Variation in GIGYF2 is not associated with Parkinson disease

Association study of DNAJC13, UCHL1, HTRA2, GIGYF2, and EIF4G1 with Parkinson's disease

Rare mutations in genes originally discovered in multigenerational families have been associated with increased risk of Parkinson's disease (PD). The involvement of rare variants in DNAJC13, UCHL1, HTRA2, GIGYF2, and EIF4G1 loci has been poorly studied or has produced conflicting results across cohorts. However, they are still being often referred to as "PD genes" and used in different models. To further elucidate the role of these 5 genes in PD, we fully sequenced them using molecular inversion probes in 2408 patients with PD and 3444 controls from 3 different cohorts. A total of 788 rare variants were identified across the 5 genes and 3 cohorts. Burden analyses and optimized sequence Kernel association tests revealed no significant association between any of the genes and PD after correction for multiple comparisons. Our results do not support an association of the 5 tested genes with PD. Combined with previous studies, it is unlikely that any of these genes plays an important role in PD. Their designation as "PARK" genes should be reconsidered.

Systematically analyzing rare variants of autosomal-dominant genes for sporadic Parkinson's disease in a Chinese cohort

Studies have shown that rare variants of Mendelian genes for Parkinson's disease (PD) contribute to sporadic PD in the Caucasian population, which lacked confirmation in the Chinese population. Because the autosomal-dominant PD (AD-PD) had a phenotype closely resembling sporadic PD, we performed a systematic analysis of 7 AD-PD genes (SNCA, LRRK2, GIGYF2, VPS35, EIF4G1, DNAJC13, and CHCHD2) in 1456 Chinese sporadic PD patients and 1568 controls. Overall, 72 rare variants were identified, 7 of which were classified as likely pathogenic, 63 of which were categorized as of uncertain significance, and 2 of them were predicted to be likely benign. These AD-PD genes represented a clear enrichment of rare variants in PD patients from a burden analysis (p = 0.003), and significant differences could still be observed when likely pathogenic variants were removed (p = 0.027). The gene-based association testing also reached significance for LRRK2 (p = 0.004) and remained statistically significant after the Bonferroni correction. This report suggested that rare variants of AD-PD genes had a role in the Chinese sporadic PD cohort, especially for those rare variants of LRRK2.

Genetic analysis of indel markers in three loci associated with Parkinson's disease

The causal mutations and genetic polymorphisms associated with susceptibility to Parkinson’s disease (PD) have been extensively described. To explore the potential contribution of insertion (I)/deletion (D) polymorphisms (indels) to the risk of PD in a Chinese population, we performed genetic analyses of indel loci in ACE, DJ-1, and GIGYF2 genes. Genomic DNA was extracted from venous blood of 348 PD patients and 325 age- and sex-matched controls without neurodegenerative disease. Genotyping of the indel loci was performed by fragment length analysis after PCR and DNA sequencing. Our results showed a statistically significant association for both allele X (alleles without 5) vs. 5 (odds ratio = 1.378, 95% confidence interval = 1.112–1.708, P = 0.003) and genotype 5/X+X/X vs. 5/5 (odds ratio = 1.681, 95% confidence interval = 1.174–2.407, P = 0.004) in the GIGYF2 locus; however, no significant differences were detected for the ACE and DJ-1 indels. After stratification by gender, no significant differences were observed in any indels. These results indicate that the GIGYF2 indel may be associated with increased risk of PD in northern China.

The contribution of GIGYF2 to Parkinson's disease: a meta-analysis

The contribution of the gene of GIGYF2, Grb10-Interacting GYF Protein 2, to Parkinson's disease (PD) is still ambiguous. To explore the contribution of GIGYF2 to PD at the genetic level, we analyzed the relationship between all reported GIGYF2 variants (including mutations and polymorphisms) and PD through a meta-analysis. Databases including Medline, Embase, etc., were searched to find relevant studies. All eligible publications have to meet the strict inclusion and exclusion criteria listed. Two authors independently selected trials, assessed the article's quality and extracted data. Odds ratios (ORs) and relative risks with 95 % confidence intervals (CIs) were used to evaluate the strength of associations. All analyses were carried out by using the Review Manager software package v.5.2. More than 100 variants of GIGYF2 were reported either or both in patients and controls in 10 included publications. The 10 publications totally included 5466 patients and 6517 controls. We conducted meta-analyses for the following variants: N56S, N457T, Del LPQQQQQQ 1209-1216, Del Q 1210 (rs10555297), rs12328151, rs2289912, rs2305138, rs3816334, A572A and H1171R. The ORs for N56S were 2.86 (95 % CI 1.10, 7.41) for PD and 4.75 (95 % CI 1.35, 16.68) for FPD. And the OR for N457T in FPD was 4.53 (95 % CI 1.04, 19.66). On the other hand, other variants involved in meta-analyses were not related to PD. This research results suggest that the N56S and N457T of GIGYF2 are risk factors for PD in Caucasians, but not in Asians.

Meta-analyses of seven GIGYF2 polymorphisms with Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder that affects ~2% of the global population aged ≥65 years. Grb10-interacting GYF protein-2 (GIGYF2) can influence the development of PD through the regulation of insulin-like growth factor-1. The aim of the present meta-analysis study was to establish the contribution of GIGYF2 polymorphisms to PD. The study was conducted based on nine eligible studies consisting of 7,246 PD patients and 7,544 healthy controls. The results indicated that the GIGYF2 C.3630A>G polymorphism increased the risk of PD by 37% [P=0.008; odds ratio (OR), 1.37; 95% confidence interval (CI), 1.08-1.73] and that the GIGYF2 C.167G>A polymorphism was significantly associated with PD (P=0.003; OR, 3.67; 95% CI, 1.56-8.68). The meta-analyses of the other five GIGYF2 polymorphisms (C.1378C>A, C.1554G>A, C.2940A>G, C.1370C>A and C.3651G>A) did not reveal any significant associations. The present meta-analyses of the GIGYF2 genetic polymorphisms may provide a comprehensive overview of this PD candidate gene for future studies.

Monogenic Parkinson's disease and parkinsonism: clinical phenotypes and frequencies of known mutations

Mutations in seven genes are robustly associated with autosomal dominant (SNCA, LRRK2, EIF4G1, VPS35) or recessive (parkin/PARK2, PINK1, DJ1/PARK7) Parkinson's disease (PD) or parkinsonism. Changes in a long list of additional genes have been suggested as causes for parkinsonism or PD, including genes for hereditary ataxias (ATXN2, ATXN3, FMR1), frontotemporal dementia (C9ORF72, GRN, MAPT, TARDBP), DYT5 (GCH1, TH, SPR), and others (ATP13A2, CSF1R, DNAJC6, FBXO, GIGYF2, HTRA2, PLA2G6, POLG, SPG11, UCHL1). This review summarizes the clinical features of diseases caused by mutations in these genes, and their frequencies. Point mutations and multiplications in SNCA cause cognitive or psychiatric symptoms, parkinsonism, dysautonomia and myoclonus with widespread alpha-synuclein pathology in the central and peripheral nervous system. LRRK2 mutations may lead to a clinical phenotype closely resembling idiopathic PD with a puzzling variety in neuropathology. Mutations in parkin/PARK2, PINK1 or DJ1/PARK7 may cause early-onset parkinsonism with a low risk for cognitive decline and a pathological process usually restricted to the brainstem. Carriers of mutations in the other genes may develop parkinsonism with or without additional symptoms, but rarely a disease resembling PD. The pathogenicity of several mutations remains unconfirmed. Although some mutations occur with high frequency in specific populations, worldwide all are very rare. The genetic cause of the majority of patients with sporadic or hereditary PD remains unknown in most populations. Clinical genetic testing is useful for selected patients. Testing strategies need to be adapted individually based on clinical phenotype and estimated frequency of the mutation in the patient's population.

Follow-up study of variants of the GIGYF2 gene in Chinese patients with Parkinson’s disease

The Grb10-interacting GYF protein-2 gene (GIGYF2) is a PARK11 gene that reportedly has a causal role in familial Parkinson’s disease (PD) among populations from Italy and France. However, no comprehensive study of the GIGYF2 gene has been conducted among PD patients from mainland China. In our previous study, the GIGYF2 gene was directly sequenced, and nine missense variants and 14 polymorphisms were identified. For these 14 polymorphisms, in the present study we performed a case–control analysis for 300 PD patients and 200 healthy controls from mainland China. The c.297T>C p.Ala99Ala polymorphism was associated with increased risk with respect to the pathogenesis of sporadic PD. In conclusion, within the Chinese population, the c.297T>C p.Ala99Ala polymorphism of the GIGYF2 gene may be associated with an increased risk of developing PD.

What genetics tells us about the causes and mechanisms of Parkinson's disease

Parkinson's disease (PD) is a common motor disorder of mysterious etiology. It is due to the progressive degeneration of the dopaminergic neurons of the substantia nigra and is accompanied by the appearance of intraneuronal inclusions enriched in α-synuclein, the Lewy bodies. It is becoming increasingly clear that genetic factors contribute to its complex pathogenesis. Over the past decade, the genetic basis of rare PD forms with Mendelian inheritance, representing no more than 10% of the cases, has been investigated. More than 16 loci and 11 associated genes have been identified so far; genome-wide association studies have provided convincing evidence that polymorphic variants in these genes contribute to sporadic PD. The knowledge acquired of the functions of their protein products has revealed pathways of neurodegeneration that may be shared between inherited and sporadic PD. An impressive set of data in different model systems strongly suggest that mitochondrial dysfunction plays a central role in clinically similar, early-onset autosomal recessive PD forms caused by parkin and PINK1, and possibly DJ-1 gene mutations. In contrast, α-synuclein accumulation in Lewy bodies defines a spectrum of disorders ranging from typical late-onset PD to PD dementia and including sporadic and autosomal dominant PD forms due to mutations in SCNA and LRRK2. However, the pathological role of Lewy bodies remains uncertain, as they may or may not be present in PD forms with one and the same LRRK2 mutation. Impairment of autophagy-based protein/organelle degradation pathways is emerging as a possible unifying but still fragile pathogenic scenario in PD. Strengthening these discoveries and finding other convergence points by identifying new genes responsible for Mendelian forms of PD and exploring their functions and relationships are the main challenges of the next decade. It is also the way to follow to open new promising avenues of neuroprotective treatment for this devastating disorder.

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.

Common variants in PARK loci and related genes and Parkinson's disease

Rare mutations in PARK loci genes cause Parkinson's disease (PD) in some families and isolated populations. We investigated the association of common variants in PARK loci and related genes with PD susceptibility and age at onset in an outbred population. A total of 1,103 PD cases from the upper Midwest, USA, were individually matched to unaffected siblings (n = 654) or unrelated controls (n = 449) from the same region. Using a sequencing approach in 25 cases and 25 controls, single nucleotide polymorphisms (SNPs) in species-conserved regions of PARK loci and related genes were detected. We selected additional tag SNPs from the HapMap. We genotyped a total of 235 SNPs and two variable number tandem repeats in the ATP13A2, DJ1, LRRK1, LRRK2, MAPT, Omi/HtrA2, PARK2, PINK1, SNCA, SNCB, SNCG, SPR, and UCHL1 genes in all 2,206 subjects. Case-control analyses were performed to study association with PD susceptibility, while cases-only analyses were used to study association with age at onset. Only MAPT SNP rs2435200 was associated with PD susceptibility after correction for multiple testing (OR = 0.74, 95% CI = 0.64-0.86, uncorrected P < 0.0001, log additive model); however, 16 additional MAPT variants, seven SNCA variants, and one LRRK2, PARK2, and UCHL1 variants each had significant uncorrected P-values. There were no significant associations for age at onset after correction for multiple testing. Our results confirm the association of MAPT and SNCA genes with PD susceptibility but show limited association of other PARK loci and related genes with PD.

New insights in gene-derived therapy: the example of Duchenne muscular dystrophy

The two therapeutic approaches currently most advanced in clinical trials for Duchenne muscular dystrophy are antisense-mediated exon skipping and forced read-through of premature stop codons. Interestingly, these approaches target the gene product rather than the gene itself. This review will explain the rationale and current state of affairs of these approaches and will then discuss how these gene-derived therapies might also be applicable to other diseases.

No evidence for pathogenic role of GIGYF2 mutation in Parkinson disease in Japanese patients

Grb10-Interacting GYF Protein-2 (GIGYF2) is a candidate gene for PARK11 locus. To date, seven different GIGYF2 missense mutations have been identified in patients with familial Parkinson disease (PD) of European descent. To clarify the pathogenic role of GIGYF2 in PD, we analyzed the frequency of GIGYF2 mutations in 389 Japanese patients with PD (including 93 patients with late-onset familial PD, 276 with sporadic PD, and 20 with a single heterozygous mutation in the PD-associated genes), and 336 Japanese normal controls, by direct sequencing and/or high-resolution melting analysis. None of the reported GIGYF2 mutations or digenic mutations were detected. Two novel non-synonymous variants were identified (p.Q1211delQ and p.H1023Q), however, we could not determine their roles in PD. In summary, we found no evidence for PD-associated roles of GIGYF2 mutations. Our data suggest that GIGYF2 is unlikely to play a major role in PD in Japanese patients, similar to other populations.

Mutational analysis of GIGYF2, ATP13A2 and GBA genes in Brazilian patients with early-onset Parkinson's disease

In the last decade, several genes have been linked to Parkinson's disease (PD), including GIGYF2, ATP13A2 and GBA. To explore whether mutations in these genes contribute to development of PD in the Brazilian population, we screened 110 patients with early-onset PD. No clearly pathogenic mutations were identified in ATP13A2 and GIGYF2. In contrast, we identified a significantly higher frequency of known pathogenic mutations in GBA gene among the PD cases (6/110=5.4%) when compared to the control group (0/155) (P=0.0047). Our results strongly support an association between GBA gene mutations and an increased risk of PD. Mutations in GIGYF2 and ATP13A2 do not seem to represent a risk factor to the development of PD in the Brazilian population. Considering the scarcity of studies on GIGYF2, ATP13A2 and GBA mutation frequency in Latin American countries, we present significant data about the contribution of these genes to PD susceptibility.

GIGYF2 is present in endosomal compartments in the mammalian brains and enhances IGF-1-induced ERK1/2 activation

GIGYF2 has been reported as a candidate gene for PARK11-linked Parkinson's disease (PD). Heterozygous knockout of GIGYF2 results in neurodegeneration, suggesting important roles for GIGYF2 (Grb10 interacting GYF protein 2) in the CNS. In this study, we used novel GIGYF2 antibodies to clarify the distribution and function of GIGYF2. GIGYF2 was widely expressed, most highly in the pancreas and testis, and moderately in brain, lung, liver, kidney and spleen. In the brain, GIGYF2 was tightly associated with membrane in the S3 fraction, and localised in neuronal perikarya and proximal dendrites. Immunohistochemical analysis indicated sites of GIGYF2 localisation throughout the mouse brain, with high levels in the cerebral cortex, hippocampus, cerebellum, olfactory bulb and brainstem nuclei, but low levels in the substantia nigra and striatum. GIGYF2 was present in endosomes immunopositive for Rab4 and Grb10. Expression of GIGYF2 altered insulin-like growth factor-1 (IGF-1) receptor trafficking and enhanced IGF-1-induced extracellular signal-regulated kinase 1/2 phosphorylation, but not IGF-1 receptor or serine/threonine protein kinase Akt phosphorylation. There were no significant differences in signalling activation between cells expressing wild-type and putative PD-associated mutant GIGYF2. In PD brains, GIGYF2 did not localise to Lewy bodies. Our findings indicate a role for GIGYF2 in the regulation of signalling at endosomes, but no contribution of GIGYF2 to the pathogenesis of PD.

Genetics of Parkinson disease and essential tremor

PURPOSE OF REVIEW

Elucidating the genetic background of Parkinson disease and essential tremor is crucial to understand the pathogenesis and improve diagnostic and therapeutic strategies.

RECENT FINDINGS

A number of approaches have been applied including familial and association studies, and studies of gene expression profiles to identify genes involved in susceptibility to Parkinson disease. These studies have nominated a number of candidate Parkinson disease genes and novel loci including Omi/HtrA2, GIGYF2, FGF20, PDXK, EIF4G1 and PARK16. A recent notable finding has been the confirmation for the role of heterozygous mutations in glucocerebrosidase (GBA) as risk factors for Parkinson disease. Finally, association studies have nominated genetic variation in the leucine-rich repeat and Ig containing 1 gene (LINGO1) as a risk for both Parkinson disease and essential tremor, providing the first genetic evidence of a link between the two conditions.

SUMMARY

Although undoubtedly genes remain to be identified, considerable progress has been achieved in the understanding of the genetic basis of Parkinson disease. This same effort is now required for essential tremor. The use of next-generation high-throughput sequencing and genotyping technologies will help pave the way for future insight leading to advances in diagnosis, prevention and cure.

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.

From genes to proteins in mendelian Parkinson's disease: an overview

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. A progressive movement disorder typified by the production of bradykinesia, tremor, rigidity, and impairment of postural reflexes, PD is characterized by a depletion of dopamine in the striatum. For the last decade, several Mendelian forms of PD have been identified. Mutations in these genes potentially lead to autosomal dominant (alpha-synuclein and LRRK2), or autosomal recessive PD (Parkin, PINK1, DJ1, and ATP13A2). This article will spotlight these six distinct genes unambiguously associated with Mendelian PD and the function of their encoded proteins.

Mutational screening and zebrafish functional analysis of GIGYF2 as a Parkinson-disease gene

The Grb10-Interacting GYF Protein-2 (GIGYF2) gene has been proposed as the Parkinson-disease (PD) gene underlying the PARK11 locus. However, association of GIGYF2 with PD has been challenged and a functional validation of GIGYF2 mutations is lacking. In this frame, we performed a mutational screening of GIGYF2 in an Italian PD cohort. Exons containing known mutations were analyzed in 552 cases and 552 controls. Thereafter, a subset of 184 familial PD cases and controls were subjected to a full coding-exon screening. These analyses identified 8 missense variations in 9 individuals (4 cases, 5 controls). Furthermore, we developed a zebrafish model of gigyf2 deficiency. Abrogation of gigyf2 function in zebrafish embryos did not lead to a drastic cell loss in diencephalic dopaminergic (DA) neuron clusters, suggesting that gigyf2 is not required for DA neuron differentiation. Notably, gigyf2 functional abrogation did not increase diencephalic DA neurons susceptibility to the PD-inducing drug MPP+. These data, together with those recently reported by other groups, suggest that GIGYF2 is unlikely to be the PARK11 gene.

GIGYF2 gene disruption in mice results in neurodegeneration and altered insulin-like growth factor signaling

Grb10-Interacting GYF Protein 2 (GIGYF2) was initially identified through its interaction with Grb10, an adapter protein that binds activated IGF-I and insulin receptors. The GIGYF2 gene maps to human chromosome 2q37 within a region linked to familial Parkinson's disease (PARK11 locus), and association of GIGYF2 mutations with Parkinson's disease has been described in some but not other recent publications. This study investigated the consequences of Gigyf2 gene disruption in mice. Gigyf2 null mice undergo apparently normal embryonic development, but fail to feed and die within the first 2 post-natal days. Heterozygous Gigyf2(+/-) mice survive to adulthood with no evident metabolic or growth defects. At 12-15 months of age, the Gigyf2(+/-) mice begin to exhibit motor dysfunction manifested as decreased balance time on a rotating horizontal rod. This is associated with histopathological evidence of neurodegeneration and rare intracytoplasmic Lewy body-like inclusions in spinal anterior horn motor neurons. There are alpha-synuclein positive neuritic plaques in the brainstem and cerebellum, but no abnormalities in the substantia nigra. Primary cultured embryo fibroblasts from Gigyf2 null mice exhibit decreased IGF-I-stimulated IGF-I receptor tyrosine phosphorylation and augmented ERK1/2 phosphorylation. These data provide further evidence for an important role of GIGYF2 in age-related neurodegeneration and IGF pathway signaling.

Pathogenesis of familial Parkinson's disease: new insights based on monogenic forms of Parkinson's disease

Parkinson's disease (PD) is one of the most common movement disorders caused by the loss of dopaminergic neuronal cells. The molecular mechanisms underlying neuronal degeneration in PD remain unknown; however, it is now clear that genetic factors contribute to the pathogenesis of this disease. Approximately, 5% of patients with clinical features of PD have clear familial etiology, which show a classical recessive or dominant Mendelian mode of inheritance. Over the decade, more than 15 loci and 11 causative genes have been identified so far and many studies shed light on their implication in not only monogenic but also sporadic form of PD. Recent studies revealed that PD-associated genes play important roles in cellular functions, such as mitochondrial functions, ubiquitin-proteasomal system, autophagy-lysosomal pathway and membrane trafficking. Furthermore, the proteins encoded by PD-associated genes can interact with each other and such gene products may share a common pathway that leads to nigral degeneration. However, their precise roles in the disease and their normal functions remain poorly understood. In this study, we review recent progress in knowledge about the genes associated with familial PD.

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.