[Association between polymorphisms in the human dopamine D3 receptor gene and genetic susceptibility of essential tremor]

OBJECTIVE

To study the association between polymorphisms in the human dopamine D3 receptor ( DRD3 ) gene and genetic susceptibility of essential tremor in different groups.

METHODS

The DRD3 gene polymorphism in ET and health control groups were analyzed with MscI restricted fragment length polymorphism ( RFLP). The results of PCR-RFLP were analyzed by using the statistical software.

RESULTS

No significant differences in alleles and allele frequency of MscI site at the DRD3 gene locus were observed between healthy control and different ET groups.

CONCLUSION

There is no association between polymorphisms MscI site at DRD3 and genetic susceptibility of ET.

Analysis of nuclear export sequence regions of FUS-Related RNA-binding proteins in essential tremor

Background and Objective

Genes encoding RNA-binding proteins, including FUS and TDP43, play a central role in different neurodegenerative diseases such as amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Recently, a mutation located in the nuclear export signal (NES) of the FUS gene has been reported to cause an autosomal dominant form of familial Essential tremor.

Material and Methods

We sequenced the exons coding the NES domains of five RNA-binding proteins (TARDBP, hnRNPA2B1, hnRNPA1, TAF15 and EWSR1) that have been previously implicated in neurodegeneration in a series of 257 essential tremor (ET) cases and 376 healthy controls. We genotyped 404 additional ET subjects and 510 healthy controls to assess the frequency of the EWSR1 p.R471C substitution.

Results

We identified a rare EWSR1 p.R471C substitution, which is highly conserved, in a single subject with familial ET. The pathogenicity of this substitution remains equivocal, as DNA samples from relatives were not available and the genotyping of 404 additional ET subjects did not reveal any further carriers. No other variants were observed with significant allele frequency differences compared to controls in the NES coding regions.

Conclusions

The present study demonstrates that the NES domains of RNA-binding proteins are highly conserved. The role of the EWSR1 p.R471C substitution needs to be further evaluated in future studies.

SLC1A2 rs3794087 does not associate with essential tremor

A recent genome-wide association study of patients with essential tremor (ET) from Germany has nominated SLC1A2 rs3794087 as a novel risk factor for disease. This association was independently replicated in the Chinese population, albeit with an opposite direction of effect. To further define the role of SLC1A2 in ET, we genotyped rs3794087 in a North American series consisting of 1347 patients with ET and controls. Statistical analysis did not identify significant differences in genotype or allele frequencies between healthy controls and patients with ET (p > 0.36). These findings therefore do not support a role for SLC1A2 rs3794087 in susceptibility to ET in the North American population. Further studies in ethnically distinct populations of patients with ET are necessary to understand whether genetic variability in SLC1A2 affects disease risk for ET.

[Essential tremor and Parkinson's disease: are they associated?]

INTRODUCTION

There is now growing evidence that essential tremor and Parkinson's disease are related.

AIM

To present the main findings from epidemiologic, genetic, clinical, imaging and pathologic studies, contrasting evidences for and against an association between essential tremor and Parkinson's disease.

DEVELOPMENT

We include a complete update of the latest findings regarding the overlap between these two disorders. There is current evidence that a history of essential tremor may herald the onset of Parkinson's disease in a subset of patients. Furthermore, the fact that the risk of essential tremor is significantly increased in relatives of patients with Parkinson's disease suggests the possibility that both conditions are genetically related, probably sharing common hereditary predisposition. Dopaminergic deficit among essential tremor patients in functional imaging studies and recent pathological studies describing Lewy bodies in some essential tremor patients, support further evidence for an overlap between both conditions, at least in a subset of patients.

CONCLUSION

The convergence of all the reviewed data suggests the possible existence of a mixed essential tremor-Parkinson's disease phenotype in some patients. However, further studies are needed to better understand this phenotype.

Autosomal dominant essential tremor: a novel family with anticipation

Essential tremor (ET) is a common progressive movement disorder characterized by a clear genetic predisposition. In the last years, many efforts have been done to map susceptibility loci for ET. Here, we report a clinical and genetic study of a family with ET showing autosomal dominant inheritance and anticipation over three generations. The family has five affected members and exhibits a remarkable anticipation of age at onset of the disease along the generations. We excluded linkage to any of the three loci previously mapped in autosomal dominant ET families. Our data suggest the existence of an additional locus in which a repeat expansion is the possible genetic defect underlying ET.

H1-MAPT and the risk for familial essential tremor

The most frequent MAPT H1 haplotype is associated with the risk for developing progressive supranuclear palsy and other neurodegenerative diseases such as Parkinson’s disease. A recent report suggests that the MAPT H1 is associated with the risk for developing essential tremor. We wanted to confirm this association in a different population. We analyzed the distribution of allelic and genotype frequencies of rs1052553, which is an H1/H2 SNP, in 200 subjects with familial ET and 291 healthy controls. rs1052553 genotype and allelic frequencies did not differ significantly between subjects with ET and controls and were unrelated with the age at onset of tremor or gender, and with the presence of head, voice, chin, and tongue tremor. Our study suggests that the MAPT H1 rs1052553 is not associated with the risk for developing familial ET in the Spanish population.

LINGO1 variants in essential tremor and Parkinson's disease

The leucine-rich repeat and Ig domain containing 1 gene (LINGO1), recently considered to be conferred increased risk of essential tremor (ET), has been also implicated in Parkinson disease (PD). As the two common movement disorders have overlapping clinical and pathological features, it has been postulated that the LINGO1 gene may play a role in the pathogenesis of the two diseases. Here, we review published reports of the LINGO1 variants in ET and PD in an attempt to better understand the molecular and pathogenic relationship of LINGO1 to the two disorders.

No evidence of association between the LINGO4 gene and essential tremor in Chinese Han patients

Essential tremor (ET) is shown an autosomal dominant mode of inheritance, with no disease-causing gene has been found. Genetic variations in the leucine-rich repeat and lg domain containing nogo receptor-interacting protein genes (LINGO1 and LINGO2) were reported to be associated with an increased risk of developing ET. To explore whether the LINGO4 gene (a homologous gene of the LINGO1 and the LINGO2 genes) plays a role in ET susceptibility, we performed genetic analysis of coding region of the LINGO4 gene in 100 patients with ET from Mainland China. Two nucleotide variants had been identified: (1) T > A transition (rs61746299), predicted to lead to the amino acid change Thr444Ser, and (2) C > T transition (rs1521179), located 12 bp downstream to the end of coding region. To evaluate whether these variants are related to ET susceptibility, we investigated a total of 150 Chinese Han ET patients (77 familial ET and 73 sporadic ET) and 300 sex, age and ethnicity matched normal controls. No significant differences in genotypic and allele distributions between patients and control subjects for rs61746299 and rs1521179 (p = 0.531 and p = 0.867 for genotypic distributions; p = 1.000 and p = 0.844 for allele distributions) were observed, suggesting variants in coding region of the LINGO4 gene may play litter or no role in the risk of ET susceptibility.

Analysis of Lingo1 variant in sporadic and familial essential tremor among Asians

OBJECTIVE - Genome-wide association study (GWAS) has identified a variant in LINGO1 (rs9652490) that increases the risk of essential tremor (ET) among Caucasians. It has been suggested that among Asians, the risk variant is relevant only for the familial forms of ET. We investigated the association of the rs9652490 variant with sporadic and familial ET in a Chinese population and conducted a pooled analysis to compare the potential differential effect between sporadic and familial ET. METHODS - rs9652490 was genotyped by direct sequencing in 117 ET and 160 controls in a Chinese population. Previous published data from another Asian population were included in the meta-analysis. RESULT - There were no significant differences in the minor allele frequency and genotype frequency between ET and controls in our Chinese population. However, in the pooled analysis involving 1201 subjects, patients with ET had a higher proportion of GG genotype compared to controls. Logistic regression analysis revealed that G allele increased the risk of ET via a recessive model. In both familial ET and sporadic ET, the G allele increased the risk via a recessive model. CONCLUSION -  While we could not demonstrate a significant association of the rs9652490 variant in our own study, pooled analysis of a much larger cohort revealed for the first time that the variant increased the risk in both familial and sporadic forms of ET among Asians, though the effect was stronger in familial ET.

Lingo2 variants associated with essential tremor and Parkinson's disease

LINGO2, a member of LRR gene family, has been linked with both Essential tremor (ET) and Parkinson's disease (PD). However, there is a lack of conclusive evidence regarding the etiologic role of LINGO2 genetic variants. We investigated the association of LINGO2 variants with ET and PD in two independent Asian countries. A total of 1,262 subjects comprising 499 controls, 436 PD patients, and 327 ET patients were included. Eight LINGO2 variants, including four single-nucleotide polymorphisms (SNPs) and four coding variants, were initially analyzed in one Asian population. SNPs that showed positive association were then replicated in the second independent Asian population, and a pooled analysis was carried out. Out of the eight variants, two SNPs (rs7033345 and rs10812774) revealed significant or strong positive trend in the first Asian population, and these were analyzed in the second Asian population. In the pooled analysis, the CC genotype at rs7033345 had a higher risk of developing PD (OR = 1.67, 95% CI = 1.18, 2.35, p = 0.003) and ET (OR = 1.50, 95% CI = 1.02, 2.20, p = 0.04) under a recessive model. The C allele at rs10812774 increased the risk of ET (OR = 1.56 95% CI = 1.10, 2.22, p = 0.01) via a recessive model. The effect size and direction of trend were in the same direction in each of the two populations. Our study demonstrated for the first time that rs7033345 is associated with PD and ET and rs10812774 with ET among Asians, suggesting that LINGO2 might act as a susceptibility gene for both conditions.

LINGO1 variants in the French-Canadian population

Essential tremor (ET) is a complex genetic disorder for which no causative gene has been found. Recently, a genome-wide association study reported that two variants in the LINGO1 locus were associated to this disease. The aim of the present study was to test if this specific association could be replicated using a French-Canadian cohort of 259 ET patients and 479 ethnically matched controls. Our genotyping results lead us to conclude that no association exists between the key variant rs9652490 and ET (P_corr = 1.00).

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.

No association with the ETM2 locus in Czech patients with familial essential tremor

OBJECTIVES

Essential tremor (ET) is one of the most common neurological movement disorders. In more than half of the cases, ET is inherited in an autosomal dominant manner, but no causative ET gene has been identified. However, several candidate loci have been reported, including the ETM2 locus that was originally found in a large American family of Czech descent.

METHODS

To ascertain the association with ETM2, we performed a genetic analysis of three polymorphic loci, etm1231, etm1234, and etm1240, located within the ETM2 candidate region in 61 Czech patients with a family history of ET and 68 healthy controls.

RESULTS

The allele frequencies were not significantly different between the patients and the controls, and we did not observe any haplotype specifically associated with ET.

CONCLUSIONS

This is the first report on the genetics of familial essential tremor in Czech patients. Our findings provide further evidence of genetic heterogeneity for ET.

Fertility in essential tremor. Data from population-based and clinical sources

BACKGROUND

The view of essential tremor (ET) as a degenerative disorder, which is now gaining support from postmortem studies, is at odds with traditional views of ET as a 'super-healthy' condition characterized by increased longevity and fertility. Longevity has recently been re-examined in ET, yet fertility, measured by number of offspring, has never been critically assessed in this disease. The objective was to determine whether ET cases and controls differ in terms of number of children.

METHODS

Family history data were collected on ET cases and controls from 2 distinct sources, a population and a clinical (referred) sample.

RESULTS

In the population, the number of children was similar in 59 cases vs. 72 controls [mean +/- SD (median) = 2.3 +/- 2.9 (1) vs. 2.2 +/- 1.8 (2); p = 0.26]. In the referred sample, number of children was similar in 184 cases vs. 241 controls [2.0 +/- 1.5 (2) vs. 1.9 +/- 1.7 (2); p = 0.33]. In adjusted analyses, results were similar.

CONCLUSIONS

Fertility, measured by number of children, was similar in cases and controls. With a newer understanding of the biological substrate of ET emerging from postmortem studies, it is important to critically reassess this and other fundamental biological questions about the disease.