No association between Parkinson's disease and low-activity alleles of catechol O-methyltransferase

Catechol-O-methyltransferase and dopamine receptor D4 gene variants: Possible association with substance abuse in Bangladeshi male

Genetic risk of substance abuse is encoded mainly by central neurochemical pathways(mostly dopaminergic system) related to reinforcement and reward. In this study a functionalpolymorphism in Catechol-O-methyltransferase (COMT) (Val158Met) and the Dopamine receptor D4 gene (DRD4) (120 bp tandem duplication) has been studied in substance abused subjects. The study was carried out with 183 substance abused subjects and 175 healthy persons with no history of substance abuse. DNA was extracted and polymorphisms were analyzed using allele-specific PCR. The impact of these two polymorphisms was also analyzed on addictive characteristics (age of starting abuse, a pattern of drug habit, and period of addiction). It was found that only the heterozygous variant of COMT polymorphism (Val/Met) (p<0.05, OR = 1.66, 95% CI = 1.044–2.658) and both homozygous (p<0.05, OR = 0.43, 95% CI = 0.193–0.937) and heterozygous (p<0.05, OR = 0.37, 95% CI = 0.172–0.826) derived variants of DRD4 120 bp tandem duplication were significantly associated with risk of substance abuse compared to controls. In case of association of these polymorphisms with an age of onset, no significant difference was found among three different genotypic groups of COMT polymorphism. Whereas, the homozygous derived variant (240 bp/240 bp) of DRD4 gene was found to have a later age of onset (20.5±0.8) for substance abuse compared to heterozygous (120 bp/240 bp) (19.1±0.8) and wild type homozygous variant (120 bp/120 bp) (16.0±0.5), which was statistically significant (p<0.05). Again, in the case of the pattern of drug habit, the frequency of the Val/Val genotype is higher in polysubstance abused (>2 drugs) subjects (p<0.05) compared to the heterozygous Val/Met containing variants. An association of period of addiction was analyzed with an individual type of substance abuse and found that heroin abused subjects have a significantly higher period of addiction (11.6±1.0) compared to other abusers (p<0.01). Further, it was found that Met/Met containing variants of COMT polymorphism has a more extended period of addiction than other genetic variants in heroin abused subjects. These results indicate that genetic variability may influence the susceptibility to the risk of substance abuse and addictive characteristics.

Genetic variations in catechol-O-methyltransferase gene are associated with levodopa response variability in Chinese patients with Parkinson's disease

Catechol-O-methyltransferase (COMT) is one of the main enzymes in dopamine metabolism and is reported to be associated with susceptibility to Parkinson’s disease (PD) and pharmacotherapy. However, researchers mostly focus on the most common polymorphism, rs4680. In this case-control study, we investigated the association of SNPs other than rs4680 with the levodopa (L-dopa) response and other clinical features in Chinese PD patients. Eleven single nucleotide polymorphisms (SNPs) in the COMT gene were genotyped, and clinical data were collected. Patients with the TT genotype of rs165728 or rs174699 had larger daily levodopa equivalent doses (LEDs) than the patients with CC and CT genotypes under the dominant model (p = 0.01421 for rs165728 and p = 0.02302 for rs174699). Under the dominant model, the patients with GG at rs4680 G > A had a lower occurrence of dyskinesia than those with AA and AG (p = 0.0196). Patients with CC at rs4633 had a lower occurrence of dyskinesia than those with TT and TC (p = 0.0429) under the dominant model. The frequencies of the rs174675 T and rs933271 C alleles were higher in PD patients than in the controls (p < 0.05). Our primary results showed the possible association of SNPs other than the most common functional rs4680 in COMT with interindividual variance in the L-dopa daily dose and susceptibility to dyskinesia in Chinese patients, although this was an exploratory study based on a small sample size. Larger and more randomized samples are necessary for further investigation.

Is there an association between the COMT gene and P300 endophenotypes?

P300 wave anomalies correlate with genetic risk for schizophrenia and constitute a plausible endophenotype for the disease. The COMT gene is thought to influence cognitive performance and to be a susceptibility gene for schizophrenia. Unlike two previous studies, we found no significant influence of the COMT gene on P300 amplitude or latency in 189 individuals examined. The well-supported role of the COMT gene both in dopamine catabolism as well as in prefrontal cognition makes a strong theoretical case for the influence of COMT Val158Met polymorphism on P300 endophenotypes. However, the available neurophysiologic evidence suggests that any such association, if present, must be very subtle.

Meta-Analysis of the Effects of the Catechol-O-Methyltransferase Val158/108Met Polymorphism on Parkinson's Disease Susceptibility and Cognitive Dysfunction

Background: There is a continued debate and inconsistent findings in previous literature about the relationship of catechol-O-methyltransferase (COMT) and Parkinson’s disease (PD) susceptibility as well as cognitive dysfunction. To substantiate this existing gap, we comprehensively examine COMT genotype effects on the development of PD and test the hypothesis that the Met158 allele of the COMT gene is associated with cognitive dysfunction by conducting a meta-analysis review.

Methods: PubMed/MEDLINE, Embase, Cochrane databases search (18/30/08) yielded 49 included studies. Data were extracted by two reviewers and included COMT genotype, publication year, diagnostic status, ancestry, the proportion of male participants, and whether genotype frequencies were consistent with Hardy–Weinberg equilibrium. Unadjusted odds ratios (ORs) were used to derive pooled estimates of PD risk overall and in subgroups defined by ethnicity, gender, and onset of disease. Moreover, the association of certain cognitive domains in PD and COMT gene type was explored. Meta-analyses were performed using random-effect models and p value–based methods. All statistical tests were two-sided. The present study was registered with PROSPERO (CRD42018087323).

Results: In the current studies, we found no association between COMT Val158/108Met polymorphism and PD susceptibility. However, the gender-stratified analyses revealed marginally significant effects in heterozygote model analyses in women (P = 0.053). In addition, stratification according to onset of PD also shows significant effects of COMT Val158/108Met polymorphism on late-onset population both in recessive (P = 0.017) and allelic (P = 0.017) genetic models. For the intelligence quotient (IQ) score and Unified Parkinson Disease Rating Scale III (UPDRS III), there was no evidence for genetic association, except in subgroup analyses in Asian populations (IQ score, P = 0.016; UPDRS III, P < 0.001).

Conclusion: The COMT Val158/108Met polymorphism is associated with the risk for PD in female or late-onset PD. Methionine/methionine carriers of Asian population performed significantly worse than the valine allele carriers in IQ score and UPDRS III.

No associations between five polymorphisms in COMT gene and migraine

OBJECTIVES

The pathophysiology of migraine headaches is not clearly understood yet. The dopaminergic system has been hypothesized to be involved in migraine pathogenesis. The aim of this study was to investigate catechol-O-methyltransferase (COMT) polymorphisms and chronic headaches. We analyzed five single nucleotide polymorphisms (SNPs) in COMT.

MATERIALS & METHODS

The study population consisted of 71 patients with migraine with aura, 152 patients with migraine without aura, 86 patients with tension-type headache, and 191 healthy controls. The selected polymorphic markers included one causing His62His (rs4633) and two non-synonymous SNPs, Ala72Ser and Val158Met (rs6267, rs4680 respectively). Two other non-polymorphic SNPs (rs6270, rs740602) were examined.

RESULTS

We found no significant differences in any genotypes, allele frequencies, or haplotypes among the patient groups and controls.

CONCLUSIONS

Our results indicate that the five polymorphisms in COMT have no association with migraineurs in Western Japan. The possibility that segments elsewhere in the gene may contain a mutation responsible for modifying the expression of COMT or the activity of the enzyme is important. We cannot conclusively exclude the entire COMT gene from being involved in migraine pathogenesis.

Association of Catechol-O-methyltransferase val/met polymorphism with cognitive function in Gilles de la Tourette syndrome patients

Gilles de la Tourette syndrome (GTS) is a kind of neuropsychiatric disorder with childhood onset. The cognitive dysfunction caused by GTS could affect the growth and learning of children and adolescents. The mechanism of cognitive functions was associated with dopaminergic system, thus we access the associations between polymorphism of some dopaminergic system-related genes including Catechol-O-methyltransferase (COMT) met/val, Dopamine receptor D4 (DRD4) exon III 48 bp VNTR (variable number of tandem repeats), Interleukin 1 (IL-1) Ra 86 bp and IL-1β exon 5, and cognitive functions in GTS patients. Genotyping analysis was performed through polymerase chain reaction (PCR). Test for cognitive functions of GTS patients included modified wisconsin card sorting test (WCST), trail making test, visual reproduction test, stroop test and verbal fluency test. The patients with COMT met/met genotype showed less perseverative errors in modified WCST test compared with patients with COMT val/val genotype (P < 0.05). Meanwhile, patients without allele val had better delayed memory in visual reproduction test, less errors in the stroop test and less perseverative errors in modified WCST test compared with patients with allele val (P < 0.05). However, no significant difference was found in cognitive functions among patients with different genotypes or alleles of polymorphisms of DRD4 exon III 48 bp VNTR, IL-1 Ra 86 bp and IL-1β exon 5 (P > 0.05). Polymorphism of COMT met/val was correlated with cognitive functions in GTS patients. This study provided basis for the analysis of molecular genetic pathology of cognitive dysfunctions in GTS.

Modulating effect of COMT Val(158)Met polymorphism on interference resolution during a working memory task

Genetic variability related to the catechol-O-methyltransferase (COMT) gene has received increasing attention in the last 15years, in particular as a potential modulator of the neural substrates underlying inhibitory processes and updating in working memory (WM). In an event-related functional magnetic resonance imaging (fMRI) study, we administered a modified version of the Sternberg probe recency task (Sternberg, 1966) to 43 young healthy volunteers, varying the level of interference across successive items. The task was divided into two parts (high vs. low interference) to induce either proactive or reactive control processes. The participants were separated into three groups according to their COMT Val(158)Met genotype [Val/Val (VV); Val/Met (VM); Met/Met (MM)]. The general aim of the study was to determine whether COMT polymorphism has a modulating effect on the neural substrates of interference resolution during WM processing. Results indicate that interfering trials were associated with greater involvement of frontal cortices (bilateral medial frontal gyrus, left precentral and superior frontal gyri, right inferior frontal gyrus) in VV homozygous subjects (by comparison to Met allele carriers) only in the proactive condition of the task. In addition, analysis of peristimulus haemodynamic responses (PSTH) revealed that the genotype-related difference observed in the left SFG was specifically driven by a larger increase in activity from the storage to the recognition phase of the interfering trials in VV homozygous subjects. These results confirm the impact of COMT genotype on inhibitory processes during a WM task, with an advantage for Met allele carriers. Interestingly, this impact on frontal areas is present only when the level of interference is high, and especially during the transition from storage to recognition in the left superior frontal gyrus.

Polymorphisms of COMT Val158Met and DAT1 3'-UTR VNTR in illicit drug use and drug-related psychiatric disorders

To investigate the involvement of COMT Val158Met and DAT1 3'-UTR VNTR genotypes in the pathogenesis of illicit drug use and drug-induced psychotic disorders (DIP), 187 substance users and 386 normal controls were recruited from Northern Taiwan. Substance users and normal controls significantly differed in allele frequencies of COMT Val158Met (p = 0.039) but not in allele frequencies of DAT1 3'-UTR VNTR (p = 0.879). However, neither allele frequencies of COMT Val158Met nor allele frequencies of DAT1 3'-UTR VNTR were associated with DIP. The findings should be confirmed in further studies of a larger sample size and a more homogenous patient group.

Association Between Catechol-O-Methyltransferase (COMT) Gene Polymorphisms, Parkinson's Disease, and Levodopa Efficacy

OBJECTIVES

We investigated the association between catechol-O-methyltransferase (COMT) gene polymorphisms and Parkinson's disease (PD) susceptibility, severity of disease, and levodopa (L-Dopa) efficacy.

SUBJECTS AND METHODS

Patients (N = 97) with primary PD and healthy volunteers (N = 102) were recruited. Disease severity was assessed with the Unified Parkinson's Disease Rating Scale (UPDRS) and Hoehn & Yahr grade at 'On stage'. Genomic DNA was extracted from blood cells. Polymerase chain reaction and sequencing were used to detect COMT mutations. Data were analyzed by SPSS 18.0. False discovery rate (FDR) or Bonferroni correction was used if the result showed P < 0.05.

RESULTS

Four COMT mutations were detected in 199 subjects: rs74745580 (only in two patients with primary PD), rs4633, rs6267, and rs3838146. There were no statistical differences in frequencies of rs4633, rs6267, and rs3838146 genotypes between PD patients and the control group. The frequency of allele rs4633T was higher in PD patients than in the control group. UPDRS score was lower in rs4633 (CT/TT) carriers and rs3838146 (-C/- -) carriers than in rs4633 (CC) and rs3838146 (CC) carriers. PD patients carrying rs6267 (GT/TT) had higher UPDRS scores than patients with rs6267 (GG) (P < 0.05). The frequencies of the three polymorphisms were not statistically different between patients who did and did not receive L-Dopa; dose and duration of L-Dopa treatment did not differ between genotypes; and there was also no difference in the ratios of loss of efficacy towards levodopa.

CONCLUSIONS

The polymorphisms rs4633, rs6267, and rs3838146 were associated with severity of PD but were not associated with L-Dopa medication.

The Val158Met COMT polymorphism is a modifier of the age at onset in Parkinson's disease with a sexual dimorphism

The catechol-O-methyltranferase (COMT) is one of the main enzymes that metabolise dopamine in the brain. The Val158Met polymorphism in the COMT gene (rs4680) causes a trimodal distribution of high (Val/Val), intermediate (Val/Met) and low (Met/Met) enzyme activity. We tested whether the Val158Met polymorphism is a modifier of the age at onset (AAO) in Parkinson's disease (PD). The rs4680 was genotyped in a total of 16 609 subjects from five independent cohorts of European and North American origin (5886 patients with PD and 10 723 healthy controls). The multivariate analysis for comparing PD and control groups was based on a stepwise logistic regression, with gender, age and cohort origin included in the initial model. The multivariate analysis of the AAO was a mixed linear model, with COMT genotype and gender considered as fixed effects and cohort and cohort-gender interaction as random effects. COMT genotype was coded as a quantitative variable, assuming a codominant genetic effect. The distribution of the COMT polymorphism was not significantly different in patients and controls (p=0.22). The Val allele had a significant effect on the AAO with a younger AAO in patients with the Val/Val (57.1±13.9, p=0.03) than the Val/Met (57.4±13.9) and the Met/Met genotypes (58.3±13.5). The difference was greater in men (1.9 years between Val/Val and Met/Met, p=0.007) than in women (0.2 years, p=0.81). Thus, the Val158Met COMT polymorphism is not associated with PD in the Caucasian population but acts as a modifier of the AAO in PD with a sexual dimorphism: the Val allele is associated with a younger AAO in men with idiopathic PD.

Association of catechol-o-methyltransferase polymorphism (Val108/158Met) with Parkinson's disease: a meta-analysis

Parkinson's disease (PD) is a common neurodegenerative disease, the risk factors of which are gaining more attentions. Among all these risk factors, catechol-o-methyltransferase (COMT) has been widely studied, and believed to be associated with PD. However, the relationship between COMT polymorphism and PD has not been confirmed hitherto. Therefore, a meta-analysis was performed to evaluate the effect of COMT polymorphism on PD patients. A total of 24 study subjects comprising 3,807 patients with PD and 3,942 unrelated healthy controls were recruited in this meta-analysis. Heterogeneity testing and sensitivity analysis were conducted with Review Manager 5.0 software (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark) and Stata software (StataCorp, College Station, TX), together with publication bias by funnel plot method and modified Egger's linear regression test. No evidences of publication bias and heterogeneity were detected. In the 24 studies, the estimated odds ratios (OR) in PD patients are 0.98 for the Met allele (95% confidence interval [0.92, 1.05]) under a fixed-effects model. The authors also conducted a stratified analysis according to geographic region among Europe, Asia, and North America, the ORs for the Met allele are 0.92, 1.02, and 1.10, respectively. According to the results of the meta-analysis, a conclusion could be drawn that polymorphism of Val108/158Met are not associated with the risk of PD. However, more convincing studies are warranted to have a solid conclusion supported.

Genetic polymorphisms involved in dopaminergic neurotransmission and risk for Parkinson's disease in a Japanese population

Background

Parkinson's disease (PD) is characterized by alterations in dopaminergic neurotransmission. Genetic polymorphisms involved in dopaminergic neurotransmission may influence susceptibility to PD.

Methods

We investigated the relationship of catechol-O-methyltransferase (COMT), monoamine oxidase B (MAOB), dopamine receptor (DR) D2 and DRD4 polymorphisms and PD risk with special attention to the interaction with cigarette smoking among 238 patients with PD and 369 controls in a Japanese population.

Results

Subjects with the AA genotype of MAOB rs1799836 showed a significantly increased risk of PD (odds ratio (OR) = 1.70, 95% confidence interval (CI) = 1.12 - 2.58) compared with the AG and GG genotypes combined. The AA genotype of COMT rs4680 was marginally associated with an increased risk of PD (OR = 1.86, 95% CI = 0.98 - 3.50) compared with the GG genotype. The DRD2 rs1800497 and DRD4 rs1800955 polymorphisms showed no association with PD. A COMT -smoking interaction was suggested, with the combined GA and AA genotypes of rs4680 and non-smoking conferring significantly higher risk (OR = 3.97, 95% CI = 2.13 - 7.41) than the AA genotype and a history of smoking (P for interaction = 0.061). No interactions of smoking with other polymorphisms were observed.

Conclusions

The COMT rs4680 and MAOB rs1799836 polymorphisms may increase susceptibility to PD risk among Japanese. Future studies involving larger control and case populations and better pesticide exposure histories will undoubtedly lead to a more thorough understanding of the role of the polymorphisms involved in the dopamine pathway in PD.

Association analysis of serotonin and catecholamine system candidate genes in obsessive-compulsive disorder in the Chinese population

Serotonin and catecholamine system studies provide increasing evidence for the importance of genetic factors in obsessive-compulsive disorder (OCD); we found that genetic linkage disequilibrium with OCD existed in the 5-HT2A-receptor promoter polymorphism -1438G/A. The results of our research strongly suggested that the -1438G/A promoter polymorphism plays a role in the psychopathology of OCD.

The effect of COMT, BDNF, 5-HTT, NRG1 and DTNBP1 genes on hippocampal and lateral ventricular volume in psychosis

BACKGROUND

Morphometric endophenotypes which have been proposed for psychotic disorders include lateral ventricular enlargement and hippocampal volume reductions. Genetic epidemiological studies support an overlap between schizophrenia and bipolar disorder, and COMT, BDNF, 5-HTT, NRG1 and DTNBP1 genes have been implicated in the aetiology of both these disorders. This study examined associations between these candidate genes and morphometric endophenotypes for psychosis.

METHOD

A total of 383 subjects (128 patients with psychosis, 194 of their unaffected relatives and 61 healthy controls) from the Maudsley Family Psychosis Study underwent structural magnetic resonance imaging and genotyping. The effect of candidate genes on brain morphometry was examined using linear regression models adjusting for clinical group, age, sex and correlations between members of the same family.

RESULTS

The results showed no evidence of association between variation in COMT genotype and lateral ventricular, and left or right hippocampal volumes. Neither was there any effect of the BDNF, 5-HTTLPR, NRG1 and DTNBP1 genotypes on these regional brain volumes.

CONCLUSIONS

Abnormal hippocampal and lateral ventricular volumes are among the most replicated endophenotypes for psychosis; however, the influences of COMT, BDNF, 5-HTT, NRG1 and DTNBP1 genes on these key brain regions must be very subtle if at all present.

Asymmetry of prefrontal cortex activities and catechol-O-methyltransferase Val158Met genotype in patients with panic disorder during a verbal fluency task: near-infrared spectroscopy study

We examined the relationship between the catechol-O-methyltransferase (COMT) Val158Met genotype and frontal lobe function by using multi-channel near-infrared spectroscopy (NIRS). The present study investigated oxygenated ([oxy-Hb]) and deoxygenated ([deoxy-Hb]) hemoglobin concentration changes during the performance of a verbal fluency task in the frontal region of 71 patients with panic disorder (PD). The activation of [oxy-Hb] on the right lateral prefrontal cortex was observed in the Met/Met genotype of the COMT gene polymorphism of PD patient groups in the analysis of NIRS, which seems to be related to the autonomic dysfunction in the pathogenesis of PD.

PRODH gene is associated with executive function in schizophrenic families

The aim of this study was to investigate the relationship between polymorphisms in the PRODH and COMT genes and selected neurocognitive functions. Six SNPs in PRODH and two SNPs in COMT were genotyped in 167 first-episode schizophrenic families who had been assessed by a set of 14 neuropsychological tests. Neuropsychological measures were selected as quantitative traits for association analysis. The haplotype of SNPs PRODH 1945T/C and PRODH 1852G/A was associated with impaired performance on the Tower of Hanoi, a problem-solving task mainly reflecting planning capacity. There was no significant evidence for association with any other neuropsychological traits for other SNPs or haplotypes of paired SNPs in the two genes. This study takes previous findings of association between PRODH and schizophrenia further by associating variation within the gene with performance on a neurocognitive trait characteristic of the illness. It fails to confirm previous reports of an association between COMT and cognitive function.

Possible relationship between the COMT gene ValMet polymorphism and psychometric IQ in girls of the Qinba region in China

OBJECTIVE

Catechol-O-methyltransferase (COMT) gene was hypothesized to have a relationship with human prefrontal cortex (PFC) function and individual cognitive abilities. The object of this study was to investigate the possible impact of genotypes of COMT Val158Met polymorphism on cognitive ability among children living in the Qinba region in China.

METHOD

A total of 305 children were included, 163 girls and 142 boys; both complete IQ evaluation and Val158Met genotyping results were obtained. The quantitative traits of psychometric IQ were calculated by using the Chinese Wechsler Intelligence Scale for Children. All subjects' genotypes of COMT gene Val158Met polymorphism were identified with the restriction fragment length polymorphism method.

RESULTS

The F test showed that the average scores (including the Full Scale IQ, Verbal Scale IQ, Performance Scale IQ and three index scores) did not significantly differ among different groups defined by Val158Met genotypes, neither in boys nor in the total group (p > 0.05). There was a significant difference between the average of Freedom from Distractibility score among different genotypes found in girls (p = 0.033).

CONCLUSION

Our results indicate that COMT gene Val158Met polymorphism may be related to the intelligence of Chinese girls, although the results cannot withstand multiple testing. Consequently, further studies with larger samples and perfect design still need place more emphasis on the gender difference and compensation effect of dopamine activity in PFC.

Detection of catechol-O-methyltransferase Val158Met polymorphism by a simple one-step tetra-primer amplification refractory mutation system-PCR

The G-->A transition at nucleotide 21881 of the human catechol-O-methyltransferase (COMT) gene represents a functional genetic polymorphism (Val158Met), rendering an enzyme with reduced activity that has been associated with psychiatric disorders and estrogen-related cancers. A new method for the detection of this polymorphism is described, based on the tetra-primer amplification refractory mutation system-polymerase chain reaction (ARMS-PCR), with a single PCR to discriminate both alleles. Two primers amplify a common amplicon independently of the allele considered. At the same time, two primers are used, differing in the 3' base. In the Val/Val or Met/Met conditions, amplification occurs both in the general amplicon and in the specific allele; in the Val/Met condition three different amplicons are produced. Direct DNA sequencing of a COMT region containing the G/A polymorphism demonstrates the validity of this tetra-primer ARMS-PCR method. Reevaluation by PCR-RFLP revealed 100% accordance for genotype adscription. Subjects carrying the COMT(HH) genotype in a Spanish population comprised 28%, and the COMT(LL) homozygotes amounted to 21%. The described method provides a fast and reliable approach for determining COMT polymorphism that can be useful in large clinical studies using minimal quantity of DNA, avoiding the timely and costly use of restriction enzymes.

Gene-environment interactions in sporadic Parkinson's disease

Much has been learned in recent years about the genetics of familial Parkinson's disease. However, far less is known about those malfunctioning genes which contribute to the emergence and/or progression of the vast majority of cases, the 'sporadic Parkinson's disease', which is the focus of our current review. Drastic differences in the reported prevalence of Parkinson's disease in different continents and countries suggest ethnic and/or environmental-associated multigenic contributions to this disease. Numerous association studies showing variable involvement of multiple tested genes in these distinct locations support this notion. Also, variable increases in the risk of Parkinson's disease due to exposure to agricultural insecticides indicate complex gene-environment interactions, especially when genes involved in protection from oxidative stress are explored. Further consideration of the brain regions damaged in Parkinson's disease points at the age-vulnerable cholinergic-dopaminergic balance as being involved in the emergence of sporadic Parkinson's disease in general and in the exposure-induced risks in particular. More specifically, the chromosome 7 ACHE/PON1 locus emerges as a key region controlling this sensitive balance, and animal model experiments are compatible with this concept. Future progress in the understanding of the genetics of sporadic Parkinson's disease depends on globally coordinated, multileveled studies of gene-environment interactions.

Direct molecular haplotyping of multiple polymorphisms within exon 4 of the human catechol-O-methyltransferase gene by liquid chromatography–electrospray ionization time-of-flight mass spectrometry

The applicability of ion-pair reversed-phase high-performance liquid chromatography hyphenated to electrospray ionization time-of-flight mass spectrometry (ICEMS) for the haplotyping of five SNPs (rs769223, rs4818, rs4986871, rs8192488, rs4680) located within exon 4 of the human catechol-O-methyltransferase (COMT, EC 2.1.1.6) gene is demonstrated. Two differently sized products of polymerase chain reaction--a 71-bp amplicon partially covering the sequence of a 124-bp amplicon--were used to determine unequivocally the allelic states of the single nucleotide polymorphisms linked on both chromosomes. The two amplicons were co-loaded onto the chromatographic column and simultaneously analyzed within a single gradient run. Using the described strategy, 101 individuals representing an Austrian population sample were typed. The obtained haplotype frequencies will serve as reference values in future association studies to examine the impact of the COMT gene on neuropsychiatric disorders. Additionally, two newly discovered polymorphic sites within the sequence of the COMT gene are described (a synonymous C>T mutation at the third position of the amino acid codon 99 in the soluble COMT protein or 149 in the membrane-bound COMT protein; a non-synonymous G>A substitution at the second position of the amino acid codon 95 in the soluble COMT protein or 145 in the membrane-bound-COMT protein).

The Association of the COMT V158M Polymorphism with Endometrial/Ovarian Cancer in HNPCC Families Adhering to the Amsterdam Criteria

Catechol-O-methyltransferase (COMT) is vital for the conjugation of catechol estrogens that are produced during oestrogen metabolism. The efficiency of this process varies due to a polymorphism in COMT, which changes valine to methionine (V158M). The Met genotypes slow the metabolism of catechol oestrogens, which are agents that are capable of causing DNA damage through the formation of DNA adducts and reactive oxygen species (ROS) production. The slower metabolism of catechol oestrogens results in there being a higher circulating concentration of these oeastrogens and consequently greater probability of DNA damage. To determine whether metabolic inefficiencies of oeastrogen metabolism are associated with the development of malignancy in hereditary non-polyposis colorectal cancer (HNPCC), we studied the V158M polymorphism in COMT in a large cohort of 498 HNPCC patients from Australia and Poland that were either mutation positive (n = 331) or negative (n = 167) for mismatch repair (MMR) gene mutations (hMLH1 or hMSH2). HNPCC is a familial predisposition to colorectal cancer (CRC) and extracolonic cancers that include endometrial cancer.

Using Real Time PCR, the COMT V158M polymorphism was examined and its association with disease expression, age of diagnosis of cancer, mutation status and mutation type was assessed in the HNPCC MMR mutation positive and negative groups. This study showed that the V158M polymorphism had no association with disease risk in the HNPCC MMR mutation positive population. However, the polymorphism was significantly associated with endometrial/ovarian cancer risk in HNPCC MMR mutation negative patients (p = 0.002). The heterozygous (Val/Met) genotype was associated with an increased risk of developing endometrial/ovarian cancer whereas the homozygous mutant (Met/Met) showed a decreased risk. The results suggest heterosis, where there is an apparent greater effect of the heterozygous state in this dichotomous trait. In conclusion, this study shows that the COMT V158M polymorphism alters the risk of developing endometrial/ovarian cancer in patients that adhere to the Amsterdam HNPCC criteria but do not have a DNA mismatch repair gene mutation.

Catechol-O-Methyltransferase and Monoamine Oxidase B Genes and Susceptibility to Sporadic Parkinson’s Disease in a Polish Population

Recent reports have proved that genetic factors play a role in the pathogenesis of sporadic Parkinson's disease (PD). It has been suggested that polymorphisms in monoamine oxidase B (MAOB) and catechol-O-methyltransferase (COMT) might increase the risk of PD. A total of 210 Polish patients with sporadic PD and 152 healthy controls were studied. The MAOB and COMT polymorphisms were identified using the polymerase chain reaction-restriction fragment length polymorphism method. The MAOB allele and genotype frequencies in PD patients did not differ significantly from the controls. A statistically lower frequency of the COMTLL genotype in patients with parkinsonism was found. The combined haplotype of the MAOB G (G/G) and COMTHL genotype showed a fourfold increase (p < 0.05) in the risk of PD in female patients in this Polish population.

The effect of monoamine oxidase B (MAOB) and catechol-O-methyltransferase (COMT) polymorphisms on levodopa therapy in patients with sporadic Parkinson's disease

OBJECTIVES

The etiology of sporadic idiopathic Parkinson's disease (PD) is considered multifactorial with both genetic and environmental factors modifying the disease expression. Recent studies suggest that polymorphism in monoamine oxidase B (MAOB) and catechol-O-methyltransferase (COMT) might influence the risk and treatment of PD. The aim of the study was to evaluate the effect of MAOB and COMT genetic polymorphism on effective daily dose of levodopa applied during the first 5 years of treatment, and to find out if a relationship exists between MAOB and COMT haplotypes and motor disturbances onset in PD patients treated with levodopa preparations.

MATERIALS AND METHODS

A total of 95 patients (40 females and 55 males) of Polish origin diagnosed with sporadic PD were enrolled into the study, and were divided into two groups. Group 1 - patients treated with doses of levodopa below 500 mg/day during the first 5 years of treatment. Group 2 - patients requiring levodopa doses exceeding 500 mg/24 h during the first 5 years of treatment. Low activity alleles of MAOB and COMT, i.e. MAOB allele A and COMT(L) as well as high activity ones, i.e. MAOB allele G and COMT(H), were determined using PCR-RFLP method.

RESULTS

No statistically significant differences were found in MAOB and COMT allele distribution in the two groups. However, the frequency of COMT(L/L) homozygotes was higher in the group treated with low doses of levodopa when compared with the second group. MAOB and COMT AG-HH haplotype predominated in the group of females treated with high daily doses of levodopa when compared with AG-LL haplotype in the group of females treated with low daily doses of levodopa (<500 mg/24 h).

CONCLUSION

The results of the study suggest that patients with COMT(L/L) genotype and possibly MAOB genotype A may benefit from more efficient and safer levodopa therapy.

Association analysis of the DRD4 and COMT genes in methamphetamine abuse

We analyzed two polymorphisms in genes encoding proteins of the dopamine system, the Val158Met polymorphism in the catechol-O-methyltransferase gene and the 120-bp VNTR polymorphism in the promoter of the dopamine D4 receptor gene for association with methamphetamine abuse. We used a case/control design with 416 methamphetamine abusing subjects and 435 normal controls. All subjects were Han Chinese from Taiwan. We found an excess of the high activity Val158 allele in the methamphetamine abuser group, consistent with several previous reports of association of this allele with drug abuse. The 120-bp VNTR polymorphism in the promoter of the dopamine D4 receptor gene itself did not show significant association with methamphetamine abuse. However, analysis of the 120-bp VNTR polymorphism and the exon 3 VNTR in the dopamine D4 receptor as a haplotype showed significant association with methamphetamine abuse, which gave an empirical P value 0.0034 for a heterogeneity model. Moreover, there were significant interactive effects between polymorphisms in the catechol-O-methyltransferase and dopamine D4 genes. The evidence of interaction between COMT 158 Val/Met and DRD4 48-bp VNTR polymorphisms (P = 0.0003, OR = 1.45, 95% CI: 1.148-1.77), and between COMT 158 Val/Met and DRD4 120 bp promoter polymorphisms (P = 0.01, OR = 1.10, 95% CI: 1.10-1.18) were significant but the latter was weak. We conclude that genetic variation in the dopamine system may encode an additive effect on risk of becoming a methamphetamine abuser.

Polymorphisms of dopamine degradation enzyme (COMT and MAO) genes and tardive dyskinesia in patients with schizophrenia

Several lines of evidence suggest that tardive dyskinesia (TD) may be associated with altered dopaminergic neurotransmission. We hypothesized that deranged dopamine degradation enzyme activities might be related to the susceptibility to TD through altered dopaminergic neurotransmission in the central nervous system. In the present study, we investigated the relationship between the gene polymorphisms of three dopamine degradation enzymes and TD. We genotyped the valine/methionine polymorphism of codon 108/158 in the catechol-O-methyltransferase (COMT) gene, the 30-bp repeat polymorphism in the promoter of the monoamine oxidase A (MAOA) gene, and the A/G polymorphism in intron 13 of the monoamine oxidase B (MAOB) gene in 206 Japanese patients with schizophrenia. No significant difference was found in total scores on the Abnormal Involuntary Movement Scale (AIMS) among the subject groups, sorted according to the COMT, MAOA and MAOB genotypes. Moreover, no significant difference was found in allele frequencies between patients with TD and patients without TD for any of the polymorphisms. As both COMT and MAO genes are involved in degrading catecholamines, we also sought evidence for additive and epistatic effects, but none was observed. Our data, therefore, do not support the hypothesis that polymorphisms in COMT, MAOA, and MAOB genes are involved individually or in combination in the predisposition to TD.

Polymorphism in candidate genes: implications for the risk and treatment of idiopathic Parkinson's disease

Idiopathic Parkinson's disease (IPD) is a progressive neurodegenerative disorder for which no restorative or neuroprotective therapy is available. Interest has recently been directed to association studies on polymorphisms of various genes, mainly those related to dopamine metabolism and transport, and their effect on response to PD, which includes primarily levodopa and dopaminomimetics. Approximately 15-20% of patients with PD do not respond to levodopa, and the majority of those who do respond develop adverse fluctuations in motor response, primarily levodopa-induced dyskinesias. This review summarizes the influence of polymorphisms in various genes on the relative risk of IPD and on levodopa efficacy. It focuses on the importance of well-designed polymorphism studies that include large samples of patients with IPD and tightly matched controls and use identical methodologies. Valid data on such polymorphisms might increase the efficacy of levodopa, decrease its side effects, and reduce the occurrence of levodopa-induced dyskinesias. They might also provide a novel diagnostic tool for PD.

Association between catechol-O-methyltransferase gene polymorphisms and wearing-off and dyskinesia in Parkinson's disease

Catechol-O-methyltransferase (COMT) is an enzyme that inactivates catecholamines, including levodopa. An amino acid change (Val-108-Met) in the COMT protein has been found to result in a change from high to low enzyme activity. In the present study, we genotyped 121 Japanese patients with Parkinson's disease (PD) and 100 controls. Comparison of the allele frequencies revealed that homozygosity for the low-activity allele was significantly more common among PD patients than the controls (p = 0.047, odds ratio = 3.23). In addition, homozygosity for the low-activity allele was overrepresented in PD patients that exhibited the 'wearing-off' phenomenon (p = 0.045, odds ratio = 3.82) or dyskinesia (p = 0.030, odds ratio = 4.80) compared with controls, although these differences were not significant after Bonferroni's correction. Our results may help understand the mechanism that cause complications of levodopa therapy in PD patients.

Combined family trio and case-control analysis of the COMT Val158Met polymorphism in European patients with anorexia nervosa

The high activity Val158 (H) allele of the dopamine-metabolizing enzyme catechol-O-methyltransferase (COMT) was associated with anorexia nervosa (AN) in a recent family trio-based study of patients from Israel. In an attempt to replicate this finding, we performed a combined family trio and case-control study in an European population from seven centers in six different countries (Austria, Germany, Great Britain, Italy [Milan], Italy [Florence], Slovenia, and Spain), together contributing a total of 372 family trios, 684 controls and 266 cases. TDT analyses of high (H) and low (L) alleles in family trios showed that H allele and L allele were each transmitted 101 times (chi(2) = 0, ns). Allele-wise case-control analysis using separate samples simply combined from the centers was also not significant, with the frequencies of the H allele 50% in cases and same in controls. Stratified analysis of data from all centers gave an odds ratio of 0.98 (Cornfield 95% confidence limits 0.78-1.24). Analysis by genotype was likewise not significant (overall chi(2) = 0.42). Because we were not able to support the primary hypothesis that Val158Met is a risk factor for AN, we did not perform secondary analysis of minimum body mass index (mBMI), age at onset or illness subtype (restricting or binge purging anorexia). Overall we found no support for the hypothesis that the Val158 allele of COMT gene is associated with AN in our combined European sample.

Interactions between genetic polymorphism of cytochrome P450-1B1, sulfotransferase 1A1, catechol-o-methyltransferase and tobacco exposure in breast cancer risk

Genetic polymorphisms of enzymes involved in the metabolism of xenobiotics and estrogens might play a role in breast carcinogenesis related to environmental exposures. In a case-only study on 282 women with breast cancer, we studied the interaction effects (ORi) between smoking habits and the gene polymorphisms of Cytochrome P450 1B1 (Val432Leu CYP1B1), Phenol-sulfotransferase 1A1 (Arg213His SULT1A1) and Catechol-O-methyltransferase (Val158Met COMT). The smokers carrying the Val CYP1B1 allele associated with a high hydroxylation activity had a higher risk of breast cancer than never smokers with the Leu/Leu genotype (ORi=2.32, 95%CI: 1.00-5.38). Also, the smokers carrying the His SULT1A1 allele associated with a low sulfation activity had a 2-fold excess risk compared to never smokers carrying Arg/Arg SULT1A1 common genotype (ORi= 2.55, 95%CI: 1.21-5.36). The His SULT1A1 allele increased the risk only in premenopausal patients. The Met COMT allele with a lower methylation activity than Val COMT did not modify the risk among smokers. The excess risk due to joint effect could result from a higher exposure to activated tobacco-compounds for women homo/heterozygous for the Val CYP1B1 allele. Also, a lower sulfation of the tobacco carcinogens among women with His SULT1A1 could increase exposure to genotoxic compounds. Alternatively, the Val CYP1B1 or His SULT1A1 allele with modified ability to metabolize estrogens could increase the level of genotoxic catechol estrogen (i.e., 4-hydroxy-estradiol) among smokers. Our study showed that gene polymorphisms of CYP1B1 and SULT1A1 induce an individual susceptibility to breast cancer among current smokers.

Lack of effect of polymorphisms in dopamine metabolism related genes on imaging of TRODAT-1 in striatum of asymptomatic volunteers and patients with Parkinson's disease

SPECT scanning using (99)Tc-TRODAT-1, a ligand that binds to dopamine transporters, may be useful for detection of early Parkinson's disease (PD), diagnosis of presymptomatic individuals, and monitoring disease progression. Understanding whether genetic factors contribute to inter-individual variability is crucial for interpreting imaging results in the context of disease pathophysiology. We tested whether polymorphisms in the genes for catechol-O-methyltransferase (COMT), monoamine-oxidase B (MAO-B), and the dopamine transporter (DAT) influence dopamine uptake parameters in the striatum in vivo in asymptomatic volunteers and patients with PD as measured with (99)Tc-TRODAT-1. (99)Tc-TRODAT-1 binding declined with age in both asymptomatic volunteers and PD patients, and depended on disease duration in PD patients. We found no significant association between COMT, MAO-B, and DAT polymorphisms and results of (99)Tc-TRODAT-1 testing in asymptomatic volunteers or patients with PD. In PD patients, the age of disease onset and speed of progression did not differ based on these polymorphisms. These results demonstrate that these specific genetic variations do not alter the fidelity of (99)Tc-TRODAT-1 as a measure of dopaminergic function in asymptomatic volunteer individuals or patients with PD.

Apolipoprotein E (APOE), PARKIN and catechol-O-methyltransferase (COMT) genes and susceptibility to sporadic Parkinson's disease in Finland

Recent studies have demonstrated that genetic factors modify susceptibility to sporadic Parkinson's disease (PD). So far the results of candidate gene studies have been conflicting. It has been suggested that polymorphisms in apolipoprotein E (APOE), PARKIN and catechol-O-methyltransferase (COMT) genes might increase the risk of PD. We studied 147 Finnish non-demented patients with sporadic PD and 137 controls. APOE epsilon allele and genotype frequencies in PD patients did not differ significantly from controls. Three single nucleotide polymorphisms of the PARKIN gene and an intronic and an exonic (Val158Met) polymorphism of the COMT gene were studied. None of these polymorphisms showed association with PD in our series. In contrast to reports in oriental populations, our results do not support a major role of APOE, PARKIN and COMT polymorphisms in PD susceptibility in the Finnish population.

Case-control study of dopamine transporter-1, monoamine oxidase-B, and catechol-O-methyl transferase polymorphisms in Parkinson's disease

We investigated the association of Parkinson's disease (PD) with dopamine transporter-1 (DAT1), monoamine oxidase-B (MAO-B), and catechol-O-methyltransferase (COMT) gene polymorphisms. Overall, we observed no significant association of PD with the DAT1-3'-variable numbers of tandem repeats, the MAO-B-(GT)(n), and the COMT-Val108Met gene polymorphisms in a sample of 319 unrelated PD cases and 196 control subjects. Analyses stratified by sex, age at examination, family history of PD, and ethnic origin also yielded negative findings, with three exceptions. We found statistically significant associations of PD with MAO-B polymorphisms in older patients and with a COMT polymorphism in younger subjects and in women. These significant differences at the two-tailed alpha level of 0.05 and restricted to subgroup analyses may have a biological basis or may be chance findings.

Association study of the low-activity allele of catechol-O-methyltransferase and alcoholism using a family-based approach

Catechol-O-methyltransferase (COMT) is a major component of the metabolic pathways of neurotransmitters such as dopamine, adrenaline, and noradrenaline. The activity of COMT is known to vary within the population; it exists in common high- and low-activity forms that are determined by a Val --> Met polymorphism at amino acid position 108/158 (in soluble or membrane-bound COMT). Recently, the low-activity allele was reported to contribute to the development of late-onset alcoholism in men. The present study extends this study by utilizing a family-based association approach, and by including individuals with early-onset alcoholism. Although no significant transmission disequilibrium was found in the overall sample of 70 parent/offspring trios (TDT = 1.43, P = 0.23), we observed a preferential transmission of the low-activity allele to patients with an early onset of disease (n = 32, TDT = 4.83, P = 0.028). Our results provide further evidence for an involvement of the COMT low-activity allele in the development of alcoholism and demonstrate the need for further studies in large samples of alcoholic patients.

Polymorphisms in genes involved in neurotransmission in relation to smoking

Smoking behavior is influenced by both genetic and environmental factors. The genetic contribution to smoking behavior is at least as great as its contribution to alcoholism. Much progress has been achieved in genomic research related to cigarette-smoking within recent years. Linkage studies indicate that there are several loci linked to smoking, and candidate genes that are related to neurotransmission have been examined. Possible associated genes include cytochrome P450 subfamily polypeptide 6 (CYP2A6), dopamine D(1), D(2), and D(4) receptors, dopamine transporter, and serotonin transporter genes. There are other important candidate genes but studies evaluating the link with smoking have not been reported. These include genes encoding the dopamine D(3) and D(5) receptors, serotonin receptors, tyrosine hydroxylase, trytophan 2,3-dioxygenase, opioid receptors, and cannabinoid receptors. Since smoking-related factors are extremely complex, studies of diverse populations and of many aspects of smoking behavior including initiation, maintenance, cessation, relapse, and influence of environmental factors are needed to identify smoking-associated genes. We now review genetic polymorphisms reported to be involved in neurotransmission in relation to smoking.

Impact of polymorphisms in xeno(endo)biotic metabolism on pattern and frequency of p53 mutations in bladder cancer

We have analyzed the tumor biopsies of 45 patients with bladder cancer for p53 mutations by direct sequencing. In addition to N-acetyltransferase-2 (NAT2) and GSTM1 allelisms, which were examined previously, we have analyzed the genetic polymorphisms of GSTT1, GSTP1, COMT, NQO1, TS-SULT and MPO in buffy coat DNA using PCR-based methods. All subjects were interviewed through a questionnaire on smoking, dietary habits and other risk factors. No specific pattern was evident for p53 mutations. Eight out of ten mutations occurred in grade 3 tumors. All p53 mutations occurred in subjects with the COMT mutated allele (p=0.03). The prevalence of cases with p53 mutations was 3.5-fold higher in subjects with wild type than in those with variant GSTP1 alleles (p=0.03). The other polymorphisms investigated were not associated with p53 mutations.

Atypical parkinsonism in Afro-Caribbean and Indian origin immigrants to the UK

This article reviews evidence for the occurrence of atypical parkinsonism in Afro-Caribbean and Indian ethnic minority subjects living in western countries, particularly the UK. Current information on the frequency, pattern, and prevalence of Parkinson's disease and parkinsonism in these communities is unclear and controversial. While several workers have suggested that there is a low prevalence of Parkinson's disease in populations of African origin, other workers have suggested a higher prevalence of Parkinson's disease in African Americans. Furthermore, little information is available in relation to the pattern of parkinsonism in these subjects. A recent phenomenologic study of parkinsonism in the French West Indies by Caparros-Lefebvre and colleagues has indicated a significantly increased frequency of atypical parkinsonism in local non-white subjects. Since 1995, we have been studying the pattern and frequency of parkinsonism in Afro-Caribbean and Indian (originating from the Indian subcontinent) patients living in the UK, with London serving as the coordinating center. Our results indicate that there is a three- to fourfold increase in the frequency of occurrence of sporadic atypical parkinsonism characterized by levodopa hyporesponsiveness, bradykinesia-dominant disease, and early cognitive dysfunction in these patients even after exclusion of patients with clinically probable multiple system atrophy, progressive supranuclear palsy, and Lewy body dementia. These findings are similar to observations made in the French West Indies. Ongoing studies in India suggest that atypical parkinsonism also affects local patients, and the pattern of parkinsonism tends to differ from Afro-Caribbean subjects in the UK. Studies are currently underway to unravel the mechanism of increased frequency of atypical parkinsonism in these ethnic groups and include genetic studies addressing polymorphisms of enzymes metabolizing levodopa, dietary neurotoxin screen and functional imaging studies of the striatum using positron emission tomography. Furthermore, the contribution of diabetes mellitus and hypertension, commonly seen in these ethnic groups, is also being examined.

Family-based linkage disequilibrium mapping using SNP marker haplotypes: application to a potential locus for schizophrenia at chromosome 22q11

Family-based linkage disequilibrium mapping using SNP markers is expected to be a major route to the identification of susceptibility alleles for complex diseases. However there are a number of methodological issues yet to be resolved, including the handling of extended haplotype data and analysis of haplotype transmission in sib-pair or family trio samples. In the present study, we have analysed two dinucleotide repeat and six SNP markers at the COMT locus at chromosome 22q11, a region implicated in psychosis, for transmission distortion in 198 Chinese schizophrenic family trios. When individual markers were analysed using the TDT, two showed modest evidence of transmission distortion (186C/T, P = 0.04; Val158Met, P = 0.01). Using haplotypes of paired markers analysed by the program TRANSMIT, the most significant P value was 0.001, for the Met158Val and 900ins/delC polymorphisms in the COMT gene. The global P value for the haplotypes of all six SNP markers tested was 0.004, largely a result of the excess transmission of two extended haplotypes which differed at the marker 408C/G. The exclusion of this marker from the analysis gave a global P value of 0.002 and produced a five marker haplotype system which was significant at P = 0.0006. This haplotype consisted of the alleles -287G:186C:Val158:900insC:ARVCF930C, which may represent a background haplotype for the transmission of a schizophrenia susceptibility allele at chromosome 22q11. Our results support the hypotheses that either COMT is itself a susceptibility gene, or more likely that this region of chromosome 22 contains a susceptibility gene that is in linkage disequilibrium with COMT alleles. Molecular Psychiatry (2000) 5, 77-84.

Astrocyte line SVG-TH grafted in a rat model of Parkinson's disease

The present review describes gene transfer into the brain using extraneuronal cells with an ex vivo approach. The mild immunological reactions in the central nervous system to grafts provided the rationale and empirical basis for brain-transplantation, to replace dying cells, of potential clinical relevance. Fetal human astrocytes were genetically engineered to express tyrosine hydroxylase, the rate-limiting enzyme for the synthesis of catecholamines. These cells were also found to produce constitutively and secrete GDNF and interleukins. Therefore, these cells may prove as a drug-delivery system for the treatment of neurological degenerative conditions such as Parkinson's disease (PD). The field of neuronal reconstruction has reached a critical threshold and there is a need to evaluate the variables that will become critical as the field matures. One of the needs is to characterize the neurochemical alterations in the microenvironment in the context of grafted-host connectivity. This review discusses the functional effects of the pharmacologically-active construct, which consists of astrocytes producing L-DOPA and GDNF. The striatum in PD that lacks the dopaminergic projection from the substantia nigra metabolizes and releases dopamine differently from normal tissue and may react to different factors released by the grafted cells. Moreover, neurochemicals of the host tissue may effect grafted cells as well. An understanding of the way in which these neurochemicals are abnormal in PD and their role in the grafted brain is critical to the improvement of reconstructive strategies using cellular therapeutic strategies.

Global variation in the frequencies of functionally different catechol-O-methyltransferase alleles

BACKGROUND

Catechol-O-methyltransferase (COMT) has been investigated as a candidate gene in many neurologic disorders involving catecholaminergic systems. The NlaIII restriction site polymorphism (RSP) at COMT is a G<-->A (site absent<-->site present) single nucleotide polymorphism (SNP) at nucleotide 322/472 (in the short or long mRNA) that results in a Val<-->Met polymorphism at amino acid 108/158 (in soluble or membrane-bound) COMT protein and different enzyme activity levels, high for Val, low for Met. COMT enzyme activity is known to vary among ethnic groups, presumably as a result of different population frequencies of these COMT alleles. We have undertaken a direct survey of allele frequencies of this polymorphism in a global sample of populations.

METHODS

We typed 1314 individuals from 30 different populations using PCR of the relevant region followed by digestion with NlaIII and electrophoresis.

RESULTS

The frequencies of the low activity allele (COMT*L, NlaIII site-present) vary significantly from 0.01 to 0.62. Europeans have nearly equal frequencies of the two alleles while the COMT*H allele is much more common in populations in all other parts of the world. Sequencing in nonhuman primates indicates that COMT*H is the ancestral allele in humans.

CONCLUSIONS

This is the first global survey of the COMT*L and COMT*H allele frequencies, confirming and extending earlier studies to show significant world-wide variation. This is also the first study establishing the COMT*L allele as the derived allele unique to humans. Henceforth, in any population-based association studies of this polymorphism, the control allele frequencies should be in agreement with these published values for corresponding ethnic groups.

Lack of allelic association of dopamine D4 receptor gene polymorphisms with Parkinson's disease in a Chinese population

Parkinson's disease (PD) is a neurodegenerative disease caused by a multitude of environmental, neurochemical, and genetic factors. The gene for human dopamine D4 receptor (DRD4) has been considered as a plausible candidate for the pathogenesis of PD. Different dopamine D4 receptor allelic forms have variable affinity toward certain neuroleptics such as clozapine, suggesting a role for dopamine D4 receptors in neurologic disorders. To test the hypothesis that the DRD4 polymorphism is associated with the susceptibility to Parkinson's disease, we have examined differences in allele frequencies of different DRD4 polymorphisms in 101 Chinese patients with PD and in 105 age-matched control subjects in Hong Kong. The DRD4 gene was analyzed by a non-radioactive polymerase chain reaction-based Southern hybridization with chemiluminescence detection. The number of polymorphic 48 base pair tandem repeats in exon 3 was identified in each study subject. The DRD4 alleles with high frequencies in the control subjects are 4-repeat allele (72.4%), 2-repeat allele (21.4%), and 7-repeat allele (3.8%) which accounted for over 97% of the total alleles in the elderly Chinese population. The most prevalent genotype in the control subjects is the 4/4 (47.6%), followed by 4/2 (38.6), 4/7 (7.6%), and 2/2 (3.0%). None of the variable number tandem repeat polymorphism showed evidence for genetic association with Parkinson's disease.

Genetic epidemiology of Parkinson's disease

The cause of Parkinson's disease (PD) is unknown. The major risk factors identified to date are family history, age, and elements of rural living. Nearly one-third of all PD cases are familial, a small subset of which appears autosomal dominant; however, the majority exhibit no clear inheritance pattern. Autosomal dominant PD is genetically heterogeneous: two PD genes have been mapped to chromosomes 2 and 4 and there may be additional as yet unidentified genes. The common forms of PD-both familial and sporadic cases-appear to involve a complex interplay of genetic susceptibility and environmental exposure. The observations that rural residence and pesticide exposure increase the risk of developing PD, and that a synthetic drug, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, can cause parkinsonism, suggest that at least a subset of PD may be caused by a toxin. Furthermore, modest but significant associations have been reported between PD susceptibility and genes that regulate metabolism of drugs and neurotoxins. There is also evidence for mitochondrial dysfunction in PD, a finding that was recently traced to anomalies in mitochondrial DNA. At the present time, the genetics of PD appear to be complex, involving multiple nuclear genes and possibly mitochondrial genes as well.

New, selective catechol-O-methyltransferase inhibitors as therapeutic agents in Parkinson's disease

Levodopa remains the most effective drug for Parkinson's disease (PD). However, its benefits are limited owing to extensive metabolism by catechol-O-methyltransferase (COMT), especially if levodopa is used in combination with peripheral dopa-decarboxylase inhibitors. A new generation of potent, orally active, selective, and reversible COMT inhibitors has become available recently. Among these, tolcapone and entacapone have been best characterised. Preclinical and clinical studies have shown that COMT inhibitors markedly enhance levodopa availability and prolong its plasma half-life. In recent large clinical trials they proved to be able to ameliorate motor fluctuations, reduce disability, and decrease levodopa requirements in PD patients. The tolerability profiles of entacapone and tolcapone are good. COMT inhibition promises to become an important means of extending the benefits of levodopa therapy in PD.