Study of LRRK2 variation in tauopathy: Progressive supranuclear palsy and corticobasal degeneration.

BACKGROUND: Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) are the most common genetic cause of Parkinson's disease (PD). Unexpectedly, tau pathology has been reported in a subset of LRRK2 mutation carriers. METHODS: To estimate the frequency of pathogenic LRRK2 mutations and to evaluate the association of common LRRK2 variants with risk of primary tauopathies, we studied 1039 progressive supranuclear palsy (PSP) and 145 corticobasal degeneration patients from the Mayo Clinic Florida brain bank and 1790 controls ascertained at Mayo Clinic. Sanger sequencing of LRRK2 exons 30, 31, 35, and 41 was performed in all patients, and genotyping of all 17 known exonic variants with minor allele frequency >0.5% was performed in patients and controls. RESULTS: LRRK2 mutational screening identified 2 known pathogenic mutations (p.G2019S and p.R1441C), each in 1 PSP patient, the novel p.A1413T mutation in a PSP patient and the rare p.R1707K mutation in a corticobasal degeneration patient. Both p.A1413T and p.R1707K mutations were predicted damaging by at least 2 of 3 prediction programs and affect evolutionary conserved sites of LRRK2. Association analysis using common LRRK2 variants only showed nominal association of the p.L153L variant with PSP. CONCLUSIONS: Our study confirms the presence of pathogenic and potentially pathogenic LRRK2 mutations in pathologically confirmed primary tauopathies, albeit with low frequency. In contrast to PD, common LRRK2 variants do not appear to play a major role in determining PSP and corticobasal degeneration risk. © 2016 International Parkinson and Movement Disorder Society.

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.

LRRK2 variation and dementia with Lewy bodies.

INTRODUCTION: The leucine-rich repeat kinase 2 (LRRK2) gene contains several variants that cause Parkinson's disease (PD) and others that modify PD risk. However, little is known about the role of LRRK2 in dementia with Lewy bodies (DLB). Aims of this study were to screen DLB patients for pathogenic LRRK2 variants and to evaluate associations between common LRRK2 variants and risk of DLB. METHODS: 417 clinical DLB patients and 1790 controls were included in the primary analysis. Additionally, 355 Lewy body disease patients assessed as having a high likelihood of clinical DLB based on neuropathological findings were included in secondary analysis. Seven pathogenic LRRK2 variants were assessed in patients, while 17 common LRRK2 exonic variants and 1 GWAS-nominated common LRRK2 PD-risk variant were evaluated for association with DLB. RESULTS: We identified carriers of 2 different pathogenic LRRK2 variants. One clinical DLB patient was a p.G2019S carrier, while in the pathological high likelihood DLB series there was one carrier of the p.R1441C mutation. However, examination of clinical records revealed the p.R1441C carrier to have PD with dementia. Evaluation of common variants did not reveal any associations with DLB risk after multiple testing adjustment. However, a non-significant trend similar to that previously reported for PD was observed for the protective p.N551K-R1398H-K1423K haplotype in the clinical DLB series (OR: 0.76, P = 0.061). CONCLUSION: LRRK2 does not appear to play a major role in DLB, however further study of p.G2019S and the p.N551K-R1398H-K1423K haplotype is warranted to better understand their involvement in determining DLB risk.

RAB39B gene mutations are not a common cause of Parkinson's disease or dementia with Lewy bodies.

Mutations in Ras-related protein Rab-39B (RAB39B) gene have been linked to X-linked early-onset Parkinsonism with intellectual disabilities. The aim of this study was to address the genetic contribution of RAB39B to Parkinson's disease (PD), dementia with Lewy bodies (DLB), and pathologically confirmed Lewy body dementia (pLBD) cases. A cohort of 884 PD, 399 DLB, and 379 pLBD patients were screened for RAB39B mutations, but no coding variants were found, suggesting RAB39B mutations are not a common cause of PD, DLB, or pLBD in Caucasian population.

MAPT haplotype diversity in multiple system atrophy.

INTRODUCTION: Multiple system atrophy (MSA) is a rare progressive neurodegenerative disorder. MSA was originally considered exclusively sporadic but reports of association with genes such as SNCA, COQ2 and LRRK2 have demonstrated that there is a genetic contribution to the disease. MAPT has been associated with several neurodegenerative diseases and we previously reported a protective association of the MAPT H2 haplotype with MSA in 61 pathologically confirmed cases. METHODS: In the present study, we assessed the full MAPT haplotype diversity in MSA patients using six MAPT tagging SNPs. We genotyped a total of 127 pathologically confirmed MSA cases, 86 patients with clinically diagnosed MSA and 1312 controls. RESULTS: We identified four significant association signals in our pathologically confirmed cases, two from the protective haplotypes H2 (MSA:16.2%, CONTROLS: 22.7%, p = 0.024) and H1E (MSA:3.0%, CONTROLS: 9.0%, p = 0.014), and two from the rare risk haplotypes H1x (MSA:3.7%, CONTROLS: 1.3%, p = 0.030) and H1J (MSA:3.0%, CONTROLS: 0.9%, p = 0.021). We evaluated the association of MSA subtypes with the common protective H2 haplotype and found a significant difference with controls for MSA patients with some degree of MSA-C (MSA-C or MSA-mixed), for whom H2 occurred in only 8.6% of patients in our pathologically confirmed series (P < 0.0001). CONCLUSIONS: Our findings provide further evidence that MAPT variation is associated with risk of MSA. Interestingly, our results suggest a greater effect size in the MSA-C compared to MSA-P for H2. Additional genetic studies in larger pathologically confirmed MSA series and meta-analytic studies will be needed to fully assess the role of MAPT and other genes in MSA.

Identification of genetic modifiers of age-at-onset for familial Parkinson's disease.

Parkinson's disease (PD) is the most common cause of neurodegenerative movement disorder and the second most common cause of dementia. Genes are thought to have a stronger effect on age-at-onset of PD than on risk, yet there has been a phenomenal success in identifying risk loci but not age-at-onset modifiers. We conducted a genome-wide study for age-at-onset. We analysed familial and non-familial PD separately, per prior evidence for strong genetic effect on age-at-onset in familial PD. GWAS was conducted in 431 unrelated PD individuals with at least one affected relative (familial PD) and 1544 non-familial PD from the NeuroGenetics Research Consortium (NGRC); an additional 737 familial PD and 2363 non-familial PD were used for replication. In familial PD, two signals were detected and replicated robustly: one mapped to LHFPL2 on 5q14.1 (PNGRC = 3E-8, PReplication = 2E-5, PNGRC + Replication = 1E-11), the second mapped to TPM1 on 15q22.2 (PNGRC = 8E-9, PReplication = 2E-4, PNGRC + Replication = 9E-11). The variants that were associated with accelerated onset had low frequencies (<0.02). The LHFPL2 variant was associated with earlier onset by 12.33 [95% CI: 6.2; 18.45] years in NGRC, 8.03 [2.95; 13.11] years in replication, and 9.79 [5.88; 13.70] years in the combined data. The TPM1 variant was associated with earlier onset by 15.30 [8.10; 22.49] years in NGRC, 9.29 [1.79; 16.79] years in replication, and 12.42 [7.23; 17.61] years in the combined data. Neither LHFPL2 nor TPM1 was associated with age-at-onset in non-familial PD. LHFPL2 (function unknown) is overexpressed in brain tumours. TPM1 encodes a highly conserved protein that regulates muscle contraction, and is a tumour-suppressor gene.

TREM2 p.R47H substitution is not associated with dementia with Lewy bodies.

Dementia with Lewy bodies (DLB) is the second leading cause of neurodegenerative dementia in the elderly and is clinically characterized by the presence of cognitive decline, parkinsonism, REM sleep behavior disorder, and visual hallucinations.(1,2) At autopsy, α-synuclein-positive Lewy-related pathology is observed throughout the brain. Concomitant Alzheimer disease-related pathology including amyloid plaques and, to a lesser degree, neurofibrillary tangles are often present.(2) The clinical characteristics of DLB share overlapping features with Alzheimer disease dementia (AD) and Parkinson disease (PD). A recent genetic association study examining known hits from PD and AD identified variants at both the α-synuclein (SNCA) and APOE loci as influencing the individual risk to DLB.(3) These findings would suggest that DLB may be a distinct disease with shared genetic risk factors with PD and AD.

MAPT haplotype H1G is associated with increased risk of dementia with Lewy bodies.

INTRODUCTION: The MAPT H1 haplotype has been associated with several neurodegenerative diseases. We were interested in exploring the role of MAPT haplotypic variation in risk of dementia with Lewy bodies (DLB). METHOD: We genotyped six MAPT haplotype tagging SNPs and screened 431 clinical DLB cases, 347 pathologically defined high-likelihood DLB cases, and 1049 controls. RESULT: We performed haplotypic association tests and detected an association with the protective H2 haplotype in our combined series (odds ratio [OR] = 0.75). We fine-mapped the locus and identified a relatively rare haplotype, H1G, that is associated with an increased risk of DLB (OR = 3.30, P = .0017). This association was replicated in our pathologically defined series (OR = 2.26, P = .035). DISCUSSION: These results support a role for H1 and specifically H1G in susceptibility to DLB. However, the exact functional variant at the locus is still unknown, and additional studies are warranted to fully explain genetic risk of DLB at the MAPT locus.

Genetic susceptibility variants in parkinsonism.

Parkinsonism is an umbrella term for a group of disorders characterized by the clinical signs of tremor, bradykinesia, rigidity, and postural instability. On neuropathologic examination parkinsonism can display alternate protein pathologies (e.g. α-synucleinopathy or tauopathy) but the degeneration of nigral neurons is consistent. The main forms of parkinsonism are, Parkinson's disease (PD), Dementia with Lewy Bodies (DLB), Multiple System Atrophy (MSA), Progressive Supranuclear Palsy (PSP) and Corticobasal Degeneration (CBD). Genetic studies from candidate gene, to unbiased genome-wide approaches including association and next-generation sequencing have nominated a number of disease determinants. Within this review we will highlight the genetic loci that are associated with disease and discuss the implications and importance for a better understanding of the genes involved and thus the underlying pathophysiology of these disorders.

Mitochondrial targeting sequence variants of the CHCHD2 gene are a risk for Lewy body disorders.

OBJECTIVE: To assess the role of CHCHD2 variants in patients with Parkinson disease (PD) and Lewy body disease (LBD) in Caucasian populations. METHODS: All exons of the CHCHD2 gene were sequenced in a US Caucasian patient-control series (878 PD, 610 LBD, and 717 controls). Subsequently, exons 1 and 2 were sequenced in an Irish series (355 PD and 365 controls) and a Polish series (394 PD and 350 controls). Immunohistochemistry and immunofluorescence studies were performed on pathologic LBD cases with rare CHCHD2 variants. RESULTS: We identified 9 rare exonic variants of unknown significance. These variants were more frequent in the combined group of PD and LBD patients compared to controls (0.6% vs 0.1%, p = 0.013). In addition, the presence of any rare variant was more common in patients with LBD (2.5% vs 1.0%, p = 0.050) compared to controls. Eight of these 9 variants were located within the gene's mitochondrial targeting sequence. CONCLUSIONS: Although the role of variants of the CHCHD2 gene in PD and LBD remains to be further elucidated, the rare variants in the mitochondrial targeting sequence may be a risk factor for Lewy body disorders, which may link CHCHD2 to other genetic forms of parkinsonism with mitochondrial dysfunction.

Role for the microtubule-associated protein tau variant p.A152T in risk of α-synucleinopathies.

OBJECTIVE: To assess the importance of MAPT variant p.A152T in the risk of synucleinopathies. METHODS: In this case-control study, we screened a large global series of patients and controls, and assessed associations between p.A152T and disease risk. We included 3,229 patients with clinical Parkinson disease (PD), 442 with clinical dementia with Lewy bodies (DLB), 181 with multiple system atrophy (MSA), 832 with pathologically confirmed Lewy body disease (LBD), and 2,456 healthy controls. RESULTS: The minor allele frequencies (MAF) in clinical PD cases (0.28%) and in controls (0.2%) were not found to be significantly different (odds ratio [OR] 1.37, 95% confidence interval [CI] 0.63-2.98, p = 0.42). However, a significant association was observed with clinical DLB (MAF 0.68%, OR 5.76, 95% CI 1.62-20.51, p = 0.007) and LBD (MAF 0.42%, OR 3.55, 95% CI 1.04-12.17, p = 0.04). Additionally, p.A152T was more common in patients with MSA compared to controls (MAF 0.55%, OR 4.68, 95% CI 0.85-25.72, p = 0.08) but this was not statistically significant and therefore should be interpreted with caution. CONCLUSIONS: Overall, our findings suggest that MAPT p.A152T is a rare low penetrance variant likely associated with DLB that may be influenced by coexisting LBD and AD pathology. Given the rare nature of the variant, further studies with greater sample size are warranted and will help to fully explain the role of p.A152T in the pathogenesis of the synucleinopathies.

Exonic Re-Sequencing of the Chromosome 2q24.3 Parkinson's Disease Locus.

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.

VPS35 and DNAJC13 disease-causing variants in essential tremor.

Exome-sequencing analyses have identified vacuolar protein sorting 35 homolog (VPS35) and DnaJ (Hsp40) homolog, subfamily C, member 13 (DNAJC13) harboring disease-causing variants for Parkinson disease (PD). Owing to the suggested clinical, pathological and genetic overlap between PD and essential tremor (ET) we assessed the presence of two VPS35 and DNAJC13 disease-causing variants in ET patients. TaqMan probes were used to genotype VPS35 c.1858G>A (p.(D620N)) (rs188286943) and DNAJC13 c.2564A>G (p.(N855S)) (rs387907571) in 571 ET patients of European descent, and microsatellite markers were used to define the disease haplotype in variant carriers. Genotyping of DNAJC13 identified two ET patients harboring the c.2564A>G (p.(N855S)) variant previously identified in PD patients. Both patients appear to share the disease haplotype previously reported. ET patients with the VPS35 c.1858G>A (p.(D620N)) variants were not observed. Although a genetic link between PD and ET has been suggested, DNAJC13 c.2564A>G (p.(N855S)) represents the first disease-causing variant identified in both, and suggests the regulation of clathrin dynamics and endosomal trafficking in the pathophysiology of a subset of ET patients.

LRRK2 exonic variants and risk of multiple system atrophy.

OBJECTIVE: 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). METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.

Analysis of COQ2 gene in multiple system atrophy.

BACKGROUND: 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. RESULTS: 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. CONCLUSIONS: 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.

Protective effect of LRRK2 p.R1398H on risk of Parkinson's disease is independent of MAPT and SNCA variants.

The best validated susceptibility variants for Parkinson's disease are located in the α-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 4 SNCA variants (rs181489, rs356219, rs11931074, and rs2583988), the MAPT H1-haplotype-defining variant rs1052553, and LRRK2 p.R1398H (rs7133914) in Caucasian (n = 10,322) and Asian (n = 2289) 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 Parkinson's disease is independent of SNCA and MAPT variants, and vice versa, in Caucasian and Asian populations.

SLC1A2 rs3794087 does not associate with essential tremor.

A recent genome-wide association study of patients with essential tremor (ET) from Germany has nominated SLC1A2 rs3794087 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 rs3794087 in a North American series consisting of 1347 patients with ET and controls. Statistical analysis did not identify significant differences in genotype or allele frequencies between healthy controls and patients with ET (p > 0.36). These findings therefore do not support a role for SLC1A2 rs3794087 in susceptibility to ET in the North American population. Further studies in ethnically distinct populations of patients with ET are necessary to understand whether genetic variability in SLC1A2 affects disease risk for ET.

GWAS risk factors in Parkinson's disease: LRRK2 coding variation and genetic interaction with PARK16.

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.

NOTCH3 variants and risk of ischemic stroke.

BACKGROUND: 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. METHODS: 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). RESULTS: 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. CONCLUSION: 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.

Population-specific frequencies for LRRK2 susceptibility variants in the Genetic Epidemiology of Parkinson's Disease (GEO-PD) Consortium.

BACKGROUND: 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 disease susceptibility displays many features that reflect the nature of complex, late-onset sporadic disorders like Parkinson's disease. METHODS: 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. RESULTS: Herein, we detail the allele frequencies for the novel risk factors (p.A419V and p.M1646T) and the protective haplotype (p.N551K-R1398H-K1423K) nominated in the original publication. Simple population allele frequencies not only can provide insight into the clinical relevance of specific variants but also can help genetically define patient groups. CONCLUSIONS: Establishing individual patient-based genomic susceptibility profiles that incorporate both risk factors and protective factors will determine future diagnostic and treatment strategies.