association between the clinical features and LRRK2 G2385R variants in male and female sex.

RESULTS

Sex distribution is similar in LRRK2 G2385R carriers and non-carriers. In male sex, LRRK2 G2385R carriers showed lower risk in cognitive impairment compared with non-carriers (OR = 0.301, p = 0.003, 95%CI 0.135-0.668). In female sex, LRRK2 G2385R carriers showed lower risk in autonomic dysfunction compared with non-carrier (OR = 0.401, p = 0.040, 95%CI 0.167-0.960). In LRRK2 G2385R non-carriers, female sex showed lower risk of impairment in activity of daily living (OR = 0.610, p = 0.021, 95%CI 0.400-0.928), excessive daytime sleepiness (OR = 0.555, p = 0.007, 95%CI 0.361-0.853), substantia nigra hyperechogenicity (OR = 0.448, p = 0.019, 95%CI 0.228-0.878), autonomic dysfunction frequency (OR = 0.626, p = 0.016, 95%CI 0.428-0.917) and higher risk in mood disorders (OR = 1.691, p = 0.022, 95%CI 1.078-2.654) compared with male. In LRRK2 G2385R carriers, female sex showed a lower risk of autonomic dysfunction (OR = 0.294, p = 0.024, 95%CI 0.102-0.849) compared with male.

CONCLUSION

In contrast to male PD patients, a more benign disease course was observed in female in both LRRK2 G2385R carriers and non-carriers. However, sex differences were less notable in PD with LRRK2 G2385R variants.

Genetic and Environmental Factors Influence the Pleomorphy of LRRK2 Parkinsonism

Missense mutations in the LRRK2 gene were first identified as a pathogenic cause of Parkinson's disease (PD) in 2004. Soon thereafter, a founder mutation in LRRK2, p.G2019S (rs34637584), was described, and it is now estimated that there are approximately 100,000 people worldwide carrying this risk variant. While the clinical presentation of LRRK2 parkinsonism has been largely indistinguishable from sporadic PD, disease penetrance and age at onset can be quite variable. In addition, its neuropathological features span a wide range from nigrostriatal loss with Lewy body pathology, lack thereof, or atypical neuropathology, including a large proportion of cases with concomitant Alzheimer's pathology, hailing LRRK2 parkinsonism as the "Rosetta stone" of parkinsonian disorders, which provides clues to an understanding of the different neuropathological trajectories. These differences may result from interactions between the LRRK2 mutant protein and other proteins or environmental factors that modify LRRK2 function and, thereby, influence pathobiology. This review explores how potential genetic and biochemical modifiers of LRRK2 function may contribute to the onset and clinical presentation of LRRK2 parkinsonism. We review which genetic modifiers of LRRK2 influence clinical symptoms, age at onset, and penetrance, what LRRK2 mutations are associated with pleomorphic LRRK2 neuropathology, and which environmental modifiers can augment LRRK2 mutant pathophysiology. Understanding how LRRK2 function is influenced and modulated by other interactors and environmental factors-either increasing toxicity or providing resilience-will inform targeted therapeutic development in the years to come. This will allow the development of disease-modifying therapies for PD- and LRRK2-related neurodegeneration.

Identification of Targets from LRRK2 Rescue Phenotypes

Parkinson’s disease (PD) is an age-dependent neurodegenerative condition. Leucine-rich repeat kinase 2 (LRRK2) mutations are the most frequent cause of sporadic and autosomal dominant PD. The exact role of LRRK2 protective variants (R1398H, N551K) together with a pathogenic mutant (G2019S) in aging and neurodegeneration is unknown. We generated the following myc-tagged UAS-LRRK2 transgenic Drosophila: LRRK2 (WT), N551K, R1398H, G2019S single allele, and double-mutants (N551K/G2019S or R1398H/G2019S). The protective variants alone were able to suppress the phenotypic effects caused by the pathogenic LRRK2 mutation. Next, we conducted RNA-sequencing using mRNA isolated from dopaminergic neurons of these different groups of transgenic Drosophila. Using pathway enrichment analysis, we identified the top 10 modules (p < 0.05), with “LRRK2 in neurons in Parkinson’s disease” among the candidates. Further dissection of this pathway identified the most significantly modulated gene nodes such as eEF1A2, ACTB, eEF1A, and actin cytoskeleton reorganization. The induction of the pathway was successfully restored by the R1398H protective variant and R1398H-G2019S or N551K-G2019S rescue experiments. The oxidoreductase family of genes was also active in the pathogenic mutant and restored in protective and rescue variants. In summary, we provide in vivo evidence supporting the neuroprotective effects of LRRK2 variants. RNA sequencing of dopaminergic neurons identified upregulation of specific gene pathways in the Drosophila carrying the pathogenic variant, and this was restored in the rescue phenotypes. Using protective gene variants, our study identifies potential new targets and provides proof of principle of a new therapeutic approach that will further our understanding of aging and neurodegeneration in PD.

CD157 and Brain Immune System in (Patho)physiological Conditions: Focus on Brain Plasticity

Ectoenzyme and receptor BST-1/CD157 has been considered as a key molecule involved in the regulation of functional activity of cells in various tissues and organs. It is commonly accepted that CD157 catalyzes NAD+ hydrolysis and acts as a component of integrin adhesion receptor complex. Such properties are important for the regulatory role of CD157 in neuronal and glial cells: in addition to recently discovered role in the regulation of emotions, motor functions, and social behavior, CD157 might serve as an important component of innate immune reactions in the central nervous system. Activation of innate immune system in the brain occurs in response to infectious agents as well as in brain injury and neurodegeneration. As an example, in microglial cells, association of CD157 with CD11b/CD18 complex drives reactive gliosis and neuroinflammation evident in brain ischemia, chronic neurodegeneration, and aging. There are various non-substrate ligands of CD157 belonging to the family of extracellular matrix proteins (fibronectin, collagen I, finbrinogen, and laminin) whose activity is required for controlling cell adhesion and migration. Therefore, CD157 could control structural and functional integrity of the blood-brain barrier and barriergenesis. On the other hand, contribution of CD157 to the regulation of brain development is rather possible since in the embryonic brain, CD157 expression is very high, whereas in the adult brain, CD157 is expressed on neural stem cells and, presumably, is involved in the neurogenesis. Besides, CD157 could mediate astrocytes' action on neural stem and progenitor cells within neurogenic niches. In this review we will summarize how CD157 may affect brain plasticity acting as a molecule at the crossroad of neurogenesis, cerebral angiogenesis, and immune regulation.

Association of rare variants in neurodegenerative genes with familial Alzheimer's disease

Objective

To investigate the impact of rare variants underlying neurodegenerative‐related genes to familial Alzheimer’s disease (AD).

Methods

We performed targeted sequencing of 277 neurodegenerative‐related genes on probands from 75 Chinese AD families non‐carrying causative mutation of dementia genes. Rare coding variants segregated in families were tested for association in an independent cohort of 506 patients with sporadic AD and 498 cognitively normal controls. East Asians data from the Exome Aggregation Consortium (ExAC) were used as a reference control.

Results

A novel rare variant, P410S of PLD3 was found in an early‐onset AD family. LRRK2 I2012T, a causative mutation of Parkinson’s disease, was identified in another early‐onset AD family. Missense variants in ABCA7 (P143S and A1507T) and CR1(T239M) were significantly associated with familial AD (P = 0.005437, 0.001383, 0.000549), a missense variant in TREM2(S183C) was significantly associated with AD (P = 0.000396) when compared with the East Asian controls in ExAC database. A non‐frameshift variant in FUS (G223del) was frequent in AD cases and significantly associated with familial AD (P = 0.008).

Interpretation

Multiple rare coding variants of causal and risk neurodegenerative genes were presented in clinically diagnosed AD families that may confer risk of AD. Our data supported that the clinical, pathological, and genetic architectures of AD, PD, and FTD/ALS may overlapping. We propose that targeted sequencing on neurodegenerative‐related genes is necessary for genetically unclear AD families.

Effect of LRRK2 G2385R Variant on Subthalamic Deep Brain Stimulation Efficacy in Parkinson's Disease in a Han Chinese Population

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment for advanced Parkinson's disease (PD). The G2385R variant of LRRK2 is a risk factor for PD in Han Chinese individuals. We retrospectively compared the clinical outcomes of STN-DBS surgery between PD Han Chinese G2385R variant carriers and non-carriers. Fifty-seven PD patients with bilateral STN-DBS were enrolled, including 8 G2385R+ variant carriers (G2385R+ group) and 49 non-carriers (G2385R- group). Clinical data included Unified Parkinson's Disease Rating Scale (UPDRS) parts I to IV, levodopa equivalent daily dose (LEDD), Mini-Mental State Examination Scale (MMSE) score, and Hamilton Depression Rating Scale (HAMD) score measured prior to DBS and 12 months post-DBS. DBS settings were also recorded. All PD patients benefited from STN-DBS surgery. There were no statistical differences between the two groups in terms of motor function, daily living activities, and LEDD reductions at 12 months post-DBS. The rigidity of the post-surgical G2385R+ group was significantly improved compared with that of the G2385R- group (P = 0.045). Post-surgical voltage in the G2385R+ group was significantly higher than that in the G2385R- group (P = 0.033). STN-DBS outcomes were not influenced by the LRRK2 G2385R variant in Han Chinese patients.

Progression in the LRRK2-Asssociated Parkinson Disease Population

Importance

Few prospective longitudinal studies have evaluated the progression of Parkinson disease (PD) in patients with the leucine-rich repeat kinase 2 (LRRK2 [OMIM 609007]) mutation. Knowledge about such progression will aid clinical trials.

Objective

To determine whether the longitudinal course of PD in patients with the LRRK2 mutation differs from the longitudinal course of PD in patients without the mutation.

Design, Setting, and Participants

A prospective comprehensive assessment of a large cohort of patients from 3 sites with LRRK2 PD or with nonmutation PD was conducted from July 21, 2009, to September 30, 2016. All patients of Ashkenazi Jewish ancestry with PD were approached at each site; approximately 80% agreed to an initial visit. A total of 545 patients of Ashkenazi Jewish descent with PD who had 1 to 4 study visits were evaluated. A total of 144 patients (26.4%) had the LRRK2 G2019S mutation. Patients with GBA (OMIM 606463) mutations were excluded from the analysis.

Main Outcomes and Measures

Linear mixed-effects models for longitudinal motor scores were used to examine the association of LRRK2 mutation status with the rate of change in Unified Parkinson's Disease Rating Scale III scores using disease duration as the time scale, adjusting for sex, site, age, disease duration, cognitive score, and levodopa-equivalent dose at baseline. Mixed-effects models were used to assess change in cognition, as measured by Montreal Cognitive Assessment scores.

Results

Among the 545 participants, 233 were women, 312 were men, and the mean (SD) age was 68.2 (9.1) years for participants with the LRRK2 mutation and 67.8 (10.7) years for those without it. Seventy-two of 144 participants with the LRRK2 mutation and 161 of 401 participants with no mutation were women. The estimate (SE) of the rate of change in the Unified Parkinson's Disease Rating Scale III motor score per year among those with the LRRK2 mutation (0.689 [0.192] points per year) was less than among those without the mutation (1.056 [0.187] points per year; difference, -0.367 [0.149] points per year; P = .02). The estimate (SE) of the difference in the rate of change of the Montreal Cognitive Assessment score between those with the LRRK2 mutation (-0.096 [0.090] points per year) and those without the mutation (-0.192 [0.102] points per year) did not reach statistical significance (difference, 0.097 [0.055] points per year; P = .08).

Conclusions and Relevance

Prospective longitudinal follow-up of patients with PD with or without the LRRK2 G2019S mutation supports data from a cross-sectional study and demonstrates a slower decline in motor Unified Parkinson's Disease Rating Scale scores among those with LRRK2 G2019S-associated PD.

A Comprehensive Analysis of Population Differences in LRRK2 Variant Distribution in Parkinson's Disease

Background:LRRK2 variants have been demonstrated to have distinct distributions in different populations. However, researchers have thus far chosen to focus on relatively few variants, such as R1628P, G2019S, and G2385R. We therefore investigated the relationship between common LRRK2 variants and PD risk in various populations.

Methods: Using a set of strict inclusion criteria, six databases were searched, resulting in the selection of 94 articles covering 49,299 cases and 47,319 controls for final pooled analysis and frequency analysis. Subgroup analysis were done for Africans, European/West Asians, Hispanics, East Asians, and mixed populations. Statistical analysis was carried out using the Mantel-Haenszel approach to determine the relationship between common LRRK2 variants and PD risk, with the significance level set at p < 0.05.

Results: In the absence of obvious heterogeneities and publication biases among the included studies, we concluded that A419V, R1441C/G/H, R1628P, G2019S, and G2385R were associated with increased PD risk (p: 0.001, 0.0004, < 0.00001, < 0.00001, and < 0.00001, respectively), while R1398H was associated with decreased risk (p: < 0.00001). In East Asian populations, A419V, R1628P, and G2385R increased risk (p: 0.001, < 0.00001, < 0.00001), while R1398H had the opposite effect (p: 0.0005). G2019S increased PD risk in both European/West Asian and mixed populations (p: < 0.00001, < 0.00001), while R1441C/G/H increased risk in European/West Asian populations only (p: 0.0004).

Conclusions: We demonstrated that LRRK2 variant distribution is different among various populations, which should inform decisions regarding the development of future genetic screening strategies.

A Comprehensive Analysis of the Association Between SNCA Polymorphisms and the Risk of Parkinson's Disease

Background: Various studies have reported associations between synuclein alpha (SNCA) polymorphisms and Parkinson's disease (PD) risk. However, the results are inconsistent. We conducted a comprehensive meta-analysis of the associations between SNCA single-nucleotide polymorphisms (SNPs) and PD risk in overall populations and subpopulations by ethnicity.

Methods: Standard meta-analysis was conducted according to our protocol with a cutoff point of p < 0.05. To find the most relevant SNCA SNPs, we used a cutoff point of p < 1 × 10⁻⁵ in an analysis based on the allele model. In the subgroup analysis by ethnicity, we divided the overall populations into five ethnic groups. We conducted further analysis on the most relevant SNPs using dominant and recessive models to identify the contributions of heterozygotes and homozygotes regarding each SNP.

Results: In our comprehensive meta-analysis, 24,075 cases and 22,877 controls from 36 articles were included. We included 16 variants in the meta-analysis and found 12 statistically significant variants with p < 0.05. After narrowing down the variants using the p < 1 × 10⁻⁵ cutoff, in overall populations, seven SNPs increased the risk of PD (rs2736990, rs356220, rs356165, rs181489, rs356219, rs11931074, and rs2737029, with odds ratios [ORs] of 1.22–1.38) and one SNP decreased the risk (rs356186, with an OR of 0.77). In the East Asian group, rs2736990 and rs11931074 increased the risk (with ORs of 1.22–1.34). In the European group, five SNPs increased the risk (rs356219, rs181489, rs2737029, rs356165, and rs11931074, with ORs of 1.26–1.37) while one SNP decreased the risk (rs356186, with an OR of 0.77). The heterozygotes and homozygotes contributed differently depending on the variant.

Conclusions: In summary, we found eight SNCA SNPs associated with PD risk, which had obvious differences between ethnicities. Seven SNPs increased the risk of PD and one SNP decreased the risk in the overall populations. In the East Asian group, rs2736990 and rs11931074 increased the risk. In the European group, rs356219, rs181489, rs2737029, rs356165, and rs11931074 increased the risk while rs356186 decreased the risk. Variants with the highest ORs and allele frequencies in our analysis should be given priority when carrying out genetic screening.

Prevalence of pre-diagnostic symptoms did not differ between LRRK2-related, GBA-related and idiopathic patients with Parkinson's disease

INTRODUCTION

Glucocerebrosidase (GBA) mutations and leucine-rich repeat kinase 2 (LRRK2) variants are the most common genetic risk factors for late-onset Parkinson's disease (PD). In this study, we aimed to investigate the differences in pre-diagnostic symptoms of PD associated with the variants.

METHODS

The participants were recruited from 24 centers across China and genotyped for LRRK2 G2385R and R1628P variants and GBA L444P mutation. Participants were surveyed with structural questionnaires for history of environmental exposure and living habits and interviewed to collect the time at onset of each symptoms before diagnosis. We compared the cumulative prevalence and manifestation pattern of symptoms between groups using multiple logistic regression, adjusting age and gender.

RESULTS

Total 1799 PD patients were recruited, including 226 patients with LRRK2 G2385R or R1628P variant, 44 with GBA L444P mutation, three with both LRRK2 and GBA mutation, and 1526 idiopathic patients. The cumulative prevalence of non-motor and typical motor symptoms did not differ between groups before diagnosis (P > 0.05). The manifestation sequences of non-motor symptoms were indistinguishable between the LRRK2-carriers, GBA-carriers, and idiopathic PD subjects, and followed the sequence of constipation, hyposmia, sleep disorders, anxiety and depression, sexual dysfunction, urinary incontinency, dizziness and cognition. Slightly higher prevalence of hypomimia and micrographia were detected in the GBA-carriers.

CONCLUSIONS

The prevalence of pre-diagnostic symptoms is almost indistinguishable between the LRRK2-carriers, GBA-carriers, and idiopathic PD before diagnosis; the sequence of the manifestation of non-motor symptoms largely conforms to the Braak stage for both genetic-related and idiopathic late-onset PD.

Genetic analysis of LRRK2 in Parkinson's disease in Han Chinese population

Mutations in Leucine-rich repeat kinase 2 (LRRK2) are recognized as the most frequent genetic factors contributing to Parkinson's disease (PD). The aim of our study was to explore LRRK2 variants in PD patients within the mainland Han Chinese population. The whole coding regions of LRRK2 from 296 PD patients were sequenced by targeted regions sequencing and exome sequencing. Eighteen rare variants were identified in 27 PD patients, and 13 of them (M100T, L153W, A459S, S722N, R792K, C925Y, R981K, S1007T, V1447M, R1677S, N2308D, N2313S, and S2350I) were firstly reported in PD. We also tried to explore the genotype-phenotype associations of LRRK2 variants in our data and found that PD with common and rare LRRK2 variants was more likely to have motor fluctuation and nonmotor symptoms. The identification of novel variants in LRRK2 suggests that this gene plays an important role in the pathogenesis and phenotype of PD in Han Chinese population, and our data also rang the alarm bell-more attention should be paid to the whole coding regions of LRRK2.

Clustering of motor and nonmotor traits in leucine-rich repeat kinase 2 G2019S Parkinson's disease nonparkinsonian relatives: A multicenter family study

OBJECTIVES

The objective of this study was to determine phenotypic features that differentiate nonparkinsonian first-degree relatives of PD leucine-rich repeat kinase 2 (LRRK2) G2019S multiplex families, regardless of carrier status, from healthy controls because nonparkinsonian individuals in multiplex families seem to share a propensity to present neurological features.

METHODS

We included nonparkinsonian first-degree relatives of LRRK2 G2019S familial PD cases and unrelated healthy controls participating in established multiplex family LRRK2 cohorts. Study participants underwent neurologic assessment including cognitive screening, olfaction testing, and questionnaires for daytime sleepiness, depression, and anxiety. We used a multiple logistic regression model with backward variable selection, validated with bootstrap resampling, to establish the best combination of motor and nonmotor features that differentiates nonparkinsonian first-degree relatives of LRRK2 G2019S familial PD cases from unrelated healthy controls.

RESULTS

We included 142 nonparkinsonian family members and 172 unrelated healthy controls. The combination of past or current symptoms of anxiety (adjusted odds ratio, 4.16; 95% confidence interval, 2.01-8.63), less daytime sleepiness (adjusted odds ratio [1 unit], 0.90; 95% confidence interval, 0.83-0.97], and worse motor UPDRS score (adjusted odds ratio [1 unit], 1.4; 95% confidence interval, 1.20-1.67) distinguished nonparkinsonian family members, regardless of LRRK2 G2019S mutation status, from unrelated healthy controls. The model accuracy was good (area under the curve = 79.3%).

CONCLUSIONS

A set of motor and nonmotor features distinguishes first-degree relatives of LRRK2 G2019S probands, regardless of mutation status, from unrelated healthy controls. Environmental or non-LRRK2 genetic factors in LRRK2-associated PD may influence penetrance of the LRRK2 G2019S mutation. The relationship of these features to actual PD risk requires longitudinal observation of LRRK2 familial PD cohorts. © 2018 International Parkinson and Movement Disorder Society.

Relationship between LRRK2 R1628P polymorphism and Parkinson's disease in Asian populations

Although the leucine-rich repeat kinase 2 (LRRK2) R1628P polymorphism has been associated with the risk of Parkinson's disease (PD) in Taiwan, China, and Singapore, there are conflicting findings regarding this relationship. Thus, the aim of the present meta-analysis was to evaluate the associations between the LRRK2 R1628P polymorphism (rs33949390) and PD in Asian populations. A search for eligible studies was performed in PubMed, Embase, SinoMed, and the China Knowledge Resource Integrated Database, and pooled odds ratios and 95% confidence intervals were used to evaluate the strength of the association between the R1628P polymorphism and PD. This meta-analysis assessed 19 studies from 14 papers that involved a total of 9,927 PD patients and 8,602 controls and found that the R1628P polymorphism was significantly associated with the risk of PD in Asian populations. Moreover, stratification analyses indicated that the R1628P polymorphism was significantly associated with an increased risk of PD among Chinese as well as non-Chinese Asian populations and an increased risk of PD in Chinese patients from China, Taiwan, and Singapore. In a stratified analysis conducted according to age, significant associations were found for both late-onset PD and early-onset PD. The present data indicate that the R1628P polymorphism of the LRRK2 gene contributes to PD susceptibility in Asian, especially Chinese, populations.

Genetic Analysis of LRRK2 R1628P in Parkinson's Disease in Asian Populations

Although the etiology of Parkinson's disease (PD) remains unclear, there is increasing evidence of genetic factors contributing to the onset of PD. Various mutations and risk variants of the gene LRRK2 have been reported, but the association between LRRK2 R1628P and PD is still inconsistent. Thus, we conducted a meta-analysis to determine the potential relationship between R1628P and PD. Our study sample was an aggregate of 17 publications, which in total consisted of 9,275 PD patients and 8,114 controls. All of these articles are of high quality according to NOS, and there was no obvious reporting bias or heterogeneity. In a general Asian population, the pooled OR of the risk genotype contrasts was 1.83 (95% CI: 1.57, 2.13). When stratified by ethnicity, the pooled ORs were 1.84 (95% CI: 1.56, 2.18) in a Chinese population and 1.79 (95% CI: 1.27, 2.52) in a non-Chinese population. Our study suggests that LRRK2 R1628P appears to be a risk factor for PD in Asian populations, both Chinese and non-Chinese.

An immunohistochemical, enzymatic, and behavioral study of CD157/BST-1 as a neuroregulator

Background

Recent rodent and human studies provide evidence in support of the fact that CD157, well known as bone marrow stromal cell antigen-1 (BST-1) and a risk factor in Parkinson’s disease, also meaningfully acts in the brain as a neuroregulator and affects social behaviors. It has been shown that social behaviors are impaired in CD157 knockout mice without severe motor dysfunction and that CD157/BST1 gene single nucleotide polymorphisms are associated with autism spectrum disorder in humans. However, it is still necessary to determine how this molecule contributes to the brain’s physiological and pathophysiological functions.

Methods

To gain fresh insights about the relationship between the presence of CD157 in the brain and its enzymatic activity, and aberrant social behavior, CD157 knockout mice of various ages were tested.

Results

CD157 immunoreactivity colocalized with nestin-positive cells and elements in the ventricular zones in E17 embryos. Brain CD157 mRNA levels were high in neonates but low in adults. Weak but distinct immunoreactivity was detected in several areas in the adult brain, including the amygdala. CD157 has little or no base exchange activity, but some ADP-ribosyl cyclase activity, indicating that CD157 formed cyclic ADP-ribose but much less nicotinic acid adenine dinucleotide phosphate, with both mobilizing Ca²⁺ from intracellular Ca²⁺ pools. Social avoidance in CD157 knockout mice was rescued by a single intraperitoneal injection of oxytocin.

Conclusions

CD157 may play a role in the embryonic and adult nervous systems. The functional features of CD157 can be explained in part through the production of cyclic ADP-ribose rather than nicotinic acid adenine dinucleotide phosphate. Further experiments are required to elucidate how the embryonic expression of CD157 in neural stem cells contributes to behaviors in adults or to psychiatric symptoms.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-017-0350-7) contains supplementary material, which is available to authorized users.

Development of LRRK2 Inhibitors for the Treatment of Parkinson's Disease

Linkage and genome-wide association studies have identified a genetic risk locus for late-onset Parkinson's disease in chromosome 12, originally identified as PARK6. The causative gene was identified to code for a large multifunctional protein, LRRK2 (leucine-rich repeat kinase 2). The combined genetic and biochemical evidence supports a hypothesis in which the LRRK2 kinase function is causally involved in the pathogenesis of sporadic and familial forms of PD, and therefore that LRRK2 kinase inhibitors could be useful for treatment. Although LRRK2 has so far not been crystallised, the use of homology modelling and crystallographic surrogates has allowed the optimisation of chemical structures such that compounds of high selectivity with good brain penetration and appropriate pharmacokinetic properties are now available for understanding the biology of LRRK2 in vitro and in vivo. This chapter reviews LRRK2 biology, the structural biology of LRRK2 and gives an overview of inhibitors of LRRK2.

Association of LRRK2 R1628P variant with Parkinson's disease in Ethnic Han-Chinese and subgroup population

Recent studies have linked certain single nucleotide polymorphisms in the leucine-rich repeat kinase 2 (LRRK2) gene with Parkinson’s disease (PD). The R1628P variant of LRRK2 may be a specific risk factor for PD in ethnic Han-Chinese populations. This study is to elucidate the epidemiological feature of R1628P in ethnic Han-Chinese population with PD. A comprehensive meta-analysis was performed to evaluate the precise association between R1628P variant and the risk for PD in ethnic Han-Chinese and subgroups stratified by gender, onset age, or family history. The analysis assessing the role of R1628P on the risk of PD in ethnic Han-Chinese supported a significant association, and the odds ratio was 1.86. We further estimate the specific prevalence in relevant ethnic Han-Chinese subgroups. After stratifying the eligible data by gender, onset age, or family history, significant associations were found in all male, female, early-onset, late-onset, familial and sporadic subgroups, and the odds ratio were 1.90, 1.94, 2.12, 1.75, 6.71 and 1.81 respectively. In conclusion, our meta-analysis suggests that R1628P variant of LRRK2 has a significant association with the risk of PD in ethnic Han-Chinese and subgroup population.

Oxidative stress: A major pathogenesis and potential therapeutic target of antioxidative agents in Parkinson's disease and Alzheimer's disease

Oxidative stress reflects an imbalance between the overproduction and incorporation of free radicals and the dynamic ability of a biosystem to detoxify reactive intermediates. Free radicals produced by oxidative stress are one of the common features in several experimental models of diseases. Free radicals affect both the structure and function of neural cells, and contribute to a wide range of neurodegenerative diseases, including Parkinson's disease and Alzheimer's disease. Although the precise mechanisms that result in the degeneration of neurons and the relevant pathological changes remain unclear, the crucial role of oxidative stress in the pathogenesis of neurodegenerative diseases is associated with several proteins (such as α-synuclein, DJ-1, Amyloid β and tau protein) and some signaling pathways (such as extracellular regulated protein kinases, phosphoinositide 3-kinase/Protein Kinase B pathway and extracellular signal-regulated kinases 1/2) that are tightly associated with the neural damage. In this review, we present evidence, gathered over the last decade, concerning a variety of pathogenic proteins, their important signaling pathways and pathogenic mechanisms associated with oxidative stress in Parkinson's disease and Alzheimer's disease. Proper control and regulation of these proteins' functions and the related signaling pathways may be a promising therapeutic approach to the patients. We also emphasizes antioxidative options, including some new neuroprotective agents that eliminate excess reactive oxygen species efficiently and have a certain therapeutic effect; however, controversy surrounds some of them in terms of the dose and length of therapy. These agents require further investigation by clinical application in patients suffering Parkinson's disease and Alzheimer's disease.

Exploring the Effects of Genetic Variants on Clinical Profiles of Parkinson's Disease Assessed by the Unified Parkinson's Disease Rating Scale and the Hoehn-Yahr Stage

Many genetic variants have been linked to familial or sporadic Parkinson’s disease (PD), among which those identified in PARK16, BST1, SNCA, LRRK2, GBA and MAPT genes have been demonstrated to be the most common risk factors worldwide. Moreover, complex gene-gene and gene-environment interactions have been highlighted in PD pathogenesis. Compared to studies focusing on the predisposing effects of genes, there is a relative lack of research investigating how these genes and their interactions influence the clinical profiles of PD. In a cohort consisting of 2,011 Chinese Han PD patients, we selected 9 representative variants from the 6 above-mentioned common PD genes to analyze their main and epistatic effects on the Unified Parkinson’s Disease Rating Scale (UPDRS) and the Hoehn and Yahr (H-Y) stage of PD. With multiple linear regression models adjusting for medication status, disease duration, gender and age at onset, none of the variants displayed significant main effects on UPDRS or the H-Y scores. However, for gene-gene interaction analyses, 7 out of 37 pairs of variants showed significant or marginally significant associations with these scores. Among these, the GBA rs421016 (L444P)×LRRK2 rs33949390 (R1628P) interaction was consistently significant in relation to UPDRS III and UPDRS total (I+II+III), even after controlling for the family-wise error rate using False Discovery Rate (FDR-corrected p values are 0.0481 and 0.0070, respectively). Although the effects of the remaining pairs of variants did not survive the FDR correction, they showed marginally significant associations with either UPDRS or the H-Y stage (raw p<0.05). Our results highlight the importance of epistatic effects of multiple genes on the determination of PD clinical profiles and may have implications for molecular classification and personalized intervention of the disease.

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

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

Genetics in Parkinson disease: Mendelian versus non-Mendelian inheritance

Parkinson's disease is a common, progressive neurodegenerative disorder, affecting 3% of those older than 75 years of age. Clinically, Parkinson's disease (PD) is associated with resting tremor, postural instability, rigidity, bradykinesia, and a good response to levodopa therapy. Over the last 15 years, numerous studies have confirmed that genetic factors contribute to the complex pathogenesis of PD. Highly penetrant mutations producing rare, monogenic forms of the disease have been discovered in singular genes such as SNCA, Parkin, DJ-1, PINK 1, LRRK2, and VPS35. Unique variants with incomplete penetrance in LRRK2 and GBA have been shown to be strong risk factors for PD in certain populations. Additionally, over 20 common variants with small effect sizes are now recognized to modulate the risk for PD. Investigating Mendelian forms of PD has provided precious insight into the pathophysiology that underlies the more common idiopathic form of disease; however, no treatment methodologies have developed. Furthermore, for identified common risk alleles, the functional basis underlying risk principally remains unknown. The challenge over the next decade will be to strengthen the findings delivered through genetic discovery by assessing the direct, biological consequences of risk variants in tandem with additional high-content, integrated datasets. This review discusses monogenic risk factors and mechanisms of Mendelian inheritance of Parkinson disease. Highly penetrant mutations in SNCA, Parkin, DJ-1, PINK 1, LRRK2 and VPS35 produce rare, monogenic forms of the disease, while unique variants within LRRK2 and GBA show incomplete penetrance and are strong risk factors for PD. Additionally, over 20 common variants with small effect sizes modulate disease risk. The challenge over the next decade is to strengthen genetic findings by assessing direct, biological consequences of risk variants in tandem with high-content, integrated datasets. This article is part of a special issue on Parkinson disease.

Parkinson-Related LRRK2 Mutation R1628P Enables Cdk5 Phosphorylation of LRRK2 and Upregulates Its Kinase Activity

Background

Recent studies have linked certain single nucleotide polymorphisms in the leucine-rich repeat kinase 2 (LRRK2) gene with Parkinson’s disease (PD). Among the mutations, LRRK2 c.4883G>C (R1628P) variant was identified to have a significant association with the risk of PD in ethnic Han-Chinese populations. But the molecular pathological mechanisms of R1628P mutation in PD is still unknown.

Principle Findings

Unlike other LRRK2 mutants in the Roc-COR-Kinase domain, the R1628P mutation didn’t alter the LRRK2 kinase activity and promote neuronal death directly. LRRK2 R1628P mutation increased the binding affinity of LRRK2 with Cyclin-dependent kinase 5 (Cdk5). Interestingly, R1628P mutation turned its adjacent amino acid residue S1627 on LRRK2 protein to a novel phosphorylation site of Cdk5, which could be defined as a typical type II (+) phosphorylation-related single nucleotide polymorphism. Importantly, we showed that the phosphorylation of S1627 by Cdk5 could activate the LRRK2 kinase, and neurons ectopically expressing R1628P displayed a higher sensitivity to 1-methyl-4-phenylpyridinium, a bioactive metabolite of environmental toxin MPTP, in a Cdk5-dependent manner.

Conclusion

Our data indicate that Parkinson-related LRRK2 mutation R1628P leads to Cdk5 phosphorylation of LRRK2 at S1627, which would upregulate the kinase activity of LRRK2 and consequently cause neuronal death.

PARK16 polymorphisms, interaction with smoking, and sporadic Parkinson's disease in Japan

Epidemiological evidence on the relationships between PARK16 single nucleotide polymorphisms (SNPs) and Parkinson's disease (PD) is inconsistent. We examined this issue in Japan. Included were 229 cases within six years of PD onset. Controls were 356 patients without neurodegenerative disease. Compared with subjects with the AA genotype of SNP rs823128, those with the AG genotype, but not the GG genotype, had a significantly reduced risk of sporadic PD. Compared with the AA genotype of SNP rs947211, both the AG genotype and the GG genotype were significantly related to an increased risk of sporadic PD. Using subjects with the AA genotype of SNP rs823156 as a reference group, there were significant inverse relationships under the additive and dominant models. No significant relationships were found between SNPs rs16856139 or rs11240572 and sporadic PD. The CAAAC, the TGAGA, and the CAGAC haplotypes were significantly related to sporadic PD. The additive interaction between SNP rs823128 and smoking affecting sporadic PD was significant, although the multiplicative interaction was not significant. The PARK16 SNPs rs823128, rs947211, and rs823156 and the CAAAC, TGAGA, and CAGAC haplotypes may be significantly associated with sporadic PD in Japan. New evidence of an additive interaction between SNP rs823156 and smoking is suggested.

Association of ARNTL and PER1 genes with Parkinson's disease: a case-control study of Han Chinese

Circadian disruptions may result in sleep problems, oxidative stress and an altered inflammatory response. These symptoms may contribute to PD pathogenesis, despite a lack of direct experimental evidence supporting this relationship. Clock genes are essential to drive and maintain circadian rhythm. To elucidate the possible role of circadian disruptions in PD, we investigated 132 tag variants in eight clock genes. We genotyped these tags within 1,394 Chinese cases and 1,342 controls using Illumina GoldenGate chips. We discovered that SNPs in ARNTL (rs900147, P = 3.33 × 10(-5), OR = 0.80) and PER1 (rs2253820, P = 5.30 × 10(-6), OR = 1.31) genes are significantly associated with PD risk. Moreover, the positive association of the ARNTL rs900147 variant was more robust in tremor dominant (TD) (P = 3.44 × 10(-4)) than postural instability and gait difficulty (PIGD) cases (P = 6.06 × 10(-2)). The association of the PER1 rs2253820 variant was more robust in PIGD (P = 5.42 × 10(-5)) than TD cases (P = 4.2 × 10(-2)). Haplotype analysis also showed that ARNTL and PER1 were associated with PD. Imputation analysis identified more SNPs within ARNTL and PER1 associated with PD, some of which may affect gene expression through altering the transcription factor binding site. In summary, our findings suggest that genetic polymorphisms in ARNTL and PER1 genes, as well as circadian disruptions, may contribute to PD pathogenesis.

Interaction between SNCA, LRRK2 and GAK increases susceptibility to Parkinson's disease in a Chinese population

PD is a complex disease, and may result from gene–gene and gene–environment interactions. There are limited studies on gene–gene interactions in PD. We and others have previously shown that SNCA rs356219, LRRK2 (rs2046932 and rs7304279) and GAK (rs1564282) are risk factors in sporadic PD. Since the expression of SNCA and neurotoxicity of alpha-synuclein are affected by LRRK2 and GAK, we hypothesize that their genetic risk variants may interact with each other. Here we investigated the interaction of SNCA rs356219, LRRK2rs7304279 and rs2046932 and GAK rs1564282 using the Multifactor Dimensionality Reduction (MDR) in a Chinese PD patient–control series (534 patients and 435 controls) and the cumulative risk effect of SNCA, LRRK2 and GAK. The MDR analysis showed a significant gene–gene interaction between the rs356219 of SNCA, rs2046932 of LRRK2 and rs1564282 of GAK. Moreover, individuals with increasing numbers of variants had an increasing likelihood of having PD, compared with those carrying none of the variants. The estimated OR for developing PD in individuals carrying 3 variants was 5.89. We demonstrated for the first time that SNPs in SNCA, LRRK2 and GAK interacted with each other to confer an increased risk of PD. In addition, PD risk increased cumulatively with the increasing number of variants.

LRRK2 A419V variant is a risk factor for Parkinson's disease in Asian population

Recently, LRRK2 A419V (rs34594498) was reported associating with Parkinson's disease (PD) in Asian population; yet the conclusion is still unobvious. We conducted a case-control study to determine the potential associations between A419V and PD in Chinese population. Five hundred PD patients and 574 health controls were genotyped. Our results showed, A419V has a significantly higher frequency among PD patients than the controls (p = 0.025, odds ratio [OR] = 2.57, 95% confidence interval [CI] [1.13-5.86]), especially in early-onset PD (p = 0.027, OR = 10.40, 95% CI [1.31-82.89]). And PD patients who carried A419V have a lower Minimum-Mental State Examination scores than PD patients who did not (p = 0.04). We also conducted a meta-analysis on A419V. In Asian population, A419V was detected at a significantly higher frequency among PD patients in contrast to controls: Z = 2.47, p = 0.01, OR = 2.11, 95% CI [1.17-3.82]. When only considering the Chinese population, the difference was more obvious with Z = 3.41, p = 0.0007, OR = 2.07, 95% CI [1.36-3.14]. The results suggest LRRK2 A419V appears to be a risk factor for PD in Asian, especially in early-onset patients. Finally, larger sample with centering on young or cognitive impairment PD patients in Asian would be preferable for further confirmation.

Association between bone marrow stromal cell antigen 1 gene polymorphisms and the susceptibility to Parkinson's disease: a meta-analysis

A number of studies have investigated the association between Parkinson's disease (PD) and genetic polymorphisms of bone marrow stromal cell antigen 1 (BST-1). However, the results to date have been conflicting. In this study a meta-analysis was performed to assess the association between BST-1 polymorphisms and PD. Previous relevant studies were identified from Medline, Embase and Cochrane databases, among which the studies evaluating the association of BST-1 polymorphisms with risk of PD were used in the meta-analysis. Summary odds ratios (ORs) and 95% confidence intervals (CIs) were determined for different genetic models using meta-analytic methods. Subgroup analysis was performed based on study designs and participant ethnicity, and sensitivity analysis was also performed. Eleven studies comprising 11,070 cases and 19,169 controls were included in this meta-analysis. ORs and 95% CIs were used to assess the strength of association. The rs4698412 variant (G→A) showed a significant summary OR of 1.12 (95% CI: 1.05-1.20; P=0.001) in an allelic model. This significant association was also observed in the subgroup analysis based on participants' ethnicity and study designs. The pooled OR of the rs11724635 variant (C→A) indicated a non-significant association with PD in a recessive model (OR, 1.16, 95% CI: 0.97-1.40; P=0.112), dominant model (OR, 1.10, 95% CI: 0.86-1.41; P=0.458) and allelic model (OR, 1.10, 95% CI: 0.95-1.27; P=0.224). Although the rs11931532 variant (T→C) did not show association with PD (OR, 0.99, 95% CI: 0.85-1.15; P=0.9), the pooled estimation of genome-wide association studies (GWAS) showed a significant connection with PD (OR, 1.19, 95% CI: 1.08-1.31; P=0.001). Sensitivity analysis supported these findings, and no evidence of publication bias was observed in the meta-analysis. Our studies suggested that the rs4698412 variant of BST-1 may increase the PD susceptibility.

Association Study between the CD157/BST1 Gene and Autism Spectrum Disorders in a Japanese Population

CD157, also referred to as bone marrow stromal cell antigen-1 (BST-1), is a glycosylphosphatidylinositol-anchored molecule that promotes pre-B-cell growth. Previous studies have reported associations between single-nucleotide polymorphisms (SNPs) of the CD157/BST1 gene with Parkinson’s disease. In an attempt to determine whether SNPs or haplotypes in the CD157/BST1 are associated with other brain disorders, we performed a case-control study including 147 autism spectrum disorder (ASD) patients at Kanazawa University Hospital in Japan and 150 unselected Japanese volunteers by the sequence-specific primer-polymerase chain reaction method combined with fluorescence correlation spectroscopy. Of 93 SNPs examined, two SNPs showed significantly higher allele frequencies in cases with ASDs than in unaffected controls (rs4301112, OR = 6.4, 95% CI = 1.9 to 22, p = 0.0007; and rs28532698, OR = 6.2, 95% CI = 1.8 to 21, p = 0.0012; Fisher’s exact test; p < 0.002 was considered significant after multiple testing correction). In addition, CT genotype in rs10001565 was more frequently observed in the ASD group than in the control group (OR = 15, 95% CI = 2.0 to 117, p = 0.0007; Fisher’s exact test). The present data indicate that genetic variation of the CD157/BST1 gene might confer susceptibility to ASDs.

Non-motor symptoms in Chinese Parkinson's disease patients with and without LRRK2 G2385R and R1628P variants

Non-motor symptoms (NMS) are common among patients with Parkinson's disease (PD). However, reports on NMS in Chinese PD population are scarce. Little is known about NMS in patients with Asian specific leucine-rich repeat kinase 2 (LRRK2) variants in G2385R and R1628P. This study aimed to elucidate the clinical characteristics of NMS in Chinese PD patients and to ascertain if there were differences in NMS between PD patients with and without LRRK2 variants. A multicenter, observational study was conducted with 1,225 sporadic PD (sPD) patients recruited from a PD cohort of the Chinese National Consortium on neurodegenerative diseases, 163 participants had the LRRK2 variants. The Non-motor Symptom Questionnaire (NMSQ) was used to screen for the presence of NMS. This study found the majority of sPD patients (97.6 %) had at least one NMS. A mean of 8.72 NMS (SD = 5.43) was reported per patient. Forgetfulness, constipation and daytime sleepiness were found to be the most frequent NMS. Moreover, the number of NMS was positively correlated with the age, disease duration, Hoehn & Yahr stage and the motor scores of the unified Parkinson's disease rating scale. Although no discrepancy was found in the number of NMS between sPD patients with and without LRRK2 variants, nocturia was less common in LRRK2 variants carriers than in non-carriers (P = 0.045). NMS appear to be prevalent in Chinese sPD population. There are no differences in the NMS phenotype between LRRK2 and no LRRK2 patients.

Anxiety- and depression-like behavior in mice lacking the CD157/BST1 gene, a risk factor for Parkinson's disease

CD157, known as bone marrow stromal cell antigen-1, is a glycosylphosphatidylinositol-anchored ADP-ribosyl cyclase that supports the survival and function of B-lymphocytes and hematopoietic or intestinal stem cells. Although CD157/Bst1 is a risk locus in Parkinson's disease (PD), little is known about the function of CD157 in the nervous system and contribution to PD progression. Here, we show that no apparent motor dysfunction was observed in young knockout (CD157 (-/-)) male mice under less aging-related effects on behaviors. CD157 (-/-) mice exhibited anxiety-related and depression-like behaviors compared with wild-type mice. These behaviors were rescued through treatment with anti-psychiatric drugs and oxytocin. CD157 was weakly expressed in the amygdala and c-Fos immunoreactivity in the amygdala was less evident in CD157 (-/-) mice than in wild-type mice. These results demonstrate for the first time that CD157 plays a role as a neuro-regulator and suggest a potential role in pre-motor symptoms in PD.

MAPT IVS1+124 C>G modifies risk of LRRK2 G2385R for Parkinson's disease in Chinese individuals

Variants of the MAPT gene have been suggested to be associated with Parkinson's disease (PD) and to modify the risk for leucine-rich repeat kinase 2 (LRRK2) Parkinsonism. However, this has not been confirmed in Asians with ethnicity-specific variants of MAPT and LRRK2. In this study, Asian-specific LRRK2 p.G2385R variant and IVS1+124 C>G, a functional single-nucleotide polymorphism located in the MAPT promoter region, were genotyped in 561 Chinese PD patients and 556 control subjects. Allelic and genotypic frequencies of the 2 variants were compared between cases and control subjects independently and in combination. As a result, the LRRK2 p.G2385R variant alone was associated with an increased risk for PD (Odds ratio, 1.86; 95% confidence intervals, 1.08-3.19; p = 0.014), whereas MAPT IVS1+124 C>G was not (p = 0.34). However, the coexistence of MAPT IVS1+124C>G significantly enhanced the LRRK2 G2385R-conferred risk for PD (Odds ratio, 2.30; 95% confidence intervals, 1.14-4.54; p = 0.012). These results provide further evidence supporting the interaction between MAPT and LRRK2 genes, which increases the susceptibility to PD in Chinese individuals.

Clinical profiles of Parkinson's disease associated with common leucine-rich repeat kinase 2 and glucocerebrosidase genetic variants in Chinese individuals

Clinical profiles of Parkinson's disease (PD) related to LRRK2 (LRRK2-PD), and GBA (GBA-PD) genes have not been reported in Chinese individuals. In this study, we have investigated motor and non-motor aspects in 1638 Chinese PD patients who carried LRRK2 G2385R or R1628P (LRRK2-PD, n = 223), GBA L444P variant (GBA-PD, n = 49), or none of the variants (idiopathic PD [IPD], n = 1366). As a result, age at onset and motor and non-motor features of LRRK2-PD patients were similar to IPD patients except for milder non-motor symptoms. In contrast, GBA-PD patients had a significantly younger age at onset and higher Unified Parkinson's Disease Rating Scale scores than LRRK2-PD and IPD patients. In addition, postural instability and gait disorders, motor complications, cognitive decline, hallucination, sexual dysfunction, and constipation were more frequent in GBA-PD than in LRRK2-PD and IPD patients, and GBA-PD patients had a worse performance for social functioning and role-emotional scores. Our study represents the first large-scale clinical study of LRRK2-PD and GBA-PD in ethnic Chinese individuals. The data suggest that both LRRK2-PD and GBA-PD are similar to IPD, except for an earlier age at onset and relatively more common non-motor symptoms in GBA-PD patients. These findings strengthen our understanding of the clinical heterogeneity of PD, and may have implications for molecular classification of the disease.

Where genotype is not predictive of phenotype: towards an understanding of the molecular basis of reduced penetrance in human inherited disease

Some individuals with a particular disease-causing mutation or genotype fail to express most if not all features of the disease in question, a phenomenon that is known as 'reduced (or incomplete) penetrance'. Reduced penetrance is not uncommon; indeed, there are many known examples of 'disease-causing mutations' that fail to cause disease in at least a proportion of the individuals who carry them. Reduced penetrance may therefore explain not only why genetic diseases are occasionally transmitted through unaffected parents, but also why healthy individuals can harbour quite large numbers of potentially disadvantageous variants in their genomes without suffering any obvious ill effects. Reduced penetrance can be a function of the specific mutation(s) involved or of allele dosage. It may also result from differential allelic expression, copy number variation or the modulating influence of additional genetic variants in cis or in trans. The penetrance of some pathogenic genotypes is known to be age- and/or sex-dependent. Variable penetrance may also reflect the action of unlinked modifier genes, epigenetic changes or environmental factors. At least in some cases, complete penetrance appears to require the presence of one or more genetic variants at other loci. In this review, we summarize the evidence for reduced penetrance being a widespread phenomenon in human genetics and explore some of the molecular mechanisms that may help to explain this enigmatic characteristic of human inherited disease.

Protective effect of LRRK2 p.R1398H on risk of Parkinson's disease is independent of MAPT and SNCA variants

The best validated susceptibility variants for Parkinson's disease are located in the α-synuclein (SNCA) and microtubule-associated protein tau (MAPT) genes. Recently, a protective p.N551K-R1398H-K1423K haplotype in the leucine-rich repeat kinase 2 (LRRK2) gene was identified, with p.R1398H appearing to be the most likely functional variant. To date, the consistency of the protective effect of LRRK2 p.R1398H across MAPT and SNCA variant genotypes has not been assessed. To address this, we examined 4 SNCA variants (rs181489, rs356219, rs11931074, and rs2583988), the MAPT H1-haplotype-defining variant rs1052553, and LRRK2 p.R1398H (rs7133914) in Caucasian (n = 10,322) and Asian (n = 2289) series. There was no evidence of an interaction of LRRK2 p.R1398H with MAPT or SNCA variants (all p ≥ 0.10); the protective effect of p.R1398H was observed at similar magnitude across MAPT and SNCA genotypes, and the risk effects of MAPT and SNCA variants were observed consistently for LRRK2 p.R1398H genotypes. Our results indicate that the association of LRRK2 p.R1398H with Parkinson's disease is independent of SNCA and MAPT variants, and vice versa, in Caucasian and Asian populations.