Genetic analysis of FGF20 variants in Chinese Han patients with essential tremor

Genomic Markers for Essential Tremor

There are many reports suggesting an important role of genetic factors in the etiopathogenesis of essential tremor (ET), encouraging continuing the research for possible genetic markers. Linkage studies in families with ET have identified 4 genes/loci for familial ET, although the responsible gene(s) have not been identified. Genome-wide association studies (GWAS) described several variants in LINGO1, SLC1A2, STK32B, PPARGC1A, and CTNNA3, related with ET, but none of them have been confirmed in replication studies. In addition, the case-control association studies performed for candidate variants have not convincingly linked any gene with the risk for ET. Exome studies described the association of several genes with familial ET (FUS, HTRA2, TENM4, SORT1, SCN11A, NOTCH2NLC, NOS3, KCNS2, HAPLN4, USP46, CACNA1G, SLIT3, CCDC183, MMP10, and GPR151), but they were found only in singular families and, again, not found in other families or other populations, suggesting that some can be private polymorphisms. The search for responsible genes for ET is still ongoing.

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.

Essential Tremor and Parkinson's Disease: Exploring the Relationship

Background

There is longstanding controversy surrounding the possible link between essential tremor (ET) and Parkinson's disease (PD). Inconsistent and unreliable diagnostic criteria may in part account for some of the difficulties in defining the relationship between these two common movement disorders.

Methods

References for this systematic review were identified using PubMed with the search terms "essential tremor" AND "Parkinson's disease" with articles published in English between 1960 and September 2018 included.

Results

In this review we provide evidence that some patients diagnosed with ET have an increased risk of developing PD years or decades after onset of action tremor. There are several still unresolved questions about the link between the two disorders including lack of verifiable diagnostic criteria for the two disorders and marked overlap in phenomenology. Here we review clinical, epidemiologic, imaging, pathologic, and genetic studies that address the ET-PD relationship. Several lines of evidence support the association between ET and PD, including overlapping motor and non-motor features, relatively high prevalence of rapid eye movement sleep behavior disorder (26-43%) in ET patients, increased prevalence of PD in patients with longstanding antecedent ET, increased prevalence of ET in family members of patients with PD, and the presence of Lewy bodies in the brains of some ET patients (15-24%).

Discussion

There is a substantial body of evidence supporting the association between ET and PD within at least a subset of patients, although the nature and possible pathogenic mechanisms of the relationship are not well understood.

Systematic analysis of genetic variants in patients with essential tremor

BACKGROUND

Essential tremor (ET), a prevalent neurological disorder, is featured by postural and kinetic tremors in upper limbs. Studies of twins and families indicate an important role for genetic factors in ET development. There are substantial overlaps between ET and Parkinson's disease (PD). The aim of this study was to examine the possible roles of genetic variants in ET development.

METHODS

A total of 200 Han Chinese ET patients and 432 ethnically matched normal controls were enrolled, and genetic analysis of 23 variants in 15 genes was performed.

RESULTS

Genotypic and allelic frequencies of the melanocortin 1 receptor gene (MC1R) variant rs34090186 showed statistically significant differences in ET patients and controls (p = 0.027 and 0.028, odds ratio = 2.789 and 2.744, 95% confidence interval: 1.084-7.179 and 1.075-7.005). No statistically significant difference was revealed in either genotypic or allelic distributions of other variants or haplotypes (all p > 0.05).

CONCLUSIONS

The discrepancies found in this study indicate the variant rs34090186 in the MC1R gene, some variants of which were reported to be related to increased risk of PD and melanoma, may play a risk role in ET, confirming a potential association between ET and PD. Evidence supporting ET-PD link will continue to accumulate and improve our understanding of any underlying mechanisms for both disorders.

Genetic Analysis of LRRK1 and LRRK2 Variants in Essential Tremor Patients

AIMS

Essential tremor (ET) is one of the most common adult-onset movement disorders. ET and Parkinson's disease (PD) overlap clinically and pathologically, which prompted this investigation into the association of PD risk variants in ET patients. This study was designed to explore the role of variants of two PD-related genes LRRK1 and LRRK2 in a Han Chinese ET population.

MATERIALS AND METHODS

Genetic analysis of LRRK1, rs2924835, and LRRK2, rs34594498, rs34410987, and rs33949390 variants was conducted on 200 Han Chinese patients with ET and 434 ethnically matched normal controls.

RESULTS

No statistically significant differences were identified in either genotypic or allelic frequencies of variants between the ET patients and the control cohort (all p > 0.05). Haplotype analysis of three LRRK2 variants (rs34594498, rs34410987, and rs33949390) showed no haplotypes displayed an association with ET risk (all p > 0.05).

CONCLUSIONS

The data suggest that LRRK1 variant (rs2924835) and LRRK2 variants (rs34594498, rs34410987, and rs33949390) are not associated with ET in this Han Chinese population.