Etiologic links between environmental and lifestyle factors and Essential tremor

Endogenous Synthesis of Tetrahydroisoquinoline Derivatives from Dietary Factors: Neurotoxicity Assessment on a 3D Neurosphere Culture

Tetrahydroisoquinoline (THIQ) alkaloids and their derivatives have a structural similarity to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a well-known neurotoxin. THIQs seem to present a broad range of actions in the brain, critically dependent on their catechol moieties and metabolism. These properties make it reasonable to assume that an acute or chronic exposure to some THIQs might lead to neurodegenerative diseases including essential tremor (ET). We developed a method to search for precursor carbonyl compounds produced during the Maillard reaction in overcooked meats to study their reactivity with endogenous amines and identify the reaction products. Then, we predicted in silico their pharmacokinetic and toxicological properties toward the central nervous system. Finally, their possible neurological effects on a novel in vitro 3D neurosphere model were assessed. The obtained data indicate that meat is an alkaloid precursor, and we identified the alkaloid 1-benzyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol (1-benz-6,7-diol THIQ) as the condensation product of phenylacetaldehyde with dopamine; in silico study of 1-benz-6,7-diol-THIQ reveals modulation of dopamine receptor D1 and D2; and in vitro study of 1-benz-6,7-diol-THIQ for cytotoxicity and oxidative stress induction does not show any difference after 24 h contact for all tested concentrations. To conclude, our in vitro data do not support an eventual neurotoxic effect for 1-benz-6,7-diol-THIQ.

Association of Diet With Essential Tremor: A Narrative Review

Essential tremor is a neurological disorder categorized by the rhythmic shaking of the upper limbs, lower limbs, neck, or head. The etiology of essential tremor is believed to be genetic variations, environmental factors, lifestyle, etc. Poor lifestyle and diet are important factors contributing to the onset of various disorders. Environment and lifestyle play a significant part in the dietary habits of an individual. Some diet components may probably be associated with the etiopathogenesis or progression of the essential tremor. Dietary habits may be a key influence on the commencement of tremors in healthy individuals. Typically, the diet of essential tremor patients is not supervised. It may also intensify the tremors in essential tremor patients. Association of the diet with the essential tremor can shed light on the root of tremor aggravating aspect and aid in diet modification in essential tremor patients. The aim of the review is to establish a relation between the diet with etiopathogenesis and the progression of essential tremor. The review includes studies providing information about essential tremor and correlating essential tremor with diet, lifestyle, environment, and genetic factors. Studies that did not provide a link to the association of essential tremor were excluded. The interpretation of the research indicated that genetic variations might be triggered due to enzymatic changes triggered by dietary patterns. Dietary components showed ambiguous, weak, strong, or no association. Essential tremor may be influenced by diet. Further research must be carried out on essential tremor patients in the nutritional domain. Physicians may monitor the diet of the essential tremor patients and record the progress of the disorder on its basis to manage the patients with essential tremor and provide better services.

Vitamin D Receptor and Binding Protein Gene Variants in Patients with Essential Tremor

Several studies have shown an association between some variants in the vitamin D receptor (VDR) and the GC vitamin D binding protein (GC) genes with the risk for Parkinson's disease or other neurological disorders. VDR rs2228570 has shown an association with essential tremor (ET) in a previous study. The aim of this study is to look for the association between several common variants in these genes and the risk for ET. We genotyped 272 patients diagnosed with familial ET and 272 age-matched controls using specific TaqMan assays for VDR rs2228570, VDR rs731236, VDR rs7975232, VDR rs739837, VDR rs78783628, GC rs7041, and GC rs4588 single nucleotide variants (SNVs). We found an association between GC rs7041 SNV and ET using recessive, codominant, and allelic models. Despite our results did not find an association between VDR rs2228570 and ET, the pooled data with those by a previous report suggest this association under recessive, codominant, and allelic models. None of the SNVs studied was related to the age at onset of tremor in ET patients. Data from the current study suggest an association between GC rs7041 and VDR rs2228570 SNVs and ET risk.

Essential tremor: Clinical perspectives and pathophysiology

Essential tremor (ET) is one of the most common neurological disorders and can be highly disabling. In recent years, studies on the clinical perspectives and pathophysiology have advanced our understanding of ET. Specifically, clinical heterogeneity of ET, with co-existence of tremor and other neurological features such as dystonia, ataxia, and cognitive dysfunction, has been identified. The cerebellum has been found to be the key brain region for tremor generation, and structural alterations of the cerebellum have been extensively studied in ET. Finally, four main ET pathophysiologies have been proposed: 1) environmental exposures to β-carboline alkaloids and the consequent olivocerebellar hyper-excitation, 2) cerebellar GABA deficiency, 3) climbing fiber synaptic pathology with related cerebellar oscillatory activity, 4) extra-cerebellar oscillatory activity. While these four theories are not mutually exclusive, they can represent distinctive ET subtypes, indicating multiple types of abnormal brain circuitry can lead to action tremor. This article is part of the Special Issue "Tremor" edited by Daniel D. Truong, Mark Hallett, and Aasef Shaikh.

Respiratory and Neurological Disease across Different Ethnic Groups Is Influenced by the Microbiome

Acute and chronic upper respiratory illnesses such as asthma, and allergic rhinitis (AR) have been linked to the presence of microorganisms in the nose. Microorganisms can exist in symbiotic or commensal relationships with the human body. However, in certain cases, opportunistic pathogens can take over, leading to altered states (dysbiosis) and causing disease. Thus, the microflora present in a host can be useful to reflect health status. The human body contains 10 trillion to 100 trillion microorganisms. Of these populations, certain pathogens have been identified to promote or undermine wellbeing. Therefore, knowledge of the microbiome is potentially helpful as a diagnostic tool for many diseases. Variations have been recognized in the types of microbes that inhabit various populations based on geography, diet, and lifestyle choices and various microbiota have been shown to modulate immune responses in allergic disease. Interestingly, the diseases affected by these changes are prevalent in certain racial or ethnic populations. These prevalent microbiome variations in these groups suggest that the presence of these microorganisms may be significantly associated with health disparities. We review current research in the search for correlations between ethnic diversity, microbiome communities in the nasal cavity and health outcomes in neurological and respiratory functions.

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.

Whole-Genome Study of a Multigenerational Family with Essential Tremor

BACKGROUND

Essential tremor (ET) is a common movement disorder with ˜5% prevalence in individuals above the age of 65, but in rare cases, it arises during childhood. Growing evidence suggests the role of cerebellum in the disease mechanism. ET is highly heritable, however, poor replication of risk loci point to its significant heterogeneity. Thus, it is important to genetically investigate kindreds with a strong aggregation of ET.

METHODS

We conducted a clinical and whole-genome investigation of a large Caucasian Canadian family, in which six out of eight patients are affected by childhood-onset ET in four consecutive generations. Eight family members were available for study, including three patients affected by ET. Whole-genome sequencing (WGS) was conducted for the four most informative individuals, followed by Sanger sequencing in the entire kindred.

RESULTS

We searched for rare variants absent in the eldest unaffected individual, but present in the patients (two siblings and their third-degree relative). Our stringent whole-genome filtering approach revealed a rare heterozygous p. Arg90Gln substitution in TCP10L (rs151233771) in all three investigated patients. Sanger sequencing confirmed the p. Arg90Gln variant and revealed its absence in the rest of the family members.

CONCLUSIONS

Whole-genome data of the family with ET resulted in a single candidate gene mapped to 21q22.11 locus (TCP10L) with the highest brain expression in cerebellum. Our study encourages future replication studies to validate the genetic link between TCP10L and ET, and suggests the p. Arg90Gln variant for functional investigation.

The Essential Tremors: Evolving Concepts of a Family of Diseases

The past 10 years has seen a remarkable advance in our understanding of the disease traditionally referred to as “essential tremor” (ET). First, the clinical phenotype of ET has been expanded from that of a bland, unidimensional, and monosymptomatic entity to one with a host of heterogeneous features. These features include a broader and more nuanced collection of tremors, non-tremor motor features (e.g., gait abnormalities) and a range of non-motor features, including cognitive, psychiatric, sleep, and other abnormalities. The natural history of these features, as well as their relationships with one another and with disease duration and severity, are better appreciated than they were previously. Studies of disease etiology have identified a number of candidate genes as well as explored several environmental determinants of disease. In addition, the decade has seen the beginnings and expansion of rigorous postmortem studies that have identified and described the postmortem changes in the brains of patients with ET. This emerging science has given rise to a new notion that the disease, in many cases, is one of cerebellar system degeneration. Across all of these studies (clinical, etiological, and pathophysiological) is the observation that there is heterogeneity across patients and that “essential tremor” is likely not a single disease but, rather, a family of diseases. The time has come to use the more appropriate terminology, “the essential tremors,” to fully describe and encapsulate what is now apparent. In this paper, the author will review the clinical, etiological, and pathophysiological findings, referred to above, and make the argument that the terminology should evolve to reflect advances in science and that “the essential tremors” is a more scientifically appropriate term.

Sleep Disorders in Patients with Essential Tremor

PURPOSE OF THE REVIEW

Patients diagnosed with essential tremor (ET) report frequent sleep complaints. This review focuses on the main findings of studies addressing sleep features in patients diagnosed with ET, updating previously reported information. Bad quality of sleep and excessive daytime somnolence are very frequent in patients with ET, although the effects of the drugs used for the therapy of ET could contribute to these complaints. REM sleep behavior disorder, restless legs, insomnia, and nocturia are frequent complaints as well. There is a lack of studies addressing polysomnographic features of ET.

Do We Belittle Essential Tremor by Calling It a Syndrome Rather Than a Disease? Yes

Essential tremor (ET) is among the most prevalent neurological diseases. Appreciation in recent years of a richer tremor phenomenology, additional motor and non-motor features, variability in the natural course of tremor, associations with a host of other neurological conditions, and etiological and pathophysiological heterogeneity have resulted in general awareness of the clinical richness of ET. Along with this evolving view of ET have surfaced several conundrums regarding nomenclature. One of these is whether ET should be labeled a "syndrome" or "disease." Here, we revisit the classical definitions of "syndrome" and "disease" and discuss ET in this context. Considering the characteristics of "disease" and "syndrome" and evaluating the characteristics of ET, it seems to fit more into the "disease" construct. There are several reasons: There is considerable knowledge of the underlying etiologies and pathophysiology of ET, in numerous studies ET has been linked with other neurological conditions, the condition is progressive and deteriorative, and therapeutic approaches are grounded in an understanding of disease mechanisms and its associated neuroanatomy. Moreover, the etiological-pathological-clinical heterogeneity suggests that ET should be regarded as a "family of diseases" more appropriately termed "the essential tremors." This nomenclatural issue is not a mere matter of words; public health implications are numerous. A condition with the label "syndrome" may not be recognized as a serious problem, may be plagued by diminished public awareness, and may not garner funds for research that a condition with the label "disease" or "diseases" would. ET should be regarded as a family of diseases.

Genetic Risk Factors for Essential Tremor: A Review

Highlights

In the current review, we thoroughly reviewed 74 identified articles regarding genes and genetic loci that confer susceptibility to ET. Over 50 genes/genetic loci have been examined for possible association with ET, but consistent results failed to be reported raising the need for collaborative multiethnic studies.

Background:

Essential tremor (ET) is a common movement disorder, which is mainly characterized by bilateral tremor (postural and/or kinetic) in the upper limbs, with other parts of the body possibly involved. While the pathophysiology of ET is still unclear, there is accumulating evidence indicating that genetic variability may be heavily involved in ET pathogenesis. This review focuses on the role of genetic risk factors in ET susceptibility.

Methods:

The PubMed database was searched for articles written in English, for studies with humans with ET, controls without ET, and genetic variants. The terms “essential tremor” and “polymorphism” (as free words) were used during search. We also performed meta-analyses for the most examined genetic variants.

Results:

Seventy four articles concerning LINGO1, LINGO2, LINGO4, SLC1A2, STK32B, PPARGC1A, CTNNA3, DRD3, ALAD, VDR, HMOX1, HMOX2, LRRK1,LRRK2, GBA, SNCA, MAPT, FUS, CYPsIL17A, IL1B, NOS1, ADH1B, TREM2, RIT2, HNMT, MTHFR, PPP2R2B, GSTP1, PON1, GABA receptors and GABA transporter, HS1BP3, ADH2, hSKCa3 and CACNL1A4 genes, and ETM genetic loci were included in the current review. Results from meta-analyses revealed a marginal association for the STK32B rs10937625 and a marginal trend for association (in sensitivity analysis) for the LINGO1 rs9652490, with ET.

Discussion:

Quite a few variants have been examined for their possible association with ET. LINGO1 rs9652490 and STK32B rs10937625 appear to influence, to some extent, ET susceptibility. However, the conflicting results and the lack of replication for many candidate genes raise the need for collaborative multiethnic studies.

Blood Harmane (1-Methyl-9H-Pyrido[3,4-b]indole) and Mercury in Essential Tremor: A Population-Based, Environmental Epidemiology Study in the Faroe Islands

BACKGROUND

Essential tremor (ET) is among the most prevalent neurological diseases. Its environmental determinants are poorly understood. Harmane (1-methyl-9H-pyrido[3, 4-b]indole), a dietary tremor-producing neurotoxin, has been linked to ET in a few studies in New York and Madrid. Mercury, also a tremor-producing neurotoxin, has not been studied in ET. The Faroe Islands have been the focus of epidemiological investigations of numerous neurological disorders.

OBJECTIVE

In this population-based, case-control study, we directly measured blood harmane concentrations (HA) and blood mercury concentrations (Hg) in ET cases and controls.

METHODS

In total, 1,328 Faroese adults were screened; 26 ET cases were identified whose (HA) and (Hg) were compared to 197 controls.

RESULTS

Although there were no statistically significant differences between diagnostic groups, median (HA) was 2.7× higher in definite ET (4.13 g-10/mL) and 1.5× higher in probable ET (2.28 g-10/mL) than controls (1.53 g-10/mL). Small sample size was a limitation. For definite ET versus controls, p = 0.126. (Hg) were similar between groups.

CONCLUSIONS

We demonstrated marginally elevated (HA) in definite and probable ET. These data are similar to those previously published and possibly extend etiological links between this neurotoxin and ET to a third locale. The study did not support a link between mercury and ET.