Genome-wide association studies (GWAS) in Parkinson’s disease (PD) have identified over 20 genomic regions associated with disease risk. Many of these loci include several candidate genes making it difficult to pinpoint the causal gene. The locus on chromosome 2q24.3 encompasses three genes: B3GALT1, STK39, and CERS6. In order to identify if the causal variants are simple missense changes, we sequenced all 31 exons of these three genes in 187 patients with PD. We identified 13 exonic variants including four non-synonymous and three insertion/deletion variants (indels). These non-synonymous variants and rs2102808, the GWAS tag SNP, were genotyped in three independent series consisting of a total of 1976 patients and 1596 controls. Our results show that the seven identified 2q24.3 coding variants are not independently responsible for the GWAS association signal at the locus; however, there is a haplotype, which contains both rs2102808 and a STK39 exon 1 6bp indel variant, that is significantly associated with PD risk (Odds Ratio [OR] = 1.35, 95% CI: 1.11–1.64, P = 0.003). This haplotype is more associated than each of the two variants independently (OR = 1.23, P = 0.005 and 1.10, P = 0.10, respectively). Our findings suggest that the risk variant is likely located in a non-coding region. Additional sequencing of the locus including promoter and regulatory regions will be needed to pinpoint the association at this locus that leads to an increased risk to PD.
The aim of this study was to evaluate the association between common exonic variants in the leucine-rich repeat kinase 2 (LRRK2) gene and risk of multiple system atrophy (MSA).
One series from the United States (92 patients with pathologically confirmed MSA, 416 controls) and a second series from the United Kingdom (85 patients with pathologically confirmed MSA, 352 controls) were included in this case-control study. We supplemented these data with those of 53 patients from the United States with clinically probable or possible MSA. Seventeen common LRRK2 exonic variants were genotyped and assessed for association with MSA.
In the combined series of 177 patients with pathologically confirmed MSA and 768 controls, there was a significant association between LRRK2 p.M2397T and MSA (odds ratio [OR] = 0.60, p = 0.002). This protective effect was observed more strongly in the US series (OR = 0.46, p = 0.0008) than the UK series (OR = 0.82, p = 0.41). We observed other noteworthy associations with MSA for p.G1624G (OR = 0.63, p = 0.006) and p.N2081D (OR = 0.15, p = 0.010). The p.G1624G-M2397T haplotype was significantly associated with MSA in the US series (p < 0.0001) and combined series (p = 0.003) but not the UK series (p = 0.67). Results were consistent when additionally including the US patients with clinical MSA, where the strongest single-variant association was again observed for p.M2397T (OR = 0.59, p = 0.0005).
These findings provide evidence that LRRK2 exonic variants may contribute to susceptibility to MSA. Validation in other series and meta-analytic studies will be important.
A recent genome-wide association study of essential tremor (ET) patients from Germany has nominated SLC1A2 rs3764087 as a novel risk factor for disease. This association was independently replicated in the Chinese population, albeit with an opposite direction of effect. To further define the role of SLC1A2 in ET we genotyped rs3764087 in a North American series consisting of 1,356 ET patients and controls. Statistical analysis did not identify significant differences in genotype or allele frequencies between healthy controls and ET patients (p>0.36). These findings therefore do not support a role for SLC1A2 rs3764087 in the susceptibility to ET in the North American population. Further studies in ethnically distinct populations of ET patients are necessary to understand whether genetic variability in SLC1A2 affects disease risk for ET.
Essential tremor; SLC1A2; association
The best validated susceptibility variants for Parkinson’s disease (PD) are located in the alpha-synuclein (SNCA) and microtubule-associated protein tau (MAPT) genes. Recently, a protective p.N551K-R1398H-K1423K haplotype in the leucine-rich repeat kinase 2 (LRRK2) gene was identified, with p.R1398H appearing to be the most likely functional variant. To date, the consistency of the protective effect of LRRK2 p.R1398H across MAPT and SNCA variant genotypes has not been assessed. To address this, we examined four SNCA variants (rs181489, rs356219, rs11931074, rs2583988), the MAPT H1-haplotype defining variant rs1052553, and LRRK2 p.R1398H (rs7133914) in Caucasian (N=10,322) and Asian (N=2,289) series. There was no evidence of an interaction of LRRK2 p.R1398H with MAPT or SNCA variants (all P≥0.10); the protective effect of p.R1398H was observed at similar magnitude across MAPT and SNCA genotypes, and the risk effects of MAPT and SNCA variants were observed consistently for LRRK2 p.R1398H genotypes. Our results indicate that the association of LRRK2 p.R1398H with PD is independent of SNCA and MAPT variants, and vice versa, in Caucasian and Asian populations.
Parkinson disease; LRRK2; SNCA; MAPT; interaction; genetics
Loss of function COQ2 mutations results in primary CoQ10 deficiency. Recently, recessive mutations of the COQ2 gene have been identified in two unrelated Japanese families with multiple system atrophy (MSA). It has also been proposed that specific heterozygous variants in the COQ2 gene may confer susceptibility to sporadic MSA. To assess the frequency of COQ2 variants in patients with MSA, we sequenced the entire coding region and investigated all exonic copy number variants of the COQ2 gene in 97 pathologically-confirmed and 58 clinically-diagnosed MSA patients from the United States.
We did not find any homozygous or compound heterozygous pathogenic COQ2 mutations including deletion or multiplication within our series of MSA patients. In two patients, we identified two heterozygous COQ2 variants (p.S54W and c.403 + 10G > T) of unknown significance, which were not observed in 360 control subjects. We also identified one heterozygous carrier of a known loss of function p.S146N substitution in a severe MSA-C pathologically-confirmed patient.
The COQ2 p.S146N substitution has been previously reported as a pathogenic mutation in primary CoQ10 deficiency (including infantile multisystem disorder) in a recessive manner. This variant is the third primary CoQ10 deficiency mutation observed in an MSA case (p.R387X and p.R197H). Therefore it is possible that in the heterozygous state it may increase susceptibility to MSA. Further studies, including reassessing family history in patients of primary CoQ10 deficiency for the possible occurrence of MSA, are now warranted to resolve the role of COQ2 variation in MSA.
Electronic supplementary material
The online version of this article (doi:10.1186/1750-1326-9-44) contains supplementary material, which is available to authorized users.
COQ2; Multiple system atrophy; Genetics; CoQ10 deficiency
Variants within the leucine-rich repeat kinase 2 gene are recognized as the most frequent genetic cause of Parkinson’s disease. Leucine-rich repeat kinase 2 variation related to susceptibility to disease displays many features that reflect the nature of complex late-onset sporadic disorders, such as Parkinson’s disease. The Genetic Epidemiology of Parkinson’s disease consortium recently performed the largest genetic association study for variants in the leucine-rich repeat kinase 2 gene across 23 different sites in 15 countries. Herein we detail the allele frequencies for the novel risk factors (p.A419V and p.M1646T) and the protective haplotype (p.N551K-R1398H-K1423K) reported in the original publication. Simple population allele frequencies can not only provide an insight into the clinical relevance of specific variants but also help genetically define patient groups. Establishing individual patient-based genomic susceptibility profiles incorporating both risk and protective factors will determine future diagnostic and treatment strategies.
Parkinson disease; LRRK2; genetics; association study
Essential Tremor is the most common form of movement disorder. Aggregation in families suggests a strong genetic component to disease. Linkage and association studies have identified several risk loci but the specific causal variants are still unknown. A recent study using whole exome sequencing identified a rare nonsense variant in the FUS gene (p.Q290X) that segregated with Essential Tremor in a large French Canadian family. In addition, two other rare FUS variants were identified (p.R216C and p.P431L) in Essential Tremor patients however co-segregation analysis with disease was not possible. In the present study, we sequenced all 15 exons of FUS in 152 familial probands with Essential Tremor and genotyped three reported FUS variants in 112 sporadic Essential Tremor patients and 716 control subjects recruited at Mayo Clinic Florida. Only known synonymous SNPs unlikely to be pathogenic were detected in our sequencing and not any of the recently identified mutations or novel ones. We conclude that the FUS mutations associated with risk of Essential Tremor are probably a rare occurrence.
Essential tremor; Fused in Sarcoma; Parkinson disease; genetic
Progressive supranuclear palsy (PSP) is a relatively common neurodegenerative tauopathy clinically characterized by parkinsonism, axial rigidity, and supranuclear gaze palsy. Pathologic findings of PSP are neuronal loss, gliosis, and neurofibrillary tangles in basal ganglia, diencephalon, and brainstem; there is increasing recognition of clinicopathologic variants of PSP.1
Mutations of the TARDBP gene encoding TDP-43 protein have been shown to cause amyotrophic lateral sclerosis and have been reported to present with clinical heterogeneity including parkinsonism. In addition, TDP-43 pathology has been observed across a spectrum of neurodegenerative disorders, including Alzheimer’s and Parkinson’s disease. Herein we report the presence of a TDP-43 mutation in a patient with a clinical diagnosis of Parkinson’s disease. The TDP-43 p.N267S substitution has been previously implicated in both amyotrophic lateral sclerosis and behavioral variant frontotemporal dementia. Our findings widen the phenotypic presentation for the TDP-43 p.N267S substitution and support a possible role for rare TDP-43 mutations presenting with Parkinson’s disease.
TDP-43; amyotrophic lateral sclerosis; Parkinson’s disease
Genetic variation in the leucine-rich repeat and Ig domain containing 1 gene (LINGO1) was recently associated with an increased risk of developing essential tremor (ET) and Parkinson disease (PD). Herein, we performed a comprehensive study of LINGO1 and its paralog LINGO2 in ET and PD by sequencing both genes in patients (ET, n=95; PD, n=96) and by examining haplotype-tagging single-nucleotide polymorphisms (tSNPs) in a multicenter North American series of patients (ET, n=1,247; PD, n=633) and controls (n=642). The sequencing study identified six novel coding variants in LINGO1 (p.S4C, p.V107M, p.A277T, p.R423R, p.G537A, p.D610D) and three in LINGO2 (p.D135D, p.P217P, p.V565V), however segregation analysis did not support pathogenicity. The association study employed 16 tSNPs at the LINGO1 locus and 21 at the LINGO2 locus. One variant in LINGO1 (rs9652490) displayed evidence of an association with ET (odds ratio (OR)=0.63; P=0.026) and PD (OR=0.54; P=0.016). Additionally, four other tSNPs in LINGO1 and one in LINGO2 were associated with ET and one tSNP in LINGO2 associated with PD (P<0.05). Further analysis identified one tSNP in LINGO1 and two in LINGO2 which influenced age at onset of ET and two tSNPs in LINGO1 which altered age at onset of PD (P<0.05). Our results support a role for LINGO1 and LINGO2 in determining risk for and perhaps age at onset of ET and PD. Further studies are warranted to confirm these findings and to determine the pathogenic mechanisms involved.
Essential tremor; Parkinson disease; LINGO1; LINGO2; Genetic association
The hexanucleotide expanded repeat (GGGGCC) in intron 1 of the C9orf72 gene is recognized as the most common genetic form of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). However, as part of the clinical phenotype, some patients present with parkinsonism. The present study investigated the potential expansion or association of the C9orf72 repeat length with susceptibility to Parkinson’s disease and related disorders, essential tremor and restless legs syndrome. One restless legs syndrome patient was shown to harbor a repeat expansion, however on clinical follow-up this patient was observed to have developed frontotemporal dementia. There was no evidence of association of repeat length on disease risk or age-at-onset for any of the three disorders. Therefore the C9orf72 hexanucleotide repeat expansion appears to be specific to TDP-43 driven amyotrophic lateral sclerosis and dementia.
C9orf72; expanded repeat; PD; ET; RLS; genetic association
Ischemic stroke shares common traditional risk factors with coronary artery disease (CAD) and myocardial infarction (MI). This study evaluated whether genetic risk factors for CAD and MI also affect susceptibility to ischemic stroke in Caucasians and African Americans.
Included in the study were a Caucasian series (713 ischemic stroke patients, 708 controls) and a small African American series (166 ischemic stroke patients, 117 controls). Twenty single nucleotide polymorphisms (SNPs) previously shown to be associated with CAD or MI were genotyped and assessed for association with ischemic stroke and ischemic stroke subtypes using odds ratios (ORs) from multivariable logistic regression models.
In Caucasians, four SNPs on chromosome 9p21 were significantly associated with risk of cardioembolic stroke, the strongest of which was rs1333040 (OR=1.55, P=0.0007); similar but weaker trends were observed for small vessel stroke, with no associations observed regarding large vessel stroke. Chromosome 9p21 SNPs were also associated with risk of ischemic stroke in African Americans (rs1333040: OR=0.65, P=0.023; rs1333042, OR=0.55, P=0.070; rs2383207: OR=0.55, P=0.070). The PSMA6 SNP rs1048990 on chromosome 14q13 was associated with overall ischemic stroke in both Caucasians (OR: 0.80, P=0.036) and African Americans (OR: 0.31, P=0.020).
Our results provide evidence that chromosome 9p21 variants are associated with cardioembolic ischemic stroke in Caucasians and with overall ischemic stroke in African Americans. The PSMA6 variant rs1048990 also appears to affect susceptibility to ischemic stroke in both populations. These findings require validation, particularly the preliminary findings regarding African Americans given the small size of that series.
genetics; single nucleotide polymorphism; ischemic stroke; coronary artery disease; myocardial infarction
Expansions of the non-coding GGGGCC hexanucleotide repeat in the chromosome 9 open reading frame 72 (C9ORF72) gene were recently identified as the long sought-after cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) on chromosome 9p. In this study we aimed to determine whether the length of the normal - unexpanded - allele of the GGGGCC repeat in C9ORF72 plays a role in the presentation of disease or affects age at onset in C9ORF72 mutation carriers. We also studied whether the GGGGCC repeat length confers risk or affects age at onset in FTD and ALS patients without C9ORF72 repeat expansions. C9ORF72 genotyping was performed in 580 FTD, 995 ALS and 160 FTD-ALS patients and 1444 controls, leading to the identification of 211 patients with pathogenic C9ORF72 repeat expansions and an accurate quantification of the length of the normal alleles in all patients and controls. No meaningful association between the repeat length of the normal alleles of the GGGGCC repeat in C9ORF72 and disease phenotype or age at onset was observed in C9ORF72 mutation carriers or non-mutation carriers.
Amyotrophic lateral sclerosis; Frontotemporal Dementia; C9ORF72; Repeat-expansion disease; Association study
Parkinson’s disease (PD) is a multifactorial movement disorder characterized by progressive neurodegeneration. Genome-wide association studies (GWAS) have nominated over fifteen distinct loci associated with risk of PD, however the biological mechanisms by which these loci influence disease risk are mostly unknown. GWAS are only the first step in the identification of disease genes: the specific causal variants responsible for the risk within the associated loci and the interactions between them must be identified to fully comprehend their impact on the development of PD. In the present study, we first attempted to replicate the association signals of 17 PD GWAS loci in our series of 1381 patients with PD and 1328 controls. BST1, SNCA, HLA-DRA, CCDC62/HIP1R and MAPT all showed a significant association with PD under different models of inheritance and LRRK2 showed a suggestive association. We then examined the role of coding LRRK2 variants in the GWAS association signal for that gene. The previously identified LRRK2 risk mutant p.M1646T and protective haplotype p.N551K-R1398H-K1423K did not explain the association signal of LRRK2 in our series. Finally, we investigated the gene-gene interaction between PARK16 and LRRK2 that has previously been proposed. We observed no interaction between PARK16 and LRRK2 GWAS variants, but did observe a non-significant trend toward interaction between PARK16 and LRRK2 variants within the protective haplotype. Identification of causal variants and the interactions between them is the crucial next step in making biological sense of the massive amount of data generated by GWAS studies. Future studies combining larger sample sizes will undoubtedly shed light on the complex molecular interplay leading to the development of PD.
Association studies in genetics; Parkinson’s disease/Parkinsonism
Alzheimer’s disease (AD) can be classified based on the relative density of neurofibrillary tangles (NFTs) in the hippocampus and association cortices into three subtypes: typical AD, hippocampal-sparing AD (HpSp AD), and limbic-predominant AD (LP AD). AD subtypes not only have pathologic, but also demographic, clinical, and genetic differences. Neurofibrillary tangle-predominant dementia (NFTD), a disorder with NFTs relatively restricted to limbic structures, shares this feature with LP AD raising the possibility that NFTD is a variant of AD. The objective criteria for pathologic diagnosis of NFTD are not available. A goal of this study was to design a mathematical algorithm that could diagnose NFTD from NFT and senile plaque (SP) counts in hippocampus and association cortices, analogous to that used to subtype AD. Moreover, we aimed to compare pathologic, demographic, clinical, and genetic features of NFTD (n = 18) with LP AD (n = 19), as well as the other AD subtypes, typical AD (n = 52) and HpSp AD (n = 17). Using digital microscopy, we confirmed that burden of phospho-tau (CP13) and of an NFT conformational epitope (Ab39) correlated with NFT densities and showed expected patterns across AD subtypes. HpSp AD had the highest and LP AD had the lowest burden of cortical CP13 and Ab39 immunoreactivity. On the other hand, cortical β-amyloid burden did not significantly differ between AD subtypes. Semi-quantitative assessment of SPs in the basal ganglia did show HpSp AD to have significantly more frequent presence of SPs compared to typical AD, which was more frequent than LP AD. Compared to LP AD, NFTD had an older age at disease onset and shorter disease duration, as well as lower Braak NFT stage. NFTs and SPs on thioflavin-S fluorescent microscopy, as well as CP13, Ab39, and Aβ immunoreactivities were very low in the frontal cortex of NFTD, differentiating NFTD from AD subtypes, including LP AD. MAPT H1H1 genotype frequency was high (~70 %) in NFTD and LP AD, and similar to typical AD, while APOE ε4 carrier state was low in NFTD. While it shares clinical similarities with regard to female sex predominance, onset in advanced age, and a slow cognitive decline, NFTD has significant pathologic differences from LP AD, suggesting that it may not merely be a variant of AD.
Alzheimer disease; Neurofibrillary tangle-predominant dementia; APOE; Digital microscopy; MAPT; Neurofibrillary tangles; Amyloid plaques; Basal ganglia
Mutations within the NOTCH3 gene cause cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). CADASIL mutations appear to be restricted to the first twenty-four exons, resulting in the gain or loss of a cysteine amino acid. The role of other exonic NOTCH3 variation not involving cysteine residues and mutations in exons 25-33 in ischemic stroke remains unresolved.
All 33 exons of NOTCH3 were sequenced in 269 Caucasian probands from the Siblings With Ischemic Stroke Study (SWISS), a 70-center North American affected sibling pair study and 95 healthy Caucasian control subjects. Variants identified by sequencing in the SWISS probands were then tested for association with ischemic stroke using US Caucasian controls collected at the Mayo Clinic (n=654), and further assessed in a Caucasian (n=802) and African American (n=298) patient-control series collected through the Ischemic Stroke Genetics Study (ISGS).
Sequencing of the 269 SWISS probands identified one (0.4%) with small vessel type stroke carrying a known CADASIL mutation (p.R558C; Exon 11). Of the 19 common NOTCH3 variants identified, the only variant significantly associated with ischemic stroke after multiple testing adjustment was p.R1560P (rs78501403; Exon 25) in the combined SWISS and ISGS Caucasian series (Odds Ratio [OR] 0.50, P=0.0022) where presence of the minor allele was protective against ischemic stroke. Although only significant prior to adjustment for multiple testing, p.T101T (rs3815188; Exon 3) was associated with an increased risk of small-vessel stroke (OR: 1.56, P=0.008) and p.P380P (rs61749020; Exon 7) was associated with decreased risk of large-vessel stroke (OR: 0.35, P=0.047) in Caucasians. No significant associations were observed in the small African American series.
Cysteine-affecting NOTCH3 mutations are rare in patients with typical ischemic stroke, however our observation that common NOTCH3 variants may be associated with risk of ischemic stroke warrants further study.
Rare mutations in the gene encoding for tau (MAPT, microtubule-associated protein tau) cause frontotemporal dementia-spectrum (FTD-s) disorders, including FTD, progressive supranuclear palsy (PSP) and corticobasal syndrome, and a common extended haplotype spanning across the MAPT locus is associated with increased risk of PSP and Parkinson's disease. We identified a rare tau variant (p.A152T) in a patient with a clinical diagnosis of PSP and assessed its frequency in multiple independent series of patients with neurodegenerative conditions and controls, in a total of 15 369 subjects.
Tau p.A152T significantly increases the risk for both FTD-s (n = 2139, OR = 3.0, CI: 1.6–5.6, P = 0.0005) and Alzheimer's disease (AD) (n = 3345, OR = 2.3, CI: 1.3–4.2, P = 0.004) compared with 9047 controls. Functionally, p.A152T (i) decreases the binding of tau to microtubules and therefore promotes microtubule assembly less efficiently; and (ii) reduces the tendency to form abnormal fibers. However, there is a pronounced increase in the formation of tau oligomers. Importantly, these findings suggest that other regions of the tau protein may be crucial in regulating normal function, as the p.A152 residue is distal to the domains considered responsible for microtubule interactions or aggregation. These data provide both the first genetic evidence and functional studies supporting the role of MAPT p.A152T as a rare risk factor for both FTD-s and AD and the concept that rare variants can increase the risk for relatively common, complex neurodegenerative diseases, but since no clear significance threshold for rare genetic variation has been established, some caution is warranted until the findings are further replicated.
Given the overlap between Parkinson disease and essential tremor, we examined genetic variants in α-synuclein (SNCA) as risk determinants for essential tremor.
Samples from 661 essential tremor subjects and 1,316 control subjects from four participating North American sites were included in this study. Parkinson disease samples (n=427) were compared against controls for two cohorts. Twenty variants were selected for association analysis within the SNCA locus. Individual logistic regression analyses against essential tremor diagnosis and then combined using meta-analysis was run for each variant.
Our results do not show a significant association between variants in the SNCA locus and risk of essential tremor, while the established association of SNCA variants with Parkinson disease risk was observed.
While genetic factors are likely to play a large role in essential tremor pathogenesis our results do not support a role for common SNCA genetic variants in risk for essential tremor.
tremor; essential tremor; association studies in genetics; Parkinson’s disease; parkinsonism; synuclein
Leucine-rich repeat kinase 2 (LRRK2) is known to harbor highly penetrant mutations linked to familial parkinsonism. However, its full polymorphic variability in relationship to Parkinson’s disease (PD) risk has not been systematically assessed.
We examined the frequency pathogenicity of 121 exonic LRRK2 variants in three ethnic series (Caucasian [N=12,590], Asian [N=2,338] and Arab-Berber [N=612]) consisting of 8,611 patients and 6,929 control subjects from 23 separate sites of the Genetic Epidemiology of Parkinson’s Disease Consortium.
Excluding carriers of previously known pathogenic mutations, new independent risk associations were found for polymorphic variants in Caucasian (p.M1646T, OR: 1.43, 95% CI: 1.15 – 1.78, P=0.0012) and Asian (p.A419V, OR: 2.27, 95% CI: 1.35 – 3.83, P=0.0011) populations. In addition, a protective haplotype was observed at >5% frequency (p.N551K-p.R1398H-p.K1423K) in the Caucasian and Asian series’, with a similar finding in the small Arab-Berber series that requires further study (combined 3-series OR: 0.82, 95% CI: 0.72 – 0.94, P=0.0043). Of the two previously reported Asian risk variants p.G2385R was found to be associated with disease (OR: 1.73, 95% CI: 1.20 – 2.49, P=0.0026) but no association was observed for p.R1628P (OR: 0.62, 95% CI: 0.36 – 1.07, P=0.087). Also in the Arab-Berber series, p.Y2189C showed potential evidence of risk association with PD (OR: 4.48, 95% CI: 1.33 – 15.09, P=0.012). Of note, two variants (p.I1371V and p.T2356I) which have been previously proposed as pathogenic were observed in patient and control subjects at the same frequency.
LRRK2 offers an example where multiple rare and common genetic variants in the same gene have independent effects on disease risk. Lrrk2, and the pathway in which it functions, is important in the etiology and pathogenesis of a greater proportion of patients with PD than previously believed.
The present study and original funding for the GEO-PD Consortium was supported by grants from Michael J. Fox Foundation. Studies at individual sites were supported by a number of funding agencies world-wide.
Parkinson disease; LRRK2; genetics
Expanded glutamine repeats of the ataxin-2 (ATXN2) protein cause spinocerebellar ataxia type 2 (SCA2), a rare neurodegenerative disorder. More recent studies have suggested that expanded ATXN2 repeats are a genetic risk factor for amyotrophic lateral sclerosis (ALS) via an RNA-dependent interaction with TDP-43. Given the phenotypic diversity observed in SCA2 patients, we set out to determine the polymorphic nature of the ATXN2 repeat length across a spectrum of neurodegenerative disorders. In this study, we genotyped the ATXN2 repeat in 3919 neurodegenerative disease patients and 4877 healthy controls and performed logistic regression analysis to determine the association of repeat length with the risk of disease. We confirmed the presence of a significantly higher number of expanded ATXN2 repeat carriers in ALS patients compared with healthy controls (OR = 5.57; P= 0.001; repeat length >30 units). Furthermore, we observed significant association of expanded ATXN2 repeats with the development of progressive supranuclear palsy (OR = 5.83; P= 0.004; repeat length >30 units). Although expanded repeat carriers were also identified in frontotemporal lobar degeneration, Alzheimer's and Parkinson's disease patients, these were not significantly more frequent than in controls. Of note, our study identified a number of healthy control individuals who harbor expanded repeat alleles (31–33 units), which suggests caution should be taken when attributing specific disease phenotypes to these repeat lengths. In conclusion, our findings confirm the role of ATXN2 as an important risk factor for ALS and support the hypothesis that expanded ATXN2 repeats may predispose to other neurodegenerative diseases, including progressive supranuclear palsy.
A variety of definitions of successful aging have been proposed, many of which relate to longevity, freedom from disease and disability, or preservation of high physical and cognitive function. Many behavioral, biomedical, and psychological factors have been linked with these various measures of successful aging, however genetic predictors are less understood. Parkinson's disease (PD) is an age-related neurodegenerative disorder, and variants in the α-synuclein gene (SNCA) affect susceptibility to PD. This exploratory study examined whether SNCA variants may also promote successful aging as defined by survival without neurological disease.
We utilized 769 controls without neurological disease (Mean age: 79 years, Range: 33–99 years) and examined the frequency of 20 different SNCA variants across age groups using logistic regression models. We also included 426 PD cases to assess the effect of these variants on PD risk.
There was a significant decline in the proportion of carriers of the minor allele of rs10014396 as age increased (P = 0.021), from 30% in controls younger than 60 to 14% in controls 90 years of age or older. Findings were similar for rs3775439, where the proportion of carriers of the minor allele declined from 32% in controls less than 60 years old to 19% in those 90 or older (P = 0.025). A number of SNCA variants, not including rs10014396 or rs3775439, were significantly associated with susceptibility to PD.
In addition to its documented roles in PD and α-synucleinopathies, our results suggest that SNCA has a role in survival free of neurological disease. Acknowledging that our findings would not have withstood correction for multiple testing, validation in an independent series of aged neurologically normal controls is needed.
A role for the immune system in the pathogenesis of Parkinson’s Disease (PD) has previously been suggested. A recent genome-wide association (GWA) study identified an association between one single nucleotide polymorphism (SNP) in the human leucocyte antigen (HLA) region (HLA-DRA rs3129882) and PD in a population of American patients with European ancestry. In that study, the minor rs3129882 allele (G) was associated with an increased risk of PD under an additive model. Due to the increased likelihood of obtaining false positive results in GWA studies compared to studies conducted based on a hypothesis-driven approach, repeated validation of findings from GWA studies are necessary. Herein, we evaluated the association between rs3129882 and PD in three different Caucasian patient-control series (combined 1,313 patients and 1,305 controls) from the US, Ireland, and Poland. We observed no association (OR: 0.96, P=0.50) between rs3129882 and PD when analyzing our data under an additive or dominant model. In contrast, when examined under a recessive model, the GG genotype was observed to be protective in the Irish (OR: 0.55, P=0.008), Polish (OR: 0.67, P=0.040) and combined (OR: 0.75, P=0.006) patient-control series. In view of these diverging results, the exact role of genetic variation at the HLA region and susceptibility to PD remains to be resolved.
Association studies; Parkinson’s disease; Human leukocyte antigen; HLA; HLA-DRA; Immune system; Genetics
We studied the independent and joint effects of the genes encoding alpha-synuclein (SNCA) and microtubule associated protein tau (MAPT) in Parkinson's 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.
Participants of Caucasian ancestry were genotyped for a total of four SNCA (rs2583988, rs181489, rs356219, rs11931074) and two MAPT (rs1052553, rs242557) SNPs. Individual and joint effects of SNCA and MAPT SNPs were investigated using fixed- and random-effects logistic regression models. Interactions were studied both on a multiplicative and an additive scale, and using a case-control and case-only approach.
Fifteen GEO-PD sites contributed a total of 5302 cases and 4161 controls. All four 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 four SNCA SNPs and rs1052553 or rs242557, neither on the multiplicative nor on the additive scale.
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 two loci is consistent with independent effects of the genes without additional interacting effects.
Parkinson disease; SNCA; MAPT; genetics; interaction; case-control
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 C>A (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 (1/692) 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.
LRRK2; Parkinson’s disease; genetic; kinase
LRRK2 mutations are recognized as the most frequent genetic cause of both familial and sporadic parkinsonism identified to date. A remarkable feature of this form of parkinsonism is the variable penetrance of symptom manifestation resulting in a wide range of age-at-onset in patients. Herein we use a functional approach to identify the Lrrk1 protein as a potential disease modifier demonstrating an interaction and heterodimer formation with Lrrk2. In addition, evaluation of LRRK1 variants in our large Lrrk2 p.G2019S-parkinsonism series from a Tunisian (n=145) identified a missense mutation (p.L416M) resulting in an average 6.2 years younger age at disease onset. In conclusion we show for the first time that the interaction of Lrrk1-Lrrk2 can form protein dimers and this interaction may influence the age of symptomatic manifestation in Lrrk2-parkinsonism patients.
LRRK2; PD; Dimerization; Genetics; p.G2019S