Retromer-dependent neurotransmitter receptor trafficking to synapses is altered by the Parkinson's disease VPS35 mutation p.D620N.

Vacuolar protein sorting 35 (VPS35) is a core component of the retromer complex, crucial to endosomal protein sorting and intracellular trafficking. We recently linked a mutation in VPS35 (p.D620N) to familial parkinsonism. Here, we characterize human VPS35 and retromer function in mature murine neuronal cultures and investigate neuron-specific consequences of the p.D620N mutation. We find VPS35 localizes to dendritic spines and is involved in the trafficking of excitatory AMPA-type glutamate receptors (AMPARs). Fundamental neuronal processes, including excitatory synaptic transmission, AMPAR surface expression and synaptic recycling are altered by VPS35 overexpression. VPS35 p.D620N acts as a loss-of-function mutation with respect to VPS35 activity regulating synaptic transmission and AMPAR recycling in mouse cortical neurons and dopamine neuron-like cells produced from induced pluripotent stem cells of human p.D620N carriers. Such perturbations to synaptic function likely produce chronic pathophysiological stress upon neuronal circuits that may contribute to neurodegeneration in this, and other, forms of parkinsonism.

Progressive dopaminergic alterations and mitochondrial abnormalities in LRRK2 G2019S knock-in mice.

Mutations in the LRRK2 gene represent the most common genetic cause of late onset Parkinson's disease. The physiological and pathological roles of LRRK2 are yet to be fully determined but evidence points towards LRRK2 mutations causing a gain in kinase function, impacting on neuronal maintenance, vesicular dynamics and neurotransmitter release. To explore the role of physiological levels of mutant LRRK2, we created knock-in (KI) mice harboring the most common LRRK2 mutation G2019S in their own genome. We have performed comprehensive dopaminergic, behavioral and neuropathological analyses in this model up to 24months of age. We find elevated kinase activity in the brain of both heterozygous and homozygous mice. Although normal at 6months, by 12months of age, basal and pharmacologically induced extracellular release of dopamine is impaired in both heterozygous and homozygous mice, corroborating previous findings in transgenic models over-expressing mutant LRRK2. Via in vivo microdialysis measurement of basal and drug-evoked extracellular release of dopamine and its metabolites, our findings indicate that exocytotic release from the vesicular pool is impaired. Furthermore, profound mitochondrial abnormalities are evident in the striatum of older homozygous G2019S KI mice, which are consistent with mitochondrial fission arrest. We anticipate that this G2019S mouse line will be a useful pre-clinical model for further evaluation of early mechanistic events in LRRK2 pathogenesis and for second-hit approaches to model disease progression.

DNAJC13 p.Asn855Ser mutation screening in Parkinson's disease and pathologically confirmed Lewy body disease patients.

BACKGROUND: Recently, a novel mutation in exon 24 of DNAJC13 gene (p.Asn855Ser, rs387907571) has been reported to cause autosomal dominant Parkinson's disease (PD) in a multi-incident Mennonite family. METHODS: In the present study the mutation containing exon of the DNAJC13 gene has been sequenced in a Caucasian series consisting of 1938 patients with clinical PD and 838 with pathologically diagnosed Lewy body disease (LBD). RESULTS: Our sequence analysis did not identify any coding variants in exon 24 of DNAJC13. Two previously described variants in intron 23 (rs200204728 and rs2369796) were observed. CONCLUSION: Our results indicate that the region surrounding the DNAJC13 p.Asn855Ser substitution is highly conserved and mutations in this exon are not a common cause of PD or LBD among Caucasian populations.

Identification of FUS p.R377W in essential tremor.

BACKGROUND AND PURPOSE: Exome sequencing analysis has recently identified a nonsense mutation in fused in sarcoma (FUS) segregating with essential tremor (ET) within a large French-Canadian family. Further characterization of FUS resulted in the identification of additional mutations in ET patients; however, their pathogenicity still remains to be confirmed. The role of FUS in an independent cohort of ET patients from Canada was evaluated. METHODS: The entire coding sequence of FUS in 217 patients diagnosed with ET was analyzed and two missense variants in 219 healthy controls were genotyped by Sanger sequencing. RESULTS: Sequencing of FUS identified a previously reported non-pathogenic mutation p.G174_G175del in one ET patient and two healthy controls, and a novel p.R377W in one patient with family history of disease. This mutation is highly conserved and strongly predicted to be damaging by in silico analysis. CONCLUSION: This study has identified a novel FUS p.R377W substitution in ET patients. Additional genotyping studies in a large number of ET patients and controls are necessary to conclusively define its pathogenicity.

Multicenter analysis of glucocerebrosidase mutations in Parkinson's disease.

BACKGROUND: Recent studies indicate an increased frequency of mutations in the gene encoding glucocerebrosidase (GBA), a deficiency of which causes Gaucher's disease, among patients with Parkinson's disease. We aimed to ascertain the frequency of GBA mutations in an ethnically diverse group of patients with Parkinson's disease. METHODS: Sixteen centers participated in our international, collaborative study: five from the Americas, six from Europe, two from Israel, and three from Asia. Each center genotyped a standard DNA panel to permit comparison of the genotyping results across centers. Genotypes and phenotypic data from a total of 5691 patients with Parkinson's disease (780 Ashkenazi Jews) and 4898 controls (387 Ashkenazi Jews) were analyzed, with multivariate logistic-regression models and the Mantel-Haenszel procedure used to estimate odds ratios across centers. RESULTS: All 16 centers could detect two GBA mutations, L444P and N370S. Among Ashkenazi Jewish subjects, either mutation was found in 15% of patients and 3% of controls, and among non-Ashkenazi Jewish subjects, either mutation was found in 3% of patients and less than 1% of controls. GBA was fully sequenced for 1883 non-Ashkenazi Jewish patients, and mutations were identified in 7%, showing that limited mutation screening can miss half the mutant alleles. The odds ratio for any GBA mutation in patients versus controls was 5.43 across centers. As compared with patients who did not carry a GBA mutation, those with a GBA mutation presented earlier with the disease, were more likely to have affected relatives, and were more likely to have atypical clinical manifestations. CONCLUSIONS: Data collected from 16 centers demonstrate that there is a strong association between GBA mutations and Parkinson's disease.

Adult neurogenesis and neurite outgrowth are impaired in LRRK2 G2019S mice.

The generation and maturation of adult neural stem/progenitor cells are impaired in many neurodegenerative diseases, among them is Parkinson's disease (PD). In mammals, including humans, adult neurogenesis is a lifelong feature of cellular brain plasticity in the hippocampal dentate gyrus (DG) and in the subventricular zone (SVZ)/olfactory bulb system. Hyposmia, depression, and anxiety are early non-motor symptoms in PD. There are parallels between brain regions associated with non-motor symptoms in PD and neurogenic regions. In autosomal dominant PD, mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are frequent. LRRK2 homologs in non-vertebrate systems play an important role in chemotaxis, cell polarity, and neurite arborization. We investigated adult neurogenesis and the neurite development of new neurons in the DG and SVZ/olfactory bulb system in bacterial artificial chromosome (BAC) human Lrrk2 G2019S transgenic mice. We report that mutant human Lrrk2 is highly expressed in the hippocampus in the DG and the SVZ of adult Lrrk2 G2019S mice. Proliferation of newly generated cells is significantly decreased and survival of newly generated neurons in the DG and olfactory bulb is also severely impaired. In addition, after stereotactic injection of a GFP retrovirus, newly generated neurons in the DG of Lrrk2 G2019S mice exhibited reduced dendritic arborization and fewer spines. This loss in mature, developed spines might point towards a decrease in synaptic connectivity. Interestingly, physical activity partially reverses the decrease in neuroblasts observed in Lrrk2 G2010S mice. These data further support a role for Lrrk2 in neuronal morphogenesis and provide new insights into the role of Lrrk2 in adult neurogenesis.

Death-associated protein kinase 1 variation and Parkinson's disease.

BACKGROUND AND PURPOSE: Mutations of the LRRK2 gene are now recognized as major risk factors for Parkinson's disease. The Lrrk2 protein is a member of the ROCO family, which also includes Lrrk1 and Dapk1. Functional genetic variants of the DAPK1 gene (rs4877365 and rs4878104) have been previously associated with Alzheimer's disease. METHODS: Herein, we assessed the role of DAPK1 variants (rs4877365 and rs4878104) in risk of Parkinson's disease with Sequenom iPLEX genotyping, employing one Taiwanese series (391 patients with Parkinson's disease, 344 controls) and five separate Caucasian series' (combined sample size 1962 Parkinson's disease patients, 1900 controls). RESULTS: We observed no evidence of association for rs4877365 and rs4878104 and risk of Parkinson's disease in any of the individual series or in the combined Caucasian series under either an additive or recessive model. CONCLUSION: These specific DAPK1 intronic variants do not increase the risk of Parkinson's disease. However, further functional studies are required to elucidate the potential therapeutic implications with the dimerization of the Dapk1 and Lrrk2 proteins.

SNCA, MAPT, and GSK3B in Parkinson disease: a gene-gene interaction study.

BACKGROUND AND PURPOSE: Recent evidence suggests that variation in the SNCA, MAPT, and GSK3B genes interacts in affecting risk for Parkinson disease (PD). In the current study, we attempt to validate previously published findings, evaluating gene-gene interactions between SNCA, MAPT, and GSK3B in association with PD. METHODS: Three Caucasian PD patient-control series from the United States, Ireland, and Norway (combined n = 1020 patients and 1095 controls) were genotyped for SNCA rs356219, MAPT H1/H2-discriminating SNP rs1052553, and GSK3B rs334558 and rs6438552. RESULTS: Our findings indicate that as previously reported, the SNCA rs356219-G allele and MAPT rs1052553 (H1 haplotype) were both associated with an increased risk of PD, whilst contrary to previous reports, GSK3B variants were not. No pair-wise interaction was observed between SNCA, MAPT, and GSK3B; the risk effects of SNCA rs356219-G and MAPT rs1052553-H1 were seen in a similar manner across genotypes of other variants, with no evidence suggesting synergistic, antagonistic, or deferential effects. CONCLUSIONS: In the Caucasian patient-control series examined, risk for PD was influenced by variation in SNCA and MAPT but not GSK3B. Additionally, those three genes did not interact in determining disease risk.

Parkinson-related genetics in patients treated with deep brain stimulation.

OBJECTIVES: To analyze the frequency of mutations associated with Parkinson's disease (PD) in a general PD population compared to patients with PD selected for deep brain stimulation (DBS) and evaluate the outcome of surgery. MATERIAL AND METHODS: A total of 630 consecutive patients with PD were genetically screened, and 60 had DBS surgery, 37 subthalamic nucleus (STN), 21 ventrointermediate nucleus of thalamus (VIM), and two globus pallidus internus (GPi). RESULTS: Mutations in LRRK2, PRKN, and PINK1 were found: the first two of these being overrepresented in STN-operated patients, but none being found in VIM-operated patients. Clinical outcome of the surgery was similar in patients with mutations compared to those without. CONCLUSIONS: In a consecutive PD population, patients treated with STN-DBS are overrepresented for PD-related mutations and they seem to benefit from DBS as well as patients without mutations.

Impaired dopaminergic neurotransmission and microtubule-associated protein tau alterations in human LRRK2 transgenic mice.

Mutations in the Leucine Rich Repeat Kinase 2 (LRRK2) gene, first described in 2004 have now emerged as the most important genetic finding in both autosomal dominant and sporadic Parkinson's disease (PD). While a formidable research effort has ensued since the initial gene discovery, little is known of either the normal or the pathological role of LRRK2. We have created lines of mice that express human wild-type (hWT) or G2019S Lrrk2 via bacterial artificial chromosome (BAC) transgenesis. In vivo analysis of the dopaminergic system revealed abnormal dopamine neurotransmission in both hWT and G2019S transgenic mice evidenced by a decrease in extra-cellular dopamine levels, which was detected without pharmacological manipulation. Immunopathological analysis revealed changes in localization and increased phosphorylation of microtubule binding protein tau in G2019S mice. Quantitative biochemical analysis confirmed the presence of differential phospho-tau species in G2019S mice but surprisingly, upon dephosphorylation the tau isoform banding pattern in G2019S mice remained altered. This suggests that other post-translational modifications of tau occur in G2019S mice. We hypothesize that Lrrk2 may impact on tau processing which subsequently leads to increased phosphorylation. Our models will be useful for further understanding of the mechanistic actions of LRRK2 and future therapeutic screening.

Association of the MAPT locus with Parkinson's disease.

BACKGROUND AND PURPOSE: Whilst an association between the tau gene (MAPT)-containing H1 haplotype and supranuclear gaze palsy (PSP) has long been recognized, the effect of H1 on risk for Parkinson's disease (PD) has remained more contentious. METHODS: Herein, we examined the association of H1 and PD in three Caucasian PD patient-control series from Ireland, Norway, and the US (combined: n = 2619), by genotyping two H1/H2 single nucleotide polymorphisms (SNPs) in MAPT (rs1052553) and in the Saitohin gene (rs62063857) and one H1-specific SNP (rs242557). RESULTS: We identified a significant association between H1/H2 and risk of PD (rs1052553 OR: 1.43, CI: 1.23-1.64; rs62063857 OR: 1.45, CI: 1.27-1.67), but no effect of the H1-specific SNP rs242557 (OR: 0.92, CI: 0.82-1.03). CONCLUSIONS: Our findings show that the H1 haplotype is a significant risk factor for PD. However, one H1-specific SNP (rs242557) previously implicated in PSP did not alter the risk of PD, indicating that distinct H1 sub-haplotypes probably drive the associations with PD and PSP.

Calbindin-1 association and Parkinson's disease.

BACKGROUND AND PURPOSE: Calcium levels have been proposed to play an important role in the selective vulnerability of nigrostriatal dopaminergic neurons in Parkinson's disease (PD). Recently, an association was reported between the calcium buffer, calbindin (rs1805874) and risk of PD in a Japanese patient-control series. METHODS: We genotyped rs1805874 in four independent Caucasian patient-control series (1543 PD patients, 1771 controls). RESULTS: There was no evidence of an association between rs1805874 and disease risk in individual populations or in the combined series (odds ratio: 1.04, 95% CI: 0.82-1.31, P = 0.74). DISCUSSION: Our study shows there is no association between rs1805874 and risk for PD in four Caucasian populations. This suggests the effect of calbindin on PD risk displays population specificity.

GRN 3'UTR+78 C>T is not associated with risk for Parkinson's disease.

BACKGROUND AND PURPOSE: A single nucleotide polymorphism in the 3'-untranslated region of the progranulin gene (GRN; 3'UTR+78C>T; rs5848) was reported to alter the risk for frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U). rs5848 is located within a micro-RNA binding site and affects the expression of GRN. METHODS: As FTLD-U patients often present with parkinsonism, we investigated the association of GRN rs5848 and risk of Parkinson's disease in two Caucasian patient-control series (n = 1413) from the US and Poland. RESULTS: No association was observed between rs5848 and susceptibility to Parkinson's disease (individual series and combined analysis). CONCLUSIONS: This finding shows that GRN rs5848 does not affect the risk of Parkinson's disease in the US and Polish populations.

Multiple alpha-synuclein gene polymorphisms are associated with Parkinson's disease in a Norwegian population.

OBJECTIVES: Previous studies have found associations between Parkinson's disease (PD) and polymorphisms located within both the alpha-synuclein gene (SNCA) promoter and other gene regions. Our aim was to study SNCA gene markers in a closely matched Norwegian PD population to examine the genetic relationship between different polymorphisms associated with the disease. METHODS: We genotyped seven single nucleotide polymorphisms (SNPs) located in the SNCA promoter and two SNPs in the 3' gene region and seven microsatellite markers located across the gene in a closely matched series of 236 PD patients and 236 controls. Linkage disequilibrium (LD) structure was examined, and association of single markers and gene haplotypes analyzed. RESULTS: Several markers located across the SNCA gene were associated with PD, including marker alleles associated with disease in previous studies (Rep1 263-bp allele, rs356165 and rs356219). CONCLUSION: LD between associated marker alleles located across the SNCA gene suggests that a single genetic effect might explain the previous reported association in the promoter and 3' regions.

LRRK2 and Parkinson's disease in Norway.

OBJECTIVES: Mutations in the LRRK2 gene have been associated with both familial and sporadic late-onset Parkinson's disease. A large number of mutations in this gene have been identified; however, for many of these variants, the pathogenicity and relative frequency are unknown. Herein, we investigate the frequency of a number of recently identified LRRK2 mutations in Norway. METHODS: We genotyped eight putatively pathogenic LRRK2 mutations (R793M, R1067Q, I1371V, IVS31+3 A>G, M1869T, R1941H, T2356I and G2385R) in a series of 433 patients with Parkinson's disease and 587 controls from Norway. An intronic polymorphism previously reported to be associated with disease susceptibility was also examined (rs10506151). RESULTS: The Lrrk2 R793M substitution was found in two healthy individuals. No other LRRK2 mutations were identified in the Norwegian population, and furthermore no association was observed between rs10506151 and Parkinson's disease (P = 0.41). CONCLUSIONS: LRRK2 mutations other than the Lrrk2 G2019S mutation are rare in Norway. Our results indicate that the Lrrk2 R793M substitution is most likely a rare polymorphism.

A comparative analysis of leucine-rich repeat kinase 2 (Lrrk2) expression in mouse brain and Lewy body disease.

Pathogenic substitutions in leucine-rich repeat kinase 2 (LRRK2, Lrrk2) have been genetically linked to familial, late-onset Parkinsonism. End-stage disease is predominantly associated with nigral neuronal loss and Lewy body pathology, but patients may have gliosis, tau or ubiquitin inclusions (pleomorphic pathology). The anatomical distribution of Lrrk2 protein may provide insight into its function in health and neurodegeneration, thus we performed a comparative study with 'in-house' and commercially available Lrrk2 antibodies using brain tissue from wild type and human Lrrk2 transgenic bacterial artificial chromosome (BAC) mice, and from diffuse Lewy body disease (DLBD) patients. Lrrk2 protein was ubiquitously expressed and relatively abundant in most brain regions, including the substantia nigra, thalamus and striatum. Lrrk2 was not a major component of Lewy body or neuritic pathology associated with Parkinson's disease. However, selective loss of dopaminergic neurons in Lrrk2-associated Parkinsonism argues the protein may have regional-specific interactions. Lrrk2 immunohistochemical staining was present in the subventricular zone, a region containing stem cells that give rise to both neurons and glia. A role for Lrrk2 in neurogenesis might provide further insight into the aberrant role of mutant protein in age-associated neurodegeneration with pleomorphic pathology.

PINK1 mutation heterozygosity and the risk of Parkinson's disease.

BACKGROUND: Mutations in the PTEN-induced kinase 1 (PINK1) gene have been identified in recessively inherited and sporadic early-onset parkinsonism (EOP). METHODS: A total of 131 Norwegian patients diagnosed with Parkinson's disease were included. Of them, 89 participants had EOP (onset < or = 50 years); the remaining had familial late-onset disease (mean age at onset 64 years). PINK1 analysis included sequencing and gene dose assessment. Mutations were examined in 350 controls. RESULTS: Heterozygous missense mutations in PINK1 were found in 3 of 131 patients; none of the patients carried homozygous or compound heterozygous mutations. One of these three patients had a father affected by Parkinson's disease, and he carried the mutation. Three new and seven known polymorphic variants were identified, although none seemed to be associated with disease risk. CONCLUSIONS: PINK1 mutations are rare in Norwegian patients with EOP and familial Parkinson's disease. However, the data suggest that some heterozygous mutations might increase the risk of developing Parkinson's disease.

Clinical and genetic features of families with frontotemporal dementia and parkinsonism linked to chromosome 17 with a P301S tau mutation.

In 9 patients with frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) with a P301S tau mutation, the predominant phenotype was frontotemporal dementia in 3 and parkinsonism in 6. Comparison of the tau genotype/haplotype carrying the mutation and the initial clinical sign showed association between H1/H1 and parkinsonism and between H1/H2 and personality change. Thus, the tau haplotype carrying the mutation and the tau genotype may be related to the clinical phenotype throughout the disease course.

Clinical and pathologic features of families with LRRK2-associated Parkinson's disease.

The etiology for Parkinson's disease (PD) remains unknown. Genetic causes have been identified with several distinct mutations. Recently, 9 mutations involving a novel gene, leucine-rich repeat kinase 2 (LRRK2), have been identified as the cause of autosomal dominant PD in kindreds, with some of them previously linked to the PARK8 locus on chromosome 12. LRRK2 mutations are relatively common genetic causes of familial and sporadic PD. In addition, these mutations have been identified in diverse populations. The clinical and pathologic features of LRRK2-associated PD are indistinguishable from idiopathic PD; however, considerable clinical and pathologic variability exists even among kindreds. This short review highlights the clinical and pathologic features in LRRK2-associated parkinsonism.