Mutations in the gene LRRK2 encoding dardarin (PARK8) cause familial Parkinson's disease: clinical, pathological, olfactory and functional imaging and genetic data

Olfaction as a biomarker in Parkinson’s disease

Olfactory dysfunction in Parkinson’s disease is common and of interest, both as a clinical finding and potential biomarker. In this article, we discuss studies characterizing the olfactory deficit in Parkinson’s disease and pathological analysis that suggests the olfactory system is a likely induction site of the neurodegenerative process. These studies have enabled research to explore the potential of olfactory dysfunction as a key component in early diagnostic strategies, as a biomarker for diagnostic purposes, a predictor of clinical outcomes and a potential therapy-independent marker of disease progression.

Development of a mechanism-based high-throughput screen assay for leucine-rich repeat kinase 2--discovery of LRRK2 inhibitors

LRRK2 is a large and complex protein that possesses kinase and GTPase activities and has emerged as the most relevant player in PD pathogenesis possibly through a toxic gain-of-function mechanism. Kinase activity is a critical component of LRRK2 function and represents a viable target for drug discovery. We now report the development of a mechanism-based TR-FRET assay for the LRRK2 kinase activity using full-length LRRK2. In this assay, PLK-peptide was chosen as the phosphoryl acceptor. A combination of steady-state kinetic studies and computer simulations was used to calculate the initial concentrations of ATP and PLK-peptide to generate a steady-state situation that favors the identification of ATP noncompetitive inhibitors. The assay was also run in the absence of GTP. Under these conditions, the assay was sensitive to inhibitors that directly interact with the kinase domain and those that modulate the kinase activity by directly interacting with other domains including the GTPase domain. The assay was optimized and used to robustly evaluate our compound library in a 384-well format. An inhibitor identified through the screen was further characterized as a noncompetitive inhibitor with both ATP and PLK-peptide and showed similar inhibition against LRRK2 WT and the mutant G2019S.

Genetic etiology of Parkinson disease associated with mutations in the SNCA, PARK2, PINK1, PARK7, and LRRK2 genes: a mutation update

To date, molecular genetic analyses have identified over 500 distinct DNA variants in five disease genes associated with familial Parkinson disease; alpha-synuclein (SNCA), parkin (PARK2), PTEN-induced putative kinase 1 (PINK1), DJ-1 (PARK7), and Leucine-rich repeat kinase 2 (LRRK2). These genetic variants include approximately 82% simple mutations and approximately 18% copy number variations. Some mutation subtypes are likely underestimated because only few studies reported extensive mutation analyses of all five genes, by both exonic sequencing and dosage analyses. Here we present an update of all mutations published to date in the literature, systematically organized in a novel mutation database (http://www.molgen.ua.ac.be/PDmutDB). In addition, we address the biological relevance of putative pathogenic mutations. This review emphasizes the need for comprehensive genetic screening of Parkinson patients followed by an insightful study of the functional relevance of observed genetic variants. Moreover, while capturing existing data from the literature it became apparent that several of the five Parkinson genes were also contributing to the genetic etiology of other Lewy Body Diseases and Parkinson-plus syndromes, indicating that mutation screening is recommendable in these patient groups.

Kinetic mechanistic studies of wild-type leucine-rich repeat kinase 2: characterization of the kinase and GTPase activities

Recent studies have identified mutations in the leucine-rich repeat kinase2 gene (LRRK2) in the most common familial forms and some sporadic forms of Parkinson's disease (PD). LRRK2 is a large and complex protein that possesses kinase and GTPase activities. Some LRRK2 mutants enhance kinase activity and possibly contribute to PD through a toxic gain-of-function mechanism. Given the role of LRRK2 in the pathogenesis of PD, understanding the kinetic mechanism of its two enzymatic properties is critical for the discovery of inhibitors of LRRK2 kinase that would be therapeutically useful in treating PD. In this report, by using LRRK2 protein purified from murine brain, first we characterize kinetic mechanisms for the LRRK2-catalyzed phosphorylation of two peptide substrates: PLK-derived peptide (PLK-peptide) and LRRKtide. We found that LRRK2 follows a rapid equilibrium random mechanism for the phosphorylation of PLK-peptide with either ATP or PLK-peptide being the first substrate binding to the enzyme, as evidenced by initial velocity and inhibition mechanism studies with nucleotide analogues AMP and AMP-PNP, product ADP, and an analogue of the peptide substrate. The binding of the first substrate has no effect on the binding affinity of the second substrate. Identical mechanistic conclusions were drawn when LRRKtide was the phosphoryl acceptor. Next, we characterize the GTPase activity of LRRK2 with a k(cat) of 0.2 +/- 0.02 s(-1) and a K(m) of 210 +/- 29 microM. A SKIE of 0.97 +/- 0.04 was measured on k(cat) for the GTPase activity of LRRK2 in a D(2)O molar fraction of 0.86 and suggested that the product dissociation step is rate-limiting, of the steps governed by k(cat) in the LRRK2-catalyzed GTP hydrolysis. Surprisingly, binding of GTP, GDP, or GMP has no effect on kinase activity, although GMP and GDP inhibit the GTPase activity. Finally, we have identified compound LDN-73794 through screen of LRRK2 kinase inhibitors. Our study revealed that this compound is a competitive inhibitor of the binding of ATP and inhibits the kinase activity without affecting the GTPase activity.

Clinical features of LRRK2 parkinsonism

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene were initially identified in large families with autosomal dominant Parkinson disease (PD). These mutations (p.R1441C, p.R1441G, p.Y1699C and p.I2020T) revealed that genetic mutations could cause clinically typical, late-onset PD. Subsequently, the p.G2019S mutation was found to be a frequent cause of both autosomal dominant and "sporadic" PD, particularly in populations in North Africa or the Middle East. Two Lrrk2 protein substitutions (p.R1628P and p.G2385R) have since been associated with susceptibility to PD in Asian populations. More than a hundred variants have been identified in the LRRK2 gene, but pathogenicity is most convincing for the p.R1441H substitution. The role in PD remains unknown for other variants because segregation with disease has not been shown. Screening these variants in very large patient-control series may help clarify their role in PD. Lrrk2 is a large, multidomain protein with pathogenic mutations occurring in several functional domains. Cell biological experiments have shown that the p.G2019S mutation increase kinase activity. This is consistent with the observation that homozygous p.G2019S carriers do not have earlier disease onset or more severe disease compared with heterozygous carries. It is now necessary to identify the regulators and substrates of Lrrk2 in order to understand the effect of each LRRK2 mutation. The identification of a large number of presymptomatic LRRK2 mutation carriers provides a unique possibility for future studies on neuroprotection. However, more insight into the basic function of Lrrk2 is needed in order to exploit this potential for translational research.

Leucine-rich repeat kinase 2 gene-associated disease: redefining genotype-phenotype correlation

BACKGROUND

Leucine-rich repeat kinase 2 (LRRK2) has emerged as the most prevalent genetic cause of Parkinson's disease (PD) among Caucasians. Patients carrying an LRRK2 mutation display significant variability of clinical and pathologic phenotypes across and within affected families.

METHODS

Herein, we review available clinical and pathologic data on patients with an LRRK2 mutation who have come to autopsy.

RESULTS

Thirty-eight patients have been reported who presented clinically with PD; parkinsonism with resistance to levodopa, supranuclear gaze palsy, or autonomic dysfunction; or tremor and dementia. Pathology showed typical PD-type Lewy body disease (LBD) in most patients, whereas in others there was 'pure' nigral degeneration (one with TDP-43-positive inclusions), diffuse LBD, or tau-, alpha-synuclein- or ubiquitin-positive pathology reminiscent of progressive supranuclear gaze palsy, multisystem atrophy, and frontotemporal dementia with ubiquitin-positive inclusions.

CONCLUSIONS

Such clinical and pathologic variability suggests Lrrk2 acts upstream from other proteins implicated in neurodegeneration. Specific mutations may be associated with alternative progressive supranuclear gaze palsy-like or 'pure' nigral degeneration phenotypes. A different effect on Lrrk2 kinase activity may play a role in such heterogeneity.

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.

The association between mutations in the lysosomal protein glucocerebrosidase and parkinsonism

A body of work has emerged over the past decade demonstrating a relationship between mutations in glucocerebrosidase gene (GBA), the gene implicated in Gaucher disease (GD), and the development of parkinsonism. Several different lines of research support this relationship. First, patients with GD who are homozygous for mutations in GBA have a higher than expected propensity to develop Parkinson's disease (PD). Furthermore, carriers of GBA mutations, particularly family members of patients with GD, have displayed an increased rate of parkinsonism. Subsequently, investigators from centers around the world screened cohorts of patients with parkinsonism for GBA mutations and found that overall, subjects with PD, as well as other Lewy body disorders, have at least a fivefold increase in the number of carriers of GBA mutations as compared to age-matched controls. In addition, neuropathologic studies of subjects with parkinsonism carrying GBA mutations demonstrate Lewy bodies, depletion of neurons of the substantia nigra, and involvement of hippocampal layers CA2-4. Although the basis for this association has yet to be elucidated, evidence continues to support the role of GBA as a PD risk factor across different centers, synucleinopathies, and ethnicities. Further studies of the association between GD and parkinsonism will stimulate new insights into the pathophysiology of the two disorders and will prove crucial for both genetic counseling of patients and family members and the design of relevant therapeutic strategies for specific patients with parkinsonism.

LRRK2 R1628P variant is a risk factor of Parkinson's disease among Han-Chinese from mainland China

Mutations in LRRK2, the gene that encodes leucine-rich repeat kinase 2 (LRRK2), are associated with autosomal dominant and sporadic forms of Parkinson's disease (PD) and are the most common genetic causes of PD. Recently, a R1628P variant has been reported as a risk factor for PD in Taiwan and Singapore. To determine the association of this variant and PD in the Han-Chinese population from mainland China, we analyzed its frequency in a cohort of 600 patients and 459 unrelated healthy controls. Forty (6.7%) patients were heterozygous and 3 (0.5%) homozygous for the R1628P variant, which was significantly more frequent than in the controls [2.4% heterozygous and 0.0% homozygous, Odds ratio = 3.14, 95%CI: 1.60-6.17, P < 0.01]. Considering the age at onset, this difference was found only in late-onset PD (older than 50) [Odds ratio = 3.76, 95% CI: 1.90-7.45, P < 0.01]. Our data confirms that the LRRK2 R1628P variant is associated with an increased risk to develop late onset PD in the ethnic Han-Chinese population.

Neuropathology of Parkinson's disease with the R1441G mutation in LRRK2

We report the neuropathological findings in a patient with Parkinson's disease (PD) associated with Basque R1441G-LRRK2/dardarin mutation. The patient was a man with disease onset at 68 years of age, with unilateral rest tremor; the Parkinsonism was well controlled with medication for 15 years. He died at the age of 86, after 18 years of evolution. The neuropathological examination disclosed mild neuronal loss in the substantia nigra pars compacta without alpha-synuclein, tau, LRRK2, or ubiquitin cytoplasmic inclusions. Lewy bodies and Lewy neurites were absent. This is the first neuropathological study of PD associated with brain with the R1441G mutation in LRRK2.

In vivo assessment of brain monoamine systems in parkin gene carriers: a PET study

PET studies in parkin-linked parkinsonism have generally been performed to assess striatal dopaminergic dysfunction and very little is known about the involvement of other monoaminergic structures in these patients. Measurements of (18)F-dopa uptake into serotonergic and noradrenergic structures provide an indication of the functional integrity of these nerve terminals. We used (18)F-dopa PET to assess changes in brain monoaminergic function associated with parkin mutations. Twelve patients with parkin-linked parkinsonism and 12 asymptomatic parkin heterozygotes were included in the study. Eleven healthy controls, 12 patients with idiopathic Parkinson's disease (IPD), and four patients with PINK1 mutations were also investigated for comparison. parkin patients and IPD patients were matched for striatal dopaminergic dysfunction, as measured by (18)F-dopa uptake. Compared to controls, parkin patients showed significant (18)F-dopa reductions in the caudate, putamen, ventral striatum, locus coeruleus, midbrain raphe, and pallidum. The same structures showed reduced uptake in IPD patients, who additionally had significant reductions in hypothalamus, ventral anterior thalamus, and pineal gland. Direct comparison of parkin with IPD patients showed that hypothalamus was targeted in IPD and midbrain raphe in parkin disease. Patients with PINK1 mutation and several parkin heterozygotes also showed monoaminergic dysfunction. These findings suggest that parkin patients and IPD patients with similar striatal dysfunction have different patterns of monoaminergic involvement, with more widespread dysfunction in IPD.

The WD40 domain is required for LRRK2 neurotoxicity

Background

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common genetic cause of Parkinson disease (PD). LRRK2 contains an “enzymatic core” composed of GTPase and kinase domains that is flanked by leucine-rich repeat (LRR) and WD40 protein-protein interaction domains. While kinase activity and GTP-binding have both been implicated in LRRK2 neurotoxicity, the potential role of other LRRK2 domains has not been as extensively explored.

Principal Findings

We demonstrate that LRRK2 normally exists in a dimeric complex, and that removing the WD40 domain prevents complex formation and autophosphorylation. Moreover, loss of the WD40 domain completely blocks the neurotoxicity of multiple LRRK2 PD mutations.

Conclusion

These findings suggest that LRRK2 dimerization and autophosphorylation may be required for the neurotoxicity of LRRK2 PD mutations and highlight a potential role for the WD40 domain in the mechanism of LRRK2-mediated cell death.

Metabolomic profiling in LRRK2-related Parkinson's disease

Background

Mutations in LRRK2 gene represent the most common known genetic cause of Parkinson's disease (PD).

Methodology/Principal Findings

We used metabolomic profiling to identify biomarkers that are associated with idiopathic and LRRK2 PD. We compared plasma metabolomic profiles of patients with PD due to the G2019S LRRK2 mutation, to asymptomatic family members of these patients either with or without G2019S LRRK2 mutations, and to patients with idiopathic PD, as well as non-related control subjects. We found that metabolomic profiles of both idiopathic PD and LRRK2 PD subjects were clearly separated from controls. LRRK2 PD patients had metabolomic profiles distinguishable from those with idiopathic PD, and the profiles could predict whether the PD was secondary to LRRK2 mutations or idiopathic. Metabolomic profiles of LRRK2 PD patients were well separated from their family members, but there was a slight overlap between family members with and without LRRK2 mutations. Both LRRK2 and idiopathic PD patients showed significantly reduced uric acid levels. We also found a significant decrease in levels of hypoxanthine and in the ratios of major metabolites of the purine pathway in plasma of PD patients.

Conclusions/Significance

These findings show that LRRK2 patients with the G2019S mutation have unique metabolomic profiles that distinguish them from patients with idiopathic PD. Furthermore, asymptomatic LRRK2 carriers can be separated from gene negative family members, which raises the possibility that metabolomic profiles could be useful in predicting which LRRK2 carriers will eventually develop PD. The results also suggest that there are aberrations in the purine pathway in PD which may occur upstream from uric acid.

Prevalence of anxiety disorders and anxiety subtypes in patients with Parkinson's disease

Anxiety disorders are common in Parkinson's disease (PD), but are not well characterized. This study determined the prevalence and clinical correlates of all DSM-IV-TR anxiety disorder diagnoses in a sample of 127 subjects with idiopathic PD who underwent comprehensive assessments administered by a psychiatrist and neurologist. A panel of six psychiatrists with expertise in geriatric psychiatry and/or movement disorders established by consensus all psychiatric diagnoses. Current and lifetime prevalence of at least one anxiety disorder diagnosis was 43% (n = 55) and 49% (n = 63), respectively. Anxiety disorder not otherwise specified, a DSM diagnosis used for anxiety disturbances not meeting criteria for defined subtypes, was the most common diagnosis (30% lifetime prevalence, n = 38). Compared with nonanxious subjects, panic disorder (n = 13) was associated with earlier age of PD onset [50.3 (12.2) vs. 61.0 (13.7) years, P < 0.01], higher rates of motor fluctuations [77% (10/13) vs. 39% (25/64), P = 0.01] and morning dystonia [38% (5/13) vs. 13% (8/62), P < 0.03]. This high prevalence of anxiety disorders, including disturbances often not meeting conventional diagnostic criteria, suggests that anxiety in PD is likely underdiagnosed and undertreated and refined characterization of anxiety disorders in PD is needed. In addition, certain anxiety subtypes may be clinically useful markers associated with disease impact in PD.

Pathogenesis of familial Parkinson's disease: new insights based on monogenic forms of Parkinson's disease

Parkinson's disease (PD) is one of the most common movement disorders caused by the loss of dopaminergic neuronal cells. The molecular mechanisms underlying neuronal degeneration in PD remain unknown; however, it is now clear that genetic factors contribute to the pathogenesis of this disease. Approximately, 5% of patients with clinical features of PD have clear familial etiology, which show a classical recessive or dominant Mendelian mode of inheritance. Over the decade, more than 15 loci and 11 causative genes have been identified so far and many studies shed light on their implication in not only monogenic but also sporadic form of PD. Recent studies revealed that PD-associated genes play important roles in cellular functions, such as mitochondrial functions, ubiquitin-proteasomal system, autophagy-lysosomal pathway and membrane trafficking. Furthermore, the proteins encoded by PD-associated genes can interact with each other and such gene products may share a common pathway that leads to nigral degeneration. However, their precise roles in the disease and their normal functions remain poorly understood. In this study, we review recent progress in knowledge about the genes associated with familial PD.

LRRK2 mutations and risk variants in Japanese patients with Parkinson's disease

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common genetic determinant of Parkinson's disease (PD) in European-derived populations, but far less is known about LRRK2 mutations and susceptibility alleles in Asians. To address this issue, we sequenced the LRRK2 coding region in 36 patients with familial PD, then genotyped variants of interest in an additional 595 PD cases and 1,641 controls who were all of Japanese ancestry. We also performed a meta-analysis of studies on G2385R, a polymorphism previously reported to associate with PD. One pathogenic (G2019S) and one putative pathogenic (R1067Q) mutation were each observed in two patients with sporadic PD. The overall mutation frequency among patients was 0.6%. G2385R was highly associated with PD under a dominant model in our dataset (adjusted OR, 1.83; 95% CI, 1.31-2.54; P = 3.3 x 10(-4)) and similar results were seen in the meta-analysis (summary OR assuming fixed effects, 2.55; 95% CI, 2.10-3.10). G2385R represents the first consistently replicated common PD susceptibility variant in a non-European population and its effect size is substantially greater than that reported for other well-validated genetic risk factors for the disease. However, LRRK2 mutations appear to be rare among Japanese patients with PD.

Mutations in the LRRK2 Roc-COR tandem domain link Parkinson's disease to Wnt signalling pathways

Mutations in PARK8, encoding LRRK2, are the most common known cause of Parkinson's disease. The LRRK2 Roc-COR tandem domain exhibits GTPase activity controlling LRRK2 kinase activity via an intramolecular process. We report the interaction of LRRK2 with the dishevelled family of phosphoproteins (DVL1-3), key regulators of Wnt (Wingless/Int) signalling pathways important for axon guidance, synapse formation and neuronal maintenance. Interestingly, DVLs can interact with and mediate the activation of small GTPases with structural similarity to the LRRK2 Roc domain. The LRRK2 Roc-COR domain and the DVL1 DEP domain were necessary and sufficient for LRRK2-DVL1 interaction. Co-expression of DVL1 increased LRRK2 steady-state protein levels, an effect that was dependent on the DEP domain. Strikingly, LRRK2-DVL1-3 interactions were disrupted by the familial PARK8 mutation Y1699C, whereas pathogenic mutations at residues R1441 and R1728 strengthened LRRK2-DVL1 interactions. Co-expression of DVL1 with LRRK2 in mammalian cells resulted in the redistribution of LRRK2 to typical cytoplasmic DVL1 aggregates in HEK293 and SH-SY5Y cells and co-localization in neurites and growth cones of differentiated dopaminergic SH-SY5Y cells. This is the first report of the modulation of a key LRRK2-accessory protein interaction by PARK8 Roc-COR domain mutations segregating with Parkinson's disease. Since the DVL1 DEP domain is known to be involved in the regulation of small GTPases, we propose that: (i) DVLs may influence LRRK2 GTPase activity, and (ii) Roc-COR domain mutations modulating LRRK2-DVL interactions indirectly influence kinase activity. Our findings also link LRRK2 to Wnt signalling pathways, suggesting novel pathogenic mechanisms and new targets for genetic analysis in Parkinson's disease.

Clinical and pathological characteristics of patients with leucine-rich repeat kinase-2 mutations

Mutations in LRRK2 are the single most common known cause of Parkinson's disease (PD). Two new PD patients with LRRK2 mutation were identified from a cohort with extensive postmortem assessment. One of these patients harbors the R793M mutation and presented with the typical clinical and pathological features of PD. A novel L1165P mutation was identified in a second patient. This patient had the classical and pathological features of PD, but additionally developed severe neuropsychological symptoms and dementia associated with abundant neurofibrillary tangles in the hippocampal formation; features consistent with a secondary diagnosis of tangle-predominant dementia. alpha-Synuclein-containing pathological inclusions in these patients also were highly phosphorylated at Ser-129, similar to other patients with idiopathic PD. These two PD patients also were characterized by the presence of occasional cytoplasmic TDP-43 inclusions in the temporal cortex, a finding that was not observed in three other patients with the G2019S mutation in LRRK2. These findings extend the clinical and pathological features that may be associated with LRRK2 mutations.

Leucine-rich repeat kinase 2 (LRRK2): a key player in the pathogenesis of Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder, with a prevalence of more than 1% after the age of 65 years. Mutations in the gene encoding leucine-rich repeat kinase-2 (LRRK2) have recently been linked to autosomal dominant, late-onset PD that is clinically indistinguishable from typical, idiopathic disease. LRRK2 is a multidomain protein containing several protein interaction motifs as well as dual enzymatic domains of GTPase and protein kinase activities. Disease-associated mutations are found throughout the multidomain structure of the protein. LRRK2, however, is unique among the PD-causing genes, because a missense mutation, G2019S, is a frequent determinant of not only familial but also sporadic PD. Thus, LRRK2 has emerged as a promising therapeutic target for combating PD. In this Mini-Review, we look at the current state of knowledge regarding the domain structure, amino acid substitutions, and potential functional roles of LRRK2.

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.

LRRK2 and neurodegeneration

Mutations in leucine-rich repeat kinase 2 gene (PARK8/LRRK2) encoding the protein Lrrk2 are causative of inherited and sporadic Parkinson's disease (PD) with phenotypic manifestations of frontotemporal lobar degeneration, corticobasal degeneration and associated motor neuron disease in some patients, and with variable penetrance. Neuropathology is characterized by loss of dopaminergic neurons in the substantia nigra pars compacta in all cases with accompanying Lewy pathology, or tau pathology or without intraneuronal inclusions, thus indicating that mutations in LRRK2 are not always manifested as Lewy body disease (LBD) or as alpha-synucleinopathy. Molecular studies have not disclosed clear association between nerve cell degeneration and modifications in the kinase activity of Lrrk2, and the pathogenesis of LRRK2 mutations remains unknown. Several morphological studies have suggested that Lrrk2 is a component of Lewy bodies and aberrant neurites in sporadic PD and Dementia with Lewy bodies, whereas other studies have indicated that Lrrk2 does not participate in Lewy body composition. Likewise, some studies have shown Lrrk2 immunoreactivity in hyper-phosphorylated tau inclusions in Alzheimer's disease (AD) and other tauopathies, whereas other studies did not find Lrrk2 in hyper-phosphorylated tau inclusions. We have used three currently used anti-Lrrk2 antibodies (NB-300-268, NB-300-267 and AP7099b) and concluded that these differences are largely dependent on the antibodies used and, particularly, on the interpretation of the origin of the multiple bands of low molecular weight species, in addition to the band corresponding to full-length Lrrk2, that recognize the majority of these antibodies. A review of the available data and our results indicate that full-length Lrrk2 is not a major component of Lewy bodies in LBDs, and of hyper-phosphorylated tau inclusions in AD and tauopathies. Bands of low molecular weight are probably not the result of post-mortem artefacts as they are also present in cultured cells processed under optimal conditions. Truncated forms of Lrrk2 and additional transcripts related with LRRK2, in the absence of spliced forms of Lrrk2 may account for Lrrk2 immunoreactivity in distinct intraneuronal inclusions.

Parkinson-linked genes and toxins that affect neuronal cell death through the Bcl-2 family

Parkinson's disease (PD) results from the death of specific neuronal populations in the CNS. Potential causative factors include environmental toxins and gene mutations that can combine to dysregulate the processing and degradation of alpha-synuclein. Oxidative stress induced by the neurotoxins MPTP, paraquat, maneb, and rotenone causes lipid peroxidation and protein misfolding that affects cell death through members of the Bcl-2 family. Sufficient activation of Bax and Bak facilitates mitochondrial outer-membrane permeabilization, which releases death-inducing factors that cause apoptotic and nonapoptotic programmed cell death. The formation of alpha-synuclein aggregates is a defining pathologic feature of PD and is induced by these neurotoxins as well as several Parkinson-linked familial mutations. Of the familial mutations identified thus far, two of the loci encode proteins associated with ubiquitin-proteasome degradation of misfolded proteins (Parkin and Uch-L1), and two encode proteins associated with mitochondria and oxidative stress (DJ-1 and PINK1). Both gene and toxin findings indicate that dopaminergic neuron losses in PD are the result of oxidative stress affecting mitochondria function and ubiquitin-proteasome activity. Here we describe how related cell death mechanisms are involved in the pathophysiology of Parkinson's disease.

Premotor Parkinson's disease: clinical features, detection, and prospects for treatment

The period immediately before the onset of motor symptoms of Parkinson's disease (PD) often has a recognizable phenotype with features including autonomic dysfunction and impaired olfaction. Subclinical dopaminergic cell loss can also be detected at this time using molecular imaging techniques. A greater recognition of the features of premotor PD and improvements in screening technologies have opened the possibility of predictive testing for PD. In addition to molecular imaging of the dopamine system, screening tests that can potentially be used to identify the physiological abnormalities in premotor PD include olfactory testing, imaging of the sympathetic innervation of the heart, transcranial ultrasound, and genetic testing for mutations known to cause hereditary PD. All of these technologies have trade-offs as screening tests for accuracy, availability, and costs. Using these tests in combination may produce a more favorable combination of reasonable cost and accuracy than using any single test alone. Ultimately, the value of screening for PD depends on development of neuroprotective treatments for PD that would create an imperative for early identification and treatment.

CHIP regulates leucine-rich repeat kinase-2 ubiquitination, degradation, and toxicity

Mutation in leucine-rich repeat kinase-2 (LRRK2) is the most common cause of late-onset Parkinson's disease (PD). Although most cases of PD are sporadic, some are inherited, including those caused by LRRK2 mutations. Because these mutations may be associated with a toxic gain of function, controlling the expression of LRRK2 may decrease its cytotoxicity. Here we show that the carboxyl terminus of HSP70-interacting protein (CHIP) binds, ubiquitinates, and promotes the ubiquitin proteasomal degradation of LRRK2. Overexpression of CHIP protects against and knockdown of CHIP exacerbates toxicity mediated by mutant LRRK2. Moreover, HSP90 forms a complex with LRRK2, and inhibition of HSP90 chaperone activity by 17AAG leads to proteasomal degradation of LRRK2, resulting in increased cell viability. Thus, increasing CHIP E3 ligase activity and blocking HSP90 chaperone activity can prevent the deleterious effects of LRRK2. These findings point to potential treatment options for LRRK2-associated PD.

Imaging the impact of genes on Parkinson's disease

Although Parkinson's disease (PD) has traditionally been considered to be a non-genetic disorder, recent progress in the neurogenetics of PD provided converging evidence that genetic factors play a relevant role in the etiology of PD. The strongest case for a genetic contribution to PD was made by the discovery of mutations in single genes that can cause autosomal dominant (alpha-synuclein (SNCA)) and leucine rich repeat kinase 2 (LRRK2) gene) or recessive (Parkin, PTEN-induced putative kinase 1 (PINK1), DJ-1, and ATP13A2 gene) forms of PD. Here, we review how structural and functional neuroimaging of individuals carrying a mutation in one of the PD genes has offered a unique avenue of research into the pathogenesis of PD. In symptomatic mutation carriers (i.e. those with overt disease), brain mapping can help to link the molecular pathogenesis of PD more directly with functional and structural changes in the intact human brain. In addition, neuroimaging of presymptomatic (i.e. non-manifesting) mutation carriers has emerged as a valuable tool to identify mechanisms of adaptive motor reorganization at the preclinical stage that may prevent or delay clinical manifestation. In addition to mutations causing monogenic forms of PD, common polymorphisms in genes that influence mono-aminergic signaling or synaptic plasticity may have modifying effects on distinct aspects of PD. We also discuss how functional and structural neuroimaging can be used to better characterize these genotype-phenotype correlations.

Emerging pathways in genetic Parkinson's disease: tangles, Lewy bodies and LRRK2

The last decade has seen clear links emerge between the genetic determinants and neuropathological hallmarks of parkinsonism and dementia, notably with the discovery of mutations in alpha-synuclein and tau. Following the description of mutations in LRRK2 linked to Parkinson's disease, characterized by variable pathology including either alpha-synuclein or tau deposition, it has been suggested that LRRK2 functions as an upstream regulator of Parkinson's disease pathogenesis. This minireview explores this model, in the context of our current understanding of the biochemistry of LRRK2, alpha-synuclein and tau.

G2019S LRRK2 mutation causing Parkinson's disease without Lewy bodies

The G2019S leucine-rich repeat kinase 2 gene (LRRK2) mutation has been identified in a significant proportion of familial and sporadic cases of Parkinson's disease (PD). Until now, information on the neuropathological changes associated with the G2019S LRRK2 mutation has been sparse. We report a 77-year-old patient who presented with a 14 year history of PD but, unexpectedly, histopathological examination disclosed mild neuronal loss in the substantia nigra without α-synuclein, tau or ubiquitin cytoplasmic inclusions. A G2019S LRRK2 mutation was eventually detected. The present case confirms that clinical PD caused by G2019S mutations can be associated with non-specific nigral degeneration without Lewy.

The spectrum of parkinsonian manifestations associated with glucocerebrosidase mutations

BACKGROUND

Mutations in the glucocerebrosidase gene (GBA) result in Gaucher disease and can be associated with a phenotype characterized by adult-onset progressive neurologic deterioration and parkinsonism.

OBJECTIVE

To define the clinical and neurologic spectrum of parkinsonian manifestations associated with GBA mutations. Design, Setting, and Patients A prospective case series of 10 patients (7 men and 3 women) with parkinsonism and GBA mutations evaluated at the National Institutes of Health Clinical Center.

MAIN OUTCOME MEASURES

The GBA genotypes were identified by means of DNA sequencing. Tests evaluating neurologic, motor, cognitive, ocular, and olfactory functions were performed and the results were analyzed by a single team.

RESULTS

Genotyping identified GBA mutations N370S, L444P, and c.84dupG and recombinant alleles. The mean age at onset of parkinsonian manifestations was 49 years (range, 39-65 years), disease duration was 7.8 years (range, 1.2-16.0 years), and Unified Parkinson Disease Rating Scale part III score was 26.3 (range, 13-38). Half of the patients reported cognitive changes later in the disease course. Six patients were diagnosed as having Parkinson disease, 3 as having Lewy body dementia, and 1 as having a "Parkinson plus" syndrome. The most frequent nonmotor finding was olfactory dysfunction. Atypical manifestations included myoclonus, electroencephalographic abnormalities, and seizures.

CONCLUSIONS

In the homozygous and heterozygous states, GBA mutations are associated with a spectrum of parkinsonian phenotypes ranging from Parkinson disease, mostly of the akinetic type, to a less common phenotype characteristic of Lewy body dementia.

The Roc domain of leucine-rich repeat kinase 2 is sufficient for interaction with microtubules

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the leading cause of genetically inherited Parkinson's disease (PD). Although this multidomain protein has been shown to have both GTPase and kinase activities through the Roc and MAPKKK domains, respectively, the protein-protein interactions and pathways involved in LRRK2-mediated signaling remain elusive. Utilizing a combination of protein pull-down assays, mass spectrometry, Western blotting, and immunofluorescence microscopy, this study identifies and describes the interaction between LRRK2 and microtubules. The Roc or GTPase-like domain of LRRK2 is sufficient for interaction with alpha/beta-tubulin heterodimers. This interaction occurs in a guanine nucleotide-independent manner, suggesting that tubulin might not be an effector of the LRRK2 GTPase domain. The R1441C pathogenic mutation, located within the Roc domain, retains interaction with alpha/beta-tubulin heterodimers, suggesting that disruption of this interaction likely is not the mechanism whereby the R1441C mutation leads to disease. At a subcellular level, endogenous LRRK2 protein was found to colocalize with alpha/beta-tubulin in primary hippocampal neurons. These findings are significant in that they link LRRK2 with microtubules, a structural component of the cell that is critically involved in the pathogenesis of several neurodegenerative diseases, including PD.

Zeroing in on LRRK2-linked pathogenic mechanisms in Parkinson's disease

The frequency and potency of mutations in the LRRK2 gene redefine the role of genetic susceptibility in Parkinson's disease. Dominant missense mutations that fulfill initial criteria for potential gain of function mechanisms coupled with enzymatic activity likely amenable to small molecule inhibition position LRRK2 as a promising therapeutic target. Herein, key observations from the clinic to the test tube are highlighted together with points of contention and outstanding critical issues. Resolution of the critical issues will expedite the development of therapies that exploit LRRK2 activity for neuroprotection strategies.

A clinical, neuropsychological and olfactory evaluation of a large family with LRRK2 mutations

We evaluated the neurological and neuropsychological profiles and olfaction as presymptomatic markers in a large family with Parkinson disease (PD) caused by the G2019S mutation in the LRRK2 gene. Five affected family members, 14 asymptomatic mutation carriers and 15 non-carriers were compared. Patients had typical dopa-responsive PD, frequently associated with cognitive impairment. Asymptomatic carriers and non-carriers could not be distinguished because of their neuropsychological status, the presence of depression or olfactory impairment. We were therefore unable to identify a presymptomatic marker of LRRK2-related PD.

Outcome of bilateral deep brain subthalamic stimulation in patients carrying the R1441G mutation in the LRRK2 dardarin gene

OBJECTIVE

Deep brain subthalamic stimulation provides symptomatic relief to patients with Parkinson's disease. The present study analyzes the postoperative outcome of deep brain subthalamic stimulation in patients carrying the R1441G mutation in the leucine-rich repeat kinase-2 (LRRK2) (dardarin) gene.

METHODS

Five of the 48 patients treated in our unit carried a mutation in the LRRK2 (dardarin) gene. All five met the Core Assessment Program for Surgical Interventional Therapies criteria for inclusion in the surgical program. Pre- and postoperative assessment (6 mo) was made using the Unified Parkinson Disease Rating Scale II, Unified Parkinson Disease Rating Scale III, and Parkinson's Disease Questionnaire-39 scores, as well as the type and dosage of drugs used.

RESULTS

The response to L-dopa after 6 months was similar to the baseline in all four patients. One suffered a stroke four months after surgery and is not eligible for evaluation. The improvements in motor response, daily life activities, and quality of life were limited (18, 22, and 33%, respectively) and were lower than those of the control group (39, 45, and 41%, respectively).

DISCUSSION

Carriers of the R1441G mutation were clinically analogous to the rest of similarly operated patients with idiopathic Parkinson's disease. However, the response to deep brain subthalamic stimulation was worse among the former. The explanation for this negative result is unclear because all patients maintained an excellent response to L-dopa. Further larger studies are needed to confirm these findings.

The nonsynonymous Thr105Ile polymorphism of the histamine N-methyltransferase is associated to the risk of developing essential tremor

OBJECTIVE

We analyzed in patients with essential tremor (ET) the Thr105Ile polymorphism of the Histamine N-methyltransferase (HNMT) enzyme that is associated to Parkinson's disease (PD) risk.

METHODS

Leukocytary DNA from 204 ET patients and a control group of 295 unrelated healthy individuals was studied for the nonsynonymous HNMT Thr105Ile polymorphism by using amplification-restriction analyses.

RESULTS

Patients with ET showed a higher frequency of homozygous HNMT 105Thr genotypes leading to high metabolic activity (p < 0.015) with a statistically significant gene-dose effect, as compared to healthy subjects. These findings were independent of gender, and of tremor localization, but the association of the HNMT polymorphism is more prominent among patients with late-onset ET (p < 0.007).

CONCLUSION

These results, combined with previous findings indicating alterations in the frequency for the HNMT Thr105Ile polymorphism in patients with PD, suggest that alterations of histamine homeostasis in the SNC are associated with the risk of movement disorders.

The G2019S LRRK2 mutation in Brazilian patients with Parkinson's disease: phenotype in monozygotic twins

Mutations in the Leucine-Rich Repeat Kinase 2 gene (LRRK2) are mainly responsible for idiopathic Parkinson's disease (PD) with either a dominant pattern of transmission or a sporadic occurrence due to the reduced penetrance. A majority of LRRK2 kindreds demonstrate an extremely variable age-at-onset in affected members of the same family. The G2019S is the most common LRRK2 mutation, which accounts for 1-5% PD patients in North America, and up to 40% of patients from an isolated Arab population. We assessed the frequency of the G2019S mutation in 83 Brazilian PD patients originally preselected for having an early age-at-onset (<50 years) and/or a positive family history. The mutation was detected in three probands (3.5%). Our clinical findings in these kindreds include the first description of the phenotype in identical twins discordant for handedness (a general phenomenon found in approximately 25% monozygotic twins). However, both twins developed right asymmetric PD. The clinical presentation of twins was strikingly similar including an identical PD onset at age 60. This observation may suggest that genetic factors predominantly determine age-at-onset.