Evaluation of a screening instrument for essential tremor

Archimedes Spiral Ratings: Determinants and Population-Based Limits of Normal

BACKGROUND

Tremor is commonly found among healthy humans or prevalently a symptom of neurological dysfunctions. However, the distinction between physiological and pathological tremor is dependent on the examiner's competence. Archimedes Spiral Rating (ASR) is a valid and reproducible semi-quantitative method to assess the severity of action tremor.

OBJECTIVES

(1) To assess the range and percentiles of ASR in a large sample seemingly free of tremor-related conditions or symptoms from the population-based CHRIS-study. (2) To analyze the influence of sex, age, and the drawing hand on ASR. (3) To define ASR limits of normal. (4) To supply exemplary Archimedes spiral drawings by each rating to favor consistent and proficient clinical evaluation.

METHODS

Accurately investigated participants were randomly sampled over 14 sex-age strata. 2686 paired spirals drawn with both hands by 1343 participants were expertly assessed on a tremor rating scale from 0 to 9.

RESULTS

ASR had a quadratic increase with age in both sexes, while it was relatively lower in the dominant compared to the non-dominant hand and in women compared to men. ASRs above sex-age specific 97.5th percentiles of 4 and 5, below and above 60 years of age, respectively, were conceivably of non-physiological nature.

CONCLUSIONS

In a large population-based sample we show a steeper increase of action tremor by age as age progresses. Relatively higher ratings among the elderly, males and the non-dominant hands, appear compatible with ASR limits of "normal" across sex-age groups. The current operational evidence may support practitioners differentiating physiological and pathological hand tremor.

ELectronic Archimedes spiral Neural Network (ELANN)

The Archimedes spiral is a clinical tool that aids in the diagnosis and monitoring of essential tremor. However, spiral ratings may vary based on experience and training of the rating physician. This study sought to generate an objective standard model for tremor evaluation using convolutional neural networks. One senior movement disorders neurologist (Neurologist 1) with over 30 years of clinical experience used the Bain and Findley Spirography Rating Scale to rate 1653 Archimedes spiral images from 46 essential tremor patients (mild to severe tremor) and 75 control subjects (no to mild tremor). Neurologist 1's labels were used as the reference standard to train the model. After training the model, a randomly selected subset of spiral testing data was re-evaluated by Neurologist 1, by a second senior movement disorders neurologist (Neurologist 2) with over 27 years of clinical experience, and by our model. Cohen's Weighted Kappa 95% confidence intervals were calculated from all rater comparisons to determine if our model performs with the same proficiency as two senior movement disorders neurologists. The Cohen's Weighted Kappa 95% confidence intervals for the agreement between the reference standard scores and Neurologist 1's rerated scores, for the agreement between the reference standard scores and Neurologist 2's scores, and for the agreement between the reference standard scores and our model's scores were 0.93-0.98, 0.86-0.94, and 0.89-0.96, respectively. With overlapping Cohen's Weighted Kappa 95% confidence intervals for all agreement comparisons, we demonstrate that our model evaluates spirals with the same proficiency as two senior movement disorders neurologists.

Assessing the Usability of an Instagram Filter in Monitoring Essential Tremor: A Proof-of-Concept Study

Background

Spiral drawing is an important test in monitoring essential tremor (ET). With the rise of telemedicine amid the coronavirus disease 2019 pandemic, a contactless tool for monitoring tremors was required. We aimed to assess the validity of a novel smartphone technology using a video-based social media platform for rapid and objective monitoring of ET.

Methods

A prospective pilot study evaluated patients with ET in 2 clinic visits. Videos of tremors were recorded using a publicly available Instagram filter and were visually compared with spirals drawn by the patients. The level of agreement among the raters was evaluated.

Results

A total of 12 patients with ET were recruited. A consensus between both raters was achieved for 11 patients (91.6%) for both spirals and videos with good interrater agreement (κ value, 0.755 ± 0.332).

Conclusion

This novel method was found to be valid and easy to use in measuring ET in real-world settings. Further research in a larger cohort is needed to suggest its use as a home-based or clinic-based monitoring tool.

Longitudinal Progression of Essential Tremor: Do Tremor Severity Scores Increase at a Uniform Rate?

Background

Few longitudinal studies assess the progression of essential tremor (ET). One unexplored issue is whether tremor severity increases across time at a uniform rate. That is, does the observed rate of change in tremor severity within a particular patient remain constant or vary across time? This question of intra-individual differences is particularly important since it reflects a primary patient concern-will the nature of change I have seen to date be what I can expect in the future?

Methods

ET cases were enrolled in a prospective, longitudinal study. We selected 35 cases and assessed tremor severity via Bain and Findley ratings of Archimedes spirals assigned by a senior movement disorders neurologist. After reviewing both the change in spiral scores and the rate of change in scores, we identified five mutually exclusive patterns of severity change. We calculated the prevalence of each category using two complementary sets of classification criteria.

Results

Length of follow-up was 4.5 to 16.0 years, mean=10.2 years. Mean baseline tremor severity score was 4.6, SD=1.6. Depending upon the classification criteria used, the tremor scores of one-third to one-half of cases did not increase in a uniform fashion but were better described as demonstrating jumps and/or reversals in scores across time.

Conclusions

We document the nature of changes in ET tremor severity scores across a ten-year period via expert ratings of Archimedes spiral drawings. Such natural history data are valuable to patients and clinicians who hope to better understand and predict the likely course of ET symptoms.

Effects of Deep Dry Needling on Tremor Severity and Functionality in Stroke: A Case Report

This study aimed to determine the effect of one session of dry needling on the severity of tremor, motor function and skills, and quality of life of a 39-year-old woman with post-stroke tremor. Myofascial trigger points (MTrP) of the following muscles were treated: extensor digitorum, flexor digitorum superficialis and profundus, brachioradialis, short head of biceps brachii, long head of triceps brachii, mid deltoid, infraspinatus, teres minor, upper trapezius, and supraspinatus. Outcomes were assessed via (i) clinical scales (activity of daily living (ADL-T24), a visual analog scale (VAS), and the Archimedes spiral), (ii) a functional test (9-Hole Peg test), and (iii) biomechanical and neurophysiological measurements (inertial sensors, electromyography (EMG), and dynamometry). The subject showed a decrease in the severity of tremor during postural (72.7%) and functional (54%) tasks after treatment. EMG activity decreased after the session and returned to basal levels 4 days after. There was an improvement post-intervention (27.84 s) and 4 days after (32.43 s) in functionality and manual dexterity of the affected limb, measured with the 9-Hole Peg test, as well as in the patient's hand and lateral pinch strength after the treatment (26.9% and 5%, respectively), that was maintained 4 days later (15.4% and 16.7%, respectively).

Early- and late-onset essential tremor patients represent clinically distinct subgroups

OBJECTIVE

Essential tremor is a very common disease defined by sparse clinical criteria. It is unlikely that essential tremor is an etiologically homogeneous disease. Stratifying broadly defined diseases using clinical characteristics has often aided the etiopathological understanding. Most studies of essential tremor show 2 distinct age at onset peaks: early and late. This study investigates phenotypical differences between early- and late-onset essential tremor patients.

METHODS

We studied a sample of 1137 tremor patients. Of these patients, 978 suffered from definite or probable essential tremor. All of the patients underwent the same standardized examination encompassing, among other items, drawing of the Archimedes spiral and assessment of the Fahn-Tolosa-Marin scale.

RESULTS

Two subgroups of early-onset (≤ 24 years of age, n = 317) and late-onset (≥ 46 years of age, n = 356) patients were selected based on the visual and mathematical analysis of the age-at-onset distribution. Tremor severity in both groups was comparable. Tremor progression measured as Archimedes spiral score and the Fahn-Tolosa-Marin subscales divided by the disease duration in 10-year bins was significantly faster in late-onset patients when compared with early-onset patients. Early-onset patients more frequently reported a positive family history and alcohol sensitivity of the tremor.

CONCLUSIONS

The age-at-onset distribution suggests a distinction between early- and late-onset tremor. Early-onset and late-onset essential tremor differ in the progression rates and the frequencies of a positive family history and history of a positive effect of alcohol on tremor. © 2016 International Parkinson and Movement Disorder Society.

How to use pen and paper tasks to aid tremor diagnosis in the clinic

When a patient presents with tremor, it can be useful to perform a few simple pen and paper tests. In this article, we explain how to maximise the value of handwriting and of drawing Archimedes spirals and straight lines as clinical assessments. These tasks take a matter of seconds to complete but provide a wealth of information that supplements the standard physical examination. They aid the diagnosis of a tremor disorder and can contribute to its longitudinal monitoring. Watching the patient’s upper limb while they write and draw may reveal abnormalities such as bradykinesia, dystonic posturing and distractibility. The finished script and drawings can then be evaluated for frequency, amplitude, direction and symmetry of oscillatory pen movements and for overall scale of penmanship. Essential, dystonic, functional and parkinsonian tremor each has a characteristic pattern of abnormality on these pen and paper tests.

Worse and Worse and Worse: Essential Tremor Patients' Longitudinal Perspectives on Their Condition

BACKGROUND

Essential tremor (ET) patients regularly inquire about their prognosis. Therefore, physicians have cause to review available medical literature for meaningful answers. Longitudinal studies are ideally suited to provide a glimpse into the evolution of tremor. Despite its high prevalence, there are surprisingly few longitudinal clinical studies of ET. Furthermore, none of them provide data from the patients' perspective. Understanding the patient vantage point is valuable as it is the starting point of personalized medicine. Given the progressive nature of ET, we hypothesized that many patients will experience an increase in symptom severity over time. However, due to a lack of clinical data, the exact nature of this progression is unclear. For example, whether patients experience a worsening at each time interval is simply not known. In this longitudinal study, we assessed whether ET patients felt that their symptoms had worsened between each follow-up evaluation and try to identify specific clinical characteristics associated with this experience.

METHODS

A cohort of 164 ET cases enrolled in a prospective, longitudinal research study. After a baseline in-person assessment, they received regular telephone evaluations for up to 5.25 years, beginning in 2009. During each follow-up evaluation, cases answered the question, "has your ET worsened since our last call?"

RESULTS

Two-thirds [104 (63.4%)] of ET cases reported worsening at one-half or more of their follow-up evaluations. Furthermore, one in four cases [44 (26.8%)] reported worsening at every follow-up evaluation. Self-reported worsening was not associated with any of the baseline clinical variables assessed, including age, gender, tremor duration, age at tremor onset, or total tremor score.

CONCLUSION

Little has been written from the patients' perspective on progression of ET. When followed longitudinally at regular intervals, a majority of ET cases we studied reported worsening one-half or more of the time; furthermore, one in four cases reported worsening at each and every assessment, indicating that they felt they were inexorably getting worse and worse with time. That there is so much self-reported worsening in ET argues against the notion that this is a static and benign condition. It suggests that patients experience it as a condition that worsens regularly and consistently.

Screening for and Estimating the Prevalence of Essential Tremor: A Random-Digit Dialing-Based Study in the New York Metropolitan Area

BACKGROUND

There are nearly no published screening instruments for essential tremor (ET). This is a remarkable fact, given its high prevalence. Here, we assess the validity of a screening questionnaire and hand-drawn spirals and also estimate the prevalence of ET in a community sample.

METHODS

Four hundred nineteen study subjects living in a geographically defined area in the New York metropolitan area were contacted using a random digit telephone dialing scheme. Seven tremor screening questions were administered and each subject drew 2 spirals. A movement disorders neurologist assigned ET diagnoses based on neurological examination.

RESULTS

The spirals were a more sensitive test than the screening questions (73.7 vs. 26.3%); specificities of the 2 tests were similar (95.5 vs. 96.8%). The combination of both tests was not superior to the use of spirals alone. The positive predictive value of the spiral test was 43.8%. The crude prevalence of ET, 19 of 419 (4.53%, 95% CI 2.92-6.97), increased with age (p = 0.049).

CONCLUSIONS

A screening spiral was more sensitive than a screening questionnaire for ET and was moderately sensitive. Nearly one-half of subjects who screened positive had ET; therefore, when screening a population, one can expect the number of true positives and false positives to be roughly equivalent.

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.

Testing for alcohol sensitivity of tremor amplitude in a large cohort with essential tremor

BACKGROUND

Improvement of essential tremor (ET) amplitude after alcohol ingestion is usually based on patient reports but a quantitative test for large numbers of patients is lacking and the percentage of ET patients with a detectable alcohol effect is therefore unknown.

METHODS

A validated and published alcohol home test was used in 104 ET patients. The Archimedes spiral was drawn before alcohol ingestion and at 4 time points after alcohol consumption and rated on a 10-point rating scale according to Bain and Findley. A second identical test without alcohol ingestion was performed by the same patients and evaluated by the same two raters to analyze the total variability of the spiral ratings.

RESULTS

Alcohol reduces tremor in ET patients as a group and a rebound effect with an increase in tremor intensity was found the next morning. Sex, family history of ET, diagnosis (definite vs. probable) and medical history of alcohol responsiveness do not predict the alcohol response. The minimal detectable difference in the spiral score was 2 due to spontaneous tremor fluctuations and inter-rater differences. The test demonstrated alcohol sensitivity of the tremor in 46% of the patients. Responsivity to alcohol could only be seen in patients with spiral scores above 3.

CONCLUSIONS

Alcohol sensitivity is a feature of ET in at least 46% of the patients. We could not find predictors for alcohol sensitivity. The minimal detectable change is 2 scores and alcohol responsivity was only detected in patients with baseline Archimedes spiral rating of ≥3.

Utility of the hand-drawn spiral as a tool in clinical-epidemiological research on essential tremor: data from four essential tremor cohorts

BACKGROUND

In descriptive epidemiological studies, investigators must screen large numbers of individuals. How one best screens populations for essential tremor (ET); however, remains an open question. The collection of a standardized writing sample (e.g., a hand-drawn spiral) is a method with many practical advantages, yet there are virtually no data on the validity of this particular method.

METHODS

Four hand-drawn spirals (2 right, 2 left) were collected from 831 ET cases across four distinct study settings (population-based study, family study, environmental epidemiological study, brain repository) and, in two of these studies, from 697 controls. Spirals were rated (range 0-3) by a senior movement disorder neurologist. These 1,528 participants also underwent a detailed neurological examination, and total tremor scores (range 0-36) and ET diagnoses were assigned by the neurologist.

RESULTS

The proportion of cases with hand-drawn spiral ratings ≥1.5 in either arm ranged from 78.8-97.0%; only 4.7% of controls had spirals with tremor of that severity. The hand-drawn spiral rating was highly correlated with the total tremor score (r = 0.65-0.73, p < 0.001).

CONCLUSIONS

The hand-drawn spiral is a sensitive and specific method of screening for ET. Furthermore, it serves as a valid measure of overall tremor severity.

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.

Polymorphisms in the glial glutamate transporter SLC1A2 are associated with essential tremor

OBJECTIVE

Sporadic, genetically complex essential tremor (ET) is one of the most common movement disorders and may lead to severe impairment of the quality of life. Despite high heritability, the genetic determinants of ET are largely unknown. We performed the second genome-wide association study (GWAS) for ET to elucidate genetic risk factors of ET.

METHODS

Using the Affymetrix Genome-Wide SNP Array 6.0 (1000K) we conducted a two-stage GWAS in a total of 990 subjects and 1,537 control subjects from Europe to identify genetic variants associated with ET.

RESULTS

We discovered association of an intronic variant of the main glial glutamate transporter (SLC1A2) gene with ET in the first-stage sample (rs3794087, p = 6.95 × 10(-5), odds ratio [OR] = 1.46). We verified the association of rs3794087 with ET in a second-stage sample (p = 1.25 × 10(-3), OR = 1.38). In the subgroup analysis of patients classified as definite ET, rs3794087 obtained genome-wide significance (p = 3.44 × 10(-10), OR = 1.59) in the combined first- and second-stage sample. Genetic fine mapping using nonsynonymous single nucleotide polymorphisms (SNPs) and SNPs in high linkage disequilibrium with rs3794087 did not reveal any SNP with a stronger association with ET than rs3794087.

CONCLUSIONS

We identified SLC1A2 encoding the major glial high-affinity glutamate reuptake transporter in the brain as a potential ET susceptibility gene. Acute and chronic glutamatergic overexcitation is implied in the pathogenesis of ET. SLC1A2 is therefore a good functional candidate gene for ET.

[Multimorbidity and successful aging: the population-based KORA-Age study]

BACKGROUND

The objective of the KORA-Age research consortium is to assess the determinants and consequences of multimorbidity in the elderly and to look into reasons for successful aging in the general public.

PATIENTS AND METHODS

In the KORA-Age cohort study 9,197 persons were included who where born in the year 1943 or before and participants of previous KORA cohort studies conducted between 1984 and 2001 (KORA: Cooperative Health Research in the Region of Augsburg). The randomized intervention study KORINNA (Coronary infarct follow-up treatment in the elderly) tested a nurse-based case management program with 338 patients with myocardial infarct and included an evaluation in health economics.

RESULTS

A total of 2,734 deaths were registered, 4,565 participants submitted a postal health status questionnaire and 4,127 participants were interviewed by telephone (response 76.2% and 68.9% respectively). A gender and age-stratified random sample of the cohort consisting of 1,079 persons took part in a physical examination (response 53.8%).

CONCLUSION

The KORA-Age consortium was able to collect data in a large population-based sample and is contributing to the understanding of multimorbidity and successful aging.

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.

A clinical test for the alcohol sensitivity of essential tremor

BACKGROUND

The objective of the study was to develop a simple diagnostic test for alcohol sensitivity of essential tremor patients. Here we describe the controlled measurements of tremor severity after alcohol ingestion and the practicability of using it as a home test.

METHODS

Ten patients were tested for alcohol sensitivity under controlled conditions in the laboratory (blood alcohol, quantitative tremor recordings, modified Fahn scale, visual analog scale, Archimedes spirals), and 15 patients were instructed to perform an alcohol test at home (visual analog scale, Archimedes spirals) following an adapted dosage of alcohol.

RESULTS

The time course of the antitremor effect showed significant improvement of up to 50% in both groups for all the outcome parameters. Tremor deteriorated after 3 hours. A quarter of the patients noticed the alcohol effect for the first time during the test.

CONCLUSIONS

Alcohol is an effective drug for essential tremor. Its effect is only short-lived and exhibits a rebound after > 3 hours and the next morning. We propose this essential tremor home test as a diagnostic tool to confirm the alcohol sensitivity of essential tremor.

Validation of digital spiral analysis as outcome parameter for clinical trials in essential tremor

Essential tremor, one of the most prevalent movement disorders, is characterized by kinetic and postural tremor affecting activities of daily living. Spiral drawing is commonly used to visually rate tremor intensity, as part of the routine clinical assessment of tremor and as a tool in clinical trials. We present a strategy to quantify tremor severity from spirals drawn on a digitizing tablet. We validate our method against a well-established visual spiral rating method and compare both methods on their capacity to capture a therapeutic effect, as defined by the change in clinical essential tremor rating scale after an ethanol challenge. Fifty-four Archimedes spirals were drawn using a digitizing tablet by nine ethanol-responsive patients with essential tremor before and at five consecutive time points after the administration of ethanol in a standardized treatment intervention. Quantitative spiral tremor severity was estimated from the velocity tremor peak amplitude after numerical derivation and Fourier transformation of pen-tip positions. In randomly ordered sets, spirals were scored by seven trained raters, using Bain and Findley's 0 to 10 rating scale. Computerized scores correlated with visual ratings (P < 0.0001). The correlation was significant at each time point before and after ethanol (P < 0.005). Quantitative ratings provided better sensitivity than visual rating to capture the effects of an ethanol challenge (P < 0.05). Using a standardized treatment approach, we were able to demonstrate that spirography time-series analysis is a valid, reliable method to document tremor intensity and a more sensitive measure for small effects than currently available visual spiral rating methods.

The psychosocial burden of essential tremor in an outpatient- and a community-based cohort

BACKGROUND AND PURPOSE

To compare psychosocial burden in patients with essential tremor (ET) in an outpatient (OPC)- and a community-based cohort (CBC).

METHODS

A sample of outpatients of a tertiary referral center (n = 180) and a community-based sample (n = 100) with ET were asked for study participation. Psychosocial aspects were assessed by a questionnaire on psychosocial aspects of ET, neuropsychological scales, quality of life, personality traits, and coping strategies.

RESULTS

One hundred and seven patients of the OPC and 90 individuals of the CBC participated and their results are descriptively presented. Statistical analysis was restricted to 38 pairs of OPC and CBC individuals matched for age, sex, and tremor severity. One-third of these individuals reported a profound impairment in everyday or professional life. Neuropsychological scales showed a severe depression in 8% of the individuals and pathologic values for the general level of psychiatric symptoms in 26%. The main coping strategy was 'active problem-orientated coping'. Patients of the OPC perceived a more severe impact of ET on their life. Multivariate analysis revealed the Beck Depression Inventory score as the only predictive factor for the outcome variables, physical and mental component scores, of the SF-12 health survey.

CONCLUSIONS

ET causes a significant psychosocial impairment, which does depend on symptom severity but also on mood with depression as the main driving factor and other so far undetermined factors.

GABA(A) receptor- and GABA transporter polymorphisms and risk for essential tremor

BACKGROUND

Clinical features and animal models of essential tremor (ET) suggest gamma-aminobutyric acid A receptor (GABA(A) R) subunits and GABA transporters as putative candidate genes.

METHODS

A total of 503 ET cases and 818 controls were investigated for an association between polymorphisms in 15 GABA(A) R and four GABA transporter genes and ET.

RESULTS

Nine nominally significant tagging SNPs (P values from 4.9×10(-2) to 5.2×10(-4) ) were found in the hypothesis generation stage. Five SNPs were followed up in a second verification stage but failed to reach significance. (P values from 0.30 to 0.77).

DISCUSSION

In our samples, no evidence of association between GABA(A) R and GABA transporter genes with ET was detected. Further studies are necessary to clarify the role of these genes in ET.

Dopamine receptor D3 gene and essential tremor in large series of German, Danish and French patients

The genetic causes of essential tremor (ET) seem to be heterogeneous. Recently, ET has been found associated with a functional variant (Ser9Gly) of the dopamine D(3) receptor (DRD3), located in the ETM1 locus on chromosome 3q13.3 described for the first time in 1997. We examined this variant in three different populations from Germany, Denmark and France. We undertook an association study of the Ser9Gly variant in 202 cases with a familial history from unrelated families with ET, 97 cases with isolated non-familial ET and 528 healthy controls. In addition, linkage and segregation analyses were carried out in 22 ET families. The distribution of genotypes and allele frequencies showed no significant differences in the whole sample and in a subanalysis of familial and sporadic cases. Age at onset of tremor, tremor duration and tremor severity did not show an association with the genotype. In addition, the DRD3 variant was not found linked to the disease in a subset of informative ET families. We did not find a significant association of the DRD3 variant with ET nor linkage to the DRD3 receptor in German, Danish and French ET patients and families, suggesting that it is unlikely to be a causal factor for ET.