Genetics of Parkinson disease and other movement disorders

Mitochondrial Neurodegenerative Diseases: Three Mitochondrial Ribosomal Proteins as Intermediate Stage in the Pathway That Associates Damaged Genes with Alzheimer's and Parkinson's

Currently, numerous research endeavors are dedicated to unraveling the intricate nature of neurodegenerative diseases. These conditions are characterized by the gradual and progressive impairment of specific neuronal systems that exhibit anatomical or physiological connections. In particular, in the last twenty years, remarkable efforts have been made to elucidate neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. However, despite extensive research endeavors, no cure or effective treatment has been discovered thus far. With the emergence of studies shedding light on the contribution of mitochondria to the onset and advancement of mitochondrial neurodegenerative disorders, researchers are now directing their investigations toward the development of therapies. These therapies include molecules designed to protect mitochondria and neurons from the detrimental effects of aging, as well as mutant proteins. Our objective is to discuss and evaluate the recent discovery of three mitochondrial ribosomal proteins linked to Alzheimer's and Parkinson's diseases. These proteins represent an intermediate stage in the pathway connecting damaged genes to the two mitochondrial neurological pathologies. This discovery potentially could open new avenues for the production of medicinal substances with curative potential for the treatment of these diseases.

Monogenic Parkinson’s Disease: Genotype, Phenotype, Pathophysiology, and Genetic Testing

Parkinson’s disease may be caused by a single pathogenic variant (monogenic) in 5–10% of cases, but investigation of these disorders provides valuable pathophysiological insights. In this review, we discuss each genetic form with a focus on genotype, phenotype, pathophysiology, and the geographic and ethnic distribution. Well-established Parkinson’s disease genes include autosomal dominant forms (SNCA, LRRK2, and VPS35) and autosomal recessive forms (PRKN, PINK1 and DJ1). Furthermore, mutations in the GBA gene are a key risk factor for Parkinson’s disease, and there have been major developments for X-linked dystonia parkinsonism. Moreover, atypical or complex parkinsonism may be due to mutations in genes such as ATP13A2, DCTN1, DNAJC6, FBXO7, PLA2G6, and SYNJ1. Furthermore, numerous genes have recently been implicated in Parkinson’s disease, such as CHCHD2, LRP10, TMEM230, UQCRC1, and VPS13C. Additionally, we discuss the role of heterozygous mutations in autosomal recessive genes, the effect of having mutations in two Parkinson’s disease genes, the outcome of deep brain stimulation, and the role of genetic testing. We highlight that monogenic Parkinson’s disease is influenced by ethnicity and geographical differences, reinforcing the need for global efforts to pool large numbers of patients and identify novel candidate genes.

Active status on phytochemistry and pharmacology of Pergularia daemia Forsk. (Trellis-vine): a review

Background

Medicinal plants play a significant role in the progress of persuasive therapeutic agents. Earlier to the innovation of synthetic drugs, human beings completely relied on the plants for the treatment of various ailments. Natural product extracts, particularly those derived from different plant species, provided the main source of Siddha, Ayurveda and Folk medicines. P. daemia is a perennial climber, traditionally reported for the treatment in a variety of diseases. In present review, we focused on the present status of phytochemical and pharmacological activities P. daemia.

Methodology

With the support of electronic databases such as Science Direct, Google Scholar, Mendeley, Scirus and PubMed central. Traditional knowledge information collected by Indian taxonomical books, survey from local rural and tribal peoples. Pharmacological data’s obtained from scientific journals published from 2000 to 2020.

Results

P. daemia extract, contains several phytochemicals, especially rich in flavonoids. These secondary metabolites synthesized from P. daemia have been reported for the treatment of various chronic diseases. In recent years, P. daemia phytoconstituents set as a key role in natural drug development as it harbours many in vitro and in vivo pharmacological activities such as anti-inflammatory, anti-cancer, anti-fertility, anti-arthritic and antimicrobial etc.,

Conclusion

P. daemia was the less studied plant compared to other medicinal plants. In this context more emphasis has to be laid on studies that discuss on the secondary metabolite activities and molecular mechanisms that work against various chronic diseases.

A new alpha-synuclein missense variant (Thr72Met) in two Turkish families with Parkinson's disease

Introduction:

Missense variants and multiplications of the alpha-synuclein gene (SNCA) are established as rare causes of autosomal dominant forms of Parkinson’s Disease (PD).

Methods:

Two families of Turkish origins with PD were studied; the SNCA coding region was analyzed by Sanger sequencing, and by whole exome sequencing (WES) in the index patient of the first and the second family, respectively. Co-segregation studies and haplotype analysis across the SNCA locus were carried out. Functional studies included in vitro thioflavin-T aggregation assay and in silico structural modelling of the alpha-synuclein (α-syn) protein.

Results:

We identified a novel heterozygous SNCA variant, c.215C > T (p.Thr72Met), segregating with PD in a total of four members in the two families. A shared haplotype across the SNCA locus was found among variant carriers, suggestive of a common ancestor. We next showed that the Thr72Met α-syn displays enhanced aggregation in-vitro, compared to the wild-type species. In silico analysis of a tetrameric α-syn structural model revealed that Threonine 72 lies in the tetrameric interface, and substitution with the much larger methionine residue could potentially destabilize the tetramer.

Conclusion:

We present clinical, genetic, and functional data supporting a causative role of the SNCA c.215C > T (p.Thr72Met) variant in familial PD. Testing for this variant in patients with PD, especially of Turkish origin, might detect additional carriers. Further functional analyses might offer new insights into the shared biochemical properties of the PD-causing SNCA missense variants, and how they lead to neurodegeneration.

PGC-1s in the Spotlight with Parkinson's Disease

Parkinson's disease is one of the most common neurodegenerative disorders worldwide, characterized by a progressive loss of dopaminergic neurons mainly localized in the substantia nigra pars compacta. In recent years, the detailed analyses of both genetic and idiopathic forms of the disease have led to a better understanding of the molecular and cellular pathways involved in PD, pointing to the centrality of mitochondrial dysfunctions in the pathogenic process. Failure of mitochondrial quality control is now considered a hallmark of the disease. The peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1) family acts as a master regulator of mitochondrial biogenesis. Therefore, keeping PGC-1 level in a proper range is fundamental to guarantee functional neurons. Here we review the major findings that tightly bond PD and PGC-1s, raising important points that might lead to future investigations.

Genes causing congenital hydrocephalus: Their chromosomal characteristics of telomere proximity and DNA compositions

Congenital hydrocephalus (CH) is caused by genetic mutations, but whether factors impacting human genetic mutations are disease-specific remains elusive. Given two factors associated with high mutation rates, we reviewed how many disease-susceptible genes match with (i) proximity to telomeres or (ii) high adenine and thymine (A + T) content in human CH as compared to other disorders of the central nervous system (CNS). We extracted genomic information using a genome data viewer. Importantly, 98 of 108 genes causing CH satisfied (i) or (ii), resulting in >90% matching rate. However, such a high accordance no longer sustained as we checked two factors in Alzheimer's disease (AD) and/or familial Parkinson's disease (fPD), resulting in 84% and 59% matching, respectively. A disease-specific matching of telomere proximity or high A + T content predicts causative genes of CH much better than neurodegenerative diseases and other CNS conditions, likely due to sufficient number of known causative genes (n = 108) and precise determination and classification of the genotype and phenotype. Our analysis suggests a need for identifying genetic basis of both factors before human clinical studies, to prioritize putative genes found in preclinical models into the likely (meeting at least one) and more likely candidate (meeting both), which predisposes human genes to mutations.

Isolated dystonia: clinical and genetic updates

Four genes associated with isolated dystonia are currently well replicated and validated. DYT-THAP1 manifests as young-onset generalized dystonia with predominant craniocervical symptoms; and is associated with mostly deleterious missense variation in the THAP1 gene. De novo and inherited missense and protein truncating variation in GNAL as well as primarily missense variation in ANO3 cause isolated focal and/or segmental dystonia with preference for the upper half of the body and older ages at onset. The GAG deletion in TOR1A is associated with generalized dystonia with onset in childhood in the lower limbs. Rare variation in these genes causes monogenic sporadic and inherited forms of isolated dystonia; common variation may confer risk and imply that dystonia is a polygenic trait in a subset of cases. Although candidate gene screens have been successful in the past in detecting gene-disease associations, recent application of whole-genome and whole-exome sequencing methods enable unbiased capture of all genetic variation that may explain the phenotype. However, careful variant-level evaluation is necessary in every case, even in genes that have previously been associated with disease. We review the genetic architecture and phenotype of DYT-THAP1, DYT-GNAL, DYT-ANO3, and DYT-TOR1A by collecting case reports from the literature and performing variant classification using pathogenicity criteria.

Microglial VPS35 deficiency regulates microglial polarization and decreases ischemic stroke-induced damage in the cortex

BACKGROUND

Vacuolar sorting protein 35 (VPS35), a critical component of retromer, is essential for selective endosome-to-Golgi retrieval of membrane proteins. It is highly expressed in microglial cells, in addition to neurons. We have previously demonstrated microglial VPS35's functions in preventing hippocampal, but not cortical, microglial activation, and in promoting adult hippocampal neurogenesis. However, microglial VPS35's role in the cortex in response to ischemic stroke remains largely unclear.

METHODS

We used mice with VPS35 cKO (conditional knockout) in microglial cells and examined and compared their responses to ischemic stroke with control mice. The brain damage, cell death, changes in glial cells and gene expression, and sensorimotor deficits were assessed by a combination of immunohistochemical and immunofluorescence staining, RT-PCR, Western blot, and neurological functional behavior tests.

RESULTS

We found that microglial VPS35 loss results in an increase of anti-inflammatory microglia in mouse cortex after ischemic stroke. The ischemic stroke-induced brain injury phenotypes, including brain damage, neuronal death, and sensorimotor deficits, were all attenuated by microglial VPS35-deficiency. Further analysis of protein expression changes revealed a reduction in CX3CR1 (CX3C chemokine receptor 1) in microglial VPS35-deficient cortex after ischemic stroke, implicating CX3CR1 as a potential cargo of VPS35 in this event.

CONCLUSION

Together, these results reveal an unrecognized function of microglial VPS35 in enhancing ischemic brain injury-induced inflammatory microglia, but suppressing the injury-induced anti-inflammatory microglia. Consequently, microglial VPS35 cKO mice exhibit attenuation of ischemic brain injury response.

Inhibitory role of peroxiredoxin 2 in LRRK2 kinase activity induced cellular pathogenesis

Parkinson's disease (PD) is a major neurodegenerative disease. One of the known genetic contributors to PD pathogenesis is leucine-rich repeat kinase 2 (LRRK2) whose mutations with elevated kinase activity could lead to both familial and sporadic PD. However, how the pathogenic kinase activity of LRRK2 is regulated remains largely unclear. Here we report that peroxiredoxin 2 (Prx2) was identified as a novel interacting protein to LRRK2 with preferential expression in dopaminergic neurons over other Prx proteins. We also confirmed that Prx2 interacted with LRRK2 through its COR domain and its overexpression significantly decreased the kinase activity of mutant LRRK2. Functionally, overexpressed Prx2 rescued the transfected cells from LRRK2 mutant induced apoptotic processes. Importantly, overexpressed Prx2 reversed the altered subcellular distribution of cation-independent mannose 6-phosphate receptor (CI-M6PR) induced by PD-mutant LRRK2. Our results suggest that, by interacting with LRRK2, Prx2 may play an inhibitory role in the LRRK2 mediated cellular toxicity in PD by inhibiting its kinase activity.

Biochemical and morphological classification of disease-associated alpha-synuclein mutants aggregates

Alpha-synuclein (a-syn) aggregation in brain is implicated in several synucleinopathies, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). Until date, at least six disease-associated mutations in a-syn (namely A30P, E46K, H50Q, G51D, A53T, and A53E) are known to cause dominantly inherited familial forms of synucleinopathies. Previous studies using recombinant proteins have reported that a subset of disease-associated mutants show higher aggregation propensities and form spectroscopically distinguishable aggregates compared to wild-type (WT). However, morphological and biochemical comparison of the aggregates for all disease-associated a-syn mutants have not yet been performed. In this study, we performed electron microscopic examination, guanidinium hydrochloride (GdnHCl) denaturation, and protease digestion to classify the aggregates from their respective point mutations. Using electron microscopy we observed variations of amyloid fibrillar morphologies among the aggregates of a-syn mutants, mainly categorized into two groups: twisted fibrils observed for both WT and E46K while straight fibrils for the other mutants. GdnHCl denaturation experiments revealed the a-syn mutants except for E46K were more resistant than WT against the denaturation. Mass spectrometry analysis of protease-treated aggregates showed a variety of protease-resistant cores, which may correspond to their morphological properties. The difference of their properties could be implicated in the clinicopathological difference of synucleinopathies with those mutations.

Animal Toxins as Therapeutic Tools to Treat Neurodegenerative Diseases

Neurodegenerative diseases affect millions of individuals worldwide. So far, no disease-modifying drug is available to treat patients, making the search for effective drugs an urgent need. Neurodegeneration is triggered by the activation of several cellular processes, including oxidative stress, mitochondrial impairment, neuroinflammation, aging, aggregate formation, glutamatergic excitotoxicity, and apoptosis. Therefore, many research groups aim to identify drugs that may inhibit one or more of these events leading to neuronal cell death. Venoms are fruitful natural sources of new molecules, which have been relentlessly enhanced by evolution through natural selection. Several studies indicate that venom components can exhibit selectivity and affinity for a wide variety of targets in mammalian systems. For instance, an expressive number of natural peptides identified in venoms from animals, such as snakes, scorpions, bees, and spiders, were shown to lessen inflammation, regulate glutamate release, modify neurotransmitter levels, block ion channel activation, decrease the number of protein aggregates, and increase the levels of neuroprotective factors. Thus, these venom components hold potential as therapeutic tools to slow or even halt neurodegeneration. However, there are many technological issues to overcome, as venom peptides are hard to obtain and characterize and the amount obtained from natural sources is insufficient to perform all the necessary experiments and tests. Fortunately, technological improvements regarding heterologous protein expression, as well as peptide chemical synthesis will help to provide enough quantities and allow chemical and pharmacological enhancements of these natural occurring compounds. Thus, the main focus of this review is to highlight the most promising studies evaluating animal toxins as therapeutic tools to treat a wide variety of neurodegenerative conditions, including Alzheimer’s disease, Parkinson’s disease, brain ischemia, glaucoma, amyotrophic lateral sclerosis, and multiple sclerosis.

Genetics of Parkinson disease

An understanding of the genetic etiology of Parkinson disease (PD) has become imperative for the modern-day neurologist. Although genetic forms cause only a minority of PD, the disease mechanisms they elucidate advance the understanding of idiopathic cases. Moreover, recently identified susceptibility variants contribute to complex-etiology PD and broaden the contribution of genetics beyond familial and early-onset cases. Dominantly inherited monogenic forms mimic idiopathic PD and are caused by mutations or copy number variations of SNCA, LRRK2, and VPS35. On the other hand, early-onset forms are associated with PARKIN, PINK1, and DJ1 mutations, nominating mitochondrial dysfunction and oxidative stress as another important molecular pathway in the causation of the disease, in addition to alpha-synuclein accumulation. Common variants in GBA are consistently identified by association studies and may be considered to be a major risk gene for PD, with markedly reduced penetrance. Other genes have been proposed to be associated with PD; however, these only cause very rare forms, if at all. Current guidelines recommend testing for LRRK2 variants in familial PD or in specific populations (ancestry), and for the recessive genes in early-onset PD. However, gene panels have made testing for multiple forms of genetic PD a viable approach.

Lack of TMEM230 mutations in patients with familial and sporadic Parkinson's disease in a Taiwanese population

Mutations in transmembrane protein 230 (TMEM230) have recently been reported to be associated with Parkinson's disease (PD) in a North American population. A highly prevalent mutation, c.550_552delTAGinsCCCGGG (p.*184ProGlyext*5) was found in 3.1% of Chinese familial PD patients. However, subsequent studies failed to replicate these findings in different populations. Our objective was to confirm the role of this gene in a large number of PD patients and controls in a Taiwanese population. Among 1,672 participants, we sequenced all coding exons and exon-intron boundary junctions of the TMEM230 gene in 180 probands with familial PD. We also genotyped the potential pathogenic variants identified and the previously reported mutations (p.Arg141Leu, p.Tyr92Cys, p.*184Trpext*5, and p.*184ProGlyext*5) in an additional cohort of 500 patients with sporadic PD, and 992 age and gender-matched neurologically normal control subjects. We did not find any of the previously reported mutations, but we observed one novel missense exonic variant, c.G68A (p.Arg23Gln), in one patient with familial PD, and two patients with sporadic PD in a heterozygous state. However, subsequent analysis of this variant in 992 controls did not find any significant associations between p.Arg23Gln and the risk of PD (0.44% vs. 0.30%, p = 0.22). Our findings suggest that genetic variants of TMEM230 do not play a major role in PD in our Taiwanese population. Further experimental studies are warranted to confirm the pathogenicity of this gene in PD disease process.

[Genetic risk variants in Parkinson's disease and other movement disorders]

Movement disorders are often genetically complex with genetic risk factors playing a major role. For example, monogenic causes of Parkinson's disease (PD) can be found in only 2-5% of patients who often have an early onset (<40 years). In the majority of patients, common genetic variants seem to contribute to the disease risk. To date, 24 genetic risk factors have been identified. For restless legs syndrome (RLS), six different risk variants have been reported but no monogenic cause is known yet. For the genetic risk factors of essential tremor and dystonia, which are less well studied, only five and two candidate variants, respectively, have been described but their roles still require independent confirmation. In this review, we provide an overview on the involved genes, their function, and discuss possible, disease mechanism-driven therapies.

Applications of CRISPR/Cas9 for Gene Editing in Hereditary Movement Disorders

Gene therapy is a potential therapeutic strategy for treating hereditary movement disorders, including hereditary ataxia, dystonia, Huntington’s disease, and Parkinson’s disease. Genome editing is a type of genetic engineering in which DNA is inserted, deleted or replaced in the genome using modified nucleases. Recently, clustered regularly interspaced short palindromic repeat/CRISPR associated protein 9 (CRISPR/Cas9) has been used as an essential tool in biotechnology. Cas9 is an RNA-guided DNA endonuclease enzyme that was originally associated with the adaptive immune system of Streptococcus pyogenes and is now being utilized as a genome editing tool to induce double strand breaks in DNA. CRISPR/Cas9 has advantages in terms of clinical applicability over other genome editing technologies such as zinc-finger nucleases and transcription activator-like effector nucleases because of easy in vivo delivery. Here, we review and discuss the applicability of CRISPR/Cas9 to preclinical studies or gene therapy in hereditary movement disorders.

Unexpected toxicity of very low dose MPTP in mice: A clue to the etiology of Parkinson's disease?

Although much progress have been made in recent years, the etiology of idiopathic Parkinson's disease remains obscure. The chance discovery that injection of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces a syndrome very similar to parkinsonism introduced the "environmental toxin" hypothesis but no toxin was ever found in any quantity in patients' brains. We have unexpectedly now found, however, that, in mice, very low doses of MPTP induce as much dopaminergic neuronal death as far higher doses. Cellular detoxification mechanisms would appear to be incapacitated at such low doses. This could infer that the barely discernible presence of an unidentified neurotoxin may be responsible for the onset of Parkinson's disease.

Computational deconvolution of genome wide expression data from Parkinson's and Huntington's disease brain tissues using population-specific expression analysis

The characterization of molecular changes in diseased tissues gives insight into pathophysiological mechanisms and is important for therapeutic development. Genome-wide gene expression analysis has proven valuable for identifying biological processes in neurodegenerative diseases using post mortem human brain tissue and numerous datasets are publically available. However, many studies utilize heterogeneous tissue samples consisting of multiple cell types, all of which contribute to global gene expression values, confounding biological interpretation of the data. In particular, changes in numbers of neuronal and glial cells occurring in neurodegeneration confound transcriptomic analyses, particularly in human brain tissues where sample availability and controls are limited. To identify cell specific gene expression changes in neurodegenerative disease, we have applied our recently published computational deconvolution method, population specific expression analysis (PSEA). PSEA estimates cell-type-specific expression values using reference expression measures, which in the case of brain tissue comprises mRNAs with cell-type-specific expression in neurons, astrocytes, oligodendrocytes and microglia. As an exercise in PSEA implementation and hypothesis development regarding neurodegenerative diseases, we applied PSEA to Parkinson's and Huntington's disease (PD, HD) datasets. Genes identified as differentially expressed in substantia nigra pars compacta neurons by PSEA were validated using external laser capture microdissection data. Network analysis and Annotation Clustering (DAVID) identified molecular processes implicated by differential gene expression in specific cell types. The results of these analyses provided new insights into the implementation of PSEA in brain tissues and additional refinement of molecular signatures in human HD and PD.

Personalized medicine in neurodegenerative diseases: how far away?

Neurodegenerative diseases are characterized by progressive dysfunction of the nervous system as a result of neuronal loss in the brain and spinal cord. Despite extensive research efforts aimed at development of new disease-modifying therapeutics, there is still no effective treatment to halt neurodegenerative processes. Thus, modification of current therapeutic and diagnostic research strategies is a goal of increasing urgency. The biggest limitation in neurodegenerative disease research is the lack of appropriate biomarkers. Discovery of universal biomarkers capable of diagnosing patients with neurodegenerative diseases, monitoring their response to therapy, and predicting disease progression seems to be a tall order. Instead, a combination of different methodologies in the discovery of biomarkers specific for each described aspect of the disease seems to be a more viable approach. Although application of personalized medicine in diagnosis and treatment of neurodegenerative diseases may seem far off, some recent developments, such as utilizing specific biological therapies in multiple sclerosis, microRNA profiling as a source of novel biomarkers in Parkinson’s disease, or combination of neuroimaging and proteomic analyses in diagnosis of Alzheimer’s disease patients, already point to the way clinical neurology may integrate new achievements in everyday practice. Combination of genomic, proteomic, glycomic, and metabolomic approaches may yield novel insights into molecular mechanisms of disease pathophysiology, which could then be integrated and translated into clinical neurology. Based on the developments during the past decade, it is feasible to predict that a personalized approach to treating neurological disorders will become more widely applicable in the coming years.

Next generation sequencing and the future of genetic diagnosis

The introduction of next generation sequencing (NGS) has led to an exponential increase of elucidated genetic causes in both extremely rare diseases and common but heterogeneous disorders. It can be applied to the whole or to selected parts of the genome (genome or exome sequencing, gene panels). NGS is not only useful in large extended families with linkage information, but may also be applied to detect de novo mutations or mosaicism in sporadic patients without a prior hypothesis about the mutated gene. Currently, NGS is applied in both research and clinical settings, and there is a rapid transition of research findings to diagnostic applications. These developments may greatly help to minimize the "diagnostic odyssey" for patients as whole-genome analysis can be performed in a few days at reasonable costs compared with gene-by-gene analysis based on Sanger sequencing following diverse clinical tests. Despite the enthusiasm about NGS, one has to keep in mind its limitations, such as a coverage and accuracy of < 100%, resulting in missing variants and false positive findings. In addition, variant interpretation is challenging as there is usually more than one candidate variant found. Therefore, there is an urgent need to define standards for NGS with respect to run quality and variant interpretation, as well as mechanisms of quality control. Further, there are ethical challenges including incidental findings and how to guide unaffected probands seeking direct-to-customer testing. However, taken together, the application of NGS in research and diagnostics provides a tremendous opportunity to better serve our patients.

STUB1 mutations in autosomal recessive ataxias - evidence for mutation-specific clinical heterogeneity

BACKGROUND

A subset of hereditary cerebellar ataxias is inherited as autosomal recessive traits (ARCAs). Classification of recessive ataxias due to phenotypic differences in the cerebellum and cerebellar structures is constantly evolving due to new identified disease genes. Recently, reports have linked mutations in genes involved in ubiquitination (RNF216, OTUD4, STUB1) to ARCA with hypogonadism.

METHODS AND RESULTS

With a combination of homozygozity mapping and exome sequencing, we identified three mutations in STUB1 in two families with ARCA and cognitive impairment; a homozygous missense variant (c.194A > G, p.Asn65Ser) that segregated in three affected siblings, and a missense change (c.82G > A, p.Glu28Lys) which was inherited in trans with a nonsense mutation (c.430A > T, p.Lys144Ter) in another patient. STUB1 encodes CHIP (C-terminus of Heat shock protein 70 - Interacting Protein), a dual function protein with a role in ubiquitination as a co-chaperone with heat shock proteins, and as an E3 ligase. We show that the p.Asn65Ser substitution impairs CHIP's ability to ubiquitinate HSC70 in vitro, despite being able to self-ubiquitinate. These results are consistent with previous studies highlighting this as a critical residue for the interaction between CHIP and its co-chaperones. Furthermore, we show that the levels of CHIP are strongly reduced in vivo in patients' fibroblasts compared to controls.

CONCLUSIONS

These results suggest that STUB1 mutations might cause disease by impacting not only the E3 ligase function, but also its protein interaction properties and protein amount. Whether the clinical heterogeneity seen in STUB1 ARCA can be related to the location of the mutations remains to be understood, but interestingly, all siblings with the p.Asn65Ser substitution showed a marked appearance of accelerated aging not previously described in STUB1 related ARCA, none display hormonal aberrations/clinical hypogonadism while some affected family members had diabetes, alopecia, uveitis and ulcerative colitis, further refining the spectrum of STUB1 related disease.

The association between ß-glucocerebrosidase mutations and parkinsonism

Mutations in the ß-glucocerebrosidase gene (GBA), which encodes the lysosomal enzyme ß-glucocerebrosidase, have traditionally been implicated in Gaucher disease, an autosomal recessive lysosomal storage disorder. Yet the past two decades have yielded an explosion of epidemiological and basic-science evidence linking mutations in GBA with the development of Parkinson disease (PD) as well. Although the specific contribution of mutant GBA to the pathogenesis of parkinsonism remains unknown, evidence suggests that both loss of function and toxic gain of function by abnormal ß-glucocerebrosidase may be important, and implicates a close relationship between ß-glucocerebrosidase and α-synuclein. Furthermore, multiple lines of evidence suggest that although GBA-associated PD closely mimics idiopathic PD (IPD), it may present at a younger age, and is more frequently complicated by cognitive dysfunction. Understanding the clinical association between GBA and PD, and the relationship between ß-glucocerebrosidase and α-synuclein, may enhance understanding of the pathogenesis of IPD, improve prognostication and treatment of GBA carriers with parkinsonism, and furthermore inform therapies for IPD not due to GBA mutations.

Cognitive and Antipsychotic Medication Use in Monoallelic GBA-Related Parkinson Disease

Mutations in glucosidase, beta, acid (GBA) are associated with cognitive impairment in Parkinson disease (PD) as well as dementia with Lewy bodies. For both of these diseases, dementia and hallucinations are typically treated with cholinesterase inhibitors and antipsychotics. However, in some lysosomal storage disorders certain antipsychotic medications are poorly tolerated. This study examined cholinesterase inhibitor and antipsychotic use in monoallelic GBA-related PD to explore potential pharmacogenetic relationships. Monoallelic GBA mutation carriers with PD (GBA-PD) with at least two clinic visits (n = 34) were matched for age-of-onset and gender to GBA and leucine-rich repeat kinase 2 (LRRK2) mutation negative idiopathic PD subjects (IPD) (n = 60). Information regarding cholinesterase inhibitor and antipsychotic use as well as impaired cognition (UPDRS Mentation >1) and hallucinations (UPDRS Thought Disorder >1) were obtained. GBA-PD more frequently reported hallucinations (HR = 5.0; p = 0.01) and they were more likely to have cognitive impairment but this was not statistically significant (HR 2.2, p = 0.07). Antipsychotic use was not significantly different between GBA-PD and IPD (HR = 1.9; p = 0.28), but GBA-PD were more likely to have sustained cholinesterase inhibitor use (HR = 3.1; p = 0.008), even after adjustment for cognition and hallucinations. Consistent with reports of worse cognition, GBA-PD patients are more likely to use cholinesterase inhibitors compared to IPD. While there was no difference in antipsychotic use between IPD and GBA-PD, persistent use of quetiapine in GBA-PD suggests that it is tolerated and that a significant interaction is unlikely. Further prospective study in larger samples with more extensive cognitive assessment is warranted to better understand pharmacogenetic relationships in GBA-PD.

Genetic variants in diseases of the extrapyramidal system

Knowledge on the genetics of movement disorders has advanced significantly in recent years. It is now recognized that disorders of the basal ganglia have genetic basis and it is suggested that molecular genetic data will provide clues to the pathophysiology of normal and abnormal motor control. Progress in molecular genetic studies, leading to the detection of genetic mutations and loci, has contributed to the understanding of mechanisms of neurodegeneration and has helped clarify the pathogenesis of some neurodegenerative diseases. Molecular studies have also found application in the diagnosis of neurodegenerative diseases, increasing the range of genetic counseling and enabling a more accurate diagno-sis. It seems that understanding pathogenic processes and the significant role of genetics has led to many experiments that may in the future will result in more effective treatment of such diseases as Parkinson’s or Huntington’s. Currently used molecular diagnostics based on DNA analysis can identify 9 neurodegenerative diseases, including spinal cerebellar ataxia inherited in an autosomal dominant manner, dentate-rubro-pallido-luysian atrophy, Friedreich’s disease, ataxia with ocu-lomotorapraxia, Huntington's disease, dystonia type 1, Wilson’s disease, and some cases of Parkinson's disease.

Paraoxonase 1 in neurological disorders

Paroxonase 1 displays multiple physiological activities that position it as a putative player in the pathogenesis of neurological disorders. Here we reviewed the literature focusing on the role of paraoxonase 1 (PON1) as a factor in the risk of stroke and the major neurodegenerative diseases. PON1 activity is reduced in stroke patients, which significantly correlates inversely with carotid and cerebral atherosclerosis. The presence of the R allele of the Q192R PON1 polymorphism seems to potentiate this risk for stroke. PON1 exerts peroxidase activities that may be important in neurodegenerative disorders associated with oxidative stress. PON1 is also a key detoxifier of organophosphates and organophosphate exposure has been linked to the development of neurological disorders in which acetylcholine plays a significant role. In Parkinson's disease most of the studies suggest no participation of either L55M or the Q192R polymorphisms in its pathogenesis. However, many studies suggest that the MM55 PON1 genotype is associated with a higher risk for Parkinson's disease in individuals exposed to organophosphates. In Alzheimer's disease most studies have failed to find any association between PON1 polymorphisms and the development of the disease. Some studies show that PON1 activity is decreased in patients with Alzheimer's disease or other dementias, suggesting a possible protective role of PON1. No links between PON1 polymorphisms or activity have been found in other neurodegenerative diseases such as multiple sclerosis and amyotrophic lateral sclerosis. PON1 is a potential player in the pathogenesis of several neurological disorders. More research is warranted to ascertain the precise pathogenic links and the prognostic value of its measurement in neurological patients.

Genetics of dystonia: what's known? What's new? What's next?

Although all forms of dystonia share the core clinical features of involuntary dystonic dyskinesia, there is not only marked phenotypic but also etiologic heterogeneity. Isolated dystonia can be caused by mutations in TOR1A (DYT1), TUBB4 (DYT4), THAP1 (DYT6), CIZ1 (DYT23), ANO3 (DYT24), and GNAL (DYT25). Combined dystonias (with parkinsonism or myoclonus) are further subdivided into persistent (TAF1 [DYT3], GCHI [DYT5], SGCE [DYT11], ATP1A3 [DYT12]), PRKRA (DYT16), and paroxysmal (MR-1 [DYT8], PRRT2 [DYT10], SLC2A1 [DYT18]. With the advent of next-generation sequencing, an unprecedented number of new dystonia genes have recently been described, including 4 in the past 12 months. Despite the need for independent confirmation, these recent findings raise 2 important questions regarding (1) the role of genetics in dystonia overall and (2) the role of different molecular mechanisms in dystonia pathogenesis. The genetic contribution to dystonia represents a continuum ranging from genetic susceptibility factors of small effect to causative genes with markedly reduced penetrance to those with full penetrance. Equally diverse and complex are the pathways and neuronal function(s) putatively involved in dystonia pathogenesis including dopamine signaling, intracellular transport, cytoskeletal dynamics, transcriptional regulation, cell-cycle control, ion channel function, energy metabolism, signal transduction, and detoxification mechanisms. In the next decade of dystonia research, we expect to see the discovery of additional dystonia genes and susceptibility factors. In this context, it will be of great interest to explore whether the diverse cellular functions of the known dystonia proteins may be linked to shared pathways and thus complete the complex puzzle of dystonia pathogenesis. © 2013 Movement Disorder Society.

p53 in neurodegenerative diseases and brain cancers

More than thirty years elapsed since a protein, not yet called p53 at the time, was detected to bind SV40 during viral infection. Thousands of papers later, p53 evolved as the main tumor suppressor involved in growth arrest and apoptosis. A lot has been done but the protein has not yet revealed all its secrets. Particularly important is the observation that in totally distinct pathologies where apoptosis is either exacerbated or impaired, p53 appears to play a central role. This is exemplified for Alzheimer's and Parkinson's diseases that represent the two main causes of age-related neurodegenerative affections, where cell death enhancement appears as one of the main etiological paradigms. Conversely, in cancers, about half of the cases are linked to mutations in p53 leading to the impairment of p53-dependent apoptosis. The involvement of p53 in these pathologies has driven a huge amount of studies aimed at designing chemical tools or biological approaches to rescue p53 defects or over-activity. Here, we describe the data linking p53 to neurodegenerative diseases and brain cancers, and we document the various strategies to interfere with p53 dysfunctions in these disorders.

Fungal-derived semiochemical 1-octen-3-ol disrupts dopamine packaging and causes neurodegeneration

Parkinson disease (PD) is the most common movement disorder and, although the exact causes are unknown, recent epidemiological and experimental studies indicate that several environmental agents may be significant risk factors. To date, these suspected environmental risk factors have been man-made chemicals. In this report, we demonstrate via genetic, biochemical, and immunological studies that the common volatile fungal semiochemical 1-octen-3-ol reduces dopamine levels and causes dopamine neuron degeneration in Drosophila melanogaster. Overexpression of the vesicular monoamine transporter (VMAT) rescued the dopamine toxicity and neurodegeneration, whereas mutations decreasing VMAT and tyrosine hydroxylase exacerbated toxicity. Furthermore, 1-octen-3-ol also inhibited uptake of dopamine in human cell lines expressing the human plasma membrane dopamine transporter (DAT) and human VMAT ortholog, VMAT2. These data demonstrate that 1-octen-3-ol exerts toxicity via disruption of dopamine homeostasis and may represent a naturally occurring environmental agent involved in parkinsonism.

Loss of PINK1 enhances neurodegeneration in a mouse model of Parkinson's disease triggered by mitochondrial stress

Parkinson's disease (PD) shows a complex etiology, where both genetic and environmental factors contribute to initiation and advance of pathology. Mitochondrial dysfunction and mutation of genes implicated in mitochondria quality control are recognized contributors to etiopathology and progression of PD. Here we report the development and characterization of a genetic mouse model of PD with a combined etiology comprising: 1) induction of mitochondrial stress achieved through the expression of a mitochondrial matrix protein that accumulates in an unfolded state and 2) deletion of PINK1 gene. Using this model we address the role of PINK1 in mitochondrial quality control and disease progression. To induce mitochondrial stress specifically in catecholaminergic neurons we generated transgenic animals where the conditional expression of mitochondrial unfolded ornithine transcarbamylase (dOTC) is achieved under the tyrosine hydroxylase (Th) promoter. The mice were characterized in terms of survival, growth and motor behaviour. The characterization was followed by analysis of cell death induced in dopaminergic neurons and responsiveness to l-dopa. We demonstrate that accumulation of dOTC in dopaminergic neurons causes neurodegeneration and motor behaviour impairment that illustrates a parkinsonian phenotype. This associates with l-dopa responsiveness validating the model as a model of PD. The combined transgenic model where dOTC is overexpressed in PINK1 KO background presents increased neurodegeneration as compared to dOTC transgenic in wild-type background. Moreover, this combined model does not show responsiveness to l-dopa. Our in vivo data show that loss of PINK1 accelerates neurodegenerative phenotypes induced by mitochondrial stress triggered by the expression of an unfolded protein in this organelle.

Genetik der Parkinson-Krankheit

Neben 9 eindeutig gesicherten monogenen Parkinson-Formen gibt es zahlreiche bekannte Risiko- oder protektive Genvarianten, die das Risiko für eine Parkinson-Erkrankung modulieren. Unter den monogenen Formen folgen 3 (PARK1/PARK4, PARK8, PARK17) einem autosomal-dominanten Erbgang und 6 einem rezessiven Vererbungsmuster (PARK2, PARK6, PARK7, PARK9, PARK14, PARK15). Ebenfalls 6 Formen gehen mit einem der idiopathischen Parkinson-Krankheit sehr ähnlichen klinischen Bild einher (PARK1/PARK4, PARK2, PARK6, PARK7, PARK8, PARK17), darunter sind PARK8 mit Mutationen im LRRK2-Gen und spätem Krankheitsbeginn bzw. PARK2 mit Mutationen im Parkin-Gen und frühem Erkrankungsalter die weitaus häufigsten. Pathophysiologisch stehen bei den monogenen Formen wie auch bei der idiopathischen Parkinson-Krankheit Mechanismen der oxidativen Modifikation, des gestörten Proteinabbaus sowie der mitochondrialen Dysfunktion im Mittelpunkt, sodass die monogenen Parkinson-Formen als humane Modellerkrankungen für die idiopathische Form dienen können.

The many faces of alpha-synuclein mutations

Since the first description of alpha-synuclein (SNCA) mutations in 1997, this gene has probably become the most intensely investigated one associated with monogenic Parkinson disease (PD). Prompted by the finding of a novel SNCA mutation, H50Q, we systematically explored the 145 published SNCA mutation carriers for a possible mutation (type)-specific clinical expression, which appears to be rather unique to SNCA mutations compared with other PD genes. The A53T mutation is associated with an approximately 10-year earlier age at onset than the other 3 known missense mutations, including the new H50Q mutation. Similarly, SNCA triplication carriers have an approximately 10-year earlier onset and a more rapid disease course than duplication carriers, who, overall closely resemble patients with idiopathic PD. Furthermore, higher order SNCA multiplications are associated with additional neurologic features, such as myoclonus. For the nonmotor features, their mere frequency appears less striking than their severity, with an early age of onset of depression or dementia, suicidal ideation, and multimodal hallucinations. We conclude that, (1) although SNCA mutations are a rare cause of PD, it remains worth testing for new mutations in this gene; (2) a differential view of SNCA mutations and variants may allow important pathophysiologic inferences even beyond monogenic PD and is warranted in the context of clinical counseling.

Genetic issues in the diagnosis of dystonias

Dystonias are heterogeneous hyperkinetic movement disorders characterized by involuntary muscle contractions which result in twisting and repetitive movements and abnormal postures. Several causative genes have been identified, but their genetic bases still remain elusive. Primary Torsion Dystonias (PTDs), in which dystonia is the only clinical sign, can be inherited in a monogenic fashion, and many genes and loci have been identified for autosomal dominant (DYT1/TOR1A; DYT6/THAP1; DYT4/TUBB4a; DYT7; DYT13; DYT21; DYT23/CIZ1; DYT24/ANO3; DYT25/GNAL) and recessive (DYT2; DYT17) forms. However most sporadic cases, especially those with late-onset, are likely multifactorial, with genetic and environmental factors interplaying to reach a threshold of disease. At present, genetic counseling of dystonia patients remains a difficult task. Recently non-motor clinical findings in dystonias, new highlights in the pathophysiology of the disease, and the availability of high-throughput genome-wide techniques are proving useful tools to better understand the complexity of PTD genetics. We briefly review the genetic basis of the most common forms of hereditary PTDs, and discuss relevant issues related to molecular diagnosis and genetic counseling.

Parallel PARKing: Parkinson's genes function in common pathway

Parkinson's disease (PD) is associated with diverse genetic and environmental susceptibilities. Functional connections between PD genes have remained elusive. In this issue of Neuron, MacLeod et al. (2013) link three PD susceptibility genes, LRRK2, PARK16, and VSP35, to a common cellular pathway and show how these deficits contribute to dysfunction.

Manganese efflux in Parkinsonism: insights from newly characterized SLC30A10 mutations

Although manganese (Mn) is required for normal cellular function, overexposure to this metal may cause an extrapyramidal syndrome resembling Parkinson's disease (PD). Notably, high whole-blood Mn levels have been reported in patients with idiopathic PD. Because Mn is both essential at low dose and toxic at higher dose; its transport and homeostasis are tightly regulated. Previously, the only protein known to be operant in cellular Mn export was the iron-regulating transporter, ferroportin (Fpn). The causal role for Mn in PD has yet to be fully understood, but evidence of a familial predisposition to PD associated with Mn toxicity is mounting. A recently discovered mutation in SLC30A10 identified its gene product as putatively involved in Mn efflux. Patients with the SLC30A10 mutation display Parkinsonian-like gate disturbances and hypermanganesemia. This review will address Mn transport proteins, the newly discovered SLC30A10 mutations and their implications to Parkinsonism and Mn regulation.

[Genetics of movement disorders]

A number of genetic causes of movement disorders including Parkinson disease, dystonia, restless legs syndrome or essential tremor have been elucidated in recent years. This process was accelerated by novel technologies including genome-wide association studies (GWAS) and next generation sequencing (NGS). Although monogenic forms are overall rare, they provide a unique opportunity to investigate mutation carriers who are still in the presymptomatic phase. As these subjects present individuals at risk to develop the disease, they have been included in longitudinal studies to unravel disease mechanisms and elucidate novel therapeutic targets. In addition, cell culture and animal studies have been performed to functionally characterize proteins mutated in different movement disorders to provide further insight into disturbed cellular pathways. In this article, we summarize known monogenic forms and the associated phenotype as well as genetic risk factors and review the function of relevant genes and proteins.

Key issues in essential tremor genetics research: Where are we now and how can we move forward?

Background

Genetics research is an avenue towards understanding essential tremor (ET). Advances have been made in genetic linkage and association: there are three reported ET susceptibility loci, and mixed but growing data on risk associations. However, causal mutations have not been forthcoming. This disappointing lack of progress has opened productive discussions on challenges in ET and specifically ET genetics research, including fundamental assumptions in the field.

Methods

This article reviews the ET genetics literature, results to date, the open questions in ET genetics and the current challenges in addressing them.

Results

Several inherent ET features complicate genetic linkage and association studies: high potential phenocopy rates, inaccurate tremor self-reporting, and ET misdiagnoses are examples. Increasing use of direct examination data for subjects, family members, and controls is one current response. Smaller moves towards expanding ET phenotype research concepts into non-tremor features, clinically disputed ET subsets, and testing phenotype features instead of clinical diagnosis against genetic data are gradually occurring. The field has already moved to considering complex trait mechanisms requiring detection of combinations of rare genetic variants. Hypotheses may move further to consider novel mechanisms of inheritance, such as epigenetics.

Discussion

It is an exciting time in ET genetics as investigators start moving past assumptions underlying both phenotype and genetics experimental contributions, overcoming challenges to collaboration, and engaging the ET community. Multicenter collaborative efforts comprising rich longitudinal prospective phenotype data and neuropathologic analysis combined with the latest in genetics experimental design and technology will be the next wave in the field.

Prominent psychiatric comorbidity in the dominantly inherited movement disorder myoclonus-dystonia

BACKGROUND

Neurological and psychiatric disorders show clinical overlap suggesting a shared pathophysiological background. We evaluated myoclonus-dystonia, a monogenic movement disorder as a disease model for inherited psychopathology.

METHOD

We investigated 12 SGCE mutation carriers using standardized neurological and psychiatric examinations to assign DSM-IV diagnoses. Furthermore, we analyzed all studies in the Medline database which included psychiatric information on SGCE mutation-positive patients.

RESULTS

Of our twelve SGCE mutation carriers, 10 were older than 16 years. Two of them (20%) reported psychiatric diagnoses before our examination, which resulted in at least one psychiatric diagnosis in seven (70%) patients, most frequently anxiety (60%), depression (30%) or both. Substance abuse was observed in 20%, whereas obsessive-compulsive disorders were absent. One mutation carrier showed Axis 2 features. In the literature analysis, the ten studies using standardized tools covering DSM-IV criteria reported prevalences similar to those in our sample. This was three times the frequency of psychiatric disorders detected in 13 studies using clinical history or patient report only.

CONCLUSION

About two thirds of SGCE mutation carriers develop psychiatric comorbidity and >80% are previously undiagnosed.