LINGO1 variants in essential tremor and Parkinson's disease

Inhibition of RhoA/ROCK Pathway in the Early Stage of Hypoxia Ameliorates Depression in Mice via Protecting Myelin Sheath

Neuroplasticity and connectivity in the central nervous system (CNS) are easily damaged after hypoxia. Long-term exposure to an anoxic environment can lead to neuropsychiatric symptoms and increases the likelihood of depression. Demyelination is an important lesion of CNS injury that may occur in depression. Previous studies have found that the RhoA/ROCK pathway is upregulated in neuropsychiatric disorders such as multiple sclerosis, stroke, and neurodegenerative diseases. Therefore, the chief aim of this study is to explore the regulatory role of the RhoA/ROCK pathway in the development of depression after hypoxia by behavioral tests, Western blotting, immunostaining as well as electron microscopy. Results showed that HIF-1α, S100β, RhoA/ROCK, and immobility time in FST were increased, sucrose water preference ratio in SPT was decreased, and the aberrant activity of neurocyte and demyelination occurred after hypoxia. After the administration of Y-27632 and fluoxetine in hypoxia, these alterations were improved. Lingo1, a negative regulatory factor, was also overexpressed after hypoxia and its expression was decreased when the pathway blocked. However, fluoxetine had no effect on the expression of Lingo1. Then, we demonstrated that demyelination was associated with failures of oligodendrocyte precursor cell proliferation and differentiation and increased apoptosis of oligodendrocytes. Collectively, our data indicate that the RhoA/ROCK pathway plays a vital role in the initial depression during hypoxia. Blocking this pathway in the early stage of hypoxia can enhance the effectiveness of antidepressants, rescue myelin damage, and reduce the expression of the negative regulatory protein of myelination. The findings provide new insight into the prophylaxis and treatment of depression.

Prodromal Markers of Parkinson's Disease in Patients With Essential Tremor

Background: Essential tremor (ET) is manifested as an isolated syndrome of bilateral upper limb action tremor. Parkinson's disease (PD) is the second most common neurodegenerative disease, with typical motor symptoms of bradykinesia, rigidity, and resting tremor. ET-PD describes the new-onset of PD in ET patients. Recently, numerous studies on epidemiology, genetics, pathology, clinical features, and neuroimaging studies are challenging the idea that ET is an isolated disease, suggesting that patients with ET have the tendency to develop PD. Methods: In this review article, we collected recent findings that reveal prodromal markers of PD in patients with ET. Results: Substantia nigra hyperechogenicity serves as a prodromal marker for predicting the development of PD in patients with ET and provides a reference for therapeutic strategies. Additional potential markers include other neuroimaging, clinical features, heart rate, and genetics, whereas others lack sufficient evidence. Conclusion: In consideration of the limited research of PD in patients with ET, we are still far from revealing the prodromal markers. However, from the existing follow-up studies on ET patients, Substantia nigra hyperechogenicity may enable further exploration of the relationship between ET and PD and the search for pathogenesis-based therapies.

[Essential tremor: genetic update]

Essential tremor (ET) is a neurological movement disorder characterised by bilateral limb kinetic/postural tremor, with or without tremor in other body parts including head, voice and lower limbs. Since no causative genes for ET have been identified, it is likely that the disorder occurs as a result of complex genetic factors interacting with various cellular and environmental factors that can result in abnormal function of circuitry involving the cerebello-thalamo-cortical pathway. Genetic analyses have uncovered at least 14 loci and 11 genes that are related to ET, as well as various risk or protective genetic factors. Limitations in ET genetic analyses include inconsistent disease definition, small sample size, varied ethnic backgrounds and many other factors that may contribute to paucity of relevant genetic data in ET. Genetic analyses, coupled with functional and animal studies, have led to better insights into possible pathogenic mechanisms underlying ET. These genetic studies may guide the future development of genetic testing and counselling, and specific, pathogenesis-targeted, therapeutic strategies.

Genetic analysis of PITX3 variants in patients with essential tremor

BACKGROUND

A clinical overlap between essential tremor (ET) and Parkinson's disease (PD) has prompted investigation whether these disorders share common genetic factors. The paired-like homeodomain transcription factor 3 gene (PITX3) has been shown to play an important role for the differentiation and survival of midbrain dopaminergic neurons in the substantia nigra pars compacta. The preferential degeneration of those dopaminergic neurons is the pathological hallmark in PD.

AIMS OF THE STUDY

The purpose of this study was to evaluate whether PITX3 variants are related to susceptibility of ET in Chinese Han population.

METHODS

Genetic analysis of two variants rs3758549 and rs4919621 of the PITX3 gene was conducted in 200 Chinese Han patients with ET and 426 controls.

RESULTS

We did not identify any statistically significant difference in either genotypic or allelic frequencies of variants between the ET patients and control cohort (all P > 0.05). Haplotype analysis of two variants in the PITX3 gene showed no potential association between the haplotypes and risk of ET (all P > 0.05).

CONCLUSIONS

Our data suggest that PITX3 variants rs3758549 and rs4919621 are not associated with ET in Chinese Han population.

Linkage of familial essential tremor to chromosome 5q35

BACKGROUND

Essential tremor is a neurological condition characterized by tremor during voluntary movement. To date, 3 loci linked to familial essential tremor have been identified.

METHODS

We examined 48 essential tremor patients in 5 large essential tremor pedigrees in our data set for genetic linkage using an Affymetrix Axiom array. Linkage analysis was performed using an affecteds-only dominant model in SIMWALK2. To incorporate all genotype information, GERMLINE was used to identify genome segments shared identical-by-descent in pairs of affecteds. Exome sequencing was performed in pedigrees showing evidence of linkage.

RESULTS

For one family, chromosomes 5 and 18 showed genome-wide significant linkage to essential tremor. Shared segment analysis excluded the 18p11 candidate region and reduced the 5q35 region by 1 megabase. Exome sequencing did not identify a potential causative variant in this region.

CONCLUSION

A locus on chromosome 5 is linked to essential tremor. Further research is needed to identify a causative variant. © 2016 International Parkinson and Movement Disorder Society.

From neurons to neuron neighborhoods: the rewiring of the cerebellar cortex in essential tremor

Remarkably little has been written on the biology of essential tremor (ET), despite its high prevalence. The olivary model, first proposed in the 1970s, is the traditional disease model for ET; however, the model is problematic for a number of reasons. Recently, intensive tissue-based studies have identified a series of structural changes in the brains of most ET cases, and nearly all of the observed changes are located in the cerebellar cortex. These studies suggest that Purkinje cells are central to the pathogenesis of ET and may thus provide a focus for the development of novel therapeutic strategies. Arising from these studies, a new model of ET proposes that the population of Purkinje cells represents the site of the initial molecular/cellular events leading to ET. Furthermore, a number of secondary changes/remodeling observed in the molecular and granular layers (i.e., in the Purkinje cell "neighborhood") are likely to be of additional mechanistic importance. On a physiological level, the presence of remodeling indicates the likely formation of aberrant synapses and the creation of new/abnormal cortical circuits in ET. Specific efforts need to be devoted to understanding the cascade of biochemical and cellular events occurring in the Purkinje cell layer in ET and its neuron neighborhood, as well as the physiological effects of secondary remodeling/rewiring that are likely to be occurring in this brain region in ET.

Neural cell adhesion molecules belonging to the family of leucine-rich repeat proteins

Leucine-rich repeats (LRRs) are motifs that form protein-ligand interaction domains. There are approximately 140 human genes encoding proteins with extracellular LRRs. These encode cell adhesion molecules (CAMs), proteoglycans, G-protein-coupled receptors, and other types of receptors. Here we give a brief description of 36 proteins with extracellular LRRs that all can be characterized as CAMs or putative CAMs expressed in the nervous system. The proteins are involved in multiple biological processes in the nervous system including the proliferation and survival of cells, neuritogenesis, axon guidance, fasciculation, myelination, and the formation and maintenance of synapses. Moreover, the proteins are functionally implicated in multiple diseases including cancer, hearing impairment, glaucoma, Alzheimer's disease, multiple sclerosis, Parkinson's disease, autism spectrum disorders, schizophrenia, and obsessive-compulsive disorders. Thus, LRR-containing CAMs constitute a large group of proteins of pivotal importance for the development, maintenance, and regeneration of the nervous system.

Elevated blood harmane (1-methyl-9H-pyrido[3,4-b]indole) concentrations in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a late-life neurodegenerative disease. Genetic and environmental factors play an etiological role. Harmane (1-methyl-9H-pyrido[3,4-b]indole) is a potent tremor-producing neurotoxin that shows structural resemblance to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

OBJECTIVES

In 2002 and 2007, we demonstrated elevated blood harmane concentrations [HA] in essential tremor (ET) cases. We now assessed whether blood [HA] were elevated in Parkinson's disease (PD) as well.

METHODS

Blood [HA] were quantified by high performance liquid chromatography. Subjects comprised 113 PD cases and 101 controls.

RESULTS

Mean log blood [HA] in PD cases was double that of controls (0.59±0.63 g(-10)/ml vs. 0.27±0.63 g(-10)/ml, p<0.001). A non-parametric test on non-transformed data (median blood [HA]=3.31 g(-10)/ml in cases and 1.44 g(-10)/ml in controls) also showed this difference (p<0.001). In unadjusted and then adjusted logistic regression analyses, log blood [HA] was associated with PD (odds ratio [OR]unadjusted 2.31, 95% confidence interval [CI] 1.46-3.67, p<0.001; OR(adjusted) 2.54, 95% CI 1.55-4.16, p<0.001). In PD, log blood [HA] co-varied with family history, being lowest in PD cases with no family history (0.54±0.60 g(-10)/ml) and highest in PD cases with a family history of both ET and PD (0.84±0.68 g(-10)/ml) (p=0.06).

CONCLUSIONS

Blood harmane appears to be elevated in PD. The finding needs to be reproduced in additional cohorts to assess its generalizability. The higher concentration in familial PD suggests that the mechanism may involve genetic factors.

What is essential tremor?

Classic essential tremor is a clinical syndrome of action tremor in the upper limbs (at least 95 % of patients) and less commonly the head, face/jaw, voice, tongue, trunk, and lower limbs, in the absence of other neurologic signs. However, the longstanding notion that essential tremor is a monosymptomatic tremor disorder is being challenged by a growing literature describing associated disturbances of tandem walking, personality, mood, hearing, and cognition. There is also epidemiologic, pathologic, and genetic evidence that essential tremor is pathophysiologically heterogeneous. Misdiagnosis of essential tremor is common because clinicians frequently overlook other neurologic signs and because action tremor in the hands is caused by many conditions, including dystonia, Parkinson disease, and drug-induced tremor. Thus, essential tremor is nothing more than a syndrome of idiopathic tremulousness, and the challenge for researchers and clinicians is to find specific etiologies of this syndrome.

Genetic analysis of the fused in sarcoma gene in Chinese Han patients with Parkinson's disease

BACKGROUND AND PURPOSE

Exome sequencing in a large essential tremor (ET) family identified a novel nonsense mutation (p.Q290X) in the fused in sarcoma gene (FUS) as the cause of this family. Because of the clinical overlap between ET and Parkinson's disease (PD), the role of FUS in an independent cohort of PD patients from China mainland was evaluated.

METHODS

The entire coding region of FUS in 508 Chinese Han patients with PD and the identified variants in 633 normal controls were evaluated. A variant was further screened in an additional 382 controls for the frequency in our population.

RESULTS

A novel variant c.696C > T (p.Y232Y) in 2 sporadic patients with PD and six variants (c.52C > A, p.P18T; c.52C > T, p.P18S; c.147C > A, p.G49G; c.291C > T, p.Y97Y; c.684C > T, p.G228G; c.1176G > A, p.M392I) without significant difference in genotypic and allelic distributions in our PD cohort were identified.

CONCLUSION

The FUS gene is not a genetic risk factor for PD in the population of Chinese Han ethnicity.

Purkinje cell axonal anatomy: quantifying morphometric changes in essential tremor versus control brains

Growing clinical, neuro-imaging and post-mortem data have implicated the cerebellum as playing an important role in the pathogenesis of essential tremor. Aside from a modest reduction of Purkinje cells in some post-mortem studies, Purkinje cell axonal swellings (torpedoes) are present to a greater degree in essential tremor cases than controls. Yet a detailed study of more subtle morphometric changes in the Purkinje cell axonal compartment has not been undertaken. We performed a detailed morphological analysis of the Purkinje cell axonal compartment in 49 essential tremor and 39 control brains, using calbindin D28k immunohistochemistry on 100-µm cerebellar cortical vibratome tissue sections. Changes in axonal shape [thickened axonal profiles (P = 0.006), torpedoes (P = 0.038)] and changes in axonal connectivity [axonal recurrent collaterals (P < 0.001), axonal branching (P < 0.001), terminal axonal sprouting (P < 0.001)] were all present to an increased degree in essential tremor cases versus controls. The changes in shape and connectivity were significantly correlated [e.g. correlation between thickened axonal profiles and recurrent collaterals (r = 0.405, P < 0.001)] and were correlated with tremor duration among essential tremor cases with age of onset >40 years. In essential tremor cases, thickened axonal profiles, axonal recurrent collaterals and branched axons were 3- to 5-fold more frequently seen on the axons of Purkinje cells with torpedoes versus Purkinje cells without torpedoes. We document a range of changes in the Purkinje cell axonal compartment in essential tremor. Several of these are likely to be compensatory changes in response to Purkinje cell injury, thus illustrating an important feature of Purkinje cells, which is that they are relatively resistant to damage and capable of mobilizing a broad range of axonal responses to injury. The extent to which this plasticity of the Purkinje cell axon is partially neuroprotective or ultimately ineffective at slowing further cellular changes and cell death deserves further study in essential tremor.

SLC1A2 variant is associated with essential tremor in Taiwanese population

Essential tremor (ET), which is one of the most common movement disorders, may lead to severe interference in quality of life. The first genome-wide association study (GWAS) has identified an association of the LINGO1 variant (rs9652490) with ET in Americans and Europeans. Recently, a second GWAS that was performed in a European population has discovered a new variant (rs3794087) of the main glial glutamate transporter (SLC1A2) that increases the risk of ET with an odds ratio of about 1.4. SLC1A2 encodes for the major glial high-affinity glutamate reuptake transporter in the brain and is a potential ET susceptibility gene. Because replication in a different ethnic population is important for validating a finding, we conducted a case-control study to investigate the SLC1A2 variant in an Asian cohort with ET in Taiwan. A total of 542 subjects (273 ET patients and 269 controls) were included. The results showed that rs3794087 was associated with ET among the Taiwanese. The odds ratio was 1.37. Our results were similar to those of the second GWAS of ET in Europeans, and this confirms that SLC1A2 may be a good functional candidate gene for ET. A replication study in another independent population is of importance to validate this association.

Genetic analysis of the leucine-rich repeat and lg domain containing Nogo receptor-interacting protein 1 gene in essential tremor

Variants in the leucine-rich repeat and lg domain containing nogo receptor-interacting protein 1 gene (LINGO1) have been identified to be associated with the increased risk of essential tremor (ET), especially among Caucasians. To explore whether the LINGO1 gene plays a role in ET susceptibility, we performed a systematic genetic analysis of the coding region in the LINGO1 gene. Four nucleotide variants have been genotyped, including three known variants (rs2271398, rs2271397, and rs3743481), and a novel G → C transition (ss491228439). Extended analysis showed no significant difference in genotypic and allelic distributions between 151 patients and 301 control subjects for these four variants (all P > 0.05). However, further sex-stratified analysis revealed that the C allele of rs2271397 and ss491228439 contributed the risk of ET in female (P = 0.017, OR = 2.139, 95 % CI 1.135 ~ 4.030 for rs2271397 and P = 0.038, OR = 1.812, 95 % CI 1.027 ~ 3.194 for ss491228439). Haplotype analysis indicated that A465-C474-C714 haplotype was significantly associated with increased risk of ET in female (P = 0.041, OR = 1.800, 95 % CI 1.020 ~ 3.178). Our results indicate that the LINGO1 variants are associated with ET in Chinese Han female patients.

LINGO1 rs9652490 and rs11856808 polymorphisms are not associated with risk for multiple sclerosis

BACKGROUND

Some recent experimental data suggest a possible role of LINGO-1 in the pathogenesis of multiple sclerosis (MS). In an attempt to identify genetic biomarkers related to MS susceptibility, we genotyped two common SNPs in the LINGO1 gene which have been associated to other neurological conditions, in patients with MS and in healthy subjects. These SNPs are linked to several SNPs within the LINGO1 gene, especially in individuals of Oriental or Caucasian descent.

METHODS

We analyzed the allelic and genotype frequency of two LINGO1 variants (rs9652490 and rs11856808) in 293 patients with MS and 318 healthy controls, using KASPar assays.

RESULTS

LINGO1 rs9652490 and rs11856808 allelic and genotype frequencies did not differ significantly between MS patients and controls. The minor allele frequencies for rs9652490 were 0.171 (95% CI = 0.140-0.201) and 0.167 (95% CI = 0.138-0.196 for cases and controls respectively (p = 0.853). For rs11856808 the minor allele frequencies were 0.317 (95% CI = 0.280-0.355) and 0.310 (95% CI = 0.274-0.346) for cases and controls, respectively (p = 0.773). Allele and genotype frequencies were unrelated with the age of onset of MS, gender, and clinical course of MS. In addition, haplotype analyses did not reveal any putative risk related to haplotypes.

CONCLUSIONS

These results suggest that LINGO1 rs9652490 and rs11856808 polymorphisms are not related with risk for MS. This study adds to other published evidence indicating that, to date, the LINGO1 SNPs studied here could be useful risk biomarkers of developing essential tremor, but not other movement disorders.

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.

Cognitive features of essential tremor: a review of the clinical aspects and possible mechanistic underpinnings

The classical concept of essential tremor (ET) as a monosymptomatic tremorogenic disorder has been questioned in the last decade as new evidence has been described. Clinical, neuroimaging, and pathological studies have described a probable structural basis (mainly in cerebellum) and evidence that ET is associated with subtle clinical cerebellar deficits and several non-motor clinical manifestations, such as cognitive and mood disorders. We performed literature searches in Medline, ISI Web of Knowledge, and PsycInfo databases. The aim of this review is to describe cognitive deficits associated with ET. First, we present a brief history of ET cognitive disorders presented. Second, we describe several clinical cross-sectional series demonstrating that ET is associated with mild cognitive deficits of attention, executive functions, several types of memory (working memory, immediate, short term, delayed, and possibly others) and, mood disorders (depression). Recent neuroimaging studies favor a cerebellar basis for these cognitive deficits. Population-based surveys confirm that mild cognitive dysfunction is not limited to severe ET cases, the entire ET group, including mild and undiagnosed cases, can be affected. Cohort studies indicated that ET cognitive deficits could be progressive and that ET patients had an increased risk of dementia. The mood and cognitive deficits in ET are in agreement with cognitive affective cerebellar syndrome described in patients with cerebellar disorders. New evidence, mainly from functional (neuroimaging) and prospective clinical studies would further bolster recent descriptions of ET clinical manifestations.

LINGO-1 and Neurodegeneration: Pathophysiologic Clues for Essential Tremor

Essential tremor (ET), one of the most common adult-onset movement disorders, has been associated with cerebellar Purkinje cell degeneration and formation of brainstem Lewy bodies. Recent findings suggest that genetic variants of the leucine-rich repeat and Ig domain containing 1 (LINGO-1) gene could be risk factors for ET. The LINGO-1 protein contains both leucine-rich repeat (LRR) and immunoglobulin (Ig)-like domains in its extracellular region, as well as a transmembrane domain and a short cytoplasmic tail. LINGO-1 can form a ternary complex with Nogo-66 receptor (NgR1) and p75. Binding of LINGO-1 with NgR1 can activate the NgR1 signaling pathway, leading to inhibition of oligodendrocyte differentiation and myelination in the central nervous system. LINGO-1 has also been found to bind with epidermal growth factor receptor (EGFR) and induce downregulation of the activity of EGFR-PI3K-Akt signaling, which might decrease Purkinje cell survival. Therefore, it is possible that genetic variants of LINGO-1, either alone or in combination with other genetic or environmental factors, act to increase LINGO-1 expression levels in Purkinje cells and confer a risk to Purkinje cell survival in the cerebellum.Here, we provide a concise summary of the link between LINGO-1 and neurodegeneration and discuss various hypotheses as to how this could be potentially relevant to ET pathogenesis.