A susceptibility locus for Parkinson's disease maps to chromosome 2p13

Allosteric Inhibition of Parkinson's-Linked LRRK2 by Constrained Peptides

Leucine-Rich Repeat Kinase 2 (LRRK2) is a large, multidomain protein with dual kinase and GTPase function that is commonly mutated in both familial and idiopathic Parkinson's Disease (PD). While dimerization of LRRK2 is commonly detected in PD models, it remains unclear whether inhibition of dimerization can regulate catalytic activity and pathogenesis. Here, we show constrained peptides that are cell-penetrant, bind LRRK2, and inhibit LRRK2 activation by downregulating dimerization. We further show that inhibited dimerization decreases kinase activity and inhibits ROS production and PD-linked apoptosis in primary cortical neurons. While many ATP-competitive LRRK2 inhibitors induce toxicity and mislocalization of the protein in cells, these constrained peptides were found to not affect LRRK2 localization. The ability of these peptides to inhibit pathogenic LRRK2 kinase activity suggests that disruption of dimerization may serve as a new allosteric strategy to downregulate PD-related signaling pathways.

Hunting for Familial Parkinson's Disease Mutations in the Post Genome Era

Parkinson’s disease (PD) is typically sporadic; however, multi-incident families provide a powerful platform to discover novel genetic forms of disease. Their identification supports deciphering molecular processes leading to disease and may inform of new therapeutic targets. The LRRK2 p.G2019S mutation causes PD in 42.5–68% of carriers by the age of 80 years. We hypothesise similarly intermediately penetrant mutations may present in multi-incident families with a generally strong family history of disease. We have analysed six multiplex families for missense variants using whole exome sequencing to find 32 rare heterozygous mutations shared amongst affected members. Included in these mutations was the KCNJ15 p.R28C variant, identified in five affected members of the same family, two elderly unaffected members of the same family, and two unrelated PD cases. Additionally, the SIPA1L1 p.R236Q variant was identified in three related affected members and an unrelated familial case. While the evidence presented here is not sufficient to assign causality to these rare variants, it does provide novel candidates for hypothesis testing in other modestly sized families with a strong family history. Future analysis will include characterisation of functional consequences and assessment of carriers in other familial cases.

Integrated Analysis of Whole Exome Sequencing and Copy Number Evaluation in Parkinson's Disease

Genetic studies of the familial forms of Parkinson’s disease (PD) have identified a number of causative genes with an established role in its pathogenesis. These genes only explain a fraction of the diagnosed cases. The emergence of Next Generation Sequencing (NGS) expanded the scope of rare variants identification in novel PD related genes. In this study we describe whole exome sequencing (WES) genetic findings of 60 PD patients with 125 variants validated in 51 of these cases. We used strict criteria for variant categorization that generated a list of variants in 20 genes. These variants included loss of function and missense changes in 18 genes that were never previously linked to PD (NOTCH4, BCOR, ITM2B, HRH4, CELSR1, SNAP91, FAM174A, BSN, SPG7, MAGI2, HEPHL1, EPRS, PUM1, CLSTN1, PLCB3, CLSTN3, DNAJB9 and NEFH) and 2 genes that were previously associated with PD (EIF4G1 and ATP13A2). These genes either play a critical role in neuronal function and/or have mouse models with disease related phenotypes. We highlight NOTCH4 as an interesting candidate in which we identified a deleterious truncating and a splice variant in 2 patients. Our combined molecular approach provides a comprehensive strategy applicable for complex genetic disorders.

Advances in the Research of Risk Factors and Prodromal Biomarkers of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world. With the advent of an aging population and improving life expectancy worldwide, the number of PD patients is expected to increase, which may lead to an urgent need for effective preventive and diagnostic strategies for PD. Although there is increasing research regarding the pathogenesis of PD, there is limited knowledge regarding the prevention of PD. Moreover, the diagnosis of PD depends on clinical criteria, which require the occurrence of bradykinesia and at least one symptom of rest tremor or rigidity. However, converging evidence from clinical, genetic, neuropathological, and imaging studies suggests the initiation of PD-specific pathology prior to the initial presentation of these classical motor clinical features by years or decades. This latent stage of neurodegeneration in PD is a particularly important stage for effective neuroprotective therapies, which might retard the progression or prevent the onset of PD. Therefore, the exploration of risk factors and premotor biomarkers is not only crucial to the early diagnosis of PD but is also helpful in the development of effective neuroprotection and health care strategies for appropriate populations at risk for PD. In this review, we searched and summarized ∼249 researches and 31 reviews focusing on the risk factors and prodromal biomarkers of PD and published in MEDLINE.

The genetics of Parkinson disease

About 15% of patients with Parkinson disease (PD) have family history and 5-10% have a monogenic form of the disease with Mendelian inheritance. To date, at least 23 loci and 19 disease-causing genes for parkinsonism have been found, but many more genetic risk loci and variants for sporadic PD phenotype have been identified in various association studies. Investigating the mutated protein products has uncovered potential pathogenic pathways that provide insights into mechanisms of neurodegeneration in familial and sporadic PD. To commemorate the 200th anniversary of Parkinson's publication of An Essay on the Shaking Palsy, we provide a comprehensive and critical overview of the current clinical, neuropathological, and genetic understanding of genetic forms of PD. We also discuss advances in screening for genetic PD-related risk factors and how they impact genetic counseling and contribute to the development of potential disease-modifying therapies.

Current understanding of the molecular mechanisms in Parkinson's disease: Targets for potential treatments

Gradual degeneration and loss of dopaminergic neurons in the substantia nigra, pars compacta and subsequent reduction of dopamine levels in striatum are associated with motor deficits that characterize Parkinson’s disease (PD). In addition, half of the PD patients also exhibit frontostriatal-mediated executive dysfunction, including deficits in attention, short-term working memory, speed of mental processing, and impulsivity. The most commonly used treatments for PD are only partially or transiently effective and are available or applicable to a minority of patients. Because, these therapies neither restore the lost or degenerated dopaminergic neurons, nor prevent or delay the disease progression, the need for more effective therapeutics is critical. In this review, we provide a comprehensive overview of the current understanding of the molecular signaling pathways involved in PD, particularly within the context of how genetic and environmental factors contribute to the initiation and progression of this disease. The involvement of molecular chaperones, autophagy-lysosomal pathways, and proteasome systems in PD are also highlighted. In addition, emerging therapies, including pharmacological manipulations, surgical procedures, stem cell transplantation, gene therapy, as well as complementary, supportive and rehabilitation therapies to prevent or delay the progression of this complex disease are reviewed.

The therapeutic potential of cell identity reprogramming for the treatment of aging-related neurodegenerative disorders

Neural cell identity reprogramming strategies aim to treat age-related neurodegenerative disorders with newly induced neurons that regenerate neural architecture and functional circuits in vivo. The isolation and neural differentiation of pluripotent embryonic stem cells provided the first in vitro models of human neurodegenerative disease. Investigation into the molecular mechanisms underlying stem cell pluripotency revealed that somatic cells could be reprogrammed to induced pluripotent stem cells (iPSCs) and these cells could be used to model Alzheimer disease, amyotrophic lateral sclerosis, Huntington disease, and Parkinson disease. Additional neural precursor and direct transdifferentiation strategies further enabled the induction of diverse neural linages and neuron subtypes both in vitro and in vivo. In this review, we highlight neural induction strategies that utilize stem cells, iPSCs, and lineage reprogramming to model or treat age-related neurodegenerative diseases, as well as, the clinical challenges related to neural transplantation and in vivo reprogramming strategies.

Leucine-Rich Repeat Kinase (LRRK2) Genetics and Parkinson's Disease

The discovery of LRRK2 mutations as a cause of Parkinson's disease (PD), including the sporadic late-onset form, established the decisive role of genetics in the field of PD research. Among LRRK2 mutations, the G2019S, mostly lying in a haplotype originating from a common Middle Eastern ancestor, has been identified in different populations worldwide. The G2385R and R1628P variants represent validated risk factors for PD in Asian populations. Here, we describe in detail the origin, the present worldwide epidemiology, and the penetrance of LRRK2 mutations. Furthermore, this chapter aims to characterize other definitely/probably pathogenic mutations and risk variants of LRRK2. Finally, we provide some general guidelines for a LRRK2 genetic testing and counseling. In summary, LRRK2 discovery revolutionized the understanding of PD etiology and laid the foundation for a promising future of genetics in PD research.

The genetic background of Parkinson's disease: current progress and future prospects

Almost two decades of genetic research in Parkinson's disease (PD) have remarkably increased our knowledge regarding the genetic basis of PD with numerous genes and genetic loci having been found to cause familial PD or affect the risk for PD. Approximately 5-10% of PD patients have monogenic forms of the disease, exhibiting a classical Mendelian type of inheritance, however, the majority PD cases are sporadic, probably caused by a combination of genetic and environmental risk factors. Nowadays, six genes, alpha synuclein, LRRK2, VPS35, Parkin, PINK1 and DJ-1, have definitely been associated with an autosomal dominant or recessive PD mode of inheritance. The advent of genome-wide association studies (GWAS) and the implementation of new technologies, like next generation sequencing (NGS) and exome sequencing has undoubtedly greatly aided the identification on novel risk variants for sporadic PD. In this review, we will summarize the current progress and future prospects in the field of PD genetics.

Clinical and neuropathological features of dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is an increasingly recognized entity which overlaps in clinical, pathological and genetic features with Alzheimer's (AD) and Parkinson's disease (PD). Clinically, it is characterized by progressive cognitive impairment with significant fluctuations in alertness, parkinsonism, and psychosis with recurrent hallucinations. The neuropathological hallmarks are the intracytoplasmic inclusions in substantia nigra typical of PD, known as Lewy bodies (LB), but widely distributed throughout paralimbic and neocortical regions. Most of the cases also coexist with a plaque predominant AD. The evidence of alpha-synuclein in LB and related neurites as well as of a synuclein fragment in AD plaques opens new links among these neurodegenerative diseases. This article will review briefly the clinical and pathologicalfeatures that DLB shares with AD and PD, as well as those that support the idea that it is a distinct disorder.

Molecular Etiology of Parkinson Disease: Recent Progress

Parkinson disease (PD) is one of the most widespread neurodegenerative disorders. In North America alone it affects 1 million people. It is a multifactorial disorder caused by genetic, various biological and environmental factors. One of the important features of PD is the dementia, which is believed to be due to the loss of dopaminergic neurons. In some cases the disease can be inherited as an autosomal dominant or recessive trait but in the majority of cases it is acquired. The biological causes of the disorder are unknown. The identification of mutations in the parkin gene in the autosomal recessive case and alpha-synuclein gene in autosomal dominant cases has opened a new avenue for studies to understand the basic biochemical mechanisms of pathogenesis. Although several types of treatments such as transplantation of cells that produce L-Dopa and direct gene delivery using adeno-associated viral vectors may correct animal models of PD, their usefulness in the human is not yet clear. A better understanding of the causes of neurodegeneration may lead to better therapies in the future.

Functional analysis of sepiapterin reductase in Drosophila melanogaster

Sepiapterin reductase (SR) is a key enzyme involved in the biosynthesis of tetrahydrobiopterin (BH4), an essential cofactor for the synthesis of important biogenic amines, including catecholamines and serotonin. BH4 deficiencies have been implicated in several neurological disorders. Here, we characterized sepiapterin reductase (SR) loss-of-function mutants in Drosophila melanogaster and demonstrated that SR mutations are responsible for hyposensitivity to oxidative stress. Biochemical analysis further revealed that SR activity and BH4 levels in SR mutants were significantly reduced. Furthermore, we showed that the levels of phosphorylated Akt and total Akt protein were increased in SR mutants. Our findings indicate that SR plays an important role in the Akt pathway and that SR mutants will be a valuable tool for investigating the physiological functions of BH4.

A mobile cloud-based Parkinson's disease assessment system for home-based monitoring

BACKGROUND

Parkinson's disease (PD) is the most prevalent movement disorder of the central nervous system, and affects more than 6.3 million people in the world. The characteristic motor features include tremor, bradykinesia, rigidity, and impaired postural stability. Current therapy based on augmentation or replacement of dopamine is designed to improve patients' motor performance but often leads to levodopa-induced adverse effects, such as dyskinesia and motor fluctuation. Clinicians must regularly monitor patients in order to identify these effects and other declines in motor function as soon as possible. Current clinical assessment for Parkinson's is subjective and mostly conducted by brief observations made during patient visits. Changes in patients' motor function between visits are hard to track and clinicians are not able to make the most informed decisions about the course of therapy without frequent visits. Frequent clinic visits increase the physical and economic burden on patients and their families.

OBJECTIVE

In this project, we sought to design, develop, and evaluate a prototype mobile cloud-based mHealth app, "PD Dr", which collects quantitative and objective information about PD and would enable home-based assessment and monitoring of major PD symptoms.

METHODS

We designed and developed a mobile app on the Android platform to collect PD-related motion data using the smartphone 3D accelerometer and to send the data to a cloud service for storage, data processing, and PD symptoms severity estimation. To evaluate this system, data from the system were collected from 40 patients with PD and compared with experts' rating on standardized rating scales.

RESULTS

The evaluation showed that PD Dr could effectively capture important motion features that differentiate PD severity and identify critical symptoms. For hand resting tremor detection, the sensitivity was .77 and accuracy was .82. For gait difficulty detection, the sensitivity was .89 and accuracy was .81. In PD severity estimation, the captured motion features also demonstrated strong correlation with PD severity stage, hand resting tremor severity, and gait difficulty. The system is simple to use, user friendly, and economically affordable.

CONCLUSIONS

The key contribution of this study was building a mobile PD assessment and monitoring system to extend current PD assessment based in the clinic setting to the home-based environment. The results of this study proved feasibility and a promising future for utilizing mobile technology in PD management.

Role of genomics in translational research for Parkinson's disease

Research on Parkinson's disease (PD) has made remarkable progress in recent decades, due largely to new genomic technologies, such as high throughput sequencing and microarray analyses. Since the discovery of a linkage of a missense mutation of the α-synuclein (αS) gene to a rare familial dominant form of PD in 1996, positional cloning and characterization of a number of familial PD risk factors have established a hypothesis that aggregation of αS may play a major role in the pathogenesis of PD. Furthermore, dozens of sensitizing alleles related to the disease have been identified by genome wide association studies (GWAS) and meta-GWAS, contributing to a better understanding of the pathological mechanisms of sporadic PD. Thus, the knowledge obtained from the association studies will be valuable for "the personal genome" of PD. Besides summarizing such progress, this paper focuses on the role of microRNAs in the field of PD research, since microRNAs might be promising as a biomarker and as a therapeutic reagent for PD. We further refer to a recent view that neurodegenerative diseases, including PD, coexist with metabolic disorders and are stimulated by type II diabetes, the most common disease among elderly populations. The development of genomic approaches may potentially contribute to therapeutic intervention for PD.

Advances in the Genetics of Parkinson's Disease: A Guide for the Clinician

Over the last 16 years, insights in clinical and genetic characteristics of Parkinson's disease (PD) have increased substantially. We summarize the clinical, genetic, and pathological findings of autosomal dominant PD linked to mutations in SNCA, leucine-rich repeat kinase 2, vacuolar protein sorting-35, and eukaryotic translation initiation factor 4 gamma 1 and autosomal recessive PD linked to parkin,PINK1, and DJ-1, as well as autosomal recessive complicated parkinsonian syndromes caused by mutations in ATP13A2,FBXO7,PLA2G6,SYNJ1, and DNAJC6. We also review the advances in high- and low-risk genetic susceptibility factors and present multisystem disorders that may present with parkinsonism as the major clinical feature and provide recommendations for prioritization of genetic testing. Finally, we consider the challenges of future genetic research in PD.

α-Synuclein in Parkinson's disease: pathogenic function and translation into animal models

Parkinson's disease is a common neurodegenerative disease characterised by the loss of dopaminergic neurons in the substantia nigra pars compacta and the formation of α-synuclein aggregates found in Lewy bodies throughout the brain. Several α-synuclein transgenic mouse models have been generated, as well as viral-mediated overexpression of wild-type and mutated α-synuclein to mimic the disease and to delineate the pathogenic pathway of α-synuclein-mediated toxicity and neurodegeneration. In this review, we will recapitulate what we have learned about the function of α-synuclein and α-synuclein-mediated toxicity through studies of transgenic animal models, inducible animal models and viral-based models.

Reprint of: revisiting oxidative stress and mitochondrial dysfunction in the pathogenesis of Parkinson disease-resemblance to the effect of amphetamine drugs of abuse

Parkinson disease (PD) is a chronic and progressive neurological disease associated with a loss of dopaminergic neurons. In most cases the disease is sporadic but genetically inherited cases also exist. One of the major pathological features of PD is the presence of aggregates that localize in neuronal cytoplasm as Lewy bodies, mainly composed of α-synuclein (α-syn) and ubiquitin. The selective degeneration of dopaminergic neurons suggests that dopamine itself may contribute to the neurodegenerative process in PD. Furthermore, mitochondrial dysfunction and oxidative stress constitute key pathogenic events of this disorder. Thus, in this review we give an actual perspective to classical pathways involving these two mechanisms of neurodegeneration, including the role of dopamine in sporadic and familial PD, as well as in the case of abuse of amphetamine-type drugs. Mutations in genes related to familial PD causing autosomal dominant or recessive forms may also have crucial effects on mitochondrial morphology, function, and oxidative stress. Environmental factors, such as MPTP and rotenone, have been reported to induce selective degeneration of the nigrostriatal pathways leading to α-syn-positive inclusions, possibly by inhibiting mitochondrial complex I of the respiratory chain and subsequently increasing oxidative stress. Recently, increased risk for PD was found in amphetamine users. Amphetamine drugs have effects similar to those of other environmental factors for PD, because long-term exposure to these drugs leads to dopamine depletion. Moreover, amphetamine neurotoxicity involves α-syn aggregation, mitochondrial dysfunction, and oxidative stress. Therefore, dopamine and related oxidative stress, as well as mitochondrial dysfunction, seem to be common links between PD and amphetamine neurotoxicity.

Genetic analysis of the FBXO48 gene in Chinese Han patients with Parkinson disease

The F-box only protein 48 gene (FBXO48) is located in 2p13.3, the disease gene locus of Parkinson disease type 3 (PARK3), and it is one of the paralogs of the F-box only protein 7 gene (FBXO7), which is a causative gene of the Parkinson disease type 15 (PARK15; also known as Parkinsonian-pyramidal disease, PPD). To determine whether genetic mutation in the coding region of the FBXO48 gene plays a role in the etiology of PD, we screened DNA samples from 350 Chinese Han patients with PD. No mutation in the coding region of the FBXO48 gene was identified in our PD cohort, suggesting that mutations in the coding region of the FBXO48 gene play little or no role in the development of PD.

Revisiting oxidative stress and mitochondrial dysfunction in the pathogenesis of Parkinson disease--resemblance to the effect of amphetamine drugs of abuse

Parkinson disease (PD) is a chronic and progressive neurological disease associated with a loss of dopaminergic neurons. In most cases the disease is sporadic but genetically inherited cases also exist. One of the major pathological features of PD is the presence of aggregates that localize in neuronal cytoplasm as Lewy bodies, mainly composed of α-synuclein (α-syn) and ubiquitin. The selective degeneration of dopaminergic neurons suggests that dopamine itself may contribute to the neurodegenerative process in PD. Furthermore, mitochondrial dysfunction and oxidative stress constitute key pathogenic events of this disorder. Thus, in this review we give an actual perspective to classical pathways involving these two mechanisms of neurodegeneration, including the role of dopamine in sporadic and familial PD, as well as in the case of abuse of amphetamine-type drugs. Mutations in genes related to familial PD causing autosomal dominant or recessive forms may also have crucial effects on mitochondrial morphology, function, and oxidative stress. Environmental factors, such as MPTP and rotenone, have been reported to induce selective degeneration of the nigrostriatal pathways leading to α-syn-positive inclusions, possibly by inhibiting mitochondrial complex I of the respiratory chain and subsequently increasing oxidative stress. Recently, increased risk for PD was found in amphetamine users. Amphetamine drugs have effects similar to those of other environmental factors for PD, because long-term exposure to these drugs leads to dopamine depletion. Moreover, amphetamine neurotoxicity involves α-syn aggregation, mitochondrial dysfunction, and oxidative stress. Therefore, dopamine and related oxidative stress, as well as mitochondrial dysfunction, seem to be common links between PD and amphetamine neurotoxicity.

Molecular genetics of familial parkinsonism

Parkinson's disease (PD) is a progressive, neurodegenerative disorder associated with tremor, rigidity, bradykinesia, and postural instability. There exists a familial form of PD that is indistinguishable from the sporadic form. In addition, there exists a class of syndromes classified as parkinsonism-plus syndromes (PPS), in which parkinsonism is an essential but not the only phenotypic characteristic. The etiology of PD remains unclear. Both environmental and genetic factors contribute to the disease pathogenesis. Recent progress in the molecular genetics of parkinsonism has demonstrated that six different chromosomal regions are associated with forms of familial parkinsonism. Mutations in four candidate genes have been identified and include both point mutations and deletions. Both gain-of-function and loss-of-function mutational mechanisms have been implicated. The molecular genetic characterization has led to a new classification of PD and PPS based on the type of genetic defect. Understanding the mechanisms by which these mutations lead to disease should provide further insights into the etiology of parkinsonism.

Clinical, pathologic and genetic studies on autosomal recessive early-onset parkinsonism with diurnal fluctuation

To clarify the genetic mode and clinical characteristics of familial early-onset parkinsonism with diurnal fluctuation, we studied 43 patients from 22 families. The estimated segregation ratio (0.2963) and absence of gender preponderance indicated autosomal recessive inheritance. Clinical features included the average age at onset of 26.1 years, parkinsonism with marked diurnal fluctuation, remarkable effect of levodopa, dyskinesias, dystonia, hyperreflexia, absence of dementia, and a benign course; autonomic symptoms were only mild if present. Autopsy study in one of our patients disclosed neuronal loss without Lewy bodies and the presence of melanin-poor neurons in the substantia nigra. Linkage analysis on 16 families mapped the disease gene to chromosome 6q25.2-27.

Clinical approach to Parkinson's disease: features, diagnosis, and principles of management

Parkinson's disease (PD) is one of the most common neurodegenerative disorders. The condition causes a heavy burden both on those affected, as well as their families. Accurate diagnosis is critical and remains founded on clinical grounds as no specific diagnostic test is available so far. The clinical picture of PD is typical in many instances; however, features distinguishing it from other disorders should be thoroughly sought. Monogenic forms of PD also have some distinctive characteristics in many cases. This text is a roadmap to accurate diagnosis in PD, as it approaches clinical features, diagnostic methodology, and leading differential diagnoses. Therapeutic issues are also briefly discussed.

Genetic basis of Parkinson's disease: inheritance, penetrance, and expression

Parkinson’s disease can be caused by rare familial genetic mutations, but in most cases it is likely to result from an interaction between multiple genetic and environmental risk factors. Over recent years, many variants in a growing number of genes involved in the pathogenesis of Parkinson’s disease have been identified. Mutations in several genes have been shown to cause familial parkinsonism. In this review, we discuss 12 of them (SNCA, LRRK2, Parkin, PINK1, DJ1, ATP13A2, PLA2G6, FBXO7, UCHL1, GIGYF2, HTRA2, and EIF4G1). Additionally, six genes have been shown conclusively to be risk factors for sporadic Parkinson’s disease, and are also discussed (GBA, MAPT, BST1, PARK16, GAK, and HLA). Many more genes and genetic loci have been suggested, but need confirmation. There is evidence that pathways involved in the rare familial forms also play a role in the sporadic form, and that the respective genes might also be risk factors for sporadic Parkinson’s disease. The identification of genes involved in the development of Parkinson’s disease will improve our understanding of the underlying molecular mechanisms, and will hopefully lead to new drug targets and treatment strategies.

Epidemiology and etiology of Parkinson's disease: a review of the evidence

The etiology of Parkinson's disease (PD) is not well understood but likely to involve both genetic and environmental factors. Incidence and prevalence estimates vary to a large extent-at least partly due to methodological differences between studies-but are consistently higher in men than in women. Several genes that cause familial as well as sporadic PD have been identified and familial aggregation studies support a genetic component. Despite a vast literature on lifestyle and environmental possible risk or protection factors, consistent findings are few. There is compelling evidence for protective effects of smoking and coffee, but the biologic mechanisms for these possibly causal relations are poorly understood. Uric acid also seems to be associated with lower PD risk. Evidence that one or several pesticides increase PD risk is suggestive but further research is needed to identify specific compounds that may play a causal role. Evidence is limited on the role of metals, other chemicals and magnetic fields. Important methodological limitations include crude classification of exposure, low frequency and intensity of exposure, inadequate sample size, potential for confounding, retrospective study designs and lack of consistent diagnostic criteria for PD. Studies that assessed possible shared etiological components between PD and other diseases show that REM sleep behavior disorder and mental illness increase PD risk and that PD patients have lower cancer risk, but methodological concerns exist. Future epidemiologic studies of PD should be large, include detailed quantifications of exposure, and collect information on environmental exposures as well as genetic polymorphisms.

Parkinson's disease: genetics and pathogenesis

Recent investigation into the mechanisms of Parkinson's disease (PD) has generated remarkable insight while simultaneously challenging traditional conceptual frameworks. Although the disease remains defined clinically by its cardinal motor manifestations and pathologically by midbrain dopaminergic cell loss in association with Lewy bodies, it is now recognized that PD has substantially more widespread impact, causing a host of nonmotor symptoms and associated pathology in multiple regions throughout the nervous system. Further, the discovery and validation of PD-susceptibility genes contradict the historical view that environmental factors predominate, and blur distinctions between familial and sporadic disease. Genetic advances have also promoted the development of improved animal models, highlighted responsible molecular pathways, and revealed mechanistic overlap with other neurodegenerative disorders. In this review, we synthesize emerging lessons on PD pathogenesis from clinical, pathological, and genetic studies toward a unified concept of the disorder that may accelerate the design and testing of the next generation of PD therapies.

Mitochondrial disfunction in Parkinson's disease

Mitochondrial structural and functional abnormalities in Parkinson's disease and experimental animal models of this pathology are described. Special attention is paid to the inactivation of mitochondrial enzymes, mutations in mitochondrial and nuclear DNA, and genomic and proteomic research of mitochondrial proteins in Parkinson's disease and experimental parkinsonism of animals.

A novel X-linked four-repeat tauopathy with Parkinsonism and spasticity

The parkinsonian syndromes comprise a highly heterogeneous group of disorders. Although 15 loci are linked to predominantly familial Parkinson's disease (PD), additional PD loci are likely to exist. We recently identified a multigenerational family of Danish and German descent in which five males in three generations presented with a unique syndrome characterized by parkinsonian features and variably penetrant spasticity for which X-linked disease transmission was strongly suggested (XPDS). Autopsy in one individual failed to reveal synucleinopathy; however, there was a significant four-repeat tauopathy in the striatum. Our objective was to identify the locus responsible for this unique parkinsonian disorder. Members of the XPDS family were genotyped for markers spanning the X chromosome. Two-point and multipoint linkage analyses were performed and the candidate region refined by analyzing additional markers. A multipoint LOD(max) score of 2.068 was obtained between markers DXS991 and DXS993. Haplotype examination revealed an approximately 20 cM region bounded by markers DXS8042 and DXS1216 that segregated with disease in all affected males and obligate carrier females and was not carried by unaffected at-risk males. To reduce the possibility of a false-positive linkage result, multiple loci and genes associated with other parkinsonian or spasticity syndromes were excluded. In conclusion, we have identified a unique X-linked parkinsonian syndrome with variable spasticity and four-repeat tau pathology, and defined a novel candidate gene locus spanning approximately 28 Mb from Xp11.2-Xq13.3.

The genetics of Parkinson disease

Parkinson disease (PD) is the second most common neurodegenerative disorder. In most instances, PD is thought to result from a complex interaction between multiple genetic and environmental factors, though rare monogenic forms of the disease do exist. Mutations in 6 genes (SNCA, LRRK2, PRKN, DJ1, PINK1, and ATP13A2) have conclusively been shown to cause familial parkinsonism. In addition, common variation in 3 genes (MAPT, LRRK2, and SNCA) and loss-of-function mutations in GBA have been well-validated as susceptibility factors for PD. The function of these genes and their contribution to PD pathogenesis remain to be fully elucidated. The prevalence, incidence, clinical manifestations, and genetic components of PD are discussed in this review.

Parkinson's disease candidate gene prioritization based on expression profile of midbrain dopaminergic neurons

Background

Parkinson's disease is the second most common neurodegenerative disorder. The pathological hallmark of the disease is degeneration of midbrain dopaminergic neurons. Genetic association studies have linked 13 human chromosomal loci to Parkinson's disease. Identification of gene(s), as part of the etiology of Parkinson's disease, within the large number of genes residing in these loci can be achieved through several approaches, including screening methods, and considering appropriate criteria. Since several of the indentified Parkinson's disease genes are expressed in substantia nigra pars compact of the midbrain, expression within the neurons of this area could be a suitable criterion to limit the number of candidates and identify PD genes.

Methods

In this work we have used the combination of findings from six rodent transcriptome analysis studies on the gene expression profile of midbrain dopaminergic neurons and the PARK loci in OMIM (Online Mendelian Inheritance in Man) database, to identify new candidate genes for Parkinson's disease.

Results

Merging the two datasets, we identified 20 genes within PARK loci, 7 of which are located in an orphan Parkinson's disease locus and one, which had been identified as a disease gene. In addition to identifying a set of candidates for further genetic association studies, these results show that the criteria of expression in midbrain dopaminergic neurons may be used to narrow down the number of genes in PARK loci for such studies.

Biochemical and molecular features of LRRK2 and its pathophysiological roles in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, and 5-10% of the PD cases are genetically inherited as familial PD (FPD). LRRK2 (leucine-rich repeat kinase 2) was first reported in 2004 as a gene corresponding to PARK8, an autosomal gene whose dominant mutations cause familial PD. LRRK2 contains both active kinase and GTPase domains as well as protein-protein interaction motifs such as LRR (leucine-rich repeat) and WD40. Most pathogenic LRRK2 mutations are located in either the GTPase or kinase domain, implying important roles for the enzymatic activities in PD pathogenic mechanisms. In comparison to other PD causative genes such as parkin and PINK1, LRRK2 exhibits two important features. One is that LRRK2's mutations (especially the G2019S mutation) were observed in sporadic as well as familial PD patients. Another is that, among the various PDcausing genes, pathological characteristics observed in patients carrying LRRK2 mutations are the most similar to patients with sporadic PD. Because of these two observations, LRRK2 has been intensively investigated for its pathogenic mechanism (s) and as a target gene for PD therapeutics. In this review, the general biochemical and molecular features of LRRK2, the recent results of LRRK2 studies and LRRK2's therapeutic potential as a PD target gene will be discussed.

Molecular mechanisms of pathogenesis of Parkinson's disease

Parkinson's disease is a complex disease characterized by a progressive degeneration of nigrostriatal dopaminergic neurons. The development of this condition is defined by the interaction between the genetic constitution of an organism and environmental factors. Analysis of the genes associated with development of monogenic forms of disease has allowed pointing out several mechanisms involved in Parkinson's disease pathogenesis such as the ubiquitin-proteasome degradation, differentiation of dopaminergic neurons, mitochondrial dysfunction, oxidative damage, and others. In this review, a variety of data which throw light on molecular mechanisms underlying pathogenesis of Parkinson's disease will be considered.

Association between the ubiquitin carboxyl-terminal esterase L1 gene (UCHL1) S18Y variant and Parkinson's Disease: a HuGE review and meta-analysis

The ubiquitin carboxyl-terminal esterase L1 gene, UCHL1, located on chromosome 4p14, has been studied as a potential candidate gene for Parkinson's disease risk. The authors conducted a Human Genome Epidemiology review and meta-analysis of published case-control studies of the UCHL1 S18Y variant and Parkinson's disease in Asian and Caucasian samples. The meta-analysis of studies in populations of Asian ancestry showed a statistically significant association between the Y allele and reduced risk of Parkinson's disease under a recessive model (odds ratio (OR) for YY vs. SY + SS = 0.79, 95% confidence interval (CI): 0.67, 0.94; P = 0.006). For a dominant model, the association was not significant in Asian populations (OR for YY + SY vs. SS = 0.88, 95% CI: 0.68, 1.14; P = 0.33). For populations of European ancestry, the meta-analysis showed a significant association between the Y allele and decreased risk of Parkinson's disease under a dominant model (OR = 0.89, 95% CI: 0.81, 0.98; P = 0.02) but not under a recessive model (OR = 0.92, 95% CI: 0.66, 1.30; P = 0.65). Using the Venice criteria, developed by the Human Genome Epidemiology Network Working Group on the assessment of cumulative evidence, the authors concluded that moderate evidence exists for an association between the S18Y variant and Parkinson's disease.

Molecular pathogenesis of Parkinson disease: insights from genetic studies

Over the past few years, genetic findings have changed our views on the molecular pathogenesis of Parkinson disease (PD), as mutations in a growing number of genes have been found to cause monogenic forms of the disorder. These mutations cause neuronal dysfunction and neurodegeneration either by a toxic gain of function, as in the case of the dominant forms of monogenic PD caused by mutations in the genes for alpha-synuclein or LRRK2, or by a loss of an intrinsic protective function, as is likely for the recessive PD genes parkin (PRKN), PINK1 and DJ-1. Evidence is emerging that at least some of the pathways uncovered in the rare monogenic forms of PD may play a direct role in the aetiology of the common sporadic disorder and that variants of the respective genes contribute to the risk of developing the disease. These findings will allow the search for new treatment strategies that focus on the underlying molecular pathophysiology, rather than simply on ameliorating symptoms.

A population-based study of parkinsonism in an Amish community

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder with unknown cause. Genetic mutations account for a minority of cases but the role of environmental factors is unclear.

METHODS

We performed a population-based screening for PD in subjects in an Amish community over age 60. PD was diagnosed using standard clinical criteria and the Unified Parkinson Disease Rating Scale motor subsection 3 (UPDRS3). Community prevalence was calculated. We constructed a community pedigree and calculated kinship coefficients, a measure of relatedness between 2 subjects, for every pair of subjects in diagnostic categories: clinically definite PD, UPDRS3 score >9, Mini-Mental State Exam (MMSE) score <25, and normal.

RESULTS

Of 262 eligible subjects, 213 agreed to participate, 15 had PD, 43 had MMSE <25, 73 had UPDRS3 >9. The prevalence of PD was 5,703/100,000 with increasing prevalence in every decade of age. Excluding first-degree relatives, normal subjects were more related to each other (0.0102, SD = 0.0266) than subjects with clinically definite PD (0.0054, SD = 0.0100; p = 0.00003), subjects with UPDRS >9 (0.0076, SD = 0.0155; p = 0.00001), and subjects with MMSE <25 (0.0090, SD = 0.0180; p = 0.00003).

CONCLUSIONS

PD and parkinsonian signs are common in this population and the prevalence increases with age. The finding that subjects with PD were not more related than normal subjects suggests that environmental factors may contribute to the parkinsonian phenotype in this community.

MITOCHONDRIAL COMPLEX I, II/III, AND IV ACTIVITIES IN FAMILIAL AND SPORADIC PARKINSON'S DISEASE

A possible role of mitochondrial respiratory chain dysfunction in the pathogenesis of sporadic Parkinson's disease (PD) has been described. There are only a few reports concerning mitochondrial involvement in familial Parkinson's disease. The present study investigated mitochondrial complex I-IV activity in patients with sporadic and familial PD, compared to controls. Platelets were isolated from venous blood and platelet mitochondria were obtained through sonication and differential centrifugation. Complex I, II/III, and IV activities were measured in 17 patients with family history of Parkinson's disease (PDF), 15 patients with sporadic Parkinson disease (PDS), and 17 age-matched, healthy controls. The mitochondrial enzyme activities did not differ significantly between patient groups and controls. In addition, there was no correlation between mitochondrial complex activities and age, severity of disease, or age at onset of disease in the patient groups. In this study, the data indicate no significant differences in mitochondrial complex I-IV activities in PDF and PDS.

Parkinson's disease: from monogenic forms to genetic susceptibility factors

Research in Parkinson's disease (PD) genetics has been extremely prolific over the past decade. More than 13 loci and 9 genes have been identified, but their implication in PD is not always certain. Point mutations, duplications and triplications in the alpha-synuclein (SNCA) gene cause a rare dominant form of PD in familial and sporadic cases. Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are a more frequent cause of autosomal dominant PD, particularly in certain ethnic groups. Loss-of-function mutations in Parkin, PINK1, DJ-1 and ATP13A2 cause autosomal recessive parkinsonism with early-onset. Identification of other Mendelian forms of PD will be a main challenge for the next decade. In addition, susceptibility variants that contribute to PD have been identified in several populations, such as polymorphisms in the SNCA, LRRK2 genes and heterozygous mutations in the beta-glucocerebrosidase (GBA) gene. Genome-wide associations and re-sequencing projects, together with gene-environment interaction studies, are expected to further define the causal role of genetic determinants in the pathogenesis of PD, and improve prevention and treatment.