No association between bipolar disorder and alleles at a functional polymorphism in the COMT gene. Biomed European Bipolar Collaborative Group

COMT and MAO-A polymorphisms and obsessive-compulsive disorder: a family-based association study

Objective

Obsessive-compulsive disorder (OCD) is a common and debilitating psychiatric illness. Although a genetic component contributes to its etiology, no single gene or mechanism has been identified to the OCD susceptibility. The catechol-O-methyltransferase (COMT) and monoamine oxidase A (MAO-A) genes have been investigated in previous OCD studies, but the results are still unclear. More recently, Taylor (2013) in a comprehensive meta-analysis of genetic association studies has identified COMT and MAO-A polymorphisms involved with OCD. In an effort to clarify the role of these two genes in OCD vulnerability, a family-based association investigation was performed as an alternative strategy to the classical case-control design.

Methods

Transmission disequilibrium analyses were performed after genotyping 13 single-nucleotide polymorphisms (eight in COMT and five in MAO-A) in 783 OCD trios (probands and their parents). Four different OCD phenotypes (from narrow to broad OCD definitions) and a SNP x SNP epistasis were also analyzed.

Results

OCD, broad and narrow phenotypes,were not associated with any of the investigated COMT and MAO-A polymorphisms. In addition, the analyses of gene-gene interaction did not show significant epistatic influences on phenotype between COMT and MAO-A.

Conclusions

The findings do not support an association between DSM-IV OCD and the variants of COMT or MAO-A. However, results from this study cannot exclude the contribution of these genes in the manifestation of OCD. The evaluation of broader spectrum phenotypes could help to understand the role of these and other genes in the pathophysiology of OCD and its spectrum disorders.

Evidence for single nucleotide polymorphisms and their association with bipolar disorder

Bipolar disorder (BD) is a complex disorder with a number of susceptibility genes and environmental risk factors involved in its pathogenesis. In recent years, huge progress has been made in molecular techniques for genetic studies, which have enabled identification of numerous genomic regions and genetic variants implicated in BD across populations. Despite the abundance of genetic findings, the results have often been inconsistent and not replicated for many candidate genes/single nucleotide polymorphisms (SNPs). Therefore, the aim of the review presented here is to summarize the most important data reported so far in candidate gene and genome-wide association studies. Taking into account the abundance of association data, this review focuses on the most extensively studied genes and polymorphisms reported so far for BD to present the most promising genomic regions/SNPs involved in BD. The review of association data reveals evidence for several genes (SLC6A4/5-HTT [serotonin transporter gene], BDNF [brain-derived neurotrophic factor], DAOA [D-amino acid oxidase activator], DTNBP1 [dysbindin], NRG1 [neuregulin 1], DISC1 [disrupted in schizophrenia 1]) to be crucial candidates in BD, whereas numerous genome-wide association studies conducted in BD indicate polymorphisms in two genes (CACNA1C [calcium channel, voltage-dependent, L type, alpha 1C subunit], ANK3 [ankyrin 3]) replicated for association with BD in most of these studies. Nevertheless, further studies focusing on interactions between multiple candidate genes/SNPs, as well as systems biology and pathway analyses are necessary to integrate and improve the way we analyze the currently available association data.

Meta-analysis of genetic association studies on bipolar disorder

Numerous candidate gene association studies of bipolar disorder (BP) have been carried out, but the results have been inconsistent. Individual studies are typically underpowered to detect associations with genes of small effect sizes. We conducted a meta-analysis of published candidate gene studies to evaluate the cumulative evidence. We systematically searched for all published candidate gene association studies of BP. We then carried out a random-effects meta-analysis on all polymorphisms that were reported on by three or more case-control studies. The results from meta-analyses of these genes were compared with the findings from a recent mega-analysis of eleven genome-wide association studies (GWAS) in BP performed by the Psychiatric GWAS Consortium (PGC). A total of 487 articles were included in our review. Among these, 33 polymorphisms in 18 genes were reported on by three or more case-control studies and included in the random-effects meta-analysis. Polymorphisms in BDNF, DRD4, DAOA, and TPH1, were found to be nominally significant with a P-value < 0.05. However, none of the findings were significant after correction for multiple testing. Moreover, none of these polymorphisms were nominally significant in the PGC-BP GWAS. A number of plausible candidate genes have been previously associated with BP. However, the lack of robust findings in our review of these candidate genes highlights the need for more atheoretical approaches to study the genetics of BP afforded by GWAS. The results of this meta-analysis and from other on-going genomic experiments in BP are available online at Metamoodics (http://metamoodics.igm.jhmi.edu).

Catechol-O-methyltransferase Val158Met polymorphism affects therapeutic response to mood stabilizer in symptomatic manic patients

Catechol-O-methyltransferase (COMT) is a candidate gene for the pathogenesis of some psychiatric disorders. The aim of this study is to examine the role of the COMT gene Val158Met polymorphism on the clinical aspects of bipolar disorder including symptomatology and therapeutic response. This study comprised 144 unrelated manic patients who met strict DSM-IV criteria for bipolar I disorder and 157 healthy unrelated controls. All subjects were of Korean ethnicity. To evaluate the clinical symptoms, we used the Young Mania Rating Scale at baseline and 6 weeks after treatment. No statistically significant difference in genotype distribution was found between manic patients and normal controls. There was also no significant difference in symptomatology among the genotypes in manic patients. In therapeutic response, however, patients with the Met/Met genotype were significantly more frequent in the non-responder than in the responder group. Our results suggest that the COMT gene polymorphism in the therapeutic response to mood stabilizers in manic patients. Further studies with a larger number of subjects and well-controlled design will be required to better understand the role of the COMT gene polymorphism on the therapeutic response to mood stabilizer in manic patients.

The genetics of bipolar disorder: genome 'hot regions,' genes, new potential candidates and future directions

Bipolar disorder (BP) is a complex disorder caused by a number of liability genes interacting with the environment. In recent years, a large number of linkage and association studies have been conducted producing an extremely large number of findings often not replicated or partially replicated. Further, results from linkage and association studies are not always easily comparable. Unfortunately, at present a comprehensive coverage of available evidence is still lacking. In the present paper, we summarized results obtained from both linkage and association studies in BP. Further, we indicated new potential interesting genes, located in genome 'hot regions' for BP and being expressed in the brain. We reviewed published studies on the subject till December 2007. We precisely localized regions where positive linkage has been found, by the NCBI Map viewer (http://www.ncbi.nlm.nih.gov/mapview/); further, we identified genes located in interesting areas and expressed in the brain, by the Entrez gene, Unigene databases (http://www.ncbi.nlm.nih.gov/entrez/) and Human Protein Reference Database (http://www.hprd.org); these genes could be of interest in future investigations. The review of association studies gave interesting results, as a number of genes seem to be definitively involved in BP, such as SLC6A4, TPH2, DRD4, SLC6A3, DAOA, DTNBP1, NRG1, DISC1 and BDNF. A number of promising genes, which received independent confirmations, and genes that have to be further investigated in BP, have been also systematically listed. In conclusion, the combination of linkage and association approaches provided a number of liability genes. Nevertheless, other approaches are required to disentangle conflicting findings, such as gene interaction analyses, interaction with psychosocial and environmental factors and, finally, endophenotype investigations.

No association of COMT Val158Met polymorphism with suicidal behavior or CSF monoamine metabolites in mood disorders

The Met allele of the Catechol-O-Methyltransferase (COMT) gene functional polymorphism (COMT-V158M) is associated with lower enzymatic activity than the Val allele and is reported to be associated with aggression, depression, and suicidal behavior. Since depression and impulsive-aggressive behavior may mediate risk for suicidal behavior, we assessed the association of this polymorphism with suicidal behavior. Clinical (impulsive aggression) and biological (CSF monoamine metabolites) endophenotypes were tested as potential mediators of the effect of genotype on suicide risk. Subjects with mood disorders (N = 486) and healthy volunteers (N = 119), all European Caucasian, were genotyped for COMT-V158M and assessed for DSM IV diagnoses, lifetime suicidal behavior, lifetime impulsivity, hostility, and aggression. CSF monoamine metabolites were assayed in a sub-sample of mood disorder patients (N = 111). We found no association between genotype and mood disorder diagnosis or with reported history of suicide attempt in mood disorder subjects. There was no association between genotype and lethality or method of suicide attempt, or with aggressive/impulsive traits. Further, there was no difference in monoamine metabolites by genotype. The COMT-V158M polymorphism was not associated with suicidal behavior in a Caucasian sample of mood disorder subjects, or with possible clinical or biological endophenotypes.

Catechol-O-methyltransferase and its inhibitors in Parkinson's disease

Parkinson's disease (PD) is a neurological disorder characterized by the degeneration of dopaminergic neurons, with consequent reduction in striatal dopamine levels leading to characteristic motor symptoms. The most effective treatment for this disease continues to be the dopamine replacement therapy with levodopa together with an inhibitor of aromatic amino acid decarboxylase (AADC). The efficacy of this therapy, however, decreases with time and most patients develop fluctuating responses and dyskinesias. The last decade showed that the use of catechol-O-methyltransferase inhibitors as adjuvants to the levodopa/AADC inhibitor therapy, significantly improves the clinical benefits of this therapy. The purpose of this article is to review the current knowledge on the enzyme catechol-O-methyltransferase (COMT) and the role of COMT inhibitors in PD as a new therapeutic approach to PD involving conversion of levodopa to dopamine at the target region in the brain and facilitation of the continuous action of this amine at the receptor sites. A historical overview of the discovery and development of COMT inhibitors is presented with a special emphasis on nebicapone, presently under clinical development, as well as entacapone and tolcapone, which are already approved as adjuncts in the therapy of PD. This article reviews human pharmacokinetic and pharmacodynamic properties of these drugs as well as their clinical efficacy and safety.

No allelic association or interaction of three known functional polymorphisms with bipolar disorder in a northern Swedish isolated population

Most genetic association studies in bipolar disorder have focussed on genes involved in major neurotransmitter systems or brain development. Functional polymorphisms in the serotonin transporter (5-HTTLPR), catechol-O-methyltransferase (Val158Met) and dopamine D3 receptor (Ser9Gly) genes have all been associated with bipolar disorder. We aimed at investigating whether these functional variants contribute to the genetic etiology of bipolar disorder in a northern Swedish isolated population. Moreover, we wanted to gain information about the synergistic contribution of these functional variants. Neither of these functional polymorphisms was associated with bipolar disorder in the northern Swedish patient-control sample nor did we find evidence of gene-gene interaction. Together, our data suggest that these functional variants are not involved in the etiology of bipolar disorder in the northern Swedish population nor did gene-gene interaction analysis support a central role of these variants in bipolar disorder.

The catechol-O-methyl transferase (COMT) gene as a candidate for psychiatric phenotypes: evidence and lessons

The enzyme catechol-O-methyl transferase (COMT), identified in the 1950s, is involved in catabolism of monoamines that are influenced by psychotropic medications, including neuroleptics and antidepressants. The COMT gene lies in a chromosomal region of interest for psychosis and bipolar spectrum disorder and a common polymorphism within the gene alters the activity of the enzyme. As a consequence, COMT has been one of the most studied genes for psychosis. On the basis of prior probabilities it would seem surprising if functional variation at COMT did not have some influence either on susceptibility to psychiatric phenotypes, modification of the course of illness or moderation of response to treatment. There is now robust evidence that variation at COMT influences frontal lobe function. However, despite considerable research effort, it has not proved straightforward to demonstrate and characterise a clear relationship between genetic variation at COMT and psychiatric phenotypes. It is of course, possible that COMT will turn out to be an unusually intractable case but it seems more likely that the experiences with this gene will provide a foretaste of the complexity of genotype-phenotype relationships that will be found for psychiatric traits. In this review, we consider the current state of evidence and the implications both for further studies of COMT and more generally for studies of other genes.

The catechol O-methyltransferase Val158Met polymorphism and herpes simplex virus type 1 infection are risk factors for cognitive impairment in bipolar disorder: additive gene-environmental effects in a complex human psychiatric disorder

BACKGROUND

Bipolar disorder is associated with deficits in cognitive functioning. The etiology of cognitive impairment in bipolar disorder may relate to both genetic and environmental factors. A valine/methionine polymorphism of the catechol O-methyltransferase gene at amino acid 158 (COMT Val158Met polymorphism) has been identified as a risk factor for cognitive impairment in schizophrenia. Serological evidence of infection with herpes simplex virus type 1 (HSV-1) has also been identified as a risk factor for cognitive impairment in bipolar disorder.

METHODS

We used Taqman technology to measure COMT Val158Met alleles in 107 individuals with bipolar disorder and in 95 controls. We also measured antibodies to HSV-1 in sera obtained from the same individuals. Cognitive functioning was assessed with the Repeatable Battery for the Assessment of Neuropsychological Status and the Letter-Number Sequencing Test. The effects of the COMT Val158Met polymorphism and antibodies to HSV-1 on cognitive functioning were analyzed with multinomial logistic regressions.

RESULTS

The COMT Val158Val genotype and serological evidence of infection with HSV-1 are independent risk factors for cognitive impairment in individuals with bipolar disorder, particularly in the domains of immediate and delayed memory. Individuals with bipolar disorder with the COMT158 Val/Val genotype and serological evidence of HSV-1 infection were more than 85 times more likely to be in the lowest quintile of cognitive functioning when compared with the highest quintile when controlling for potential confounding variables such as symptom severity and education. Control individuals did not display this association.

CONCLUSION

Both the COMT Val158Met polymorphism and serological evidence of HSV-1 infection affect cognitive functioning in individuals with bipolar disorder.

Major affective disorders and schizophrenia: a common molecular signature?

Psychiatric disorders, including affective disorders (AD) and schizophrenia (SZ) are among the most common disabling brain diseases in Western populations and result in high costs in terms of morbidity as well as mortality. Although their etiology and pathophysiology is largely unknown, family-, twin-, and adoption studies argue for a strong genetic determination of these disorders. These studies indicate that there is between 40 and 85% heritability for these disorders but point also to the importance of environmental factors. Therefore, any research strategy aiming at the identification of genes involved in the development of AD and SZ should account for the complex nature (multifactorial) of these disorders. During the last decade, molecular genetic studies have contributed a great deal to the identification of genetic factors involved in complex disorders. Here we provide a comprehensive review of the most promising genes for AD and SZ, and the methods and approaches that were used for their identification. Also, we discuss the current knowledge and hypotheses that have been formulated regarding the effect of variations on protein functioning as well as recent observations that point to common molecular mechanisms.

The Val158Met polymorphism of the human catechol-O-methyltransferase (COMT) gene may influence morphine requirements in cancer pain patients

Catechol-O-methyltransferase (COMT) inactivates dopamine, epinephrine and norepinephrine in the nervous system. A common functional polymorphism (Val158Met) leads to a three- to-four-fold variation in the COMT enzyme activity, the Met form displaying lower enzymatic activity. The Val158Met polymorphism affects pain perception, and subjects with the Met/Met genotype have the most pronounced response to experimental pain. Based on this information we analyzed the influence from the COMT Val158Met polymorphism on the efficacy of morphine in a cohort of patients suffering from cancer pain. We genotyped 207 Caucasian cancer patients on morphine treatment with respect to the Val158Met polymorphism and compared the morphine doses, serum concentrations of morphine and morphine metabolites between the genotype groups. Patients with the Val/Val genotype (n=44) needed more morphine (155+/-160 mg/24 h) when compared to the Val/Met (117+/-100 mg/24 h; n=96) and the Met/Met genotype (95+/-99 mg/24 h; n=67) groups (P=0.025). This difference was not explained by other factors such as duration of morphine treatment, performance status, time since diagnosis, perceived pain intensity, adverse symptoms, or time until death. These results suggest that genetic variation in the COMT gene may contribute to variability in the efficacy of morphine in cancer pain treatment.

Association between COMT (Val158Met) functional polymorphism and early onset in patients with major depressive disorder in a European multicenter genetic association study

The available data from preclinical and pharmacological studies on the role of the C-O-methyl transferase (COMT) support the hypothesis that abnormal catecholamine transmission has been implicated in the pathogenesis of mood disorders (MD). We examined the relationship of a common functional polymorphism (Val108/158Met) in the COMT gene, which accounts for four-fold variation in enzyme activity, with 'early-onset' (EO) forms (less than or equal to 25 years) of MD, including patients with major depressive disorder (EO-MDD) and bipolar patients (EO-BPD), in a European multicenter case-control sample. Our sample includes 378 MDD (120 EO-MDD), 506 BPD (222 EO-BPD) and 628 controls. An association was found between the high-activity COMT Val allele, particularly the COMT Val/Val genotype and EO-MDD. These findings suggest that the COMT Val/Val genotype may be involved in EO-MDD or may be in linkage disequilibrium with a different causative polymorphism in the vicinity. The COMT gene may have complex and pleiotropic effects on susceptibility and symptomatology of neuropsychiatric disorders.

Recent findings on the genetic basis of bipolar disorder

What began as a search for a specific gene for bipolar disorder has now become a search for multiple susceptibility genes as it has be-come clear that the genetic basis of bipolar disorder probably involves multiple genes interacting with each other and with environmental components in as-yet mysterious ways. This article reviews the most recent findings and the emerging picture in the genetics of bipolar disorder.

Molecular genetics of affective disorders

Evidence for familial aggregation in Affective Disorders (AD) has been provided in classical studies. Linkage and association genetic studies have been proposed to detect genetic factors implicated in AD. However, findings from molecular genetic studies remain inconclusive. Nevertheless, current research is focusing on the phenotypes, both sub- and endophenotypes. In addition, recent advances in technology, such as microarrays, provide new tools in psychiatric genetics. These different approaches offer a new optimism era in the search of genetic factors in AD.

COMT: a common susceptibility gene in bipolar disorder and schizophrenia

A variety of psychiatric illnesses, including schizophrenia and bipolar disorder, have been reported in patients with microdeletion on chromosome 22q11-a region which includes the catechol-O-methyltransferase (COMT) gene. The variety of psychiatric manifestations in patients with the 22q11 microdeletion and the role of COMT in the degradation of catecholamine neurotransmitters may thus suggest a general involvement of the COMT gene in psychiatric diseases. We have previously reported on a significant association between a COMT haplotype and schizophrenia. In this study, we attempt to test for association between bipolar disorder and the polymorphisms implicated in schizophrenia. The association between COMT and bipolar disorder was tested by examining the allele and haplotype found to be associated with schizophrenia. A significant association between bipolar disorder and COMT polymorphisms was found. The estimated relative risk is greater in women, a result consistent with our previous findings in schizophrenia. We suggest that polymorphisms in the COMT gene may influence susceptibility to both diseases--and probably also a wider range of behavioral traits.

Genetic screening for susceptibility to depression: can we and should we?

OBJECTIVE

To summarize current knowledge about genetic susceptibility to mood disorders and examine ethical and policy issues that will need to be addressed if robustly replicated susceptibility alleles lead to proposals to screen and intervene with persons at increased genetic risk of developing mood disorders.

METHOD

Empirical studies and reviews of the genetics of unipolar and bipolar depression were collected via MEDLINE and psycINFO database searches.

RESULTS

A number of candidate genes for depression have been identified, each of which increases the risk of mood disorders two- or threefold. None of the associations between these alleles and mood disorders have been consistently reported to date.

CONCLUSIONS

Screening the population for genetic susceptibility to mood disorders is unlikely to be a practically useful policy (given plausible assumptions). Until there are effective treatments for persons at increased risk, screening is arguably unethical. Screening within affected families to advise on risks of developing depression would entail screening children and adolescents, raising potentially serious ethical issues of consent and stigmatization. Genetic research on depression should continue under appropriate ethical guidelines that protect the interests of research participants.

Association studies of bipolar disorder

Association studies in outbred populations represent an important paradigm for investigation of complex traits, such as bipolar disorder, both to follow-up regions of interest from linkage studies (by systematic linkage disequilibrium mapping and positional candidate studies) and for pure functional studies. The advantages of the association method include its relative robustness to genetic heterogeneity and the ability to detect much smaller effect sizes than are detectable using feasible sample sizes in linkage studies. The candidate gene approach is potentially very powerful, particularly when used within the context of a VAPSE (variation affecting protein structure or expression) paradigm, but a major problem is that the efficiency in the choice of candidates is inevitably a function of the level of previous understanding of disease pathophysiology. To date, most candidate gene studies in bipolar disorder have focussed on the major neurotransmitter systems that are influenced by medication used in clinical management of the disorder. Early studies often used anonymous markers in the hope of detecting linkage disequilibrium but recently direct examination of polymorphisms of known or presumed functional relevance has become more usual. Most studies in the literature have been of the unrelated case-control design with samples rarely exceeding 200-300 subjects. No definitive findings have yet emerged although there have been some interesting preliminary findings including those with polymorphisms within the genes encoding catechol-o-methyl transferase (COMT), monoamine oxidase A (MAOA) and the serotonin transporter (hSERT; 5-HTT). In this article we critically review the current status of the literature within the context of the important methodological issues and limitations inherent in the use of association studies for genetic dissection of bipolar disorder. We conclude by examining likely future directions and developments in the field.

Genetics of affective disorders

Despite substantial evidence for heritability in affective disorders the contributing genes have proven elusive. Here we discuss the genetic epidemiology of depression, as well as methodological issues and results from molecular genetic studies. There has been rapid advances in genetics, genomics and statistical modelling, facilitating the search for molecular mechanisms underlying affective disorders and several strategies reviewed in this paper hold promise to provide progress in the field. Considering the poorly understood biological basis of vulnerability to affective disorders, the identification of genes involved in the pathophysiology will unravel mechanisms and pathways that could permit more personalized therapeutic strategies and result in new targets for pharmacological intervention.

Molecular genetics of bipolar disorder

Alteration of monoaminergic neurotransmission is implicated in the pathophysiology of bipolar disorder (manic-depressive illness). Candidate genes participating in monoaminergic neurotransmission, especially serotonin transporter and monoamine oxidase A, may be associated with bipolar disorder. And the regulating regions of these genes and the molecules participating in intracellular signal transduction are now under investigation. To date, 13 whole genome positional cloning studies have been performed and many candidate loci identified. Using patients from a pedigree in which schizophrenia, depression or bipolar disorder have been linked with a balanced translocation at 1 and 11, candidate pathogenetic genes were cloned as DISC1 (disrupted in schizophrenia-1) and DISC2. Recently, pathogenetic mutations have been identified in two genetic diseases frequently co-morbid with mood disorder; WFS1 for Wolfram syndrome and ATP2A2 (SERCA2) for Darier's disease. Transmission of bipolar disorder may be characterized by anticipation and parent-of-origin effect, and extended CTG repeat at SEF2-1B gene was identified from a bipolar patient. However, its pathogenetic role was not supported by subsequent studies. Association of bipolar disorder with mitochondrial DNA has also been suggested. The role of genomic imprinting is also possible because linkage to 18p11 is limited to paternally transmitted pedigrees. These results warrant further study of molecular genetics of bipolar disorder.

Candidate gene studies of bipolar disorder

Genetic factors undoubtedly play an important role in determining vulnerability to bipolar disorder but the task of finding susceptibility genes is not trivial. Candidate gene studies, usually employing the association approach, offer the potential to discover the genes of relatively modest effect size that are expected for a complex genetic disorder. Candidate gene approaches depend crucially on our current understanding of disease pathophysiology, and attention has consequently been focussed on a limited range of neurotransmitter systems implicated by the action of drug treatments. Despite no unequivocal, consistently replicated findings, a number of intriguing results have emerged in the literature, both for bipolar disorder in general and for subtypes such as bipolar affective puerperal psychosis and rapid cycling bipolar illness. Genes of particular current interest include those encoding the serotonin transporter, monoamine oxidase A (MAOA) and catechol-O-methyl transferase (COMT). As susceptibility genes are found and knowledge of aetiology advanced it is likely that many more candidate genes in novel biological systems will attract attention.

Lack of association between the functional variant of the catechol-o-methyltransferase (COMT) gene and early-onset alcoholism associated with severe antisocial behavior

Addictive drugs, including ethanol, increase the brain's dopaminergic transmission, and catechol-o-methyltransferase (COMT) enzyme has a crucial role in dopamine inactivation. A common functional polymorphism in the COMT gene results in a three- to four-fold variation in enzyme activity. In a previous study, we found an association between type 1 (with late-onset but without prominent antisocial behavior) alcoholism and the low activity allele of the COMT gene. In this work we analyzed whether the COMT polymorphism has any effect on the development of type 2 (with early-onset and habitual impulsive violent behavior) alcoholism. The COMT genotype was determined in 62 impulsive violent recidivist offenders with early-onset (type 2) alcoholism, 123 late-onset nonviolent (type 1) alcoholics, and 267 race and gender-matched controls. The allele and genotype frequencies of these groups were compared with each other and also with previously published data from 3,140 Finnish blood donors. The type 2 alcoholics did not differ from either the blood donors or the controls. The low activity (L) allele frequency was higher among type 1 alcoholics (chi(2) = 4.98, P = 0.026) when compared with type 2 cases. The odds ratio for type 1 alcoholism as compared with type 2 alcoholism for those subjects with the LL genotype versus the HH genotype was 3.0 (95% confidence interval 1.1-8.4, P = 0.017). The results suggest that COMT genotype has no major role in the development of early-onset alcoholism with severe antisocial behavior.

Ultradian rapid cycling in prepubertal and early adolescent bipolarity is not in transmission disequilibrium with val/met COMT alleles

BACKGROUND

Prepubertal children and early adolescents with bipolar disorders (PEA-BP) who participate in the ongoing study "Phenomenology and Course of Pediatric Bipolar Disorders" have a high prevalence of ultradian (within 24-hour periods) rapid cycling. Based on a case-control finding reported in bipolar (BP) adults of an association between rapid and ultradian rapid cycling with the low-activity allele of catechol-O-methyltransferase (l-COMT), study of linkage and linkage disequilibrium of l-COMT in the PEA-BP population seemed warranted.

METHODS

Genotypes on a subset of the larger PEA-BP sample, for whom trio blood collection was complete (i. e., probands and both of their biological parents), were used to perform transmission disequilibrium tests (TDTs). Diagnoses were established from a comprehensive battery that included WASH-U-KSADS (Washington University Kiddie Schedule for Affective Disorders and Schizophrenia) given to both mothers and children and from consensus conferences. Probands with PEA-BP (N = 52) were 10.9 +/- 2.8 years old at index episode; had a mean age of BP onset at 8.0 +/- 3.8 years; were severely impaired, with a mean Children's Global Assessment Scale score of 44.5 +/- 8.9; and manifested the cardinal features of BP (84.6% had euphoric mood, 76.9% had grandiosity, and 57.7% had psychosis). Ultradian rapid cycling occurred in 75%. Genotyping of the single nucleotide polymorphism at COMT was performed using automated capillary electrophoresis single-strand conformational polymorphism with detection by laser-induced fluorescence.

RESULTS

Transmission disequilibrium tests were not significant for preferential transmission of l-COMT for the ultradian rapid-cycling subgroup or for the entire PEA-BP sample.

CONCLUSIONS

The lack of linkage disequilibrium between l-COMT and ultradian rapid cycling in the PEA-BP sample compared to reported findings of an association in case-control studies of adults is discussed in terms of age-specific developmentally relevant phenotypes, anticipatory mechanisms, and heterogeneity. Repeat TDT analyses after these PEA-BP probands reach their adult phenotypes will be informative.

COMT and DRD3 polymorphisms, environmental exposures, and personality traits related to common mental disorders

In a community sample of 2,327 Caucasians, we tested the hypotheses that polymorphisms in the COMT and DRD3 genes are associated with personality traits conferring vulnerability to anxiety, depression, or alcohol misuse, or with current symptoms of these; and that the association is stronger in persons who also have been exposed to stressor experiences. To conserve resources and to allow replication, the genetic analysis was undertaken in two stages. For the COMT polymorphism, no statistically significant associations were found in the first sample of 862 persons. The remainder of the sample was therefore not analysed for that gene. For the DRD3 polymorphism, those in the first sample with at least one of the Ser(9) alleles had significantly higher scores in neuroticism (p=0.006) and behavioral inhibition (p=0.003). There was a trend, failing to meet the 1% significance criterion, for those with this genotype also to have higher depression and anxiety. The groups did not differ in alcohol use. In persons with the Ser(9) allele who were also exposed to stressors, there was a higher level of depression at the 5% level; and the depression level was higher in homozygotes. But when the remainder of the sample (1,465) was analysed, none of the associations reached statistical significance. We conclude that neither the COMT nor DRD3 polymorphisms are associated with anxiety, depression, or alcohol abuse. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:102-107, 2000

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.

Psychiatric genetics: back to the future

For the last decade or more geneticists have been predicting that advances in molecular genetics are going to revolutionize our understanding of psychiatric disorders and human behavior. However, with a few exceptions, these expectations have yet to be fulfilled. As the century draws to a close and we contemplate the prospect of the complete sequence of the human genome it seems timely to consider the state of the field and to consider carefully how it might advance, the problems to be faced and the resources required. Molecular Psychiatry (2000) 5, 22-31.

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.

Methylation pharmacogenetics: catechol O-methyltransferase, thiopurine methyltransferase, and histamine N-methyltransferase

Methyl conjugation is an important pathway in the biotransformation of many exogenous and endogenous compounds. Pharmacogenetic studies of methyltransferase enzymes have resulted in the identification and characterization of functionally important common genetic polymorphisms for catechol O-methyltransferase, thiopurine methyltransferase, and histamine N-methyltransferase. In recent years, characterization of these genetic polymorphisms has been extended to include the cloning of cDNAs and genes, as well as a determination of the molecular basis for the effects of inheritance on these methyltransferase enzymes. The thiopurine methyltransferase genetic polymorphism is responsible for clinically significant individual variations in the toxicity and therapeutic efficacy of thiopurine drugs such as 6-mercaptopurine. Phenotyping for the thiopurine methyltransferase genetic polymorphism represents one of the first examples in which testing for a pharmacogenetic variant has entered standard clinical practice. The full functional implications of pharmacogenetic variation in the activities of catechol O-methyltransferase and histamine N-methyltransferase remain to be determined. Finally, experimental strategies used to study methylation pharmacogenetics illustrate the rapid evolution of biochemical, pharmacologic, molecular, and genomic approaches that have been used to determine the role of inheritance in variation in drug metabolism, effect, and toxicity.

Low activity allele of catechol-o-methyltransferase gene and Japanese unipolar depression

Several studies have shown that depressed patients have significantly lower catechol-o-methyltransferase (COMT) activity than healthy controls. Two COMT genes coding for low activity, COMTL, and high activity, COMTH have been identified. We undertook an association study on 75 depressive disorder patients, 40 bipolar disorder patients and 135 healthy controls. All the subjects were Japanese. Patients with depressive disorders exhibited a significantly higher rate of genotypes with the COMTL allele than healthy controls (p = 0.012), which was not the case in patients with bipolar disorders. The presence of the COMTL allele was significantly associated with depressive disorders (odds ratio 2.19, 95% CI 1.19-4.03). Our results suggest the COMTL allele contributed to the etiologies of depressive disorders.