Genetics of bipolar affective disorder

Genealogy Study of Three Generations of Patients with Bipolar Mood Disorder Type I

INTRODUCTION

The purpose of this research is genealogy examination of three generation of bipolar mood disorder Type I patients.

METHODS

Patients selected using Poisson sampling method from 100 patients with bipolar mood disorder Type I, referring to a psychiatric center of Amir Kabir Hospital of Arak, Iran. Examine issues such as physical ailments, psychological review of living and deceased family members of each patient, drawn family pedigree using pedigree chart, check the relationship of the different pattern of the autosomal dominant and recessive disease, sex-linked dominant and recessive and linked to Y chromosome have been performed on patients. Different methods used in this study are pedigree chart and young mania rating scale and SPSS and Pearson's correlation test for analyzing the data collected.

RESULTS

Among the studied inheritance patterns, the most common inheritance pattern was autosomal recessive. There was a significant relationship between age, number of generation, and inheritance patterns with physical ailments in families of patients with bipolar mood disorder (P < 0.05), but there was no significant association with mental illness (P > 0.05). Furthermore, there was a significant relation between generation and skin, gastrointestinal, ovarian, lung, coronary heart disease, diabetes mellitus, hypertension, Cerebrovascular accident (CVA), hyperlipidemia, cardiomyopathy, hypothyroidism, and kidney disease in patients with bipolar affective disorder Type I (P < 0.05).

CONCLUSION

The results showed that autosomal recessive was the most pattern of inheritance and there is a significant relationship between generation and some physical disorders in patients with bipolar mood disorder Type I.

Multiple levels of impaired neural plasticity and cellular resilience in bipolar disorder: developing treatments using an integrated translational approach

OBJECTIVES

This paper reviews the neurobiology of bipolar disorder (BD), particularly findings associated with impaired cellular resilience and plasticity.

METHODS

PubMed/Medline articles and book chapters published over the last 20 years were identified using the following keyword combinations: BD, calcium, cytokines, endoplasmic reticulum (ER), genetics, glucocorticoids, glutamate, imaging, ketamine, lithium, mania, mitochondria, neuroplasticity, neuroprotection, neurotrophic, oxidative stress, plasticity, resilience, and valproate.

RESULTS

BD is associated with impaired cellular resilience and synaptic dysfunction at multiple levels, associated with impaired cellular resilience and plasticity. These findings were partially prevented or even reversed with the use of mood stabilizers, but longitudinal studies associated with clinical outcome remain scarce.

CONCLUSIONS

Evidence consistently suggests that BD involves impaired neural plasticity and cellular resilience at multiple levels. This includes the genetic and intra- and intercellular signalling levels, their impact on brain structure and function, as well as the final translation into behaviour/cognitive changes. Future studies are expected to adopt integrated translational approaches using a variety of methods (e.g., microarray approaches, neuroimaging, genetics, electrophysiology, and the new generation of -omics techniques). These studies will likely focus on more precise diagnoses and a personalized medicine paradigm in order to develop better treatments for those who need them most.

The bipolar disorder prodrome revisited: Is there a symptomatic pattern?

OBJECTIVES

To assess the phenomenology and course of pre-(hypo)manic and pre-depressed prodromal symptoms, including mood swings, as precursors of bipolar disorder (BD) in a German multi-center study.

METHODS

Semi-structured interviews [Bipolar Prodrome Symptom Scale-Retrospective (BPSS-R); Semi-structured Interview for Mood Swings] were administered to patients within 8 years of BD (BD I, BD II) onset.

RESULTS

Forty two outpatients were included (40.5% male, mean age 35.1±10.0 years, illness onset at 30.5±9.5 years). Feeling extremely energetic (85.7%), racing thoughts (78.6%), physical agitation (76.2%), overtalkativeness (71.4%), and low sleep requirement (71.4%) occurred most frequently prior to the first (hypo)manic episode, whereas depressed mood (83.0%), reduced vitality (81.0%), physical exhaustion (78.6%), tiredness (76.2%), and insomnia (66.7%) preceded pre-depressively. Mood lability (p=.006), odd ideas (p=.003) and the psychosis index score (p=.003) differed significantly in prevalence depending on the episodes' mood. Extremely energetic (p=.046), overtalkativeness (p<.001), and racing thoughts (p=.013) lasted significantly longer prior to depression. Neither severity nor frequency of prodromal symptoms differed significantly. Most of the symptoms emerged during the proximal prodromal phase. Links between mood swings and subsequent BD were found.

LIMITATIONS

Symptoms were evaluated retrospectively with self-reporting tools in bipolar patients from academic treatment settings without comparison to clinical controls.

CONCLUSIONS

Not only specific depressive or manic but also general symptoms occurred prior to both affective episodes. The pre-depressive prodrome lasted longer than the pre-manic one, but severity and frequency did not differ significantly. Mood swings and disturbed diurnal rhythm occurred prior to both episodes as early signs of BD.

Further evidence for linkage of bipolar disorder to chromosomes 6 and 17 in a new independent pedigree series

OBJECTIVES

We have previously reported the results of a linkage analysis of bipolar disorder in an initial set of 20 pedigrees ascertained through collaboration among three sites. We now report the results of our genome-wide linkage analysis in an independent sample of 34 pedigrees segregating bipolar disorder.

METHODS

Families were ascertained through a bipolar I or II disorder proband for the presence of bipolar I disorder, bipolar II disorder, or recurrent major depression in at least two other family members. A total of 440 markers at an average spacing of 8 cM were genotyped in 229 family members using fluorescent methods.

RESULTS

Initial nonparametric analyses of chromosomes 6 and 17 provided evidence for a modest replication of linkage to these chromosomes previously reported in other studies. Additional analyses using multipoint parametric methods provided further evidence to support the 6q25 region with a heterogeneity logarithm of odds score of 3.28. Evidence from two-point parametric analyses also provides a modest replication of our previous findings of linkage to the 23 cM region of chromosome 22q13 in our original University of California, San Diego sample of 20 families and 57 families from the National Institute of Mental Health bipolar disorder sample.

CONCLUSIONS

Our results suggest replication of some reported linkage peaks, such as 6q25 and 17p12; however, other peaks from our own previous study, such as 5p15, 13q32, and 22q13, were either not replicated or were only modestly replicated in these analyses.

[Heritability of bipolar affective disorder--family study]

BACKGROUND/AIM

Bipolar affective disorder is mental disorder with polygenic type of heredity. Heritability--relation between genetic and environmental variance is used to estimate the level of influence of genetic variance to phenotype variance. Study results show decreasing trend in the value of heritability of bipolar affective disorder, thus indicating that this disorder is a complex behavioral threshold characteristic. Therefore, the aim of this study was to estimate the contribution of genetic variance to phenotype variance of bipolar affective disorder, i.e. to estimate heritability of this disorder.

METHODS

By the use of a questionnaire, 80 patients with over crossed threshold for bipolar affective disorder were asked for functional information about the members of their families belonging to the first degree of relation (fathers, mothers and full-sibs). By using "Applet for calculating heritability for threshold traits (disease)", and regression analysis, heritability of bipolar affective disorder as well as its statistical significance, were estimated (chi2 test).

RESULTS

Heritability and relationship of genetic and environmental variance of bipolar affective disorder is 0.2 with statistically significant difference from zero (p < 0.001).

CONCLUSION

The estimated contribution of genetic variance to phenotype variance of bipolar affective disorder is low being 20%, while the contribution of environmental variance is 80%. This result contributes to the understanding of bipolar affective disorder as a complex behavioral threshold trait.

Replication study of association between ADCYAP1 gene polymorphisms and schizophrenia

The adenylate cyclase-activating polypeptide 1 (ADCYAP1) gene encodes a neuropeptide with neurotransmission activity, which is known as the pituitary adenylate cyclase-activating polypeptide. Associations of two polymorphisms, rs1893154 and rs2856966 (Asp54Gly), in the ADCYAP1 gene with schizophrenia were reported earlier by a Japanese case-control study. In this study, we tried to confirm the association in 2027 Japanese patients with schizophrenia and 2058 controls. The power to detect an association was more than 0.9. However, we did not detect allelic associations of rs1893154 with schizophrenia (P=0.36). Although rs2856966 was nominally significant (P=0.045), the association was in the opposite direction from that reported earlier. Combined data and meta-analysis of the two studies comprising nearly 6000 Japanese case-control patients did not show significant associations (P=0.53-0.86). It is concluded that single-nucleotide polymorphisms, including Asp54Gly, of the ADCYAP1 gene are unlikely to play a sizeable role in the genetic susceptibility to schizophrenia.

GABRB2 in schizophrenia and bipolar disorder: disease association, gene expression and clinical correlations

The SCZ (schizophrenia)-associated GABA(A) receptor (gamma-aminobutyric acid type A receptor) beta(2) subunit gene GABRB2 was recently associated with BPD (bipolar disorder). Although weaker than its association with SCZ, significant association of GABRB2 with BPD was found in both German and Chinese, especially for the haplotypes rs1816071-rs187269 and rs1816072-rs187269 for which the M-M variants showed higher frequency in disease than the control. Significant genotype-dependent reduction in GABRB2 expression was shown for BPD, but to a lesser extent than that for SCZ. Temporal effects on GABRB2 expression were observed. Moreover, for the homozygous major genotypes of rs1816071, rs1816072 and rs187269, expression increased with time in CON but decreased in SCZ and BPD. The genotypes of these three SNPs (single nucleotide polymorphisms) were further correlated with antipsychotics dosage in SCZ cohorts. The findings highlight the importance of GABRB2 in neuropsychiatric disease aetiology, with respect to haplotype association, as well as reduction of and temporal effects on gene expression in both SCZ and BPD, but to a lesser extent in the latter, supporting the suggestion that functional psychosis can be conceptualized as a continuous spectrum of clinical phenotypes rather than as distinct categories.

Abnormal dose-response melatonin suppression by light in bipolar type I patients compared with healthy adult subjects

OBJECTIVE

Among potential endophenotypes proposed for bipolar affective disorder focusing on circadian abnormalities associated with the illness has particularly high face validity. Melatonin sensitivity to light is one circadian endophenotype proposed as useful in bipolar disorder. The aim of this study was to investigate melatonin sensitivity to light over a range of light intensities in order to compare and contrast responses in bipolar I patients with those of healthy adult volunteers.

METHODS

The study included seven patients (4 females, 3 males) with bipolar I disorder and 34 control participants (22 females, 12 males) with no personal or family history of affective illness. Melatonin sensitivity to light was determined in all patients and participants across a range of light intensities (0, 200, 500 and 1000 lux).

RESULTS

The results indicated that patients showed melatonin super-sensitivity to light in comparison with controls, a response that was consistent across the entire light intensity range investigated.

CONCLUSION

The study provides further evidence for a super sensitive response in bipolar I patients and suggests that its potential usefulness as an endophenotypic marker of the illness is deserving of further research.

Pituitary adenylate cyclase-activating polypeptide is associated with schizophrenia

Pituitary adenylate cyclase-activating polypeptide (PACAP, ADCYAP1: adenylate cyclase-activating polypeptide 1), a neuropeptide with neurotransmission modulating activity, is a promising schizophrenia candidate gene. Here, we provide evidence that genetic variants of the genes encoding PACAP and its receptor, PAC1, are associated with schizophrenia. We studied the effects of the associated polymorphism in the PACAP gene on neurobiological traits related to risk for schizophrenia. This allele of the PACAP gene, which is overrepresented in schizophrenia patients, was associated with reduced hippocampal volume and poorer memory performance. Abnormal behaviors in PACAP knockout mice, including elevated locomotor activity and deficits in prepulse inhibition of the startle response, were reversed by treatment with an atypical antipsychotic, risperidone. These convergent data suggest that alterations in PACAP signaling might contribute to the pathogenesis of schizophrenia.

The PIP5K2A gene and schizophrenia in the Chinese population--a case-control study

Results from a number of molecular and pharmacological studies suggest that the phosphatidylinositol-4-phosphate 5-kinase IIalpha (PIP5K2A) gene may be involved in the development of schizophrenia. A recent family-based transmission disequilibrium test in the German and Israeli populations found that four single nucleotide polymorphisms, rs1417374, rs10828317, rs746203 and rs8341 in this gene or nearby intergenic regions are significantly associated with schizophrenia. The objective of our study was to investigate whether these four SNPs are also associated with schizophrenia in the Chinese population. Our study found that SNP rs8341 (p=0.0045, Odds Ratio=1.415, 95%CI=1.113-1.799 for the minor allele) and a haplotype (p=0.0039, Odds Ratio=1.440, 95%CI=1.123-1.845) are significantly associated with schizophrenia. Our results confirm that the PIP5K2A gene merits further study as a susceptible gene for schizophrenia.

Practice parameter for the assessment and treatment of children and adolescents with bipolar disorder

This practice parameter reviews the literature on the assessment and treatment of children and adolescents with bipolar disorder. The parameter focuses primarily on bipolar 1 disorder because that is the type most often studied in juveniles. The presentation of bipolar disorder in youth, especially children, is often considered atypical compared with that of the classic adult disorder, which is characterized by distinct phases of mania and depression. Children who receive a diagnosis of bipolar disorder in community settings typically present with rapid fluctuations in mood and behavior, often associated with comorbid attention-deficit/hyperactivity disorder and disruptive behavior disorders. Thus, at this time it is not clear whether the atypical forms of juvenile mania and the classic adult form of the disorder represent the same illness. The question of diagnostic continuity has important treatment and prognostic implications. Although more controlled trials are needed, mood stabilizers and atypical antipsychotic agents are generally considered the first line of treatment. Although patients may respond to monotherapy, combination pharmacotherapy is necessary for some youth. Behavioral and psychosocial therapies are also generally indicated for juvenile mania to address disruptive behavior problems and the impact of the illness on family and community functioning.

MLC1 gene is associated with schizophrenia and bipolar disorder in Southern India

BACKGROUND

Chromosome 22q13 has shown linkage with schizophrenia (SCZ) and bipolar affective disorder (BPAD). A missense mutation in MLC1 (putative cation-channel gene on 22q13) co-segregating with periodic catatonic schizophrenia has been reported. We have investigated the relationship of MLC1 with SCZ and BPAD in Southern India.

METHODS

All exons and flanking intronic sequences of MLC1 were screened for novel variations. Case-control (216 BPAD, 193 SCZ, 116 control subjects) and family-based analyses (113 BPAD, 107 SCZ families) were performed to evaluate association of MLC1 with these disorders.

RESULTS

We found 33 MLC1 sequence variations, including three novel mutations: Val210Ile, Leu308Gln, and Arg328His in six BPAD cases and Val210Ile in one control individual. Minor allele of a common variation, ss16339182 (in approximately 6 Kb Linkage-Disequilibrium [LD]-block) was associated with BPAD in case-control (p = .03) and family-based analyses (transmitted/nontransmitted [T/NT]-44/20; p = .003). Association was observed for rs2235349 and rs2076137 with SCZ and ss16339163 with BPAD in case-control study. Using Block 2 haplotype tagging single nucleotide polymorphisms (htSNPs), GC haplotype revealed association (p = .02) and excess transmission (p = .002) with BPAD.

CONCLUSIONS

Association of MLC1 with SCZ and BPAD suggests involvement of a common pathway. Rare missense mutations and common variants associated with BPAD favors hypothesis about likely involvement of both rare and common polymorphisms in etiology of this complex disorder.

Diagnostic interview assessed neuropsychiatric disorder comorbidity in 334 individuals with obsessive-compulsive disorder

Is obsessive-compulsive disorder (OCD) a discrete disorder? Three hundred thirty-four individuals with OCD were interviewed using the Structured Clinical Interview for DSM (SCID). Results demonstrate that OCD is highly comorbid with other neuropsychiatric disorders, with 92% of OCD study participants receiving one or more additional Axis I DSM diagnoses. Among these additional diagnoses, lifetime mood disorders (81%) and anxiety disorders (53%) were the most prevalent. With the exception of substance-related disorders and specific phobias, all disorders assessed were found in considerably higher frequency than in the general population, indicating that OCD is associated with highly complex comorbidity. These data have implications for genetic studies of OCD and disorders related to OCD, as well as for specific psychotherapeutic and psychopharmacologic interventions.

Methylomics in psychiatry: Modulation of gene-environment interactions may be through DNA methylation

Fine-tuning of neuronal connections during development is regulated through environmental interactions. Some fine-tuning occurs through changes in gene expression and/or epigenetic gene-specific DNA methylation states. DNA methylation occurs by transfer of a methyl group from S-adenosyl methionine to cytosine residues in the dinucleotide sequence CpG. Although CpG sequences spread throughout the genome are usually heavily methylated, those occurring in CpG islands in the promoter regions of genes are less methylated. In most cases, the extent of DNA methylation correlates with the extent of gene inactivation. Other known epigenetic mechanisms include histone deacetylation and chromatin remodeling, RNA inhibition, RNA modification, and DNA rearrangement. Exposure memory expressed as epigenetic DNA modifications allows genomic plasticity and short-term adaptation of each generation to their environment. Environmental factors that affect DNA methylation include diet, proteins, drugs, and hormones. Induced methylation changes may produce altered gene response upon subsequent hormonal stimulation. The gene-specific DNA methylation state may be preserved upon transmission through mitosis and meiosis. An increasing amount of data implicates a role for DNA methylation in multi-factorial psychiatric disorders. For example, L-methionine treatment can exacerbate psychosis; while valproate, a drug producing hypomethylated DNA, reduces such symptoms. Hypermethylation of the promoter region of the RELN gene correlates with reduced gene expression. This gene's protein Reelin, which is necessary for neuronal migration and synaptogenesis, is reduced in schizophrenia and bipolar disorder, suggesting hypermethylation of the promoter region in these disorders. Some evidence implicates methylation of the promoter regions of the DRD2 and HTR2A genes in schizophrenia and mood disorders as well. DNA methylation usually increases with age, although hypomethylation of the promoter region of the amyloid A4 precursor gene during aging may play a role in Alzheimer's disease. More studies are needed to define the role of methylomics and other epigenetic phenomena in the nervous system.

Ethnicity-independent genetic basis of functional psychoses: a genotype-to-phenotype approach

The functional psychoses schizophrenia, schizoaffective disorder, and bipolar illness represent complex clinical syndromes that are characterized by phenotypic heterogeneity. Yet evidence from numerous studies suggests that (1) the prevalence of schizophrenia and bipolar illness is with 1% very similar across ethnicities, and (2) a strong genetic component is involved in the disorders' pathogenesis. Using data from different US-American ethnicities (77 families with a total of 17 unaffected and 170 affected sib pairs; 276 marker loci), we searched for ethnicity-independent oligogenic susceptibility loci for which the between-sib genetic similarity in affected sib pairs deviated from the expected values. Specifically, we addressed the question of the extent to which genetic risk factors and their interactions constitute multigenic inheritance of functional psychoses across populations and might constitute universal targets for treatment. Our novel multivariate genotype-to-phenotype search strategy was based on a genetic similarity function that allowed us to quantify the inter-individual genetic distances d(x(i), x(j)) between the allelic genotype patterns x(i), x(j) of any two subjects i, j with respect to n loci l(1), l(2), em leader l(n). Thus, we were able to assess the between-ethnicity, the within-ethnicity, and the within-family genetic similarities. The problem of ethnicity-independent vulnerability was addressed by treating the Afro-American families as "training" samples, while the non-Afro-American families served as independent "test" samples. We evaluated the between-sib similarities, which were expected to deviate from "0.5" in affected sib pairs if the region of interest contained markers close to vulnerability genes. The reference value "0.5" was derived from the parent-offspring similarities that are always 0.5, irrespective of the affection status of parents and offspring. We found 12 vulnerability loci on chromosomes 1, 4, 5, 6, 13, 14, 18, and 20, that were reproducible across the two samples under comparison and therefore, likely to constitute an ethnicity-independent, oligogenic vulnerability model of functional psychoses. The elevated vulnerability appeared to be unspecific and to act in such a way that exogenous factors become more likely to trigger the onset of psychiatric illnesses.

JI. Genomewide linkage analyses of bipolar disorder: a new sample of 250 pedigrees from the National Institute of Mental Health Genetics Initiative

We conducted genomewide linkage analyses on 1,152 individuals from 250 families segregating for bipolar disorder and related affective illnesses. These pedigrees were ascertained at 10 sites in the United States, through a proband with bipolar I affective disorder and a sibling with bipolar I or schizoaffective disorder, bipolar type. Uniform methods of ascertainment and assessment were used at all sites. A 9-cM screen was performed by use of 391 markers, with an average heterozygosity of 0.76. Multipoint, nonparametric linkage analyses were conducted in affected relative pairs. Additionally, simulation analyses were performed to determine genomewide significance levels for this study. Three hierarchical models of affection were analyzed. Significant evidence for linkage (genomewide P<.05) was found on chromosome 17q, with a peak maximum LOD score of 3.63, at the marker D17S928, and on chromosome 6q, with a peak maximum LOD score of 3.61, near the marker D6S1021. These loci met both standard and simulation-based criteria for genomewide significance. Suggestive evidence of linkage was observed in three other regions (genomewide P<.10), on chromosomes 2p, 3q, and 8q. This study, which is based on the largest linkage sample for bipolar disorder analyzed to date, indicates that several genes contribute to bipolar disorder.

Is preadolescent mania the same condition as adult mania? A British perspective

Until relatively recently, the prevailing view was that mania was uncommon in preadolescent children. In the past 15 years, however, there has been increasing interest in the idea that mania may be much more common at younger ages than previously recognized. This article is concerned with the issue of whether preadolescent mania represents the same kind of problem as adult mania. It reviews concepts of bipolar disorder and mania in adults and preadolescents, some of the issue that arise in diagnosing mania in children, and the evidence for continuities between preadolescent and adult mania. The diagnosis of mania in preadolescent children often requires that inferences are made about the meaning of some symptoms but it is not always clear that these inferences are valid. It is concluded that the extant evidence does not provide a clear conclusion about the links between preadolescent and adult mania. More work is needed on the phenomenology and diagnosis of mania in children, on its natural history and on its familial correlates.

Identification of candidate genes for schizophrenia based on natural resistance to infectious diseases

BACKGROUND

Identification of candidate genes for schizophrenia may be more successful than genome screens as the latter have not found consistent linkages.

OBJECTIVE

To assist in the gene search, a model of schizophrenia based on resistance to infectious diseases, rather than susceptibility, is proposed. The theory blends the geography of schizophrenia with the assumption that genes that cause schizophrenia likely evolved and persist from selection pressure. The theory includes the notion that schizophrenia enhances biological survival at the cost of psychological and social functioning.

METHOD

To demonstrate the utility of using this model, the Medline literature was searched for resistance genes, mostly identified in mice.

RESULTS

Based on homologous locations in the human genome, these resistance genes are shown to be located in human chromosome regions linked significantly, in at least one genome screen, with schizophrenia or some physiologically related function or condition associated with schizophrenia.

CONCLUSIONS

The infectious disease resistance theory of schizophrenia is offered as a viable model for understanding the origins of schizophrenia. The theory also allows for the inclusion of persistent infections, seasonal variability and translational pathophysiology to contribute to the etiology of schizophrenia.

Genetically mediated brain abnormalities in schizophrenia

Schizophrenia is a highly heritable, neurobehavioral disorder; however, the mode of inheritance is complex, and linkage findings have been difficult to replicate. Some consistent linkage findings have emerged on chromosomes 1, 6, 8, 11, 13, 15, and 22. New methods are being developed for candidate gene identification, including the use of neurobiologic phenotypes observed in relatives of persons with schizophrenia. Neuroimaging studies of relatives implicate abnormal hippocampal structure and inefficient prefrontal network functioning, probably representing mild variants of the abnormalities observed in schizophrenia. These characteristics may represent stable markers of vulnerability to schizophrenia, because they are not confounded by effects of antipsychotic drugs or psychosis. Recent studies provide evidence for a small role of the catechol-O-methyltransferase gene on 22q, and the serotonin receptor transporter gene on 17q11-q12 in the development of schizophrenia. Linking genes and brain regions or networks is an important step in identification of the pathophysiology of schizophrenia.

Central GABAergic systems and depressive illness

Clinical depression and other mood disorders are relatively common mental illnesses but therapy for a substantial number of patients is unsatisfactory. For many years clinicians and neuroscientists believed that the evidence pointed toward alterations in brain monoamine function as the underlying cause of depression. This point of view is still valid. Indeed, much of current drug therapy appears to be targeted at central monoamine function. Other results, though, indicate that GABAergic mechanisms also might play a role in depression. Such indications stem from both direct and indirect evidence. Direct evidence has been gathered in the clinic from brain scans or postmortem brain samples, and cerebrospinal fluid (CSF) and serum analysis in depressed patients. Indirect evidence comes from interaction of antidepressant drugs with GABAergic system as assessed by in vivo and in vitro studies in animals. Most of the data from direct and indirect studies are consistent with GABA involvement in depression.

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.

Imaging genomics

The recent completion of a working draft of the human genome sequence promises to provide unprecedented opportunities to explore the genetic basis of individual differences in complex behaviours and vulnerability to neuropsychiatric illness. Functional neuroimaging, because of its unique ability to assay information processing at the level of brain within individuals, provides a powerful approach to such functional genomics. Recent fMRI studies have established important physiological links between functional genetic polymorphisms and robust differences in information processing within distinct brain regions and circuits that have been linked to the manifestation of various disease states such as Alzheimer's disease, schizophrenia and anxiety disorders. Importantly, all of these biological relationships have been revealed in relatively small samples of healthy volunteers and in the absence of observable differences at the level of behaviour, underscoring the power of a direct assay of brain physiology like fMRI in exploring the functional impact of genetic variation.

Serotonin transporter gene polymorphism influences age at onset in patients with bipolar affective disorder

Serotonin transporter (SLC6A4) gene polymorphism is associated with several behavioral and psychiatric traits. In bipolar affective disorder, two polymorphisms of the SLC6A4 gene, a variable number of tandem repeats in the second intron and a 44 bp insertion/deletion in the serotonin transporter gene linked polymorphic region (5-HTTLPR), have been extensively studied. The findings are conflicting possibly because of the heterogeneity of bipolar disorder. Early-onset bipolar disorder appears to be clinically and genetically more homogeneous and was recently suggested to be associated with the 5-HTTLPR polymorphism. We tested the association between two polymorphisms of the SLC6A4 gene and age at onset (AAO) in a sample of bipolar patients. For both SLC6A4 gene polymorphisms, AAO of subjects with different genotypes were compared. SLC6A4 genotype distributions of different AAO groups were also compared. The variable number of tandem repeats (VNTR) polymorphism significantly influences the AAO but the serotonin transporter gene linked polymorphic region (5-HTTLPR) polymorphism did not. Patients carrying at least one VNTR STin2.12 allele began their illness later whereas patients carrying the 'ss' genotype tended to begin their illness earlier. Differential sampling procedures may influence the proportion of AAO subgroups in a given association study, and therefore these results may explain the conflicting results obtained in studies of the association between the SLC6A4 gene polymorphism and bipolar affective disorder (BPAD).

Apparent replication of suggestive linkage on chromosome 16 in the NIMH genetics initiative bipolar pedigrees

Analyses of a replication sample of families collected as part of the National Institute of Mental Health (NIMH) Genetics Initiative for bipolar disorder provide further evidence for linkage to a region of chromosome 16. Families who had a bipolar I (BPI) proband and at least one BPI or schizoaffective, bipolar type (SABP) first-degree relative were ascertained for the purpose of identifying genes involved in bipolar affective disorder. A series of hierarchical models of affected status was used in linkage analyses. Initial genetic analyses of chromosomes 3, 5, 15, 16, 17, and 22, completed at Indiana University in 540 subjects from 97 families, suggested evidence of linkage to chromosomes 5, 16, and 22 [Edenberg et al., 1997: Am J Med Genet 74:238-246]. Genotyping was subsequently performed on these chromosomes in a replication sample of 353 individuals from 56 families. Nonparametric linkage analyses were performed using both affected relative and sibling pair methods. Analyses in the new sample on chromosome 16, using the broadest model of affected status, corroborate previously reported suggestive linkage to the marker D16S2619. Combining the initial and replication samples further increased the evidence of linkage to this region, with a peak lod score of 2.8.

Family, twin, and adoption studies of bipolar disease

Bipolar disease features states of severe depression that usually fluctuate with at least one episode of intense elation or mania. It is a disorder that has been thought for some time to have a heritable component. The lifetime prevalence of bipolar disease in the general population is approximately 1%. In contrast, family studies have shown the approximate lifetime risk of a first-degree relative of a bipolar proband to be 5% to 10%. Moreover, studies of monozygotic twins show that their risk of contracting the disease is as much as 75 times greater than that for the general population. In addition, adoption studies have demonstrated that biological relatives of bipolar patients are substantially more likely to have the disorder than are adoptive relatives.