LRRK2 p.G2019S Mutation Is Not Common among Alzheimer’s Disease Patients in Brazil

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene have emerged as a potential common cause for both sporadic and familial Parkinson’s Disease (PD) in different populations. The pleomorphic features exhibited by LRRK2 mutation carriers and the central role of Lrrk2 protein in the proper functioning of central nervous system suggest that mutations in this protein might be involved in multiple cellular processes leading to other neurodegenerative disorders than PD. The location of LRRK2 gene on chromosome 12, close to a linkage peak for familial late-onset Alzheimer’s Disease (AD), highlights that LRRK2 mutations might be involved in AD pathogenesis. We screened the most common LRRK2 mutation (p.G2019S) in a series of 180 consecutive patients clinically diagnosed with Alzheimer Disease (AD). We identified the p.G2019S in one AD patient with no PD signs, indicating that this mutation is not a common etiological factor for AD in our population (0.5%), corroborating recent data found in Norwegian, North American, Chinese and Italian populations. Nevertheless, these observations together with new information about the Lrrk2 critical multifunctionality do not rule out the possible influence of other variants within LRRK2 in AD, so that other screenings focusing in the whole extension of the LRRK2 using larger sized confirmed AD sample are urgently needed.     

No association of the LRRK2 genetic variants with Alzheimer's disease in Han Chinese individuals

The leucine-rich repeat kinase–2 (LRRK2) gene has been regarded as 1 of the most common genetic causes of Parkinson's disease (PD). We hypothesized that LRRK2-susceptible allele(s) for PD might pose a risk for Alzheimer's disease (AD). In this study, we screened 12 LRRK2 gene variants in 2 independent cohorts from southwestern China (341 AD patients and 435 normal individuals) and eastern China (297 AD patients and 384 normal individuals), to discern the potential association between this gene and AD. No variant was identified to be associated with AD in either case-control sample. As both of the cohorts were of Han Chinese origin, we combined the LRRK2 variant data for the 2 sample sets together (a total of 638 AD patients and 819 normal individuals) and still found no association between the LRRK2 gene and AD, suggesting that LRRK2 gene variants may not affect the development of AD in Han Chinese individuals.     

Variants in the LRRK1 gene and susceptibility to Parkinson's disease in Norway

The discovery of LRRK2 gene mutations in late-onset Parkinson's disease (PD) has irrevocably established the role of genetics in the etiology of PD. The LRRK1 gene is the single homolog of LRRK2. A high degree of homology exists between LRRK1 and LRRK2, indicative of shared functions and/or pathways. One study has examined LRRK1 in familial parkinsonism by complete sequencing of the gene, reporting 4 novel non-synonymous coding variants within the LRRK1 gene. One of these variants (ss65713826) was identified in a Norwegian proband. We investigated whether five common polymorphisms or these recently identified coding changes within LRRK1 are associated with PD in the Norwegian population. Two rare coding variants ss65713826 and ss65713830 were more frequent in patients than controls. However, their identification in healthy controls and lack of co-segregation with disease suggests they may represent benign polymorphisms.     

The dardarin G 2019 S mutation is a common cause of Parkinson's disease but not other neurodegenerative diseases

Mutations in the leucine-rich kinase 2 gene (LRRK 2) encoding dardarin, on chromosome 12, are a common cause of familial and sporadic Parkinson's disease. The most common mutation, a heterozygous 6055 G>A transition (G 2019 S) accounts for approximately 3--10% of familial Parkinson's disease and 1--8% sporadic Parkinson's disease in several European-derived populations. Some families with disease caused by LRRK 2 mutations have been reported to include patients with highly variable clinical and pathological features. We screened for the most common LRRK 2 mutation in a series of patients with Parkinson's Disease, Alzheimer's disease, Progressive Supranuclear Palsy, Multiple System Atrophy and frontotemporal dementia, as well as in neurologically normal controls. The mutation was found only in Parkinson's disease patients or their relatives and not in those with other neurodegenerative disease.     

Deep sequencing of the LRRK2 gene in 14,002 individuals reveals evidence of purifying selection and independent origin of the p.Arg1628Pro mutation in Europe

Genetic variation in LRRK2 predisposes to Parkinson disease (PD), which underpins its development as a therapeutic target. Here, we aimed to identify novel genotype-phenotype associations that might support developing LRRK2 therapies for other conditions. We sequenced the 51 exons of LRRK2 in cases comprising 12 common diseases (n = 9,582), and in 4,420 population controls. We identified 739 single-nucleotide variants, 62% of which were observed in only one person, including 316 novel exonic variants. We found evidence of purifying selection for the LRRK2 gene and a trend suggesting that this is more pronounced in the central (ROC-COR-kinase) core protein domains of LRRK2 than the flanking domains. Population genetic analyses revealed that LRRK2 is not especially polymorphic or differentiated in comparison to 201 other drug target genes. Among Europeans, we identified 17 carriers (0.13%) of pathogenic LRRK2 mutations that were not significantly enriched within any disease or in those reporting a family history of PD. Analysis of pathogenic mutations within Europe reveals that the p.Arg1628Pro (c4883G>C) mutation arose independently in Europe and Asia. Taken together, these findings demonstrate how targeted deep sequencing can help to reveal fundamental characteristics of clinically important loci.     

Comprehensive analysis of LRRK2 in publicly available Parkinson's disease cases and neurologically normal controls

Mutation of LRRK2, encoding dardarin, is the most common known genetic cause of Parkinson's disease (PD). The large size of this gene and the relative ease with which the most common mutations can be screened means that although more than 50 LRRK2 screening papers have been published, few have analyzed the entire coding sequence. Furthermore, no comprehensive sequence-based analysis has been performed on control samples. Here, we present sequencing of all coding exons in a series of 275 PD cases and 275 neurologically normal controls and analysis of the LRRK2 locus for whole gene multiplications or deletions. We also present case-control SNP association results using 74 SNPs genotyped across LRRK2. We identified six novel disease-associated missense mutations, including two that altered the same residue of the protein. These data and analysis of previously reported disease-segregating mutations shows that the majority of disease-causing mutations lie in the C-terminal half of the protein.     

A novel mutation in the PSEN2 gene (N141Y) associated with early-onset autosomal dominant Alzheimer's disease in a Chinese Han family

The mutations in the presenilin 2 (PSEN2) gene as causes of early-onset familial Alzheimer's disease (AD) have never been reported in Asia. We conducted a phenotype and pedigree study by performing neuropathological examination and target region sequencing in a family of 3 generations. Six members in this family developed dementia in their fifth decade and died in their sixth decade. The proband was diagnosed clinically with AD, which was confirmed by an autopsy. Target region sequencing showed a novel missense mutation at codon 141 (N141Y) of the PSEN2 gene that predicts an Asparagine-to-Tyrosine substitution in the affected individuals. The result was validated by Sanger sequencing in 7 family members (2 affected and 5 unaffected). The mutation was absent in the 5 clinically unaffected relatives and 188 control subjects. No influence of the APOE genotype was observed. We are the first to demonstrate a novel PSEN2 N141Y mutation in a Chinese Han family with early-onset AD.     

Mutational analysis in early-onset familial Alzheimer's disease in Mainland China

Mutations of 3 causative genes, namely presenilin 1 (PSEN1), presenilin 2 (PSEN2), and amyloid precursor protein (APP), have been identified as the major causes of early-onset familial Alzheimer's disease (EOFAD). Recently, a GGGGCC repeat expansion in the noncoding region of C9orf72 was also detected in some patients with clinically diagnosed familial Alzheimer's disease. The prevalence of causative gene mutations in patients with EOFAD has been reported in previous studies but their prevalence remains unclear in Mainland China. The aim of this study was to characterize the common causative gene mutation spectrum and genotype-phenotype correlations in Chinese patients with EOFAD. Genetic screening for mutations in PSEN1, PSEN2, and APP was conducted in a total of 32 families with clinical diagnoses of EOFAD from Mainland China. Subsequently, a hexanucleotide repeat expansion in C9orf72 was detected in all patients. Four novel mutations in PSEN1 (p.A434T, p.I167del, p.F105C, and p.L248P) were identified in 4 respective families, and 1 previously recognized pathogenic mutation in APP (p.V717I) was detected in another 2 unrelated families. The PSEN2 mutation and pathogenic repeat expansions of C9orf72 were not detected in all patients. To the best of our knowledge, this is the first cohort report of a causative gene screen in patients with EOFAD in Mainland China. The analysis of the genetic-clinical correlations in this cohort supports the idea that the clinical phenotype might be influenced by specific genetic defects.     

Digenic parkinsonism: investigation of the synergistic effects of PRKN and LRRK2

The complex genetic etiology of Parkinson's disease (PD) is indicative of a multifactorial syndrome. A combination of gene-gene and gene-environment interactions may determine a variable phenotypic outcome. Recently a direct gene/protein interaction between two of the most common genetic causes of parkinsonism PRKN and LRRK2 has been postulated. We have identified three Spanish patients simultaneously harboring mutations in PRKN and LRRK2. In comparison to other Spanish patients with a single LRRK2 or PRKN mutation, the three double-mutation patients reported here do not present with an earlier age-at-onset or a faster progression of disease. Although the clinical findings do not support a synergistic effect of LRRK2 and PRKN, a potential genetic interplay might be concealed by the modulating effects of other genes. Nevertheless, this work demonstrates that the presence of mutations in one familial gene should not serve as exclusion criteria in a screen for further genetic variation. Direct interaction of Lrrk2 and parkin proteins was not observed in co-immunoprecipitation pull down experiments. However, in vivo studies are required to assess whether there is an indirect link between Lrrk2 and parkin in disease pathogenesis.     

Comprehensive evaluation of common genetic variation within LRRK2 reveals evidence for association with sporadic Parkinson's disease

Parkinson's disease (PD) is a complex neurodegenerative disorder whose aetiologies are largely unknown. To date, mutations in six genes have been found causal for some rare familial forms of the disease and common variation within at least three of these is associated with the more common sporadic forms of PD. LRRK2 is the most recently identified familial PD gene, although its role in sporadic disease is unknown. In this study, we have performed the first comprehensive evaluation of common genetic variation within LRRK2 and investigated its contribution to risk of sporadic PD. We first characterized the linkage disequilibrium within LRRK2 using a panel of densely spaced SNPs across the gene. We then identified a subset of tagging-SNPs (tSNP) that capture the majority of common variation within LRRK2. Both single tSNP and tSNP haplotype analyses, using a large epidemiologically matched sporadic case-control series comprising 932 individuals, yielded significant evidence for disease association. We identified a haplotype that dramatically increases disease risk when present in two copies (OR=5.5, 95%CI=2.1-14.0, P=0.0001). Thus, we provide the first evidence that common genetic variation within LRRK2 contributes to the risk of sporadic PD in the Chinese population.     

DLB and PDD: a role for mutations in dementia and Parkinson disease genes?

Based on the substantial overlap in clinical and pathological characteristics of dementia with Lewy bodies (DLB) and Parkinson disease with dementia (PDD) with Alzheimer disease (AD) and Parkinson disease (PD) we hypothesized that these disorders might share underlying genetic factors. The contribution of both sequence and copy number variants (CNVs) in known AD and PD genes to the genetic etiology of DLB and PDD however is currently unclear. Therefore, we performed a gene-based mutation analysis of all major AD and PD genes in 99 DLB and 75 PDD patients, including familial and sporadic forms, from Flanders, Belgium. Also, copy number variants in APP, SNCA, and PARK2 were determined. In the AD genes we detected proven pathogenic missense mutations in PSEN1 and PSEN2, and 2 novel missense variants in PSEN2 and MAPT. In the PD genes we identified 1 SNCA duplication, the LRRK2 R1441C founder mutation and 4 novel heterozygous missense variants with unknown pathogenicity. Our results suggest a contribution of established AD and PD genes to the genetic etiology of DLB and PDD though to a limited extent. They do support the hypothesis of a genetic overlap between members of the Lewy body disease spectrum, but additional genes still have to exist.     

LRRK2 G2019S is a common mutation in Spanish patients with late-onset Parkinson's disease

Mutations in the leucine-rich repat kinase 2 (LRRK2) gene have been shown to cause both autosomal dominant and sporadic Parkinson's disease (PD). The common G2019S mutation shows wide geographical distribution while R1441G has been only reported in Northern Spain. The overall frequency of these mutations remains to be established. To determine the prevalence of G2019S and R1441G mutations in our population of Cantabria (Northern Spain), we recruited 105 consecutive PD patients and 310 controls and conducted genetic analysis of these mutations. G2019S was detected in eight late-onset patients (7.6%). Five of them had no relevant family history. R1441G was not detected in any of our study subjects. The prevalence of G2019S mutation in unselected late-onset PD patients might be higher than previously reported: 3/16 (18.7%) of familial PD and 5/82 (6.1%) of sporadic PD.     

Mutation analysis of LRRK2, SCNA, UCHL1, HtrA2 and GIGYF2 genes in Chinese patients with autosomal dorminant Parkinson's disease

Autosomal dorminant Parkinson's disease (ADPD) has been associated with mutations in the SCNA, LRRK2, UCHL1, HtrA2 and GIGYF2 genes. We studied the prevalence of variants in all five genes in 12 Chinese unrelated families with ADPD and 4 families with both essential tremor (ET) and Parkinson's disease (PD) phenotypes using direct sequencing analysis. We found 27 variants in the LRRK2 gene, eight in GIGYF2 gene, three in the SCNA and UCHL1 gene respectively, in which five variants were novel. However, no pathogenic mutations in the five genes were found in these families. Our result indicated that SCNA, LRRK2, UCHL1, HtrA2 and GIGYF2 genes' mutations might not be a main reason for Chinese ADPD.     

A study of LRRK2 mutations and Parkinson's disease in Brazil

Mutations in the Leucine-rich repeat kinase 2 (LRRK2) gene are known as a common cause of Parkinson's disease (PD) among patients from different geographic origins. In this study, we evaluated the prevalence of LRRK2 mutations in exons 31 and 41 in a cohort of 154 consecutive, unrelated Brazilian patients with familial or sporadic PD, including early and late onset patients. The LRRK2 p.G2019S mutation was present in heterozygous state in three index cases (approximately 2%), and in three additional relatives. No carriers of this mutation were found among 250 control chromosomes. Clinically, all mutation-positive patients presented a typical PD phenotype and a good response to levodopa. Mutation segregation analysis in a large sibling showed incomplete penetrance of the p.G2019S. Our findings suggest that the LRRK2 p.G2019S mutation has a substantial contribution to PD susceptibility among Brazilian population and add new clues to current research of this disease.     

A novel LRRK2 mutation in a mainland Chinese patient with familial Parkinson's disease

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) are known to cause typical, late-onset familial Parkinson's disease in different geographic origins. However, there was no report about mutations of LRRK2 gene in mainland China. The 51 coding exons and intron/exon boundaries of the LRRK2 gene were sequenced in nine families with Parkinson's disease. A novel LRRK2 missense mutation resulting in a single amino acid substitution K616R was present in one family with a dominant form of PD, and not in 200 controls. The patient presented with slowly progressive resting tremor, dyskinesia, and responded well to l-dopa. In conclusion, we identified a novel mutation in LRRK2 gene, which was the first mutation of LRRK2 found in the mainland Chinese population with familial Parkinson's disease.     

Exome sequencing reveals an unexpected genetic cause of disease: NOTCH3 mutation in a Turkish family with Alzheimer's disease

Alzheimer's disease (AD) is a genetically complex disorder for which the definite diagnosis is only accomplished postmortem. Mutations in 3 genes (APP, PSEN1, and PSEN2) are known to cause AD, but a large number of familial cases do not harbor mutations in these genes and several unidentified genes that contain disease-causing mutations are thought to exist. We performed whole exome sequencing in a Turkish patient clinically diagnosed with Alzheimer's disease from a consanguineous family with a complex history of neurological and immunological disorders and identified a mutation in NOTCH3 (p.R1231C), previously described as causing cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Complete screening of NOTCH3 in a cohort of 95 early onset AD cases and 95 controls did not reveal any additional pathogenic mutations. Although the complex history of disease in this family precluded us to establish segregation of the mutation found with disease, our results show that exome sequencing is a rapid, cost-effective and comprehensive tool to detect genetic mutations, allowing for the identification of unexpected genetic causes of clinical phenotypes. As etiological based therapeutics become more common, this method will be key in diagnosing and treating disease.     

Absence/rarity of commonly reported LRRK2 mutations in Indian Parkinson's disease patients

Recent discovery of pathogenic mutations in the leucine-rich repeat kinase 2 (LRRK2) gene in Parkinson's disease (PD) patients in different ethnic groups have raised a hope of diagnostic screening and genetic counseling. We investigated the six most commonly reported mutations in LRRK2 gene among Indian PD patients, using PCR-RFLP method. Mutations G2019S, R1441C, R1441G, and R1441H were screened in 1012 individuals (PD, 800; controls, 212) while mutations I2012T and I2020T were screened in 748 PD patients. We did not observe any of these six mutations in this study sample except in a single female young onset PD patient who showed a heterozygous G2019S mutation. The absence of mutations was reconfirmed by sequencing of probands from several autosomal dominant PD families. Our observations suggest that these mutations may be a rare cause of PD among Indians and therefore of little help for diagnostic screening and genetic counseling for Indian PD patients.     

Founder mutation p.R1441C in the leucine-rich repeat kinase 2 gene in Belgian Parkinson's disease patients

We determined the prevalence of mutations in two major functional domains of the leucine-rich repeat kinase 2 gene (LRRK2) in Belgian Parkinson's disease (PD) patients (N=304) of which 18.1% were familial PD patients. Ten patients were heterozygous for five different missense mutations (3.29%) of whom six carried the same mutation p.R1441C (1.97%). All six p.R1441C carriers were familial PD patients explaining 10.7% of familial PD in the Belgian patient group. Moreover, they shared a common disease haplotype of 21 consecutive markers in a region of 438 kb, suggesting that they are distant descendants of a single common ancestor. Clinically, p.R1441C carriers had typical levodopa-responsive parkinsonism with tremor as the most common presenting feature. Their age at onset was highly variable and ranged from 39 to 73 years, suggesting the influence of modifying factors. The remaining four patients were heterozygous each for a novel missense mutation located in the Roc or kinase domain. The pathogenic nature of these mutations remains to be determined, though we have genetic evidence that at least some represent rare but benign variants rather than causal mutations. The latter observation indicates that prudence is needed in diagnostic testing of LRRK2 in PD patients. Functional data should underlie a conclusion on the pathogenic nature of some mutations that have not been conclusively linked to disease.     

Mechanistic insight into the dominant mode of the Parkinson's disease-associated G2019S LRRK2 mutation

Pathogenic mutations in the leucine-rich repeat kinase-2 (LRRK2) gene cause autosomal-dominant and certain cases of sporadic Parkinson's disease (PD). The G2019S substitution in LRRK2 is the most common genetic determinant of PD identified so far, and maps to a specific region of the kinase domain called the activation segment. Here, we show that autophosphorylation of LRRK2 is an intermolecular reaction and targets two residues within the activation segment. The prominent pathogenic G2019S mutation in LRRK2 results in altered autophosphorylation, and increased autophosphorylation and substrate phosphorylation, through a process that seems to involve reorganization of the activation segment. Our results suggest a molecular mechanistic explanation for how the G2019S mutation enhances the catalytic activity of LRRK2, thereby leading to pathogenicity. These findings have important implications for therapeutic strategies in PD.     

Evaluation of the role of LRRK2 gene in Parkinson's disease in an East Indian cohort

Leucine rich repeat kinase 2 (LRRK2) gene defects cause Parkinson's disease (PD). Recently, LRRK2 has also been shown by genome wide association (GWA) studies to be a susceptibility gene for the disease. In India mutations in LRRK2 is a rare cause of PD. We, therefore, genotyped 64 SNPs across LRRK2 in 161 control samples and finally studied 6 haplotype tagging SNPs for association-based study on 300 cases and 446 ethnically matched controls to explore the potential role of LRRK2 as a susceptibility gene in PD for East Indians. We did not find any significant allele/ genotype or haplotype associations with PD suggesting that common genetic variants within LRRK2 play limited role in modulating PD among East Indians. In addition, we also screened for the common mutations (viz. p.R1441C, p.R1441G, p.R1441H, p.Y1699C, p.G2019S), and a risk variant common among Asians (p.G2385R) but did not observe any of the above mentioned variants in our cohort. Our study, therefore, strongly suggests that LRRK2 has minimal role as a candidate and susceptibility gene in PD pathogenesis among East Indians.