LRRK2 mutation in familial Parkinson's disease in a Taiwanese population: clinical, PET, and functional studies

Overview of the Impact of Pathogenic LRRK2 Mutations in Parkinson's Disease

Leucine-rich repeat kinase 2 (LRRK2) is a large protein kinase that physiologically phosphorylates and regulates the function of several Rab proteins. LRRK2 is genetically implicated in the pathogenesis of both familial and sporadic Parkinson's disease (PD), although the underlying mechanism is not well understood. Several pathogenic mutations in the LRRK2 gene have been identified, and in most cases the clinical symptoms that PD patients with LRRK2 mutations develop are indistinguishable from those of typical PD. However, it has been shown that the pathological manifestations in the brains of PD patients with LRRK2 mutations are remarkably variable when compared to sporadic PD, ranging from typical PD pathology with Lewy bodies to nigral degeneration with deposition of other amyloidogenic proteins. The pathogenic mutations in LRRK2 are also known to affect the functions and structure of LRRK2, the differences in which may be partly attributable to the variations observed in patient pathology. In this review, in order to help researchers unfamiliar with the field to understand the mechanism of pathogenesis of LRRK2-associated PD, we summarize the clinical and pathological manifestations caused by pathogenic mutations in LRRK2, their impact on the molecular function and structure of LRRK2, and their historical background.

Review of the epidemiology and variability of LRRK2 non-p.Gly2019Ser pathogenic mutations in Parkinson's disease

Parkinson's disease (PD) is a heterogenous neurodegenerative disorder. Genetic factors play a significant role, especially in early onset and familial cases. Mutations are usually found in the LRRK2 gene, but their importance varies. Some mutations, such as p.Arg1441Cys or other alterations in the 1441 codon, show clear correlation with PD, whereas others are risk factors found also in healthy populations or have neglectable consequences. They also exhibit various prevalence among different populations. The aim of this paper is to sum up the current knowledge regarding the epidemiology and pathogenicity of LRRK2 mutations, other than the well-established p.Gly2019Ser. We performed a review of the literature using PubMed database. 103 publications met our inclusion criteria. p.Arg1441Cys, p.Arg1441Gly, p.Arg1441His, p.Arg1441Ser are the most common pathogenic mutations in European populations, especially Hispanic. p.Asn1437His is pathogenic and occurs mostly in the Scandinavians. p.Asn1437Ser and p.Asn1437Asp have been reported in German and Chinese cohorts respectively. p.Ile2020Thr is a rare pathogenic mutation described only in a Japanese cohort. p.Met1869Thr has only been reported in Caucasians. p.Tyr1699Cys, p.Ile1122Val have only been found in one family each. p.Glu1874Ter has been described in just one patient. We found no references concerning mutation p.Gln416Ter. We also report the first case of a Polish PD family whose members carried p.Asn1437His.

Homozygous mutation of the LRRK2 ROC domain as a novel genetic model of parkinsonism

Background

Parkinson’s disease (PD) is one of the most important neurodegenerative disorders in elderly people. Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are found in a large proportion of the patients with sporadic and familial PD. Mutations can occur at different locations in the LRRK2. Patients with LRRK2 ROC-COR mutations face an increased risk of typical motor symptoms of PD, along with cognitive decline. An animal model with a monogenic LRRK2 gene mutation is a suitable model for exploring the pathophysiology of PD and identifying potential drug therapies. However, the effect of homozygous (HOM) LRRK2 in PD pathophysiology is unclear.

Methods

We established human LRRK2 (hLRRK2) R1441G HOM transgenic (Tg) mice to explore the phenotype and pathological features that are associated with hLRRK2 R1441G Tg mouse models and discuss the potential clinical relevance. The open field test (OFT) was performed to examine motor and nonmotor behaviors. A CatWalk analysis system was used to study gait function. [¹⁸F]FDOPA PET was used to investigate functional changes in the nigrostriatal pathway in vivo. Transmission electron microscopy was used to examine the morphological changes in mitochondria and lysosomes in the substantia nigra.

Results

The R1441G HOM Tg mice demonstrated gait disturbance and exhibited less anxiety-related behavior and exploratory behavior than mice with hLRRK2 at 12 months old. Additionally, [¹⁸F]FDOPA PET showed a reduction in FDOPA uptake in the striatum of the HOM Tg mice. Notably, there was significant lysosome and autophagosome accumulation in the cytoplasm of dopaminergic neurons in R1441G hemizygous (HEM) and HOM mice. Moreover, it was observed using transmission electron microscopy (TEM) that the mitochondria of R1441G Tg mice were smaller than those of hLRRK2 mice.

Conclusion

This animal provides a novel HOM hLRRK2 R1441G Tg mouse model that reproduces some phenotype of Parkinsonism in terms of both motor and behavioral dysfunction. There is an increased level of mitochondrial fission and no change in the fusion process in the group of HOM hLRRK2 R1441G Tg mouse. This mutant animal model of PD might be used to study the mechanisms of mitochondrial dysfunction and explore potential new drug targets.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-022-00844-9.

Connectivity of corticostriatal circuits in nonmanifesting LRRK2 G2385R and R1628P carriers

BACKGROUND

Neuroimaging studies have shown that the functional connectivity (FC) of corticostriatal circuits in nonmanifesting leucine-rich repeat kinase 2 (LRRK2) G2019S mutation carriers mirrors neural changes in idiopathic Parkinson's disease (PD). In contrast, neural network changes in LRRK2 G2385R and R1628P mutations are unclear. We aimed to investigate the FC of corticostriatal circuits in nonmanifesting LRRK2 G2385R and R1628P mutation carriers (NMCs).

METHODS

Twenty-three NMCs, 28 PD patients, and 29 nonmanifesting noncarriers (NMNCs) were recruited. LRRK2 mutation analysis was performed on all participants. Clinical evaluation included MDS-UPDRS.

RESULTS

When compared to NMNCs, NMCs showed significantly reduced FC between the caudate nucleus and superior frontal gyrus and cerebellum, and between the nucleus accumbens and parahippocampal gyrus, amygdala, and insula. We also found increased striatum-cortical FC in NMCs.

CONCLUSIONS

Although the corticostriatal circuits have characteristic changes similar to PD, the relatively intact function of the sensorimotor striatum-cortical loop may result in less possibility of developing parkinsonian motor symptoms for the NMCs. This study helps explain why LRRK2 G2385R and R1628P mutations are risk factors rather than pathogenic mutations for PD and suggests that various LRRK2 mutations have distinct effects on neural networks.

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.

Colonic Leucine-Rich Repeat Kinase 2 Expression Is Increased and Associated With Disease Severity in Patients With Parkinson’s Disease

Background

Mutations in leucine-rich repeat kinase 2 (LRRK2) comprise a common genetic risk factor for Parkinson’s disease (PD) and inflammatory bowel disease (IBD). We investigated the expression of LRRK2 in colonic biopsies obtained from a cohort of PD patients and healthy controls.

Methods

A cohort of 51 PD patients and 40 age- and gender-matched controls who have colonic biopsied samples were recruited. Among these participants, 26 individuals (12 PD patients and 14 controls) had a series of colon biopsies. For the patients with PD, the first biopsies were taken before the PD diagnosis. The colonic expression of LRRK2 was assayed by immunohistochemical staining.

Results

The fraction of LRRK2-positive cells among the total cell count in biopsied colonic tissues was significantly higher in PD patients than controls (0.81% ± 0.53% vs. 0.45% ± 0.39%; P = 0.02). Colonic LRRK2 immunoreactivity was higher in those with LRRK2 genetic variants compared to those with wild type LRRK2 (2.44% ± 1.15% vs. 0.21 ± 0.13%, P < 0.01). Age had no effect on LRRK2 expression (P = 0.96). LRRK2 expression correlated with disease severity in regards to motor symptoms measured by the UPDRS part III scores (r = 6335, P < 0.001) and cognitive dysfunction measured by the mini-mental status examination scores (r = -0.5774, P < 0.001). PD patients in the prodromal phase had a steeper increase in colonic LRRK2 expression compared to controls during the serial colon biopsy assessment (P < 0.01).

Conclusion

Colonic LRRK2 expression was increased in PD patients compared to controls, and the expression level correlated with disease severity.

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

A Double-Blind, Randomized, Controlled Trial of Lovastatin in Early-Stage Parkinson's Disease

BACKGROUND

Recent evidence indicates that lipophilic statins have a neuroprotective benefit in animal models of Parkinson's disease (PD). The objective of this study was to evaluate whether lovastatin has the potential to slow motor symptom progression in patients with early-stage PD.

METHODS

This double-blind, randomized, placebo-controlled trial enrolled 77 patients with early-stage PD between May 23, 2017, and July 12, 2018, with follow-up ending September 1, 2019. Lovastatin 80 mg/day or placebo with 1:1 randomization was administered for 48 weeks. Mean change in the parts I-III scores of the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS), changes in the striatal dopamine uptake ratio measured by ¹⁸ F-dopa PET scan, and changes in PD medications between baseline and the week 48 visit were measured.

RESULTS

Of the 77 randomized patients, 70 (90.9%) completed the study. There was a slightly beneficial trend of the MDS-UPDRS motor score in the lovastatin group (-3.18 ± 5.50) compared with the placebo group (-0.50 ± 6.11); P = 0.14 adjusted for age, sex, disease duration, and baseline LEDD. Mean percentage change in the striatal ¹⁸ F-dopa uptake ratio deteriorated less in the lovastatin group than in the placebo group on the dominant side of caudate (1.2% ± 7.3% vs -7.1% ± 8.2%, P < 0.01) and putamen (2.3% ± 7.1% vs -6.4% ± 8.1%, P < 0.01). We found no between-group differences in the change in part I or part II MDS-UPDRS scores. Lovastatin was generally well tolerated.

CONCLUSIONS

Lovastatin treatment in patients with early-stage PD was associated with a trend of less motor symptom worsening and was well tolerated. A future larger long-term follow-up study is needed to confirm our findings. © 2021 International Parkinson and Movement Disorder Society.

LRRK2 and the Endolysosomal System in Parkinson's Disease

Mutations in leucine-rich repeat kinase 2 (LRRK2) cause autosomal dominant familial Parkinson’s disease (PD), with pathogenic mutations enhancing LRRK2 kinase activity. There is a growing body of evidence indicating that LRRK2 contributes to neuronal damage and pathology both in familial and sporadic PD, making it of particular interest for understanding the molecular pathways that underlie PD. Although LRRK2 has been extensively studied to date, our understanding of the seemingly diverse functions of LRRK2 throughout the cell remains incomplete. In this review, we discuss the functions of LRRK2 within the endolysosomal pathway. Endocytosis, vesicle trafficking pathways, and lysosomal degradation are commonly disrupted in many neurodegenerative diseases, including PD. Additionally, many PD-linked gene products function in these intersecting pathways, suggesting an important role for the endolysosomal system in maintaining protein homeostasis and neuronal health in PD. LRRK2 activity can regulate synaptic vesicle endocytosis, lysosomal function, Golgi network maintenance and sorting, vesicular trafficking and autophagy, with alterations in LRRK2 kinase activity serving to disrupt or regulate these pathways depending on the distinct cell type or model system. LRRK2 is critically regulated by at least two proteins in the endolysosomal pathway, Rab29 and VPS35, which may serve as master regulators of LRRK2 kinase activity. Investigating the function and regulation of LRRK2 in the endolysosomal pathway in diverse PD models, especially in vivo models, will provide critical insight into the cellular and molecular pathophysiological mechanisms driving PD and whether LRRK2 represents a viable drug target for disease-modification in familial and sporadic PD.

Three-step two-pot automated production of NCA [18F]FDOPA with FlexLab module

Automated three-step two-pot production of no-carrier-added (NCA) [¹⁸F]FDOPA was first implemented in the iPHASE FlexLab module. Decay-corrected radiochemical yield (RCY) of [¹⁸F]FDOPA synthesized by this method was 10~14% (n = 7) with a synthesis time of ~110 min [¹⁸F]FDOPA was obtained in > 95% of radiochemical purity with a molar activity of ~431 GBq/μmol. With the method successfully implementing on the commercial FlexLab module and its built-in step-by-step activity monitoring, further processes optimization would be achieved.

A clinical and genetic study of early-onset and familial parkinsonism in taiwan: An integrated approach combining gene dosage analysis and next-generation sequencing

Background

Recent genetic progress has allowed for the molecular diagnosis of Parkinson's disease. However, genetic causes of PD vary widely in different ethnicities. Mutational frequencies and clinical phenotypes of genes associated with PD in Asian populations are largely unknown. The objective of this study was to identify the mutational frequencies and clinical spectrums of multiple PD‐causative genes in a Taiwanese PD cohort.

Methods

A total of 571 participants including 324 patients with early‐onset parkinsonism (onset age, <50 years) and 247 parkinsonism pedigrees were recruited at a tertiary referral center in Taiwan from 2002 to 2017. Genetic causes were identified by an integrated approach including gene dosage analysis, a targeted next‐generation sequencing panel containing 40 known PD‐causative genes, repeat‐primed polymerase chain reaction, and whole‐exome sequencing analysis.

Results

Thirty of the 324 patients with early‐onset parkinsonism (9.3%) were found to carry mutations in Parkin, PINK1, or PLA2G6 or had increased trinucleotide repeats in SCA8. Twenty‐nine of 109 probands with autosomal‐recessive inheritance of parkinsonism (26.6%) were found to carry mutations in Parkin, PINK1, GBA, or HTRA2. The genetic causes for the 138 probands with an autosomal‐dominant inheritance pattern of parkinsonism were more heterogeneous. Seventeen probands (12.3%) carried pathogenic mutations in LRRK2, VPS35, MAPT, GBA, DNAJC13, C9orf72, SCA3, or SCA17. A novel missense mutation in the UQCRC1 gene was found in a family with autosomal‐dominant inheritance parkinsonism via whole‐exome sequencing analysis.

Conclusions

Our findings provide a better understanding of the genetic architecture of PD in eastern Asia and broaden the clinical spectrum of PD‐causing mutations. © 2019 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

The unlikely partnership between LRRK2 and α-synuclein in Parkinson's disease

Our understanding of the mechanisms underlying Parkinson's disease, the once archetypical nongenetic neurogenerative disorder, has dramatically increased with the identification of α-synuclein and LRRK2 pathogenic mutations. While α-synuclein protein composes the aggregates that can spread through much of the brain in disease, LRRK2 encodes a multidomain dual-enzyme distinct from any other protein linked to neurodegeneration. In this review, we discuss emergent datasets from multiple model systems that suggest these unlikely partners do interact in important ways in disease, both within cells that express both LRRK2 and α-synuclein as well as through more indirect pathways that might involve neuroinflammation. Although the link between LRRK2 and disease can be understood in part through LRRK2 kinase activity (phosphotransferase activity), α-synuclein toxicity is multilayered and plausibly interacts with LRRK2 kinase activity in several ways. We discuss common protein interactors like 14-3-3s that may regulate α-synuclein and LRRK2 in disease. Finally, we examine cellular pathways and outcomes common to both mutant α-synuclein expression and LRRK2 activity and points of intersection. Understanding the interplay between these two unlikely partners in disease may provide new therapeutic avenues for PD.

Chemosensory dysfunction in neurodegenerative diseases

A number of neurodegenerative diseases are accompanied by disordered smell function. The degree of dysfunction can vary among different diseases, such that olfactory testing can aid in differentiating, for example, Alzheimer's disease (AD) from major affective disorder and Parkinson's disease (PD) from progressive supranuclear palsy. Unfortunately, altered smell function often goes unrecognized by patients and physicians alike until formal testing is undertaken. Such testing uniquely probes brain regions not commonly examined in physical examinations and can identify, in some cases, patients who are already in the "preclinical" stage of disease. Awareness of this fact is one reason why the Quality Standards Committee of the American Academy of Neurology has designated smell dysfunction as one of the key diagnostic criteria for PD. The same recommendation has been made by the Movement Disorder Society for both the diagnosis of PD and identification of prodromal PD. Similar suggestions are proposed to include olfactory dysfunction as an additional research criterion for the diagnosis of AD. Although taste impairment, i.e., altered sweet, sour, bitter, salty, and umami perception, has also been demonstrated in some disorders, taste has received much less scientific attention than smell. In this review, we assess what is known about the smell and taste disorders of a wide range of neurodegenerative diseases and describe studies seeking to understand their pathologic underpinnings.

LRRK 2 gene mutations in the pathophysiology of the ROCO domain and therapeutic targets for Parkinson's disease: a review

Parkinson’s disease (PD) is the most common movement disorder and manifests as resting tremor, rigidity, bradykinesia, and postural instability. Pathologically, PD is characterized by selective loss of dopaminergic neurons in the substantia nigra and the formation of intracellular inclusions containing α-synuclein and ubiquitin called Lewy bodies. Consequently, a remarkable deficiency of dopamine in the striatum causes progressive disability of motor function. The etiology of PD remains uncertain. Genetic variability in leucine-rich repeat kinase 2 (LRRK2) is the most common genetic cause of sporadic and familial PD. LRRK2 encodes a large protein containing three catalytic and four protein-protein interaction domains. Patients with LRRK2 mutations exhibit a clinical and pathological phenotype indistinguishable from sporadic PD. Recent studies have shown that pathological mutations of LRRK2 can reduce the rate of guanosine triphosphate (GTP) hydrolysis, increase kinase activity and GTP binding activity, and subsequently cause cell death. The process of cell death involves several signaling pathways, including the autophagic–lysosomal pathway, intracellular trafficking, mitochondrial dysfunction, and the ubiquitin–proteasome system. This review summarizes the cellular function and pathophysiology of LRRK2 ROCO domain mutations in PD and the perspective of therapeutic approaches.

Leucine-Rich Repeat Kinase (LRRK2) Genetics and Parkinson's Disease

The discovery of LRRK2 mutations as a cause of Parkinson's disease (PD), including the sporadic late-onset form, established the decisive role of genetics in the field of PD research. Among LRRK2 mutations, the G2019S, mostly lying in a haplotype originating from a common Middle Eastern ancestor, has been identified in different populations worldwide. The G2385R and R1628P variants represent validated risk factors for PD in Asian populations. Here, we describe in detail the origin, the present worldwide epidemiology, and the penetrance of LRRK2 mutations. Furthermore, this chapter aims to characterize other definitely/probably pathogenic mutations and risk variants of LRRK2. Finally, we provide some general guidelines for a LRRK2 genetic testing and counseling. In summary, LRRK2 discovery revolutionized the understanding of PD etiology and laid the foundation for a promising future of genetics in PD research.

Clinical heterogeneity of LRRK2 p.I2012T mutation

INTRODUCTION

Leucine-rich repeat kinase 2 (LRRK2) mutations are the most common genetic cause of Parkinson's disease (PD). However, only few cases carrying LRRK2 mutations have been reported in Taiwanese PD patients.

METHODS

We used targeted next generation sequencing (NGS), covering 24 candidate genes involved in neurodegenerative disorders, to analyze 40 probands with familial PD, and 10 patients with mixed neurodegenerative disorders. Sanger sequencing of the identified mutation in the first set of the study was performed in additional 270 PD patients, including 139 familial PD and 131 early-onset PD (onset age less than 50 years old), and 300 age/gender matched control subjects.

RESULTS

We found a missense variant, p.I2012T, in the LRRK2 gene in one sporadic patient having early-onset frontotemporal dementia with parkinsonism and dystonia. Sanger sequencing this substitution in additional 270 PD patients in the second set of the study revealed two additional variant carriers: one having autosomal-dominant familial PD, and one with sporadic PD. The p.I2012T substitution was absent in 300 normal control subjects. Analyzing family members of the proband with p.I2012T revealed co-segregation of the variant and parkinsonism. Clinical presentations, levodopa responses, and ^Tc99mTRODAT-SPECT imaging findings of this index family were similar to idiopathic PD.

CONCLUSIONS

Our results revealed clinical heterogeneity of the LRRK2 p.I2012T substitution, and demonstrated the use of targeted NGS for genetic diagnosis in multiplex families with PD or mixed neurodegenerative disorders.

Genetic variants ofLRRK2 in Taiwanese Parkinson's disease

Genetic variants of leucine-rich repeat kinase 2 (LRRK2) were reported to alter the risk for Parkinson's disease (PD). However, the genetic spectrum of LRRK2 variants has not been clearly disclosed yet in Taiwanese population. Herein, we sequenced LRRK2 coding region in 70 Taiwanese early onset PD patients (age at onset ≤ 50), and found six amino acid-changing single nucleotide polymorphisms (SNPs, N551K, R1398H, R1628P, S1647T, G2385R and M2397T), one reported (R1441H) and 2 novel missense (R767H and S885N) mutations. We examined the frequency of identified LRRK2 variants by genotyping 573 Taiwanese patients with PD and 503 age-matched control subjects. The results showed that PD patients demonstrated a higher frequency of G2385R A allele (4.6%) than control subjects (2.1%; odds ratio = 2.27, 95% confidence interval: 1.38-3.88, P = 0.0017). Fewer PD patients (27.7%) carried the 1647T-2397T haplotype as compared with the control subjects (33.0%; odds ratio = 0.80, 95% confidence interval: 0.65-0.97, P = 0.0215). However, the frequency of 1647T-2385R-2397T haplotype (4.3%) in PD patients was still higher than in control subjects (1.9%, odds ratio: 2.15, 95% confidence interval: 1.27-3.78, P = 0.0058). While no additional subject was found to carry R767H and R1441H, one more patient was observed to carry the S885N variant. Our results indicate a robust risk association regarding G2385R and a new possible protective haplotype (1647T-2397T). Gene-environmental interaction and a larger cohort study are warranted to validate our findings. Additionally, two new missense mutations (R767H and S885N) regarding LRRK2 in PD patients were identified. Functional studies are needed to elucidate the effects of these LRRK2 variants on protein function.

Vitamin D receptor genetic variants and Parkinson's disease in a Taiwanese population

Patients with Parkinson's disease (PD) have hypovitaminosis D status and genetic variants of vitamin D receptor (VDR) gene are recently shown to be associated with PD in a large-scale genome-wide association study in a Caucasian population. Few studies examined VDR genetic variants in large-scale Asian patients with PD. We therefore genotyped 6 VDR genetic variants in a total of 1492 Taiwanese subjects, including 700 patients with PD and 792 age and/or gender matched control subjects. We did not observe any significant associations between the studied genetic variants of VDR and the risk of PD. Our data suggest that genetic variations of the VDR gene did not play a major role in a Taiwanese PD population. Further studies of VDR and its interaction with serum vitamin D levels are warranted to clarify the potential role of vitamin D in PD pathogenesis.

Validation of microarray data in human lymphoblasts shows a role of the ubiquitin-proteasome system and NF-kB in the pathogenesis of Down syndrome

BACKGROUND

Down syndrome (DS) is a complex disorder caused by the trisomy of either the entire, or a critical region of chromosome 21 (21q22.1-22.3). Despite representing the most common cause of mental retardation, the molecular bases of the syndrome are still largely unknown.

METHODS

To better understand the pathogenesis of DS, we analyzed the genome-wide transcription profiles of lymphoblastoid cell lines (LCLs) from six DS and six euploid individuals and investigated differential gene expression and pathway deregulation associated with trisomy 21. Connectivity map and PASS-assisted exploration were used to identify compounds whose molecular signatures counteracted those of DS lymphoblasts and to predict their therapeutic potential. An experimental validation in DS LCLs and fetal fibroblasts was performed for the most deregulated GO categories, i.e. the ubiquitin mediated proteolysis and the NF-kB cascade.

RESULTS

We show, for the first time, that the level of protein ubiquitination is reduced in human DS cell lines and that proteasome activity is increased in both basal conditions and oxidative microenvironment. We also provide the first evidence that NF-kB transcription levels, a paradigm of gene expression control by ubiquitin-mediated degradation, is impaired in DS due to reduced IkB-alfa ubiquitination, increased NF-kB inhibitor (IkB-alfa) and reduced p65 nuclear fraction. Finally, the DSCR1/DYRK1A/NFAT genes were analysed. In human DS LCLs, we confirmed the presence of increased protein levels of DSCR1 and DYRK1A, and showed that the levels of the transcription factor NFATc2 were decreased in DS along with a reduction of its nuclear translocation upon induction of calcium fluxes.

CONCLUSIONS

The present work offers new perspectives to better understand the pathogenesis of DS and suggests a rationale for innovative approaches to treat some pathological conditions associated to DS.

Comprehensive LRRK2 and GBA screening in Portuguese patients with Parkinson's disease: identification of a new family with the LRRK2 p.Arg1441His mutation and novel missense variants

Mutations in the LRRK2 and GBA genes are increasingly recognized as frequent determinants of familial and sporadic Parkinson's disease (PD). However, for several populations, accurate data on the prevalence and types of mutations are not available, because previous studies have not investigated the complete coding regions of these genes in large samples. We studied 312 PD patients ascertained at a single centre in Lisbon, Portugal. In 61 patients, with familial PD, we sequenced the entire open reading frames and exon-intron boundaries of LRRK2 and GBA. In LRRK2, we identified ten heterozygous p.Gly2019Ser (16.4%), and two heterozygous p.Arg1441His carriers (3.3%); furthermore, six patients each carried a novel LRRK2 heterozygous variant (five coding and one 3'-UTR variants) of undetermined pathogenic role. Segregation of the p.Arg1441His mutation with PD was observed in the families of both carriers. None of these variants were identified in 138 healthy controls. Screening of GBA revealed no mutations. In the remaining 251 PD patients (25 familial and 226 sporadic) we found ten additional carriers of the heterozygous p.Gly2019Ser and no carriers of the other mutations. Thus, the p.Gly2019Ser mutation was detected in a total number of 20 carriers out of 312 patients (6.4%), including twelve familial (14%) and eight sporadic patients (3.5%). This comprehensive study confirms that p.Gly2019Ser is the most important genetic cause of PD known so far in Portugal and supports the contention that p.Arg1441His is also a PD-causing mutation. These findings have relevance for the genetic testing and counseling of PD patients in this population.

Mutational analysis of FBXO7 gene in Parkinson's disease in a Taiwanese population

Mutations in the FBXO7 gene cause an autosomal-recessive early-onset parkinsonism with pyramidal tract signs. Its role in typical Parkinson's disease (PD) without pyramidal features is unclear. We assayed FBXO7 gene in 900 participants comprising 448 PD patients and 452 age- and sex-matched control subjects from Taiwan. The entire FBXO7 coding region and intron-exon boundaries were sequenced. We identified 2 novel missense substitutions, p.Ile87Thr and p.Asp328Arg, in a single heterozygous state in 2 early-onset PD patients individually (1.1% early-onset PD). These 2 variants were not observed in control subjects with a total of 904 normal alleles. Additionally, we also found 1 noncoding variant, exon 1 IVS-329C>T, modestly associated with PD. The frequency of the CT/TT genotype was higher in PD patients compared with control subjects (odds ratio, 1.43; 95% confidence interval, 1.02-2.01; p = 0.04). The clinical phenotypes of genetic variant carriers are similar to that seen in idiopathic PD. We conclude that FBXO7 gene contributes little to typical PD in our population. Further studies in other ethnic cohorts will be important to address its potential pathophysiological role in PD.

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

Variants in the LRRK2 gene are well-characterized genetic predisposing factors for PD worldwide, and LRRK2-associated PD is often indistinguishable from idiopathic PD (IPD). However, considerable heterogeneity of LRRK2-PD suggests the existence of additional genetic and/or environmental modifiers for LRRK2 carriers, which have yet to be confirmed by large-scale human studies. In a Chinese cohort consisting of 2013 sporadic PD patients and 1971 controls, we investigated the modification of the two Asian-specific LRRK2 variants, G2385R and R1628P, by variants of five other PD-associated genes/loci (SNCA, MAPT, GBA, BST1, PARK16). Of all the PD patients, 13.1% carried LRRK2 G2385R and/or R1628P variant. Among these carriers, a total of 15 different polygenic genotypes were detected representing different combination patterns between LRRK2 variants and those of the other genes/loci, which, alone or in combination, significantly modified the LRRK2-related risk for PD and the patients' ages at onset (AAOs). These results not only represent the largest replication data affirming the association between PD and all the six genes/loci in Chinese, but for the first time suggest that multiple PD-associated genetic factors modify both the penetrance and AAO of LRRK2 parkinsonism. This finding may have important implications for elucidating pathophysiologic mechanisms relevant to both LRRK2-associated and idiopathic PD. However, testing interactions among multiple genes by genetic association studies is still challenging. Future studies with much larger sample sizes are needed to confirm our findings.

Olfaction in Parkinson's disease and related disorders

Olfactory dysfunction is an early 'pre-clinical' sign of Parkinson's disease (PD). The present review is a comprehensive and up-to-date assessment of such dysfunction in PD and related disorders. The olfactory bulb is implicated in the dysfunction, since only those syndromes with olfactory bulb pathology exhibit significant smell loss. The role of dopamine in the production of olfactory system pathology is enigmatic, as overexpression of dopaminergic cells within the bulb's glomerular layer is a common feature of PD and most animal models of PD. Damage to cholinergic, serotonergic, and noradrenergic systems is likely involved, since such damage is most marked in those diseases with the most smell loss. When compromised, these systems, which regulate microglial activity, can influence the induction of localized brain inflammation, oxidative damage, and cytosolic disruption of cellular processes. In monogenetic forms of PD, olfactory dysfunction is rarely observed in asymptomatic gene carriers, but is present in many of those that exhibit the motor phenotype. This suggests that such gene-related influences on olfaction, when present, take time to develop and depend upon additional factors, such as those from aging, other genes, formation of α-synuclein- and tau-related pathology, or lowered thresholds to oxidative stress from toxic insults. The limited data available suggest that the physiological determinants of the early changes in PD-related olfactory function are likely multifactorial and may include the same determinants as those responsible for a number of other non-motor symptoms of PD, such as dysautonomia and sleep disturbances.

Mutation analysis of LRRK2, SCNA, UCHL1, HtrA2 and GIGYF2 genes in Chinese patients with autosomal dorminant Parkinson's disease

Autosomal dorminant Parkinson's disease (ADPD) has been associated with mutations in the SCNA, LRRK2, UCHL1, HtrA2 and GIGYF2 genes. We studied the prevalence of variants in all five genes in 12 Chinese unrelated families with ADPD and 4 families with both essential tremor (ET) and Parkinson's disease (PD) phenotypes using direct sequencing analysis. We found 27 variants in the LRRK2 gene, eight in GIGYF2 gene, three in the SCNA and UCHL1 gene respectively, in which five variants were novel. However, no pathogenic mutations in the five genes were found in these families. Our result indicated that SCNA, LRRK2, UCHL1, HtrA2 and GIGYF2 genes' mutations might not be a main reason for Chinese ADPD.

Novel variant Pro143Ala in HTRA2 contributes to Parkinson's disease by inducing hyperphosphorylation of HTRA2 protein in mitochondria

Mutations in the gene encoding the mitochondrial protein high temperature requirement A2 (HTRA2) are inconsistently associated with a risk of Parkinson's disease (PD). We assessed the presence of HTRA2 mutations among patients with PD and performed functional assay of identified mutations or variants. Among the total 1,373 subjects, the entire HTRA2 coding region was sequenced in 113 early-onset PD (EOPD), 20 familial PD patients and 150 control subjects. An additional 390 sporadic late-onset PD patients and 700 controls were subsequently screened to validate possible mutations found in the first set. We identified two novel heterozygous variants, c.427C > G (Pro143Ala) and c.906 +3 G > A, in 2 (1.5%) EOPD patients. The missense variant, Pro143Ala, was also observed in one late-onset PD patient but was absent in total 850 control subjects (relative risk 2.3, 95% CI 1.5-2.8, P = 0.04). Expressing Pro143Ala variant of HTRA2 in primary dopaminergic neurons causes neurite degeneration. Following exposure to rotenone, the ultra-structural mitochondrial abnormality, the percentage of mitochondrial dysfunction and apoptosis in cells carrying the HTRA2 Pro143Ala variant was significantly higher than wild-type cells. Mechanistically, protein level of phosphorylated HTRA2 was increased in cells carrying the Pro143Ala variant, suggesting Pro143Ala variant promotes HTRA2 phosphorylation with resultant mitochondrial dysfunction. Our results support a biologically relevant role of HTRA2 in PD susceptibility in Taiwanese. Further large-scale association studies are warranted to confirm the role of HTRA2 Pro143Ala variant in the risk of PD.

LRRK2 Parkinson's disease: from animal models to cellular mechanisms

Mutations in the gene encoding leucine-rich repeat kinase 2 (LRRK2) play a major role in the development of Parkinson's disease. The most frequently defined mutations of LRRK2 are located in the central catalytic region of the LRRK2 protein, suggesting that dysregulations of its enzymatic activities contribute to PD pathogenesis. Herein, we review recent progress in research concerning how LRRK2 mutations affect cellular pathways and lead to neuronal degeneration. We also summarize recent evidence revealing the endogenous function of LRRK2 protein within cells. These concepts can be used to further understand disease pathophysiology and serve as a platform to develop therapeutic strategies for the treatment of Parkinson's disease.

Dopamine turnover increases in asymptomatic LRRK2 mutations carriers

Increase in dopamine (DA) turnover was found to occur early in symptomatic Parkinson's disease (PD) and to be functionally related to the dopamine transporter (DAT). The objectives of this study were to examine changes in DA turnover in the asymptomatic PD phase; to compare them with changes in other dopaminergic markers, and to investigate a possible relationship between DAT and DA turnover. Eight subjects from families at increased risk of PD due to LRRK2 mutation were investigated. Positron emission tomography imaging was performed with: ¹⁸F-fluorodopa to determine the effective DA distribution volume (EDV), the inverse of DA turnover, and the DA uptake rate K(occ), a marker of DA synthesis and storage; ¹¹C-methylphenidate (MP, a DAT marker) and ¹¹C-dihydrotetrabenazine (DTBZ, a VMAT2 marker) to estimate the binding potentials BP(ND_MP) and BP(ND_DTBZ). On average, EDV showed the largest reduction from age-matched control values (42%) followed by BP(ND_MP) (23%) and BP(ND_DTBZ) (17%), whereas K(occ) remained in the normal range for all subjects. No correlation was found between EDV and any other marker. DA turnover was found to be elevated in asymptomatic mutation carriers at increased risk of PD. Such change was determined to be larger than and statistically independent from changes observed with the other markers. These results support a compensatory role of increased DA turnover in presymptomatic disease and indicate that at this stage, in contrast to the symptomatic PD phase, increased turnover is not related to DAT.

The LRRK2 G2019S mutation as the cause of Parkinson's disease in Ashkenazi Jews

Mutations in the leucine rich repeat kinase 2 gene (LRRK2) are recognized as the most common cause of genetic Parkinsonism to date. The G2019S mutation has been implicated as an important determinant of Parkinson's disease (PD) in both Ashkenazi Jewish and North African Arab populations with carrier frequency of 29.7% among familial and 6% in sporadic Ashkenazi Jewish PD cases. PD patients with the G2019S mutation display similar clinical characteristics to patients with sporadic PD. While the function of the LRRK2 protein has yet to be fully determined, its distribution coincides with brain areas most affected by PD. The G2019S mutation is believed to be responsible for up-regulation of LRRK2 kinase activity, which may ultimately play a role in neuronal loss. The utility of LRRK2 G2019S screening in family members of Ashkenazi PD patients is discussed. LRRK2 G2019S mutation carriers without PD may be an ideal population for the study of possible neuroprotective strategies as they become available, and for furthering the understanding of the pathogenesis and long-term clinical outcomes of the disease.

A novel LRRK2 mutation in a mainland Chinese patient with familial Parkinson's disease

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) are known to cause typical, late-onset familial Parkinson's disease in different geographic origins. However, there was no report about mutations of LRRK2 gene in mainland China. The 51 coding exons and intron/exon boundaries of the LRRK2 gene were sequenced in nine families with Parkinson's disease. A novel LRRK2 missense mutation resulting in a single amino acid substitution K616R was present in one family with a dominant form of PD, and not in 200 controls. The patient presented with slowly progressive resting tremor, dyskinesia, and responded well to l-dopa. In conclusion, we identified a novel mutation in LRRK2 gene, which was the first mutation of LRRK2 found in the mainland Chinese population with familial Parkinson's disease.

Leucine-rich repeat kinase 2 mutations and Parkinson's disease: three questions

Mutations in the gene encoding LRRK2 (leucine-rich repeat kinase 2) were first identified in 2004 and have since been shown to be the single most common cause of inherited Parkinson’s disease. The protein is a large GTP-regulated serine/threonine kinase that additionally contains several protein–protein interaction domains. In the present review, we discuss three important, but unresolved, questions concerning LRRK2. We first ask: what is the normal function of LRRK2? Related to this, we discuss the evidence of LRRK2 activity as a GTPase and as a kinase and the available data on protein–protein interactions. Next we raise the question of how mutations affect LRRK2 function, focusing on some slightly controversial results related to the kinase activity of the protein in a variety of in vitro systems. Finally, we discuss what the possible mechanisms are for LRRK2-mediated neurotoxicity, in the context of known activities of the protein.

Parkinson's disease: from monogenic forms to genetic susceptibility factors

Research in Parkinson's disease (PD) genetics has been extremely prolific over the past decade. More than 13 loci and 9 genes have been identified, but their implication in PD is not always certain. Point mutations, duplications and triplications in the alpha-synuclein (SNCA) gene cause a rare dominant form of PD in familial and sporadic cases. Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are a more frequent cause of autosomal dominant PD, particularly in certain ethnic groups. Loss-of-function mutations in Parkin, PINK1, DJ-1 and ATP13A2 cause autosomal recessive parkinsonism with early-onset. Identification of other Mendelian forms of PD will be a main challenge for the next decade. In addition, susceptibility variants that contribute to PD have been identified in several populations, such as polymorphisms in the SNCA, LRRK2 genes and heterozygous mutations in the beta-glucocerebrosidase (GBA) gene. Genome-wide associations and re-sequencing projects, together with gene-environment interaction studies, are expected to further define the causal role of genetic determinants in the pathogenesis of PD, and improve prevention and treatment.

The G2019S LRRK2 Mutation is Rare in Korean Patients with Parkinson's Disease and Multiple System Atrophy

BACKGROUND AND PURPOSE

The LRRK2 (PARK8; OMIM607060) substitution was recently identified as a causative mutation for Parkinson's disease (PD). The pathologic heterogeneity of LRRK2-positive patients suggests that mutation of the LRRK2 gene is associated with the pathogenesis of PD and Parkinson-plus disorders, such as multiple system atrophy (MSA). We previously reported that the G2019S LRRK2 mutation-which is the most common LRRK2 mutation-was not found in a sample of 453 Korean PD patients. In the present study, we extended the screening for the G2019S mutation to a larger group of PD and MSA patients.

METHODS

We performed a genetic analysis of the G2019S mutation in 877 patients with PD and 199 patients with MSA using a standard PCR and restriction digestion method.

RESULTS

None of the subjects carried the G2019S mutation.

CONCLUSIONS

The results of the present study support that the G2019S mutation is extremely rare in PD and is unlikely to be associated with MSA in the Korean population.