Tremor and longevity in relatives of patients with Parkinson's disease, essential tremor, and control subjects

Essential tremor

Essential tremor (ET) is one of the most common movement disorders, with a reported >60 million affected individuals worldwide. The definition and underlying pathophysiology of ET are contentious. Patients present primarily with motor features such as postural and action tremors, but may also have other non-motor features, including cognitive impairment and neuropsychiatric symptoms. Genetics account for most of the ET risk but environmental factors may also be involved. However, the variable penetrance and challenges in validating data make gene-environment analysis difficult. Structural changes in cerebellar Purkinje cells and neighbouring neuronal populations have been observed in post-mortem studies, and other studies have found GABAergic dysfunction and dysregulation of the cerebellar-thalamic-cortical circuitry. Commonly prescribed medications include propranolol and primidone. Deep brain stimulation and ultrasound thalamotomy are surgical options in patients with medically intractable ET. Further research in post-mortem studies, and animal and cell-based models may help identify new pathophysiological clues and therapeutic targets and, together with advances in omics and machine learning, may facilitate the development of precision medicine for patients with ET.

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.

Which disease features run in essential tremor families? A systematic review

Essential tremor is a common and highly heritable movement disorder. It is largely unknown, however, to what extent family members share overlapping symptoms. Such knowledge would be useful, as it may lead to the definition of familial essential tremor phenotypes, which will aid the ongoing search for genotypes. Also, this information can be used by clinicians in patient counselling. Therefore, we conducted a systematic review to provide an overview of the evidence on which essential tremor features run in families, to assess the literature's strengths and weaknesses, and to provide recommendations for future studies. PubMed was searched resulting in 460 titles: sixteen articles ultimately proved fit for inclusion. The results are represented in line with the Axis 1 classification of tremor as published in the latest Consensus Statement. In summary, we found varying levels of positive evidence for familial aggregation of age at onset, disease progression, alcohol responsiveness, parkinsonism and dystonia. Evidence on midline tremor was conflicting. The evidence on familial clustering was negative for cerebellar signs and action tremor asymmetry. Although the level of evidence is modest, it seems that some disease features are indeed familial, while other features are not. We discuss complicating factors, such as state-vs-trait dependency of characteristics, the place of familial dystonia, and the development of diagnostic criteria for essential tremor over time. In the future, comprehensive replication studies are needed, with the addition of several characteristics that have not been investigated so far, as the next step towards discovery of essential tremor phenotypes.

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.

Clinical and Imaging Study of Isolated and Mixed Rest and Action Tremor-Essential Tremor versus Parkinson's Disease

BACKGROUND

Some patients present an unusual association of both action tremor (AT) and rest tremor (RT) making the differential diagnosis between essential tremor (ET) and Parkinson's disease (PD) difficult.

AIM

To investigate this particular clinical picture trying to focus on possible peculiar clinical inferences.

PATIENTS AND METHODS

Twenty-three patients with atypical tremor syndrome were selected for the study. They underwent neurological examination, neuroimaging study, and brain DaTSCAN single-photon emission computed tomography.

RESULTS

Twenty-three patients were evaluated; 17 presented mixed-tremor syndrome, while six patients showed only isolated AT or RT. DaTSCAN was pathological in 19 patients and normal in 3 patients. The emerging statistical data highlighted a positive correlation between disease duration and DaTSCAN abnormalities; Fisher's exact test showed a marked difference in evolution toward a dysfunction of dopaminergic pathways in patients with both AT and RT phenotype.

CONCLUSION

The possible correlation between PD and ET has often been discussed without any clear findings. Are these patients suffering from ET prone to develop PD? Or are they the expression of a specific clinical phenotype? Our clinical survey has not led to absolute considerations; however, it seeks to highlight the clinical markers that might arouse the suspicion of extrapyramidal disease in patients with atypical tremor syndrome.

Knowledge gaps and research recommendations for essential tremor

Essential tremor (ET) is a common cause of significant disability, but its etiologies and pathogenesis are poorly understood. Research has been hampered by the variable definition of ET and by non-standardized research approaches. The National Institute of Neurological Disorders and Stroke (USA) invited experts in ET and related fields to discuss current knowledge, controversies, and gaps in our understanding of ET and to develop recommendations for future research. Discussion focused on phenomenology and phenotypes, therapies and clinical trials, pathophysiology, pathology, and genetics. Across all areas, the need for collaborative and coordinated research on a multinational level was expressed. Standardized data collection using common data elements for genetic, clinical, neurophysiological, and pathological studies was recommended. Large cohorts of patients should be studied prospectively to collect bio-samples, characterize the natural history of the clinical syndrome including patient-oriented outcomes, investigate potential etiologies of various phenotypes, and identify pathophysiological mechanisms. In particular, cellular and system-level mechanisms of tremor oscillations should be elucidated because they may yield effective therapeutic targets and biomarkers. A neuropathology consortium was recommended to standardize postmortem analysis and further characterize neuropathological observations in the cerebellum and elsewhere. Furthermore, genome-wide association studies on large patient cohorts (>10,000 patients) may allow the identification of common genes contributing to risk, and whole exome or genome sequencing may enable the identification of genetic risk and causal mutations in cohorts and well-characterized families.

Current concepts of essential tremor

Essential tremor is clinically defined but there is increasing evidence that it is not a unique entity. Its pathophysiology has been studied with many methods but may also vary between subtypes. Neurophysiologically, there is strong evidence that a specific cerebello-thalamo-cortical loop is abnormally oscillating. The cause of its uncontrolled oscillation is not yet understood. The clear proof of a degenerative cause is still lacking and abnormal receptors or other causes of altered non-progressive functional disturbance cannot be excluded. Strong evidence supports the major involvement of the cerebellum and there is ample evidence that GABA is the main neurotransmitter involved in the pathophysiology in ET. Genetics have provided so far only a few rare subtypes which are due to specific mutations but there is no doubt that it is mostly a hereditary condition. There is evidence that the large subgroup of late onset tremor is a separate condition and this tremor is an independent risk factor for earlier mortality and comes with signs of premature aging (aging-related tremor). It will be important to improve phenotyping of patients in more detail possibly to include not only features of the tremor itself but also other clinical assessments like force measurements or cognitive testing. Based on these variables, we may be able to better understand the presumably different mechanisms underlying different variants of the disease.

Fragile X-associated tremor/ataxia syndrome: phenotypic comparisons with other movement disorders

OBJECTIVE

The purpose of this paper is to review the typical cognitive and motor impairments seen in fragile X-associated tremor/ataxia syndrome (FXTAS), essential tremor (ET), Parkinson disease (PD), spinocerebellar ataxias (SCAs), multiple system atrophy (MSA), and progressive supranuclear palsy (PSP) in order to enhance diagnosis of FXTAS patients.

METHODS

We compared the cognitive and motor phenotypes of FXTAS with each of these other movement disorders. Relevant neuropathological and neuroimaging findings are also reviewed. Finally, we describe the differences in age of onset, disease severity, progression rates, and average lifespan in FXTAS compared to ET, PD, SCAs, MSA, and PSP. We conclude with a flow chart algorithm to guide the clinician in the differential diagnosis of FXTAS.

RESULTS

By comparing the cognitive and motor phenotypes of FXTAS with the phenotypes of ET, PD, SCAs, MSA, and PSP we have clarified potential symptom overlap while elucidating factors that make these disorders unique from one another. In summary, the clinician should consider a FXTAS diagnosis and testing for the Fragile X mental retardation 1 (FMR1) gene premutation if a patient over the age of 50 (1) presents with cerebellar ataxia and/or intention tremor with mild parkinsonism, (2) has the middle cerebellar peduncle (MCP) sign, global cerebellar and cerebral atrophy, and/or subcortical white matter lesions on MRI, or (3) has a family history of fragile X related disorders, intellectual disability, autism, premature ovarian failure and has neurological signs consistent with FXTAS. Peripheral neuropathy, executive function deficits, anxiety, or depression are supportive of the diagnosis.

CONCLUSIONS

Distinct profiles in the cognitive and motor domains between these movement disorders may guide practitioners in the differential diagnosis process and ultimately lead to better medical management of FXTAS patients.

FUS-linked essential tremor associated with motor dysfunction in Drosophila

Essential tremor (ET) is one of the most common adult-onset neurological disorders which produce motor and non-motor symptoms. To date, there are no gold standard pathological hallmarks of ET, and despite a strong genetic contribution toward ET development, only a few pathogenic mutations have been identified. Recently, a pathogenic FUS-Q290X mutation has been reported in a large ET-affected family; however, the pathophysiologic mechanism underlying FUS-linked ET is unknown. Here, we generated transgenic Drosophila expressing hFUS-WT and hFUS-Q290X and targeted their expression in different tissues. We found that the targeted expression of hFUS-Q290X in the dopaminergic and the serotonergic neurons did not cause obvious neuronal degeneration, but it resulted in motor dysfunction which was accompanied by impairment in the GABAergic pathway. The involvement of the GABAergic pathway was supported by rescue of motor symptoms with gabapentin. Interestingly, we observed gender specific downregulation of GABA-R and NMDA-R expression and reduction in serotonin level. Overexpression of hFUS-Q290X also caused an increase in longevity and this was accompanied by downregulation of the IIS/TOR signalling pathway. Our in vivo studies of the hFUS-Q290X mutation in Drosophila link motor dysfunction to impairment in the GABAergic pathway. Our findings would facilitate further efforts in unravelling the pathophysiology of ET.

Memory Similarities Between Essential Tremor and Parkinson's Disease: A Final Common Pathway?

OBJECTIVE

A growing body of literature supports the view that essential tremor (ET) involves alteration of cerebellar-thalamo-cortical networks which can result in working memory and executive deficits. In this study, we tested the hypothesis that individuals with ET would exhibit worse performance on memory tasks requiring more intrinsic organization and structuring (i.e., word lists) relative to those with fewer 'executive' demands (i.e., stories), similar to that previously observed in individuals with Parkinson's disease (PD).

METHOD

Participants included a convenience sample of 68 ET patients and 68 idiopathic PD patients, retrospectively matched based on age, education, and sex. All patients underwent routine neuropsychological evaluation assessing recent memory, auditory attention/working memory, language, and executive function. Memory measures included the Hopkins Verbal Learning Test-R and WMS-III Logical Memory.

RESULTS

Both ET and PD patients performed significantly worse on word list than story memory recall tasks. The magnitude of the difference between these two memory tasks was similar for ET and PD patients. In both patient groups, performance on measures of executive function and auditory attention/working memory was not distinctly correlated with word list vs. story recall.

CONCLUSIONS

These findings suggest that frontal-executive dysfunction in both ET and PD may negatively influence performance on memory tests that are not inherently organized. Although the pathophysiology of these two 'movement disorders' are quite distinct, both have downstream effects on thalamo-frontal circuitry which may provide a common pathway for a similar memory phenotype. Findings are discussed in terms of neuroimaging evidence, conceptual models, and best practice.

Tremor in the elderly: Essential and aging-related tremor

BACKGROUND

Isolated tremor in the elderly is commonly diagnosed as essential tremor (ET). The prevalence of tremor increases steeply with increasing age, whereas hereditary tremor is becoming less common. Moreover, late-manifesting tremor seems to be associated with dementia and earlier mortality. We hypothesize that different entities underlie tremor in the elderly.

METHODS

Two thousand four hundred forty-eight subjects from the Longitudinal Study of Aging Danish Twins older than 70 y answered screening questions for ET in 2001. Two thousand fifty-six (84%) participants drew Archimedes spirals to measure their tremor severity, and classical aging phenotypes were assessed. A subgroup of 276 individuals fulfilling either screening criteria for ET or being controls were personally assessed. Medications and mortality data are available.

RESULTS

The spiral score increased with age. The spiral score correlated with tremor severity. For the whole cohort, mortality was significantly correlated with the spiral score, and higher spiral scores were associated with lower physical and cognitive functioning. Multivariate analysis identified higher spiral scores as an independent risk factor for mortality. In contrast, the ET patients did not show an increased but rather a lower mortality rate although it was not statistically significant. Consistent with a slower than normal aging, they were also physically and cognitively better functioning than controls.

CONCLUSIONS

Because incident tremors beyond 70 y of age show worse aging parameters and mortality than controls and ET, we propose to label it 'aging-related tremor' (ART). This tremor starts later in life and is accompanied by subtle signs of aging both cognitively and physically. More detailed clinical features and pathogenesis warrant further assessment.

Update on genetics of essential tremor

Despite the research, few advances in the etiopathogenesis on essential tremor (ET) have been made to date. The high frequency of positive family history of ET and the observed high concordance rates in monozygotic compared with dizygotic twins support a major role of genetic factors in the development of ET. In addition, a possible role of environmental factors has been suggested in the etiology of ET (at least in non-familial forms). Although several gene variants in the LINGO1 gene may increase the risk of ET, to date no causative mutated genes have been identified. In this review, we summarize the studies performed on families with tremor, twin studies, linkage studies, case-control association studies, and exome sequencing in familial ET.

Tremor associated with focal and segmental dystonia

BACKGROUND AND PURPOSE

Tremor occurs in 10-85% of patients with focal dystonia as so-called dystonic tremor or tremor associated with dystonia. The aim of this study was to assess the incidence and to characterize parameters of tremor accompanying focal and segmental dystonia.

MATERIAL AND METHODS

One hundred and twenty-three patients with diagnosis of focal and segmental dystonia together with 51 healthy controls were included in the study. For each participant, clinical examination and objective assessment (accelerometer, electromyography, graphic tablet) of hand tremor was performed. Frequency and severity of tremor were assessed in three positions: at rest (rest tremor); with hands extended (postural tremor); during 'finger-to-nose' test and during Archimedes spiral drawing (kinetic tremor). Based on the mass load test, type of tremor was determined as essential tremor type or enhanced physiological type.

RESULTS

The incidence of tremor was significantly higher in dystonic patients as compared to controls (p = 0.0001). In clinical examination, tremor was found in 50% of dystonic patients, and in instrumental assessment in an additional 10-20%. The most frequent type of tremor was postural and kinetic tremor with 7 Hz frequency and featured essential tremor type. In the control group, tremor was detected in about 10% of subjects as 9-Hz postural tremor of enhanced physiological tremor type. No differences were found between patients with different types of dystonia with respect to the tremor incidence, type and parameters (frequency and severity). No correlations between tremor severity and dystonia severity were found either.

The relationship between Parkinson's disease and essential tremor: review of clinical, epidemiologic, genetic, neuroimaging and neuropathological data, and data on the presence of cardinal signs of parkinsonism in essential tremor

BACKGROUND

The possible relationship between essential tremor (ET) and Parkinson's disease (PD) has been controversial since the first description of PD. However, there is increasing evidence suggesting an overlap between these two disorders. The aim of this review is to examine the relationship between PD and ET, focusing on clinical, epidemiologic, genetic, neuroimaging, and neuropathological data, and the presence of cardinal parkinsonism symptoms in ET.

METHODS

We conducted a PubMed search for articles published between 1966 and November 2011 regarding the relationship between ET and PD and the presence of postural tremor in PD patients; the presence of rest tremor, rigidity, and slowed movements in ET patients is reviewed.

RESULTS

Clinical series, follow-up studies of ET patients, and case-control and genetic epidemiological studies indicate that ET is associated with increased risk for PD. Some neuroimaging studies and neuropathological reports suggest an association between the two diseases. ET patients show high prevalence of rest tremor, and at least seven studies described slowed movements (possibly related to cerebellar dysfunction and/or bradykinesia) in patients with ET.

DISCUSSION

There is reasonable epidemiological and clinical evidence to support a link between ET and PD, although it is not clear what factors predict ET patient risk for developing PD or, more rarely, of PD patients developing ET. Future multicentric and multidisciplinary studies including epidemiological, clinical, neuroimaging, genetic, and neuropathological assessments are required to understand these associations.

Revisiting the relationship between essential tremor and Parkinson's disease

BACKGROUND

The relationship between essential tremor and Parkinson's disease has been a subject of reviews and debates for long time, but there is now growing evidence that the two common movement disorders are pathogenically related, at least in some patient populations.

METHODS

PubMed as well as authors' own files were searched for relevant keywords regarding overlap between the disorders in clinical features as well as on epidemiologic, genetic, imaging, and pathological studies.

RESULTS

New findings in each of these categories are critically reviewed and placed in the context of previously published data.

DISCUSSION

Although we believe that there is compelling evidence for the notion that some patients with "pure" ET evolve into PD, the biologic nature of the association is not well understood. Furthermore, it is not clear what factors predict which ET patients later develop PD and whether patients with PD are more likely to develop ET. Further epidemiologic, clinical, genetic, imaging, and pathological studies are needed to better understand this mixed, ET-PD phenotype.

Association between essential tremor and other neurodegenerative diseases: what is the epidemiological evidence?

BACKGROUND

The possible links between essential tremor (ET) and Parkinson's disease (PD) and, more recently, between ET and Alzheimer's disease (AD) have been of great interest, particularly with the emergence of postmortem data suggesting that ET itself may be a neurodegenerative disease. Given the very high population prevalence of ET, its possible role as a risk factor for PD and AD is of special significance. At the center of this debate is the burgeoning evidence from epidemiological studies, examining whether there is an increased co-occurrence of these conditions within the same individuals or within families.

METHODS

We conducted a PubMed search from 1966 to March 2011 and reviewed the epidemiological evidence, restricting our analyses to studies that generated quantifiable measures of association (odds ratios or relative risks), thereby being able to assess the role of chance.

RESULTS

The most robust evidence, from case-control, prospective and familial aggregation studies, indicates that ET is associated with increased odds and increased risks of both PD and AD.

CONCLUSIONS

There is reasonable epidemiological evidence to support a link between ET and these neurodegenerative diseases. Further studies are needed to corroborate the current results, provide additional estimates of effect and begin to explore the mechanistic underpinnings for these intriguing associations.

Tremor in Parkinson's disease is not associated with the DRD3 Ser9Gly polymorphism

A common subset of genetic risk factors for Parkinson's disease (PD) and essential tremor (ET) has been postulated. Recently, an association between the dopamine D(3) receptor (DRD3) Ser9Gly polymorphism and ET has been reported. We studied whether PD tremor is influenced by Ser9Gly in a genetic association study based on the gene bank of the German Competence Network on Parkinson's disease. The study included analyses of motor predominance (mixed, hypokinetic, and tremor), and tremor type (resting, postural, and action). We did not identify any effect of DRD3 Ser9Gly on tremor in PD, even when regarding various symptom combinations to avoid missing a weak effect on the phenotype. Additional studies incorporating symptoms at disease onset, and grading of tremor response to dopaminergic therapy, are warranted.

Gamma-aminobutyric acid (GABA) receptor rho (GABRR) polymorphisms and risk for essential tremor

Some clinical and experimental data suggest a possible role of gamma-aminobutyrate (GABA)-ergic mechanisms in the pathophysiology of essential tremor (ET), such as the improvement of ET with some GABAergic drugs and the development of an experimental model of ET in GABA A receptor alpha-1 knockout mice (postural and kinetic tremor and motor incoordination similar to human ET). To investigate the possible association between the GABA receptor subtype rho1, rho2, and rho3 (GABRR1, GABRR2, and GABRR3) genotypes and allelic variants of the single nucleotide polymorphisms GABRR1-M26V (Met26Val, rs12200969), GABRR1-H27R (His26Arg, rs1186902), GABRR2-T455M (Thr55Met, rs282129), and GABRR3-Y205X (Tyr205X, rs832032), and the risk for ET, we studied the frequency of the previously mentioned GABRR genotypes and allelic variants in 200 patients with ET and 250 healthy controls using TaqMan genotyping. The frequencies of the GABBR1 genotypes and allelic variants of the studied polymorphisms did not differ significantly between patients with ET and controls, and were unrelated with the age at onset of tremor, gender, localization of tremor, and response of tremor to ethanol. These data suggest that the single nucleotide polymorphisms studied in the GABBR genes are not related to the risk for ET.

Essential tremor in Parkinson's disease kindreds from a population of similar genetic background

To investigate the possible association between essential tremor (ET) and Parkinson's disease (PD) we conducted a prospective clinical and epidemiological study in a population of similar genetic background. The first-degree relatives of 303 PD probands and 249 controls from Crete were evaluated for the presence of ET. In addition, the possible co-occurrence of ET and PD in the same family or in the same individual was investigated. Results showed that ET was present in the relatives of PD patients more often than in those of controls (OR:3.64, P < 0.001). The risk was even greater (OR: 4.48) when the affected proband had tremor-dominant or mixed PD. Female relatives and siblings of PD patients were more likely to have ET than male relatives and parents of PD patients (OR: 4.36 v/s 2.89 and 4.49 v/s 2.74, respectively). Twelve subjects had both ET and PD phenotypes. While this may have occurred by chance, a number of families were identified in which ET and PD were coinherited through the same parental line. Hence, in certain families ET and PD are genetically related probably sharing common hereditary predisposition.

Dopamine receptor D3 (DRD3) genotype and allelic variants and risk for essential tremor

To investigate the possible association between dopamine receptor D3 genotype (DRD3) and allelic variants and the risk for developing essential tremor (ET). Leukocytary DNA from 201 patients with ET and 282 healthy controls was studied for the genotype DRD3 and the occurrence of DRD3 allelic variants by using allele-specific PCR amplification and MslI-RFLP's analyses. A meta-analysis of previous studies was performed. The frequencies of the DRD3Ser/Gly genotype and of the allelic variant DRDGly were significantly higher in patients with ET than in controls (P < 0.017 and <0.005, respectively), These findings were especially relevant in women (OR = 1.73, 95% CI: 1.15-2.59, P = 0.008), and in patients with earlier onset of the disease with (P = 0.014). The frequencies of the DRD3Ser/Gly and DRD3Gly/Gly genotypes and of the allelic variant DRD3Gly in patients were significantly higher in patients with voice tremor, but not with head, tongue, or chin tremor, than in controls. The meta-analysis indicated association of variant genotypes with ET risk (OR = 1.18, 95% CI 1.01-1.38). These results suggest that DRD3 genotype and the variant DRD3Gly allelic variant is associated with the risk for and age at onset of ET, and with the risk for voice tremor, in Caucasian Spanish people.

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.

Evidence of increased odds of essential tremor in Parkinson's disease

In a case control study using a standardized protocol, 600 subjects were evaluated for essential tremor (ET). We demonstrated that ET was significantly more frequent in patients with Parkinson's disease (PD) (12/204, 5.9%) compared to diseased controls (2/206, 1%) and healthy controls (1/190, 0.5%). A regression analysis with ET as outcome and group (either PD or healthy controls or diseased controls) as independent variable (adjusting for age and sex) revealed that PD had higher odds of having ET than diseased controls (OR = 5.43, 95% CI = 1.16, 25.39, P < 0.001) and healthy controls (OR = 10.87, 95% CI = 1.39, 85.15, P < 0.001). The low frequency of ET in our controls was further confirmed in a follow-up study in a group of age and gender matched general medical patients who attended an outpatient clinic (0% frequency). Eight of 204 PD (3.9%) compared to none of diseased (0%) (P = 0.004) and healthy controls (0%) (P = 0.008) had a prior diagnosis of ET. The duration of ET symptoms in patients with PD was 25.1 +/- 19.6 (range 3-60) years. A multivariate analysis demonstrated that a lower dose of levodopa (OR = 0.993, 95%CI for OR = 0.988, 0.997, P < 0.001) and a higher age of onset of disease (OR = 1.108, 95%CI for OR = 1.035, 1.187, P < 0.001) were associated with increased odds of PD with ET, compared to patients with PD without ET. In our Asian population, patients with PD were 5 to 10 times more likely to have ET compared to diseased and healthy controls, suggesting that the association of ET and PD is unlikely to be ethnicity-specific.

Glutathione-S-transferase P1 polymorphism and risk for essential tremor

Glutathione-S-transferases (GST) are polymorphic enzymes that participate in the metabolism of carcinogens (including those of tobacco smoke) and pesticides. We investigated the possible association between the GSTP1 genotype and allelic variants and the risk for essential tremor (ET). We studied the frequency of the GSTP1 genotypes and allelic variants in 200 patients with ET and 220 healthy controls using PCR-RFLP method. The association between GSTP1 polymorphism and the exposure to some environmental factors (agricultural work, pesticides, well-water and smoking-cigarettes habit) was also studied in a subgroup of patients. The frequencies of the GSTP1 genotypes and allelic variants did not differ significantly between patients with ET and controls or between patients with ET exposed to agricultural work, well water and cigarette smoking versus those non-exposed. Mutated allelic variants were significantly more frequent in patients with ET exposed to pesticides versus those non-exposed. GSTP1 polymorphism was unrelated with the age of onset of ET. GSTP1 genotypes and allelic variants were not related with the risk for ET with the possible exception of those patients exposed to pesticides.

A population-based study of mortality in essential tremor

BACKGROUND

Although data are sparse, people with essential tremor (ET) are usually assumed to have mortality rates similar to those in the general population. Because ET is common, particularly among older adults, an influence of ET on the life span would have important public health implications. The authors compared the risks of mortality in patients with ET and control subjects without ET.

METHODS

A prospective, population-based design was used to compare the risk of mortality in participants with ET vs controls in three communities in central Spain. Participants were evaluated at baseline (1994 to 1995) and at follow-up 3 years later (1997 to 1998). The relative risk (RR) of mortality (ET vs controls) was estimated using Cox proportional hazards models that excluded participants with Parkinson disease or dementia.

RESULTS

Mean baseline age was 73.5 +/- 6.4 years. There were 33 (16.4%) deaths among 201 ET cases and 465 (13.9%) among 3,337 controls. In an unadjusted Cox model, risk of mortality was increased in ET (RR = 1.59, 95% CI = 1.11 to 2.27, p = 0.01). In a Cox model that adjusted for baseline age, gender, educational category, current ethanol drinking, use of antidepressant medication, and community, RR = 1.45, 95% CI = 1.01 to 2.08, p = 0.04. In an adjusted Cox model restricted to persons with longer (>3 years) follow-up, RR = 4.69 (95% CI = 2.18 to 10.07, p = 0.001).

CONCLUSIONS

In this longitudinal, prospective study, the risk of mortality was increased in essential tremor. Additional studies of incident cases are needed to confirm these results.

Alcohol dehydrogenase 2 genotype and allelic variants are not associated with the risk for essential tremor

OBJECTIVE

To investigate the possible association between alcohol dehydrogenase 1B, beta-polypeptide (ADH2) genotype and allelic variants and the risk for developing essential tremor (ET).

METHODS

Leukocytary DNA from 204 ET patients and 200 healthy controls was studied for the genotype ADH2 and the occurrence of ADH2 allelic variants using allele-specific polymerase chain reaction amplification and MslI-restriction fragment length polymorphism's analyses.

RESULTS

The frequencies of the ADH2*1/ADH2*2 genotype and of the allelic variant ADH2*2 did not differ significantly in ET patients when compared with those of the controls. The mean age at onset of ET did not differ significantly between patients with genotypes ADH2*1/ADH2*2 and ADH2*1/ADH2*1. The frequencies of the genotype ADH2*1/ADH2*2 and of the allelic variant ADH2*2 in patients with voice, tongue, and chin tremors did not differ from those of the controls, whereas patients with voice tremor showed lower frequencies of mutated genotypes and ADH2*2 alleles. The frequencies of ADH2 genotypes and ADH2 alleles did not differ significantly between patients who did not drink ethanol and those who reported improvement, no improvement, or unknown response of tremor to ethanol.

CONCLUSIONS

These results suggest that ADH2 genotype and allelic variants are not associated with the risk for ET in white Spanish people.

Parkinsonism and essential tremor in a family with pseudo-dominant inheritance of PARK2: an FP-CIT SPECT study

We report a family with 5 affected individuals manifesting either essential tremor (ET), Parkinsonism, or both, consistent with pseudo-dominant inheritance of PARK2. Two homozygotes presented postural and kinetic tremor several years before the onset of Parkinsonism. Postural and kinetic tremor mimicking ET was the only feature in 1 homozygous and 2 heterozygous carriers of the mutation. Striatal dopamine transporter density was reduced in accordance with phenotype and number of mutated alleles. In 3 homozygotes and 1 heterozygote, a 2-year follow-up single photon emission computed tomography suggested no progression of nigrostriatal deficit.

Changes at the CYP2C locus and disruption of CYP2C8/9 linkage disequilibrium in patients with essential tremor

To identify low-penetrance genes related to sporadic essential tremor (ET) at the CYP2C locus, located in chromosome 10 q23.33. Leukocytary DNA from 200 ET patients and a control group of 300 unrelated healthy individuals with known CYP2C19 genotypes was studied for common CYP2C8 and CYP2C9 allelic variants by using amplification-restriction analyses. Patients with ET showed the following differences compared with healthy subjects: a 1.6-fold reduction in the frequency for CYP2C8*3 (p=0.006), a 1.35-fold reduction of CYP2C9*2 (p=0.05) and a 1.52-fold reduction in the frequency for CYP2C9*3 (p=0.07). The frequency for patients with ET carrying at least one defective allele was 1.33-fold reduced as compared with healthy subjects (p=0.002). In addition, a disruption of the CYP2C8*3/CYP2C9*2 linkage disequilibrium was observed in ET patients, with a 2.1-fold reduction in the percentage for carriers of the haplotype CYP2C8*3 plus CYP2C9*2 in ET patients (p=0.0001). These findings were independent of gender, age, age of onset, or clinical symptoms. These results suggest that alterations at the CYP2C gene locus are associated with the risk for ET.

Parkinsonism and tremor disorders. A clinical approach

Differentiation of idiopathic Parkinson's disease from other causes of Parkinsonism, such as Multiple System Atrophy, Progressive Supranuclar Palsy and Vascular Parkinsonism can be difficult. Clinicopathological studies suggest that the clinical diagnosis of idiopathic Parkinson's disease is 76% reliable. Also, clinical differentiation of tremor prominent Parkinsonism from Essential Tremor or Drug induced Parkinsonism may be problematic, especially in the early stages of the disease. Since these disorders are obviously different in clinical progress, it is important for the clinician to address the patient's and family's concerns about prognosis from a firm diagnostic footing. In this article the clinical features of the common and important causes of Parkinsonism and tremor disorders are reviewed and a practical approach is suggested.

Exploring the relationship between essential tremor and Parkinson's disease

Although essential tremor (ET) and Parkinson's disease (PD) are considered distinct disorders, there is overlap in some clinical features. In some PD patients, a long-standing postural tremor in the hands may precede the onset of parkinsonian features by several years or decades. Furthermore, large families with both ET and PD phenotypes have been described and autopsy studies have demonstrated Lewy body pathology in brains of ET patients. Functional neuroimaging suggests that some ET patients have dopaminergic deficit. We examine here the evidence for and against an association between ET and PD, and critically review data supporting the notion that a subset of ET patients is predisposed to developing PD.

Familial essential tremor with apparent autosomal dominant inheritance: should we also consider other inheritance modes?

A positive family history is present in many patients with essential tremor (ET), but twin studies and segregation analysis have suggested that ET is not entirely a genetic disorder. Two genetic loci have been identified in autosomal dominant (AD) ET and polymorphisms in the DRD3 and HS1-BP3 genes have been proposed as the possible susceptibility factors for ET. There is also evidence for further genetic heterogeneity. We evaluated 4 unrelated large kindreds with ET with an apparent AD mode of transmission. Each kindred spanned at least 3 generations and contained at least 13 living affected subjects who met criteria for definitive ET. None of the pedigrees had evidence for inheritance of ET from both parents. Known genetic ET loci were excluded in these families. We detected a preferential transmission of ET in every kindred and the proportion of affected offspring varied from 75% to 90% (P < 0.05) in the generations with complete ascertainment. Our data indicate that non-Mendelian preferential transmission of an affected allele is a feature in many ET kindreds with multiple affected members and an apparent AD mode of inheritance. ET may have a complex etiology. Additional genetic models need to be considered, including an interaction of susceptibility genes and environmental risk factors.

Increased risk of essential tremor in first-degree relatives of patients with Parkinson's disease

We conducted a historical cohort study of 981 first-degree relatives of 162 patients with Parkinson's disease (PD) and of 838 first-degree relatives of 147 controls representative of the population of Olmsted County, Minnesota. In addition, we studied 2,684 first-degree relatives of 411 patients with PD referred to the Mayo Clinic. Relatives were interviewed and screened for tremor either directly or through a proxy, and those who screened positive were examined or copies of their medical records were obtained to confirm the diagnosis of essential tremor (ET). We also obtained ET information from a medical records-linkage system (family study method). In the population-based sample, the risk of ET was significantly increased for relatives of patients with onset of PD<or=66 years (first tertile; hazard ratio [HR]=2.24; 95% confidence interval [95% CI]=1.26-3.98; P=0.006). In the referral-based sample, the risk of ET among relatives increased with younger onset of PD in patients (linear trend; P=0.001), and was higher in relatives of PD patients with the tremor-predominant or mixed form when compared with relatives of patients with the akinetic-rigid form, and in men compared with women. These findings suggest that PD and ET may share familial susceptibility factors.

CYP2C19 polymorphism and risk for essential tremor

Many patients with essential tremor (ET) develop acute adverse effects to primidone. We investigated the association between CYP2C19 polymorphism (possibly related to primidone metabolism) and the risk for developing essential ET and acute adverse effects to primidone. Leukocytary DNA from 200 ET patients and 300 healthy controls was studied for the genotype CYP2C19 and the occurrence of CYP2C19 allelic variants by using allele-specific PCR amplification and Sma I and BamH I RFLP analyses. The frequencies of the genotype CYP2C19*1/CYP2C19*2 and of the allelic variant CYP2C19*2 were significantly higher in ET patients than in controls. The mean age at onset of ET did not differ significantly between patients with genotypes CYP2C19*1/CYP2C19*2andCYP2C19*1/CYP2C19*1. The frequencies of the genotype CYP2C19*1/CYP2C19*2 and the allelic variant CYP2C19*2 were similar in ET patients who developed acute adverse effects to primidone, in those who tolerated primidone and in controls; the frequencies were also similar in patients with head, voice, tongue and chin tremor compared with controls. These results suggest that heterozygosis CYP2C19*1/CYP2C19*2 is associated with the risk for ET, but not with the age at onset of ET, the presentation of acute side effects of primidone, or the existence of head, voice, tongue or chin tremor.

HS1-BP3 gene variant is common in familial essential tremor

Essential tremor (ET) is a movement disorder characterized by a postural or kinetic tremor of the hands, head, or voice. It is typically a familial condition and affects 1% to 4% of the general population. The trait is genetically linked to chromosome 2p in some families. A variant (828C-->G) in exon 7 of the hematopoietic-specific protein 1 binding protein 3 gene (HS1-BP3) on chromosome 2p recently has been found to segregate with ET in 2 families. To determine the frequency of this variant in a larger series, we studied patients with ET, Parkinson disease (PD), and controls without tremor. Affected singletons representing 73 families from the United States with dominantly inherited ET, 35 individuals with PD, and 304 healthy controls older than age 60 were tested for the 828C-->G variant in exon 7 of the HS1-BP3 gene by a BseYI restriction enzyme digest of the polymerase chain reaction product. Heterozygous carriers of the mutant allele were identified in 12 individuals with ET (16.4%) and in 1 individual with PD and postural tremor (3%). All of the healthy controls (608 chromosomes) were homozygous for the wild-type allele. The 828C-->G genetic variant in the HS1-BP3 gene occurs relatively frequently in subjects with ET. The variant may also be found in some individuals with PD and postural tremor. The HS1-BP3 gene plays a putative role in regulating catecholamine and serotonin metabolism, but the functional consequences of the amino acid substitution (A265G) caused by this genetic variant is unknown.

Kinetic tremor in Parkinson's disease--an underrated symptom

Since the first description of the disorder which we now call "Parkinson's Disease" (PD) much has changed not only because of new therapeutic possibilities. Initially only the rest tremor was described. Today it is generally accepted that PD can be accompanied by different forms of tremor. Nevertheless the kinetic tremor is hardly examined and no attention is paid to it in clinical rating scales although it can already be found in old published drawings of PD-patients. To date instrumented investigations do not capture the most common kinetic tremor of PD that seems to be frequent under everyday life conditions. In order to assess the significance of kinetic tremor in PD, tremor during a spiral drawing task was investigated in an open study involving 870 patients. The results indicate that a combination of rest, postural and kinetic tremors constitute the most frequent tremor constellation in PD.