VPS35 mutations in Parkinson disease

The identification of genetic causes for Mendelian disorders has been based on the collection of multi-incident families, linkage analysis, and sequencing of genes in candidate intervals. This study describes the application of next-generation sequencing technologies to a Swiss kindred presenting with autosomal-dominant, late-onset Parkinson disease (PD). The family has tremor-predominant dopa-responsive parkinsonism with a mean onset of 50.6 ± 7.3 years. Exome analysis suggests that an aspartic-acid-to-asparagine mutation within vacuolar protein sorting 35 (VPS35 c.1858G>A; p.Asp620Asn) is the genetic determinant of disease. VPS35 is a central component of the retromer cargo-recognition complex, is critical for endosome-trans-golgi trafficking and membrane-protein recycling, and is evolutionarily highly conserved. VPS35 c.1858G>A was found in all affected members of the Swiss kindred and in three more families and one patient with sporadic PD, but it was not observed in 3,309 controls. Further sequencing of familial affected probands revealed only one other missense variant, VPS35 c.946C>T; (p.Pro316Ser), in a pedigree with one unaffected and two affected carriers, and thus the pathogenicity of this mutation remains uncertain. Retromer-mediated sorting and transport is best characterized for acid hydrolase receptors. However, the complex has many types of cargo and is involved in a diverse array of biologic pathways from developmental Wnt signaling to lysosome biogenesis. Our study implicates disruption of VPS35 and retromer-mediated trans-membrane protein sorting, rescue, and recycling in the neurodegenerative process leading to PD.

DNAJC13 mutations in Parkinson disease

A Saskatchewan multi-incident family was clinically characterized with Parkinson disease (PD) and Lewy body pathology. PD segregates as an autosomal-dominant trait, which could not be ascribed to any known mutation. DNA from three affected members was subjected to exome sequencing. Genome alignment, variant annotation and comparative analyses were used to identify shared coding mutations. Sanger sequencing was performed within the extended family and ethnically matched controls. Subsequent genotyping was performed in a multi-ethnic case-control series consisting of 2928 patients and 2676 control subjects from Canada, Norway, Taiwan, Tunisia, and the USA. A novel mutation in receptor-mediated endocytosis 8/RME-8 (DNAJC13 p.Asn855Ser) was found to segregate with disease. Screening of cases and controls identified four additional patients with the mutation, of which two had familial parkinsonism. All carriers shared an ancestral DNAJC13 p.Asn855Ser haplotype and claimed Dutch-German-Russian Mennonite heritage. DNAJC13 regulates the dynamics of clathrin coats on early endosomes. Cellular analysis shows that the mutation confers a toxic gain-of-function and impairs endosomal transport. DNAJC13 immunoreactivity was also noted within Lewy body inclusions. In late-onset disease which is most reminiscent of idiopathic PD subtle deficits in endosomal receptor-sorting/recycling are highlighted by the discovery of pathogenic mutations VPS35, LRRK2 and now DNAJC13. With this latest discovery, and from a neuronal perspective, a temporal and functional ecology is emerging that connects synaptic exo- and endocytosis, vesicular trafficking, endosomal recycling and the endo-lysosomal degradative pathway. Molecular deficits in these processes are genetically linked to the phenotypic spectrum of parkinsonism associated with Lewy body pathology.

Translation initiator EIF4G1 mutations in familial Parkinson disease

Genome-wide analysis of a multi-incident family with autosomal-dominant parkinsonism has implicated a locus on chromosomal region 3q26-q28. Linkage and disease segregation is explained by a missense mutation c.3614G>A (p.Arg1205His) in eukaryotic translation initiation factor 4-gamma (EIF4G1). Subsequent sequence and genotype analysis identified EIF4G1 c.1505C>T (p.Ala502Val), c.2056G>T (p.Gly686Cys), c.3490A>C (p.Ser1164Arg), c.3589C>T (p.Arg1197Trp) and c.3614G>A (p.Arg1205His) substitutions in affected subjects with familial parkinsonism and idiopathic Lewy body disease but not in control subjects. Despite different countries of origin, persons with EIF4G1 c.1505C>T (p.Ala502Val) or c.3614G>A (p.Arg1205His) mutations appear to share haplotypes consistent with ancestral founders. eIF4G1 p.Ala502Val and p.Arg1205His disrupt eIF4E or eIF3e binding, although the wild-type protein does not, and render mutant cells more vulnerable to reactive oxidative species. EIF4G1 mutations implicate mRNA translation initiation in familial parkinsonism and highlight a convergent pathway for monogenic, toxin and perhaps virally-induced Parkinson disease.

Heterozygous PINK1 p.G411S increases risk of Parkinson's disease via a dominant-negative mechanism

See Gandhi and Plun-Favreau (doi:10.1093/aww320) for a scientific commentary on this article.

Heterozygous mutations in recessive Parkinson’s disease genes have been postulated to increase disease risk. Puschmann et al. report a genetic association between heterozygous PINK1 p.G411S and Parkinson’s disease. They provide structural and functional explanations for a partial dominant-negative effect of the mutant protein, which impairs wild-type PINK1 activity through hetero-dimerization.

See Gandhi and Plun-Favreau (doi:10.1093/aww320) for a scientific commentary on this article.

It has been postulated that heterozygous mutations in recessive Parkinson’s genes may increase the risk of developing the disease. In particular, the PTEN-induced putative kinase 1 (PINK1) p.G411S (c.1231G>A, rs45478900) mutation has been reported in families with dominant inheritance patterns of Parkinson’s disease, suggesting that it might confer a sizeable disease risk when present on only one allele. We examined families with PINK1 p.G411S and conducted a genetic association study with 2560 patients with Parkinson’s disease and 2145 control subjects. Heterozygous PINK1 p.G411S mutations markedly increased Parkinson’s disease risk (odds ratio = 2.92, P = 0.032); significance remained when supplementing with results from previous studies on 4437 additional subjects (odds ratio = 2.89, P = 0.027). We analysed primary human skin fibroblasts and induced neurons from heterozygous PINK1 p.G411S carriers compared to PINK1 p.Q456X heterozygotes and PINK1 wild-type controls under endogenous conditions. While cells from PINK1 p.Q456X heterozygotes showed reduced levels of PINK1 protein and decreased initial kinase activity upon mitochondrial damage, stress-response was largely unaffected over time, as expected for a recessive loss-of-function mutation. By contrast, PINK1 p.G411S heterozygotes showed no decrease of PINK1 protein levels but a sustained, significant reduction in kinase activity. Molecular modelling and dynamics simulations as well as multiple functional assays revealed that the p.G411S mutation interferes with ubiquitin phosphorylation by wild-type PINK1 in a heterodimeric complex. This impairs the protective functions of the PINK1/parkin-mediated mitochondrial quality control. Based on genetic and clinical evaluation as well as functional and structural characterization, we established p.G411S as a rare genetic risk factor with a relatively large effect size conferred by a partial dominant-negative function phenotype.

Large-scale replication and heterogeneity in Parkinson disease genetic loci

OBJECTIVE

Eleven genetic loci have reached genome-wide significance in a recent meta-analysis of genome-wide association studies in Parkinson disease (PD) based on populations of Caucasian descent. The extent to which these genetic effects are consistent across different populations is unknown.

METHODS

Investigators from the Genetic Epidemiology of Parkinson's Disease Consortium were invited to participate in the study. A total of 11 SNPs were genotyped in 8,750 cases and 8,955 controls. Fixed as well as random effects models were used to provide the summary risk estimates for these variants. We evaluated between-study heterogeneity and heterogeneity between populations of different ancestry.

RESULTS

In the overall analysis, single nucleotide polymorphisms (SNPs) in 9 loci showed significant associations with protective per-allele odds ratios of 0.78-0.87 (LAMP3, BST1, and MAPT) and susceptibility per-allele odds ratios of 1.14-1.43 (STK39, GAK, SNCA, LRRK2, SYT11, and HIP1R). For 5 of the 9 replicated SNPs there was nominally significant between-site heterogeneity in the effect sizes (I(2) estimates ranged from 39% to 48%). Subgroup analysis by ethnicity showed significantly stronger effects for the BST1 (rs11724635) in Asian vs Caucasian populations and similar effects for SNCA, LRRK2, LAMP3, HIP1R, and STK39 in Asian and Caucasian populations, while MAPT rs2942168 and SYT11 rs34372695 were monomorphic in the Asian population, highlighting the role of population-specific heterogeneity in PD.

CONCLUSION

Our study allows insight to understand the distribution of newly identified genetic factors contributing to PD and shows that large-scale evaluation in diverse populations is important to understand the role of population-specific heterogeneity.

Novel pathogenic LRRK2 p.Asn1437His substitution in familial Parkinson's disease

Genealogical investigation of a large Norwegian family (F04) with autosomal dominant parkinsonism has identified 18 affected family members over four generations. Genetic studies have revealed a novel pathogenic LRRK2 mutation c.4309 A>C (p.Asn1437His) that co-segregates with disease manifestation (LOD = 3.15, θ = 0). Affected carriers have an early age at onset (48 ± 7.7 SD years) and are clinically asymmetric and levodopa responsive. The variant was absent in 623 Norwegian control subjects. Further screening of patients from the same population identified one additional affected carrier (1 of 692) with familial parkinsonism who shares the same haplotype. The mutation is located within the Roc domain of the protein and enhances GTP-binding and kinase activity, further implicating these activities as the mechanisms that underlie LRRK2-linked parkinsonism.

A multi-centre clinico-genetic analysis of the VPS35 gene in Parkinson disease indicates reduced penetrance for disease-associated variants

Background

Two recent studies identified a mutation (p.Asp620Asn) in the vacuolar protein sorting 35 gene as a cause for an autosomal dominant form of Parkinson disease . Although additional missense variants were described, their pathogenic role yet remains inconclusive.

Methods and results

We performed the largest multi-center study to ascertain the frequency and pathogenicity of the reported vacuolar protein sorting 35 gene variants in more than 15,000 individuals worldwide. p.Asp620Asn was detected in 5 familial and 2 sporadic PD cases and not in healthy controls, p.Leu774Met in 6 cases and 1 control, p.Gly51Ser in 3 cases and 2 controls. Overall analyses did not reveal any significant increased risk for p.Leu774Met and p.Gly51Ser in our cohort.

Conclusions

Our study apart from identifying the p.Asp620Asn variant in familial cases also identified it in idiopathic Parkinson disease cases, and thus provides genetic evidence for a role of p.Asp620Asn in Parkinson disease in different populations worldwide.

Independent and joint effects of the MAPT and SNCA genes in Parkinson disease

OBJECTIVE

We studied the independent and joint effects of the genes encoding alpha-synuclein (SNCA) and microtubule-associated protein tau (MAPT) in Parkinson disease (PD) as part of a large meta-analysis of individual data from case-control studies participating in the Genetic Epidemiology of Parkinson's Disease (GEO-PD) consortium.

METHODS

Participants of Caucasian ancestry were genotyped for a total of 4 SNCA (rs2583988, rs181489, rs356219, rs11931074) and 2 MAPT (rs1052553, rs242557) single nucleotide polymorphism (SNPs). Individual and joint effects of SNCA and MAPT SNPs were investigated using fixed- and random-effects logistic regression models. Interactions were studied on both a multiplicative and an additive scale, and using a case-control and case-only approach.

RESULTS

Fifteen GEO-PD sites contributed a total of 5,302 cases and 4,161 controls. All 4 SNCA SNPs and the MAPT H1-haplotype-defining SNP (rs1052553) displayed a highly significant marginal association with PD at the significance level adjusted for multiple comparisons. For SNCA, the strongest associations were observed for SNPs located at the 3' end of the gene. There was no evidence of statistical interaction between any of the 4 SNCA SNPs and rs1052553 or rs242557, neither on the multiplicative nor on the additive scale.

INTERPRETATION

This study confirms the association between PD and both SNCA SNPs and the H1 MAPT haplotype. It shows, based on a variety of approaches, that the joint action of variants in these 2 loci is consistent with independent effects of the genes without additional interacting effects.

Germline mutation induction at mouse repeat DNA loci by chemical mutagens

Mutation rates at two expanded simple tandem repeat (ESTR) loci were studied in the germline of male mice exposed to two monofunctional alkylating agents, ethylnitrosourea (ENU) and isopropyl methanesulfonate (iPMS), and a topoisomerase II inhibitor, etoposide. Pre-meiotic exposure to the alkylating agents resulted in a highly significant increase in ESTR mutation rate, but did not alter post-meiotically exposed cells. Pre-meiotic mutation induction by ENU and iPMS was linear within the interval of doses from 12.5 to 25mg/kg and reached a plateau at higher concentrations. Paternal exposure to etoposide resulted in ESTR mutation induction at meiotic stages but did not affect post- or pre-meiotic cells. The pattern of ESTR mutation induction after pre-meiotic and meiotic exposure to chemical mutagens was similar to that previously obtained by various traditional approaches for monitoring germline mutation in mice. The results of this study show that ESTR loci provide a new efficient experimental system for monitoring the genetic effects of chemical mutagens, capable of detecting increases in mutation rates at low doses of exposure.

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

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

Nuclear Receptor NR1H3 in Familial Multiple Sclerosis

Multiple sclerosis (MS) is an inflammatory disease characterized by myelin loss and neuronal dysfunction. Despite the aggregation observed in some families, pathogenic mutations have remained elusive. In this study, we describe the identification of NR1H3 p.Arg415Gln in seven MS patients from two multi-incident families presenting severe and progressive disease, with an average age at onset of 34 years. Additionally, association analysis of common variants in NR1H3 identified rs2279238 conferring a 1.35-fold increased risk of developing progressive MS. The p.Arg415Gln position is highly conserved in orthologs and paralogs, and disrupts NR1H3 heterodimerization and transcriptional activation of target genes. Protein expression analysis revealed that mutant NR1H3 (LXRA) alters gene expression profiles, suggesting a disruption in transcriptional regulation as one of the mechanisms underlying MS pathogenesis. Our study indicates that pharmacological activation of LXRA or its targets may lead to effective treatments for the highly debilitating and currently untreatable progressive phase of MS.

Genome-wide association study in essential tremor identifies three new loci

We conducted a genome-wide association study of essential tremor, a common movement disorder characterized mainly by a postural and kinetic tremor of the upper extremities. Twin and family history studies show a high heritability for essential tremor. The molecular genetic determinants of essential tremor are unknown. We included 2807 patients and 6441 controls of European descent in our two-stage genome-wide association study. The 59 most significantly disease-associated markers of the discovery stage were genotyped in the replication stage. After Bonferroni correction two markers, one (rs10937625) located in the serine/threonine kinase STK32B and one (rs17590046) in the transcriptional coactivator PPARGC1A were associated with essential tremor. Three markers (rs12764057, rs10822974, rs7903491) in the cell-adhesion molecule CTNNA3 were significant in the combined analysis of both stages. The expression of STK32B was increased in the cerebellar cortex of patients and expression quantitative trait loci database mining showed association between the protective minor allele of rs10937625 and reduced expression in cerebellar cortex. We found no expression differences related to disease status or marker genotype for the other two genes. Replication of two lead single nucleotide polymorphisms of previous small genome-wide association studies (rs3794087 in SLC1A2, rs9652490 in LINGO1) did not confirm the association with essential tremor.

DNM3 and genetic modifiers of age of onset in LRRK2 Gly2019Ser parkinsonism: a genome-wide linkage and association study

BACKGROUND

Leucine-rich repeat kinase 2 (LRRK2) mutation 6055G→A (Gly2019Ser) accounts for roughly 1% of patients with Parkinson's disease in white populations, 13-30% in Ashkenazi Jewish populations, and 30-40% in North African Arab-Berber populations, although age of onset is variable. Some carriers have early-onset parkinsonism, whereas others remain asymptomatic despite advanced age. We aimed to use a genome-wide approach to identify genetic variability that directly affects LRRK2 Gly2019Ser penetrance.

METHODS

Between 2006 and 2012, we recruited Arab-Berber patients with Parkinson's disease and their family members (aged 18 years or older) at the Mongi Ben Hamida National Institute of Neurology (Tunis, Tunisia). Patients with Parkinson's disease were diagnosed by movement disorder specialists in accordance with the UK Parkinson's Disease Society Brain Bank criteria, without exclusion of familial parkinsonism. LRRK2 carrier status was confirmed by Sanger sequencing or TaqMan SNP assays-on-demand. We did genome-wide linkage analysis using data from multi-incident Arab-Berber families with Parkinson's disease and LRRK2 Gly2019Ser (with both affected and unaffected family members). We assessed Parkinson's disease age of onset both as a categorical variable (dichotomised by median onset) and as a quantitative trait. We used data from another cohort of unrelated Tunisian LRRK2 Gly2019Ser carriers for subsequent locus-specific genotyping and association analyses. Whole-genome sequencing in a subset of 14 unrelated Arab-Berber individuals who were LRRK2 Gly2019Ser carriers (seven with early-onset disease and seven elderly unaffected individuals) subsequently informed imputation and haplotype analyses. We replicated the findings in separate series of LRRK2 Gly2019Ser carriers originating from Algeria, France, Norway, and North America. We also investigated associations between genotype, gene, and protein expression in human striatal tissues and murine LRRK2 Gly2019Ser cortical neurons.

FINDINGS

Using data from 41 multi-incident Arab-Berber families with Parkinson's disease and LRRK2 Gly2019Ser (150 patients and 103 unaffected family members), we identified significant linkage on chromosome 1q23.3 to 1q24.3 (non-parametric logarithm of odds score 2·9, model-based logarithm of odds score 4·99, θ=0 at D1S2768). In a cohort of unrelated Arab-Berber LRRK2 Gly2019Ser carriers, subsequent association mapping within the linkage region suggested genetic variability within DNM3 as an age-of-onset modifier of disease (n=232; rs2421947; haplotype p=1·07 × 10^-7). We found that DNM3 rs2421947 was a haplotype tag for which the median onset of LRRK2 parkinsonism in GG carriers was 12·5 years younger than that of CC carriers (Arab-Berber cohort, hazard ratio [HR] 1·89, 95% CI 1·20-2·98). Replication analyses in separate series from Algeria, France, Norway, and North America (n=263) supported this finding (meta-analysis HR 1·61, 95% CI 1·15-2·27, p=0·02). In human striatum, DNM3 expression varied as a function of rs2421947 genotype, and dynamin-3 localisation was perturbed in murine LRRK2 Gly2019Ser cortical neurons.

INTERPRETATION

Genetic variability in DNM3 modifies age of onset for LRRK2 Gly2019Ser parkinsonism and informs disease-relevant translational neuroscience. Our results could be useful in genetic counselling for carriers of this mutation and in clinical trial design.

FUNDING

The Canada Excellence Research Chairs (CERC), Leading Edge Endowment Fund (LEEF), Don Rix BC Leadership Chair in Genetic Medicine, National Institute on Aging, National Institute of Neurological Disorders and Stroke, the Michael J Fox Foundation, Mayo Foundation, the Roger de Spoelberch Foundation, and GlaxoSmithKline.

Defining neurodegeneration on Guam by targeted genomic sequencing

OBJECTIVE

Amyotrophic lateral sclerosis/parkinsonism-dementia complex has been described in Guam, Western Papua, and the Kii Peninsula of Japan. The etiology and pathogenesis of this complex neurodegenerative disease remains enigmatic.

METHODS

In this study, we have used targeted genomic sequencing to evaluate the contribution of genetic variability in the pathogenesis of amyotrophic lateral sclerosis, parkinsonism, and dementia in Guamanian Chamorros.

RESULTS

Genes previously linked to or associated with amyotrophic lateral sclerosis, parkinsonism, dementia, and related neurodegenerative syndromes were sequenced in Chamorro subjects living in the Mariana Islands. Homozygous PINK1 p.L347P, heterozygous DCTN1 p.T54I, FUS p.P431L, and HTT (42 CAG repeats) were identified as pathogenic mutations.

INTERPRETATION

The findings explain the clinical, pathologic, and genetic heterogeneity observed in some multi-incident families and contribute to the excess incidence of neurodegeneration previously reported on Guam.

Association of alpha-, beta-, and gamma-Synuclein with diffuse lewy body disease

OBJECTIVE

To determine the association of the genes that encode alpha-, beta-, and gamma-synuclein (SNCA, SNCB, and SNCG, respectively) with diffuse Lewy body disease (DLBD).

DESIGN

Case-control study. Subjects A total of 172 patients with DLBD consistent with a clinical diagnosis of Parkinson disease dementia/dementia with Lewy bodies and 350 clinically and 97 pathologically normal controls.

INTERVENTIONS

Sequencing of SNCA, SNCB, and SNCG and genotyping of single-nucleotide polymorphisms performed on an Applied Biosystems capillary sequencer and a Sequenom MassArray pLEX platform, respectively. Associations were determined using chi(2) or Fisher exact tests.

RESULTS

Initial sequencing studies of the coding regions of each gene in 89 patients with DLBD did not detect any pathogenic substitutions. Nevertheless, genotyping of known polymorphic variability in sequence-conserved regions detected several single-nucleotide polymorphisms in the SNCA and SNCG genes that were significantly associated with disease (P = .05 to <.001). Significant association was also observed for 3 single-nucleotide polymorphisms located in SNCB when comparing DLBD cases and pathologically confirmed normal controls (P = .03-.01); however, this association was not significant for the clinical controls alone or the combined clinical and pathological controls (P > .05). After correction for multiple testing, only 1 single-nucleotide polymorphism in SNCG (rs3750823) remained significant in all of the analyses (P = .05-.009).

CONCLUSION

These findings suggest that variants in all 3 members of the synuclein gene family, particularly SNCA and SNCG, affect the risk of developing DLBD and warrant further investigation in larger, pathologically defined data sets as well as clinically diagnosed Parkinson disease/dementia with Lewy bodies case-control series.

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.

Genetic variation of Omi/HtrA2 and Parkinson's disease

Variants in the Omi/HtrA2 gene have been nominated as a cause of Parkinson's disease. This sequencing study of Omi/HtrA2 in 95 probands with apparent autosomal dominant inheritance of Parkinson's disease did not identify any pathogenic mutations. In addition, there was no association between common variations in the Omi/HtrA2 gene and susceptibility to Parkinson's disease in any of our four patient-control series (n=2373). Taken together our results do not support a role for Omi/HtrA2 variants in the pathogenesis of Parkinson's disease.

Characterization of DCTN1 genetic variability in neurodegeneration

OBJECTIVE

Recently, mutations in DCTN1 were found to cause Perry syndrome, a parkinsonian disorder with TDP-43-positive pathology. Previously, mutations in DCTN1 were identified in a family with lower motor neuron disease, in amyotrophic lateral sclerosis (ALS), and in a family with ALS/frontotemporal dementia (FTD), suggesting a central role for DCTN1 in neurodegeneration.

METHODS

In this study we sequenced all DCTN1 exons and exon-intron boundaries in 286 samples diagnosed with Parkinson disease (PD), frontotemporal lobar degeneration (FTLD), or ALS.

RESULTS

This analysis revealed 36 novel variants (9 missense, 5 silent, and 22 noncoding). Segregation analysis in families and association studies in PD, FTLD, and ALS case-control series did not identify any variants segregating with disease or associated with increased disease risk.

CONCLUSIONS

This study suggests that pathogenic mutations in DCTN1 are rare and do not play a common role in the development of Parkinson disease, frontotemporal lobar degeneration, or amyotrophic lateral sclerosis.

An evaluation of the impact of MAPT, SNCA and APOE on the burden of Alzheimer's and Lewy body pathology

PURPOSE

The study investigates the effects of genetic factors on the pathology of Alzheimer's disease (AD) and Lewy body (LB) diseases, including Parkinson's disease and dementia with Lewy bodies.

METHODS

A multicentre autopsy series (762 brain samples) with AD, LB or vascular pathology was examined. The effects of the tau gene (MAPT) H1 haplotype, the H1 specific SNP rs242557, APOE and the α-synuclein gene (SNCA) 3'UTR SNP rs356165 on the burden of AD and LB pathology were assessed. Neurofibrillary tangles (NFTs) were counted in four brain regions, senile plaques in five and LBs in four. Braak NFT stage, brain weight and presence of vascular pathology were also documented.

RESULTS

MAPT H1 associated with lower counts of NFTs in the middle frontal (p<0.001) and inferior parietal (p=0.005) cortices, and also with lower counts of senile plaques in the motor cortex (p=0.001). Associations of MAPT H1 with increased LB counts in the middle frontal cortex (p=0.011) and inferior parietal cortex (p=0.033) were observed but were not significant after multiple testing adjustment. The APOE ε4 allele was strongly associated with overall Alzheimer type pathology (all p≤0.001). SNCA rs356165 and the MAPT H1 specific SNP rs242557 did not associate with AD or LB pathology.

CONCLUSION

This study shows for the first time that MAPT H1 is associated with reduced Alzheimer type pathology which could have important implications for the understanding of disease mechanisms and their genetic determinants.

Purinergic receptors P2RX4 and P2RX7 in familial multiple sclerosis

Genetic variants in the purinergic receptors P2RX4 and P2RX7 have been shown to affect susceptibility to multiple sclerosis (MS). In this study, we set out to evaluate whether rare coding variants of major effect could also be identified in these purinergic receptors. Sequencing analysis of P2RX4 and P2RX7 in 193 MS patients and 100 controls led to the identification of a rare three variant haplotype (P2RX7 rs140915863:C>T [p.T205M], P2RX7 rs201921967:A>G [p.N361S], and P2RX4 rs765866317:G>A [p.G135S]) segregating with disease in a multi-incident family with six family members diagnosed with MS (logarithm of odds = 3.07). Functional analysis of this haplotype in HEK293 cells revealed impaired P2X7 surface expression (P < 0.01), resulting in over 95% inhibition of adenosine triphosphate (ATP)-induced pore function (P < 0.001) and a marked reduction in phagocytic ability (P < 0.05). In addition, transfected cells showed 40% increased peak ATP-induced inward current (P < 0.01), and a greater Ca2+ response to the P2X4 135S variant compared with wild type (P < 0.0001). Our study nominates rare genetic variants in P2RX4 and P2RX7 as major genetic contributors to disease, further supporting a role for these purinergic receptors in MS and the disruption of transmembrane cation channels leading to impairment of phagocytosis as the pathological mechanisms of disease.

The effect of LRP5 polymorphisms on bone mineral density is apparent in childhood

Bone mass acquired during childhood is the primary determinant of adult bone mineral density (BMD) and osteoporosis risk. Bone accrual is subject to genetic influences. Activating and inactivating LRP5 gene mutations elicit extreme bone phenotypes, while more common LRP5 polymorphisms are associated with normal variation of BMD. Our aim was to test the hypothesis that LRP5 gene polymorphisms influence bone mass acquisition during childhood. The association between LRP5 gene polymorphisms and bone size and mineralization was examined in 819 unrelated British Caucasian children (n = 429 boys) aged 9 years. Height, weight, pubertal status (where available), total-body and spinal bone area, bone mineral content (BMC), BMD, and area-adjusted BMC (aBMC) were assessed. Dual-energy X-ray absorptiometry (DXA)-gene associations were assessed by linear regression, with adjustment for age, gender, pubertal status, and body size parameters. There were 140, 79, 12, and 2 girls who achieved Tanner stages I-IV, respectively, and 179 and 32 boys who achieved Tanner stages I and II, respectively. The rs2,306,862 (N740N) coding polymorphism in exon 10 of the LRP5 gene was associated with spinal BMD and aBMC (each P = 0.01) and total-body BMD and aBMC (P = 0.04 and 0.03, respectively). Adjusting for pubertal stage strengthened associations between this polymorphism and spinal BMD and aBMC (P = 0.01 and 0.002, respectively). Individuals homozygous for the T allele had greater spinal BMD and aBMC scores than those homozygous for the C allele. A dose effect was apparent as the mean spinal BMD and aBMC of heterozygous TC individuals were intermediate between those of their TT and CC counterparts. The N740N polymorphism in exon 10 of LRP5 was associated with spinal BMD and aBMC in pre- and early pubertal children. These results indicate that LRP5 influences volumetric bone density in childhood, possibly through effects on trabecular bone formation.

LRRK2 expression in idiopathic and G2019S positive Parkinson's disease subjects: a morphological and quantitative study

AIMS

Mutations in the gene encoding leucine-rich repeat kinase-2 (LRRK2) have been established as a common genetic cause of Parkinson's disease (PD). The distribution of LRRK2 mRNA and protein in the human brain has previously been described, although it has not been reported in PD cases with the common LRRK2 G2019S mutation.

METHODS

To further elucidate the role of LRRK2 in PD, we determined the localization of LRRK2 mRNA and protein in post-mortem brain tissue from control, idiopathic PD (IPD) and G2019S positive PD cases.

RESULTS

Widespread neuronal expression of LRRK2 mRNA and protein was recorded and no difference was observed in the morphological localization of LRRK2 mRNA or protein between control, IPD and G2019S positive PD cases. Using quantitative real-time polymerase chain reaction, we demonstrated that there is no regional variation in LRRK2 mRNA in normal human brain, but we have identified differential expression of LRRK2 mRNA with significant reductions recorded in limbic and neocortical regions of IPD cases compared with controls. Semi-quantitative analysis of LRRK2 immunohistochemical staining demonstrated regional variation in staining intensity, with weak LRRK2 immunoreactivity consistently recorded in the striatum and substantia nigra. No clear differences were identified in LRRK2 immunoreactivity between control, IPD and G2019S positive PD cases. LRRK2 protein was identified in a small proportion of Lewy bodies.

CONCLUSIONS

Our data suggest that widespread dysregulation of LRRK2 mRNA expression may contribute to the pathogenesis of IPD.

A comparative study of LRRK2, PINK1 and genetically undefined familial Parkinson's disease

Genetic classification of Parkinson's disease (PD) subtypes may become the preferred diagnostic tool for neurologists. Herein we compare clinical features from a large cohort of patients with familial PD of unknown aetiology or attributable to distinct genetic forms. Comprehensive neurological examinations were performed in 231 familial PD patients from Tunisia. Analysis was previously performed to screen for mutations in leucine rich repeat kinase 2 (LRRK2), PTEN induced kinase 1 (PINK1) and parkin (PRKN). Clinical features were compared between patients with genetically undefined PD (n=107) and those with LRRK2 (n=73) and PINK1 (n=42) mutations using regression analyses adjusted for gender, age of onset and disease duration. PRKN cases (n=9) were too few for meaningful statistical analysis. In comparison with genetically undefined patients, LRRK2 mutation carriers had more severe motor symptoms (median Unified Parkinson's Disease Rating Scale scores approximately 1.6 times higher, p<0.001), a higher rate of dyskinesia (OR 4.21, p=0.002) and use of dopamine agonists (OR 3.64, p<0.001), and less postural tremor (OR 0.21, p<0.001). PINK1 mutation carriers presented an increased rate of drug induced dyskinesia (OR 3.81, p=0.007) and a lower rate of postural tremor (OR 0.16, p<0.001) than genetically undefined patients. As expected, PINK1 patients had younger ages and ages at disease onset, and a longer disease duration compared with LRRK2 mutation carriers and genetically undefined patients. Clinical differences between LRRK2, PINK1 and genetically undefined familial PD appear more pronounced than previously appreciated, and may prove useful in clinical practice. As future therapies are targeted to specific protein abnormalities, identifying the genetic causes and associated clinical and pathological features will determine diagnosis, preventative medicine and drug intervention strategies.