Genetic association between monoamine oxidase and manic-depressive illness: comparison of relative risk and haplotype relative risk data

MAOA Variants and Genetic Susceptibility to Major Psychiatric Disorders

Monoamine oxidase A (MAOA) is a mitochondrial enzyme involved in the metabolism of several biological amines such as dopamine, norepinephrine, and serotonin, which are important neurochemicals in the pathogenesis of major psychiatric illnesses. MAOA is regarded as a functional plausible susceptibility gene for psychiatric disorders, whereas previous hypothesis-driven association studies obtained controversial results, a reflection of small sample size, genetic heterogeneity, or true negative associations. In addition, MAOA is not analyzed in most of genome-wide association studies (GWAS) on psychiatric disorders, since it is located on Chromosome Xp11.3. Therefore, the effects of MAOA variants on genetic predisposition to psychiatric disorders remain obscure. To fill this gap, we collected psychiatric phenotypic (schizophrenia, bipolar disorder, and major depressive disorder) and genetic data in up to 18,824 individuals from diverse ethnic groups. We employed classical fixed (or random) effects inverse variance weighted methods to calculate summary odds ratios (OR) and 95 % confidence intervals (CI). We identified a synonymous SNP rs1137070 showing significant associations with major depressive disorder (p = 0.00067, OR = 1.263 for T allele) and schizophrenia (p = 0.0039, OR = 1.225 for T allele) as well as a broad spectrum of psychiatric phenotype (p = 0.000066, OR = 1.218 for T allele) in both males and females. The effect size was similar between different ethnic populations and different gender groups. Collectively, we confirmed that MAOA is a risk gene for psychiatric disorders, and our results provide useful information toward a better understanding of genetic mechanism involving MAOA underlying risk of complex psychiatric disorders.

Monoamine oxidase a gene polymorphisms and bipolar disorder in Iranian population

BACKGROUND

Bipolar disorder (BPD) is a common and severe mood disorder. Although genetic factors have important rolesin the etiology of bipolar disorder, no specific gene has been identified in relation to this disorder. Monoamine oxidase gene is suggested to be associated with bipolar disorder in many studies.

OBJECTIVES

This study aimed to investigatethe role of MAOA gene polymorphisms in the etiology of bipolar disorder in Iranian population.

PATIENTS AND METHODS

This study is a case-control study, with convenient sampling. Three common polymorphisms, a CA microsatellite, a VNTR, and a RFLP were typed in 156 bipolar patients and 173 healthy controls. Patients were chosen from Imam Hossein General Hospital, Psychiatry Ward (Tehran/Iran). Controlsamples for this study consisted of 173 healthy individuals recruitedby convenient sampling. Allelic distributions of these polymorphisms were analyzed in bipolar and control groups to investigate any association with MAOA gene.

RESULTS

Significant associations were observed regarding MAOA-CA (P = 0.016) and MAOA-VNTR (P = 0.004) polymorphisms in the bipolar females. There was no association between MAOA-RFLP and bipolar disorder.

CONCLUSIONS

The obtained results confirm some previous studies regardinga gender specific association of MAOA gene with the bipolar disorder.

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).

Association analysis of monoamine oxidase A gene and bipolar affective disorder in Han Chinese

Background

Monoamine oxidase A (MAOA) is a mitochondrial enzyme involved in degrading several different biological amines, including serotonin. Although several pieces of evidence suggested that MAOA is important in the etiology of bipolar affective disorder (BPD), associations for markers of the MAOA gene with BPD were not conclusive and the association has not been investigated in Taiwanese population. This study was designed to illustrate the role of MAOA in the etiology of BPD in Han Chinese.

Methods

Two markers, a dinucleotide polymorphism in exon 2 and a functional uVNTR on the promoter of the MAOA gene, were used to study the genetic association in 108 unrelated patients with BPD and 103 healthy controls. Allelic distributions of two polymorphisms were analyzed and, caused the MAOA located at X chromosome, haplotype association was performed using haplotype unambiguously assigned in male participants.

Results

While no difference in allelic distributions of two MAOA polymorphisms was found, the risk haplotype 114S was associated with BPD in male patients (P = 0.03). The significance, however, was not found in female patients with 114S haplotype.

Conclusion

Results from this study suggest that MAOA may have a gender-specific and small effect on the etiology of BPD in Taiwan. Due to the limited sample size, results from this study need to be confirmed in replicates.

Specific binding of [3H]Ro 19-6327 (lazabemide) to monoamine oxidase B is increased in frontal cortex of suicide victims after controlling for age at death

Previous studies have reported negative findings for the association among brain monoamine oxidase B (MAO-B) and suicidal behaviour. However those studies did not adequately control their main results for the influence of confounding variables such as age at death. We have evaluated the association of MAO-B density (assessed by [3H]Ro 19-6327 - lazabemide - binding) with type of death (suicide victims vs non-suicide controls) after controlling for age at death. Frontal cortex samples from 43 subjects (21 suicides, 22 controls) were assayed for MAO-B density at a single concentration of lazabemide (8 nM). A linear regression modelling approach comparing nested models resulted with both type of death (p<0.05) and age of death (p<0.01) as main explanatory variables for the variability of MAO-B density. Suicide victims had >30% more binding sites for lazabemide than controls. Contrary to previous reports, MAO-B density seems to increase in suicide victims.

Carving chaos: genetics and the classification of mood and psychotic syndromes

Though Kraepelin's century-old division of major mental illness into mood disorder and schizophrenia remains in place, debate abounds over the most appropriate classification. Although these arguments previously rested solely on clinical grounds, they now are rooted in genetics and neurobiology. This article reviews evidence from the fields of genetic epidemiology, linkage, association, cytogenetics, and gene expression. Taken together, these data suggest some overlap in the genes that predispose to bipolar disorder and schizophrenia. One gene, DAOA (D-amino acid oxidase activator, also known as G72), has been repeatedly implicated as an overlap gene, while DISC1 and others may constitute additional shared susceptibility genes. Further, some evidence implicates syndromes of co-occurring mood and psychotic symptoms in association with the putative risk alleles in overlap genes. From a nosologic perspective, the existence of overlap genes, coupled with the genotype-phenotype correlations discovered to date, supports the reality of the much debated schizoaffective disorder. Potential non-overlap syndromes--such as nonpsychotic bipolar disorder or cyclothymic temperament, on the one hand, and negative symptoms or the deficit syndrome, on the other--could turn out to have their own unique genetic determinants. If genotypes are to be the anchor points of a clinically useful system of classification, they must ultimately be shown to inform prognosis, treatment, and prevention. No gene variants have yet met these tests in bipolar disorder or schizophrenia.

Effect of population stratification on case-control association studies. I. Elevation in false positive rates and comparison to confounding risk ratios (a simulation study)

OBJECTIVES

This is the first of two articles discussing the effect of population stratification on the type I error rate (i.e., false positive rate). This paper focuses on the confounding risk ratio (CRR). It is accepted that population stratification (PS) can produce false positive results in case-control genetic association. However, which values of population parameters lead to an increase in type I error rate is unknown. Some believe PS does not represent a serious concern, whereas others believe that PS may contribute to contradictory findings in genetic association. We used computer simulations to estimate the effect of PS on type I error rate over a wide range of disease frequencies and marker allele frequencies, and we compared the observed type I error rate to the magnitude of the confounding risk ratio.

METHODS

We simulated two populations and mixed them to produce a combined population, specifying 160 different combinations of input parameters (disease prevalences and marker allele frequencies in the two populations). From the combined populations, we selected 5000 case-control datasets, each with either 50, 100, or 300 cases and controls, and determined the type I error rate. In all simulations, the marker allele and disease were independent (i.e., no association).

RESULTS

The type I error rate is not substantially affected by changes in the disease prevalence per se. We found that the CRR provides a relatively poor indicator of the magnitude of the increase in type I error rate. We also derived a simple mathematical quantity, Delta, that is highly correlated with the type I error rate. In the companion article (part II, in this issue), we extend this work to multiple subpopulations and unequal sampling proportions.

CONCLUSION

Based on these results, realistic combinations of disease prevalences and marker allele frequencies can substantially increase the probability of finding false evidence of marker disease associations. Furthermore, the CRR does not indicate when this will occur.

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.

Serotonin gene polymorphisms and bipolar I disorder: focus on the serotonin transporter

The pathogenesis of bipolar disorder may involve, at least in part, aberrations in serotonergic neurotransmission. Hence, serotonergic genes are attractive targets for association studies of bipolar disorder. We have reviewed the literature in this field. It is difficult to synthesize results as only one polymorphism per gene was typically investigated in relatively small samples. Nevertheless, suggestive associations are available for the 5HT2A receptor and the serotonin transporter genes. With the availability of extensive polymorphism data and high throughput genotyping techniques, comprehensive evaluation of these genes using adequately powered samples is warranted. We also report on our investigations of the serotonin transporter, SLC6A4 (17q11.1-q12). An insertion/deletion polymorphism (5HTTLPR) in the promoter region of this gene has been investigated intensively. However, the results have been inconsistent. We reasoned that other polymorphism/s may contribute to the associations and the inconsistencies may be due to variations in linkage disequilibrium (LD) patterns between samples. Therefore, we conducted LD analyses, as well as association and linkage using 12 polymorphisms, including 5HTTLPR. We evaluated two samples. The first sample consisted of 135 US Caucasian nuclear families having a proband with bipolar I disorder (BDI, DSM IV criteria) and available parents. For case-control analyses, the patients from these families were compared with cord blood samples from local Caucasian live births (n = 182). Our second, independent sample was recruited through the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD, 545 cases, 548 controls). No significant associations were detected at the individual polymorphism or haplotype level using the case-control or family-based analyses. Our analyses do not support association between SLC6A4 and BDI families. Further studies using sub-groups of BDI are worthwhile.

Monoamine Oxidase A and Tryptophan Hydroxylase Gene Polymorphisms

Most of the candidate gene studies in bipolar disorder have focused on the major neurotransmitter systems that are influenced by drugs used in the treatment of this disorder. The monoamine oxidase A (MAOA) and the tryptophan hydroxylase (TPH1, TPH2) genes are two of the candidates that have been tested in a series of association studies using unrelated or family-based controls. This review summarizes the existing association studies regarding these genes. Most of these studies were based on the unrelated case-control design with samples of 50 to 600 subjects. Regarding MAOA, three meta-analyses with partially overlapping samples supported a modest effect of this gene in bipolar disorder in female Caucasians. However, as several studies could not replicate these findings, more work is necessary to demonstrate unequivocally the involvement of MAOA in bipolar disorder and establish the biological mechanism underlying the genetic association. With respect to TPH1 and TPH2, the majority of studies did not provide evidence for an association between these genes and bipolar disorder. The genes are more likely to be related to suicidal behavior than to bipolar disorder.

An association between a functional polymorphism in the monoamine oxidase a gene promoter, impulsive traits and early abuse experiences

Monoamine oxidase A (MAOA) activity is altered in mood disorders and lower activity associated with aggressive behavior. The gene has a functional polymorphism with a variable number tandem repeat (VNTR) in the upstream regulatory region (MAOA-uVNTR). In this study, we examined possible associations between the MAOA-uVNTR polymorphism and mood disorders, suicidal behavior, aggression/impulsivity, and effects of reported childhood abuse. In total, 663 unrelated subjects with a psychiatric disorder and 104 healthy volunteers were genotyped for the 30 base pair functional VNTR. A novel repeat variation was identified. No statistically significant associations were found between this functional MAOA-uVNTR polymorphism and mood disorders or suicide attempts. However, the lower expression allele was associated with a history of abuse before 15 years of age in male subjects and with higher impulsivity in males but not females. Our results suggest that the lower expression of the MAOA-uVNTR polymorphism is related to a history of early abuse and may sensitize males, but not females, to the effects of early abuse experiences on impulsive traits in adulthood. The polymorphism may be a marker for impulsivity that in turn may contribute to the risk for abuse. This trait could then be further aggravated by abuse.

Genome scan of a second wave of NIMH genetics initiative bipolar pedigrees: chromosomes 2, 11, 13, 14, and X

As part of the on-going NIMH Genetics Initiative on Bipolar Disorder, we have ascertained 153 multiplex bipolar pedigrees and genotyped them in two waves. We report here the genome scan results for chromosomes 2, 11, 13, 14, and X in the second wave of 56 families. A total of 354 individuals were genotyped and included in the current analyses, including 5 with schizoaffective/bipolar (SA/BP), 139 with bipolar I disorder (BPI), 41 with bipolar II disorder (BPII), and 43 with recurrent unipolar depression (RUP). Linkage analyses were carried out with multi-point parametric and non-parametric affected relative pair methods using three different definitions of the affected phenotype: (model 1) SA/BP and BPI; (model 2) SA/BP, BPI, and BPII; and (model 3) SA/BP, BPI, BPII, and RUP. The best findings were on 11p15.5 (NPL = 2.96, P = 0.002) and Xp11.3 (NPL = 2.19, P = 0.01). These findings did not reach conventional criteria for significance, but they were located near regions that have been identified in previous genetic studies of bipolar disorder. The relatively modest but consistent findings across studies may suggest that these loci harbor susceptibility genes of modest effect in a subset of families. Large samples such as that being collected by the NIMH Initiative will be necessary to examine the heterogeneity and identify these susceptibility genes.

Pharmacogenetics of lithium prophylaxis in mood disorders: analysis of COMT, MAO-A, and Gbeta3 variants

We studied the possible association between the prophylactic efficacy of lithium in mood disorders and the following gene variants: catechol-O-methyltransferase (COMT) G158A, monoamine oxydase A (MAO-A) 30-bp repeat, G-protein beta 3-subunit (Gbeta3) C825T. A total of 201 subjects affected by bipolar (n = 160) and major depressive (n = 41) disorder were followed prospectively for an average of 59.8 months and were typed for their gene variants using PCR techniques. COMT, MAO-A, and Gbeta3 variants were not associated with lithium outcome, even when possible stratification effects such as sex, polarity, age at onset, duration of lithium treatment, and previous episodes were included in the model. The pathways influenced by those variants are not therefore involved with long-term lithium outcome in our sample.

Association study of MAO-A, COMT, 5-HT2A, DRD2, and DRD4 polymorphisms with illness time course in mood disorders

The aim of our study was to investigate a possible influence of monoamine oxydase A (MAO-A), catechol-O-methyltransferase (COMT), serotonin receptor 2A (5-HT2A), dopamine receptor D2 (DRD2), and dopamine receptor D4 (DRD4) gene variants on timing of recurrence in mood disorders. Gene variants were determined using PCR-based techniques in 550 inpatients affected by recurrent mood disorders (major depressives: n = 212; bipolars: n = 338), rapid cycling mood disorder (n = 81), and 663 controls. We investigated possible genetic influences by comparing illness time course of subjects subdivided according to genotype using multivariate analysis of variance (MANOVA). We could not observe a significantly different time course. No demographic and clinical variables such as sex, age or polarity of onset, presence of psychotic features, genetic loading, or education level influenced the observed results. Our results suggest that MAO-A, COMT, 5-HT2A, DRD2, and DRD4 gene variants are not involved in susceptibility toward different time courses in mood disorders.

Review of bipolar molecular linkage and association studies

This paper reviews the history of molecular genetic linkage and linkage disequilibrium (LD) or association studies of bipolar disorder (BPD). The topic is introduced with a brief discussion of various genetic concepts, including linkage and linkage disequilibrium. It is emphasized that criteria for declaring linkage must include independent confirmation by multiple groups of investigators. Given that the inherited susceptibility for BPD is most likely explained by multiple genes of small effect, simulations indicate that universal confirmation of valid linkages cannot be expected due to sampling variation and genetic heterogeneity. With this background, several valid linkages of BPD to genomic regions are reviewed, including some which may be shared with schizophrenia. These results suggest that nosology must be changed to reflect the genetic origins of the multiple disorders which are collectively described by the term, BPD. The history of BPD LD studies is reviewed, using monoamine oxidase as as an example. Some suggestions of improving these BPD LD are offered.

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.

Association analysis of the functional monoamine oxidase A gene promoter polymorphism in psychiatric disorders

Functional characterization studies revealed that transcriptional activity of the human monoamine oxidase A (MAOA) gene is modulated by a polymorphic repetitive sequence located approximately 1.2 kb upstream of the ATG codon. To investigate the possible influence of the allelic variants of the MAOA gene-linked polymorphic region (MAOA-LPR) on the genetic predisposition to psychiatric disorders, we have performed a case-control association study. 174 patients with affective disorders and 258 patients with schizophrenia according to DSM-IV, as well as 229 population controls were tested. Statistical analysis showed no significant differences in allele or genotype frequencies between control and patient groups. Our results suggest that there is no association between MAOA-LPR genotype and susceptibility to recurrent major depression, bipolar disorder, and schizophrenia in our population.

Lack of linkage disequilibrium between serotonin transporter protein gene (SLC6A4) and bipolar disorder

The serotonin transporter (5HTT) gene appears to be of particular interest as 5HTT is the selective site of action of selective serotonin reuptake inhibitors (SSRIs) that successfully treat bipolar depression (BP). The 5HTT gene is located on chromosome 17q11.1-q12 and has a 44 bp deletion/insertion functional polymorphism in the promoter region (SLC6A4). Results from association studies on SLC6A4 and BP disorder are conflicting. The aim of the present study was to investigate for the presence of linkage disequilibrium between SLC6A4 and BP disorder. One hundred thirty-three Bipolar I or Bipolar II probands with their living parents were recruited. Diagnoses were assessed by the structured interview for the Diagnostic and Statistical Manual of Mental Disorders, fourth edition [DSM-IV, American Psychiatric Association, 1994] (SCID-I). Genotyping was performed with standard procedures and data were analyzed using the Transmission Disequilibrium Test [TDT, Spielman et al., 1993: Am J Hum Genet 52: 506-516]. One hundred two triads were informative for the analysis. Each of the two alleles of the SLC6A4 was transmitted at the same rate to bipolar probands (chi(2) = 0.692, df = 1, P = NS). Thus, it appears unlikely that the SLC6A4 plays a fundamental role in the pathogenesis of BP disorder. However, further studies focusing on the role of the 5HTT gene in predicting the response to SSRIs in BP patients might be worthwhile.

Searching high and low: a review of the genetics of bipolar disorder

OBJECTIVES

To review the methodologies and findings in the genetics of bipolar disorder (BPD), and to suggest future directions for research.

METHODS

Reports of family, twin, adoption, linkage, association, cytogenetic, and animal model studies, and segregation analyses in English, were identified from multiple MEDLINE searches. Hand searches were carried out in bibliographies from review articles.

RESULTS

Family, twin, and adoption studies have provided strong evidence for a genetic etiology in BPD. Early reports of linkage of BPD to DNA markers at several chromosomal sites have not proven robust, perhaps because of the complex nature of BPD inheritance. However, linkage findings in the 1990s, on chromosomes 18, 21q, 12q, and 4p, have provided leads that are being pursued through both genetic and physical mapping. No gene has yet been definitively implicated in BPD.

CONCLUSIONS

Strategies for increasing the power to detect BPD genes include: (1) dividing the phenotype into genetically meaningful subtypes to decrease heterogeneity: and (2) ascertaining a very large family sample--a multicenter study now in progress will collect 700 bipolar I sibling pairs. BPD may result from several genes acting in concert so that new multilocus statistical methods could enhance the capacity to detect loci involved. Family-based association studies using a very large number of newly identified single nucleotide polymorphisms (SNPs) may allow for more efficient screening of the genome. As the Human Genome Project approaches its goal of isolating all genes by 2003, the data generated is likely to speed identification of candidate BPD genes.

Association analysis between mood disorder and monoamine oxidase gene

To ascertain whether mood disorders, including bipolar and unipolar, are genetically associated with the monoamine oxidase A (MAOA) or monoamine oxidase B (MAOB) gene in the Chinese population, 132 cases of mood disorder and 88 normal controls were genotyped for the MAOA(CA)n, MAOB(GT)n, and MAOB(TG)n loci by the method of amplification fragment length polymorphism. Among 132 cases with mood disorder, eight alleles (size: 112-126 bp) of locus MAOA(CA)n, 12 alleles (size: 168-198 bp) of locus MAOB(GT)n, and nine alleles (size: 195-213 bp) of locus MAOB(TG)n were observed. Comparison of the allele frequency of the three loci showed no difference between mood disorder cases and normal controls on average. When each group was stratified into several subgroups, significant differences were found. On the MAOA(CA)n locus, the frequency of 116 bp allele was higher in the female bipolar disorder cases (0.2581) compared with that in the female unipolar disorder patients (0.1154) (Z=2.15, p<0. 05). On the MAOB(GT)n locus, the frequency of 180 bp allele was higher in bipolar disorder patients (0.1579) than that in normal controls (0.0678) (Z=2.05, p<0.05). The frequency of this allele was even higher in female bipolar disorder patients (0.1719) than that in female normal controls (0.0541). On the MAOB(TG)n locus, the frequency of 205 bp allele was higher in female bipolar disorder patients (0.6406) than that in female normal controls (0.4375) (Z=2. 17, p<0.05). For the unipolar disorder patients, the frequency of this allele was higher in female cases (0.5222) than that in male cases (0.1818) (Z=3.49, p<0.05). As for association studies, significant association between bipolar disorder and MAOB gene was detected. For the 180 bp allele of MAOB(GT)n, the relative risk (RR) of biploar versus normal control was 2.58 (p<0.05), and the RR of female bipolar disorder versus female normal control was 3.63 (p<0. 05). For the 205 bp allele of MAOB(TG)n, the RR of female bipolar disorder versus female normal control was 2.29 (p<0.05). Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:12-14, 2000.