[123I]Ioflupane imaging in Caucasians and non-Caucasians: Are there any differences?

PURPOSE OF THE REPORT: To compare diagnostic performance of [123I]ioflupane SPECT imaging in different racial groups. In previous registration trials of [123I]ioflupane, 99% of the subjects enrolled were Caucasians. MATERIALS AND METHODS: A multicenter retrospective case-control study was conducted to evaluate whether the diagnostic performance of [123I]ioflupane SPECT imaging is different in non-Caucasians than in Caucasians matched by age, sex, and final clinical diagnosis. Subjects who had received an initial diagnosis of suspected Parkinson's disease (PD) or essential tremor (ET) and then underwent [123I]ioflupane SPECT imaging to assist with the subject's final clinical diagnosis were enrolled. Each subject's image was rated as normal or abnormal by 3 blinded expert readers. The majority interpretation was then compared with the final clinical diagnosis. Diagnostic performance of [123I]ioflupane SPECT imaging (as measured by positive percent agreement (equivalent to sensitivity), negative percent agreement (equivalent to specificity), overall percent agreement (OPA), and measures of inter-rater agreement) were compared between the Caucasian and non-Caucasian groups. RESULTS: In total, 102 non-Caucasians (58 with PD and 44 with ET as a final clinical diagnosis) and 102 Caucasians (58 with PD, 43 with ET, and 1 with "other") were included in the intent-to-diagnose (ITD) population. There was no significant difference between Caucasians and non-Caucasians in the diagnostic performance of [123I]ioflupane SPECT imaging as measured by sensitivity, specificity, OPA, and measures of inter-rater agreement. CONCLUSION: In this study, the diagnostic performance of [123I]ioflupane SPECT imaging was comparable between Caucasians and non-Caucasians.

Genetic Analysis of LRRK1 and LRRK2 Variants in Essential Tremor Patients.

AIMS: Essential tremor (ET) is one of the most common adult-onset movement disorders. ET and Parkinson's disease (PD) overlap clinically and pathologically, which prompted this investigation into the association of PD risk variants in ET patients. This study was designed to explore the role of variants of two PD-related genes LRRK1 and LRRK2 in a Han Chinese ET population. MATERIALS AND METHODS: Genetic analysis of LRRK1, rs2924835, and LRRK2, rs34594498, rs34410987, and rs33949390 variants was conducted on 200 Han Chinese patients with ET and 434 ethnically matched normal controls. RESULTS: No statistically significant differences were identified in either genotypic or allelic frequencies of variants between the ET patients and the control cohort (all p > 0.05). Haplotype analysis of three LRRK2 variants (rs34594498, rs34410987, and rs33949390) showed no haplotypes displayed an association with ET risk (all p > 0.05). CONCLUSIONS: The data suggest that LRRK1 variant (rs2924835) and LRRK2 variants (rs34594498, rs34410987, and rs33949390) are not associated with ET in this Han Chinese population.

Genetic analysis of the CHCHD2 gene in Chinese patients with familial essential tremor.

Recently, Funayama et al. identified CHCHD2 as a novel causative gene of Parkinson disease (PD). However, the relationship between CHCHD2 and essential tremor (ET) patients was still unknown. Genetic analysis of CHCHD2 gene was conducted in 60 probands of ET families with autosomal dominant inheritance and 90 healthy controls in Chinese population. No pathogenic CHCHD2 mutation was found in ET patients. However, we identified one rare variant, c.5C>T, a reported risk variant for sporadic PD in Japanese populations, and examined the frequency of three common variants. Our results suggested that CHCHD2 mutations may be rare in Chinese familial ET patients.

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

Essential tremor (ET) is one of the most frequent neurological disorders with elusive etiology, typically characterized by postural and kinetic tremors. Evidence reveals that genetic components are implicated in the development of ET and there are some overlaps between ET and Parkinson's disease in clinical features and etiology. Variants in the fibroblast growth factor 20 gene (FGF20) have been reported to be associated with the risk of Parkinson's disease. To evaluate the association between the FGF20 gene variants and ET susceptibility, we conducted genetic analysis of five FGF20 variants (rs1721100, rs1989754, rs10089600, rs12720208, and rs17550360) in 200 patients with ET and 426 ethnically-matched Chinese Han normal controls. Statistical analysis did not identify significant differences in genotypic or allelic frequencies of variants between ET patients and normal controls (all P>0.05). No related haplotype was found to be related to the risk of ET. The findings indicate the FGF20 gene might not play a dominating role in the genetic predisposition to ET in Chinese Han population.

SLC1A2 rs3794087 does not associate with essential tremor.

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

Identification of a novel risk variant in the FUS gene in essential tremor.

OBJECTIVE: A nonsense mutation in the amyotrophic lateral sclerosis gene FUS has been found to segregate in a large family with essential tremor (ET). Coding variants in this gene have not been comprehensively evaluated in ET. We conducted a genetic analysis of FUS for pathogenic and novel coding variants in 2 case-control cohorts among ethnic Chinese. METHODS: In a study that involved 7,548 subjects, we first sequenced all the exon and exon-intronic boundaries of FUS in 84 ET samples. Potential causative variants that were identified were then genotyped in 2 separate case-control cohorts involving 263 additional ET samples and 5,919 controls (set 1) and 250 ET cases and 250 controls (set 2), and 782 diseased controls of Chinese ethnicity from 2 different Asian countries. RESULTS: We identified a novel variant, Met392Ile, in exon 12 of the FUS gene. This variant was associated with ET in set 1 (odds ratio = 4.72 [95% confidence interval = 1.90-11.71], p = 0.0037). The association was subsequently validated in set 2 (joint analysis odds ratio = 3.92 [95% confidence interval = 1.57-9.82], p = 8.6 × 10(-4)). No association was observed in another neurologic cohort of patients with Parkinson disease, and no other potential pathogenic mutations were identified. CONCLUSION: We identified a novel risk variant, Met392Ile, in the FUS gene that increases susceptibility of ET among ethnic Chinese. Further studies in other ethnic populations are needed to determine whether this is an ethnic-specific risk factor.

Fused in Sarcoma (FUS) gene mutations are not a frequent cause of essential tremor in Europeans.

FUS/TLS (denoting fused in sarcoma/translocated in liposarcoma [MIM 137070]) codifies an RNA binding protein. Mutations in this gene cause amyotrophic lateral sclerosis (ALS; MIM 608030). Essential tremor (ET [MIM 190300]) is the most frequent movement disorder. Despite its strong familiar aggregation, recently a whole exome sequencing study has identified FUS mutations as a cause of familial ET. To determine whether mutations in FUS are also common in other populations, we sequenced FUS gene in 178 unrelated Spanish subjects with ET. We detected only an intronic single-pair nucleotide deletion (c.1293-37delC), which was predicted to affect mRNA splicing. However, leukocyte mRNA analysis showed no changes in FUS expression. In conclusion, coding or splicing FUS mutations are not a frequent cause of ET in the Spanish population.

LINGO1 variants in the French-Canadian population.

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

Prevalence of essential tremor in Araihazar, Bangladesh: a population-based study.

BACKGROUND: Essential tremor (ET) is one of the most common neurological diseases. Few prevalence studies have been conducted in South Asia, and none in Bangladesh, one of the most populated countries in the world. We estimated the prevalence of ET in a population-based study in Araihazar, Bangladesh. METHODS: As part of an in-person evaluation in a health outcomes study, each study participant produced 2 handwriting samples, from which ET diagnoses were assigned by 2 independent movement disorder neurologists. RESULTS: The crude prevalence of ET (age ≥18 years) was 19/1,229 [1.5%, 95% confidence interval (CI) = 1.0-2.4], and was similar in men and women. The crude prevalence was 2.5% in participants aged ≥40 years and was one half that (1.3%) among younger participants (<40 years), although the difference did not reach statistical significance (p = 0.18). The age-adjusted prevalence (United States 2000 census) was 2.0% (95% CI = 1.2-2.8). CONCLUSION: The crude prevalence of ET in Araihazar, Bangladesh, was 1.5%. There is 1 other population-based study in a developing country (Turkey) which, like ours, did not restrict enrollment to middle-aged or elderly individuals and did not rely on screening questionnaires; the crude prevalence in the 2 studies is very similar.

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

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

Prevalence of essential tremor in a multiethnic, community-based study in northern Manhattan, New York, N.Y.

BACKGROUND: Our aims were to: (1) estimate the prevalence of essential tremor (ET) in a community-based study in northern Manhattan, New York, N.Y., USA; (2) compare prevalence across ethnic groups, and (3) provide prevalence estimates for the oldest old. METHODS: This study did not rely on a screening questionnaire. Rather, as part of an in-person neurological evaluation, each participant produced several handwriting samples, from which ET diagnoses were assigned. RESULTS: There were 1,965 participants (76.7 +/- 6.9 years, range = 66-102 years); 108 had ET [5.5%, 95% confidence interval (CI) = 4.5-6.5%]. Odds of ET were robustly associated with Hispanic ethnicity versus white ethnicity [odds ratio (OR) = 2.19, 95% CI = 1.03-4.64, p = 0.04] and age (OR = 1.14, 95% CI = 1.03-1.26, p = 0.01), i.e. with every 1 year advance in age, the odds of ET increased by 14%. Prevalence reached 21.7% among the oldest old (age > or = 95 years). CONCLUSIONS: This study reports a significant ethnic difference in the prevalence of ET. The prevalence of ET was high overall (5.5%) and rose markedly with age so that in the oldest old, more than 1 in 5 individuals had this disease.

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.

Prevalence of essential tremor in Singapore: a study on three races in an Asian country.

To investigate the prevalence of Essential Tremor (ET) in Singapore and compare the rates between Singaporean Chinese, Malays, and Indians, a community-based survey among a disproportionate random sample of 15,000 individuals (9000 Chinese, 3000 Malays, 3000 Indians) aged 50 years and above was conducted. In phase 1, trained interviewers conducted a door-to-door survey using a screening questionnaire for Parkinson's disease. In phase 2, medical specialists examined participants who screened positive to evaluate for the presence of postural or kinetic tremor of the upper limbs, or head tremor. Participants with suspected ET had their diagnosis confirmed in phase 3 by a movement disorders specialist and fellow based on the latest core diagnostic criteria. Forty participants with classic ET were identified. The prevalence rate (PR) of ET was 2.37 per 1000 (95% CI: 1.65-3.32), age-adjusted to UICC world standard population. The PR was significantly higher in males (p=0.01) and increased significantly with age (p<0.001). Indians (PR=4.94 per 1000, 95% CI: 2.63-9.04) were 1.8 times more likely to have ET than Chinese (PR=2.77 per 1000, 95% CI: 1.78-4.17) (p=0.08). No Malays with ET were identified. The data suggest that the prevalence of ET increases with age, is higher in males and may be higher amongst Indians.

Electroclinical and genetic findings in a family with cortical tremor, myoclonus, and epilepsy.

We report a five-generation family showing cortical tremor, myoclonus, and epilepsy, originating from Naples, Italy. Eleven members, aged 24-56 years (mean: 39.2 years), suffered from hand tremor and myoclonus, whereas generalized seizures occurred in six. Electrophysiological study confirmed the presence of cortical reflex myoclonus in all affected members. In addition, giant somatosensory-evoked potential components and enhanced long loop reflex I were found also in three presymptomatic members who manifested hand tremor and myoclonus at upper limbs after 1.5 years of follow-up. Genetic study of the pedigree revealed a significant linkage on chromosome 2p (maximum lod score = 5.9). Further observations are needed to clarify the pathophysiology of this condition.

Association of the C677T and A1298C polymorphisms of methylenetetrahydrofolate reductase gene in patients with essential tremor in Turkey.

Essential tremor (ET) is a most common human movement disorder of unknown etiology. Previous reports have shown that the C677T polymorphism of methylenetetrahydrofolate reductase gene has been associated with neurodegenerative disorders. To investigate the role of methylenetetrahydrofolate reductase gene polymorphisms in essential tremor, we analyzed the alleles and genotypes of methylenetetrahydrofolate reductase (MTHFR) C677T and MTHFR A1298C in a total of 158 unrelated essential tremor patients and compared them with those of 246 unrelated healthy control subjects, using a polymerase chain reaction restriction fragment length polymorphism method. The allele frequency of MTHFR 677T was 35.76% in the essential tremor cases and 30.08% in the controls. We obtained statistically significant results for MTHFR677 and also for MTHFR1298. The MTHFR T677T genotype was overrepresented and was statistically significant. The T677T/A1298A and C677C/C1298C compound genotypes were similarly statistically significant. The C677C/A1298A compound genotype provided protection for essential tremor. In conclusion, the MTHFR 677T, 1298C alleles and MTHFR T677T genotype and T677T/A1298A, and C677C/C1298C compound genotypes are genetic risk factors for essential tremor in Turkey.

Regional and racial differences in the prevalence of physician-diagnosed essential tremor in the United States.

For reasons that are unclear, prevalence estimates of essential tremor (ET) differ considerably across the United States. Separate communities have never been sampled within the framework of the same study to substantiate these differences. We estimated the prevalence of physician-diagnosed ET in the elderly in four communities in the United States in whom the same screening questions were used, and examined whether this prevalence differed between Caucasians and African Americans. The Cardiovascular Health Study recruited a sample of Medicare beneficiaries >/=65 years of age from four communities in different regions of the United States. In 1998 to 1999, 3,494 participants (mean age, 80.0 years; range, 70-103 years) answered a 12-question screen for ET, including the question, "has a doctor diagnosed you as having familial tremor or benign essential tremor?" Fifty-four participants reported that a doctor had diagnosed them as having ET (1.5%; 95% confidence interval, [CI], 1.1-2.0%). Prevalence was similar across the four communities (1.1-2.0%). A larger proportion of Caucasians than African Americans reported a diagnosis of ET (1.7% vs. 0.4%; odds ratio = 4.9; 95% CI, 1.2-20.2; P = 0.028). In a logistic regression analysis, physician-diagnosed ET was associated with Caucasian ethnicity (P = 0.038) but not with age, gender, education, mental status or depression scores, income, smoking status, or alcohol consumption. When a standardized screening question was used, the proportion of participants with physician-diagnosed ET was similar across four communities, suggesting that the prevalence of this condition may be less variable than is often reported. Caucasians were five times more likely to have physician-diagnosed ET than were African Americans. This study does not provide an explanation for this difference, which deserves further study.