The COMT and DRD3 genes interacted in bipolar I but not bipolar II disorder

DRD3 Ser9Gly polymorphism and treatment response to antipsychotics in schizophrenia: A meta-analysis

The association between dopamine D3 receptor (DRD3) Ser9Gly polymorphism and treatment response to antipsychotic drugs (APDs) in schizophrenia (SCZ) has been widely reported with inconsistent results, thus we performed an updated meta-analysis to derive a more precise estimation of the relationship. PubMed, Cochrane Library, Medline, Embase, CNKI, Weipu and Wanfang databases were searched for eligible studies published until March 2022. Odds ratios (ORs) with 95 % confidence intervals (CIs) were used to assess the strength of the associations in four genetic models. A total of 13 studies with 1769 patients were included in this meta-analysis. Our findings suggested that Ser9Gly polymorphism was significantly associated with treatment response to APDs in SCZ in allele model (Ser vs Gly, OR = 0.72, 95 % CI = 0.58-0.89, P = 0.002), recessive model (Ser/Ser vs Ser/Gly + Gly/Gly, OR = 0.55, 95 % CI = 0.36-0.86, P = 0.008) and co-dominant model (Ser/Ser vs Gly/Gly, OR = 0.57, 95 % CI = 0.33-0.99, P = 0.045) in Caucasians, but not in Asians. meta-regression revealed that the associations were not confounded by mean age, male ratio and treatment duration (P > 0.05). In summary, our results indicated the DRD3 Ser9Gly may influence the efficacy of APDs in specific genetic models, of which Ser allele and Ser/Ser genotype contributed to poor treatment response in Caucasians.

Frequency of the Dopamine Receptor D3 (rs6280) vs. Opioid Receptor µ1 (rs1799971) Polymorphic Risk Alleles in Patients with Opioid Use Disorder: A Preponderance of Dopaminergic Mechanisms?

While opioids are a powerful class of drugs that inhibit transmission of pain signals, their use is tarnished by the current epidemic of opioid use disorder (OUD) and overdose deaths. Notwithstanding published reports, there remain gaps in our knowledge of opioid receptor mechanisms and their role in opioid seeking behavior. Thus, novel insights into molecular, neurogenetic and neuropharmacological bases of OUD are needed. We propose that an addictive endophenotype may not be entirely specific to the drug of choice but rather may be generalizable to altered brain reward circuits impacting net mesocorticolimbic dopamine release. We suggest that genetic or epigenetic alterations across dopaminergic reward systems lead to uncontrollable self-administration of opioids and other drugs. For instance, diminished availability via knockout of dopamine D3 receptor (DRD3) increases vulnerability to opioids. Building upon this concept via the use of a sophisticated polymorphic risk analysis in a human cohort of chronic opioid users, we found evidence for a higher frequency of polymorphic DRD3 risk allele (rs6280) than opioid receptor µ1 (rs1799971). In conclusion, while opioidergic mechanisms are involved in OUD, dopamine-related receptors may have primary influence on opioid-seeking behavior in African Americans. These findings suggest OUD-targeted novel and improved neuropharmacological therapies may require focus on DRD3-mediated regulation of dopaminergic homeostasis.

Altered cerebellar gray matter and cerebellar-cortex resting-state functional connectivity in patients with bipolar disorder Ⅰ

BACKGROUND

Bipolar disorder (BP) is a common psychiatric disorder characterized by extreme fluctuations in mood. Recent studies have indicated the involvement of cerebellum in the pathogenesis of BP. However, no study has focused on the precise role of cerebellum exclusively in patients with bipolar I disorder (BP-I).

METHODS

Forty-five patients with BP-I and 40 healthy controls were recruited. All subjects underwent clinical evaluation and Magnetic Resonance diffusion Tension Imaging scans. For structural images, we used a spatially unbiased infratentorial template toolbox to isolate the cerebellum and then preformed voxel-based morphometry (VBM) analyses to assess the difference in cerebellar gray matter volume (GMV) between the two groups. For the functional images, we chose the clusters that survived from VBM analysis as seeds and performed functional connectivity (FC) analysis. Between-group differences were assessed using the independent Students t test or the nonparametric Mann-Whitney U Test. For multiple comparisons, the results were further corrected with Gaussian random field (GRF) approach (voxel-level P < 0.001, cluster-level P < 0.05).

RESULTS

Compared with healthy controls, BP-I patients showed significantly decreased GMV in left lobule V and left lobule VI (P < 0.05, GRF corrected). The FC of cerebellum with bilateral superior temporal gyrus, bilateral insula, bilateral rolandic operculum, right putamen, and left precentral gyrus was disrupted in BP-I patients (P < 0.05, GRF corrected).

CONCLUSIONS

BP-I patients showed decreased cerebellar GMV and disrupted cerebellar-cortex resting-state FC. This suggests that cerebellar abnormalities may play an important role in the pathogenesis of BP-I.

Shared and specific patterns of dynamic functional connectivity variability of striato-cortical circuitry in unmedicated bipolar and major depressive disorders

BACKGROUND

Accumulating studies have found structural and functional abnormalities of the striatum in bipolar disorder (BD) and major depressive disorder (MDD). However, changes in intrinsic brain functional connectivity dynamics of striato-cortical circuitry have not been investigated in BD and MDD. This study aimed to investigate the shared and specific patterns of dynamic functional connectivity (dFC) variability of striato-cortical circuitry in BD and MDD.

METHODS

Brain resting-state functional magnetic resonance imaging data were acquired from 128 patients with unmedicated BD II (current episode depressed), 140 patients with unmedicated MDD, and 132 healthy controls (HCs). Six pairs of striatum seed regions were selected: the ventral striatum inferior (VSi) and the ventral striatum superior (VSs), the dorsal-caudal putamen (DCP), the dorsal-rostral putamen (DRP), and the dorsal caudate and the ventral-rostral putamen (VRP). The sliding-window analysis was used to evaluate dFC for each seed.

RESULTS

Both BD II and MDD exhibited increased dFC variability between the left DRP and the left supplementary motor area, and between the right VRP and the right inferior parietal lobule. The BD II had specific increased dFC variability between the right DCP and the left precentral gyrus compared with MDD and HCs. The MDD had increased dFC variability between the left VSi and the left medial prefrontal cortex compared with BD II and HCs.

CONCLUSIONS

The patients with BD and MDD shared common dFC alteration in the dorsal striatal-sensorimotor and ventral striatal-cognitive circuitries. The patients with MDD had specific dFC alteration in the ventral striatal-affective circuitry.

Differences in mitochondrial DNA copy number between patients with bipolar I and II disorders

Mitochondria play a critical role in energy metabolism. Genetic, postmortem brain, and brain imaging studies of bipolar disorder (BD) patients indicated that mitochondrial dysfunction might explain BD pathophysiology. Mitochondrial function can be indirectly evaluated by measuring mitochondrial DNA (mtDNA) copy numbers. We recruited 186 bipolar I disorder (BD1) and 95 bipolar II disorder (BD2) patients, and age- and sex-matched controls. MtDNA copy numbers in peripheral blood cells were measured via quantitative polymerase chain reaction. We explored parameters (including age and clinical features) that might affect mtDNA copy numbers. We found that BD1 patients had a lower mtDNA copy number than controls and that mtDNA copy number was negatively associated with the number of mood episodes. BD2 patients had a higher mtDNA copy number than controls. Thus, changes in mitochondrial function may influence BD pathophysiology. The opposite directions of the association with mtDNA copy number in BD1 and BD2 patients suggests that the difference in pathophysiology may be associated with mitochondrial function.

Insula activity in resting-state differentiates bipolar from unipolar depression: a systematic review and meta-analysis

Symptomatic overlap of depressive episodes in bipolar disorder (BD) and major depressive disorder (MDD) is a major diagnostic and therapeutic problem. Mania in medical history remains the only reliable distinguishing marker which is problematic given that episodes of depression compared to episodes of mania are more frequent and predominantly present at the beginning of BD. Resting-state functional magnetic resonance imaging (rs-fMRI) is a non-invasive, task-free, and well-tolerated method that may provide diagnostic markers acquired from spontaneous neural activity. Previous rs-fMRI studies focused on differentiating BD from MDD depression were inconsistent in their findings due to low sample power, heterogeneity of compared samples, and diversity of analytical methods. This meta-analysis investigated resting-state activity differences in BD and MDD depression using activation likelihood estimation. PubMed, Web of Science, Scopus and Google Scholar databases were searched for whole-brain rs-fMRI studies which compared MDD and BD currently depressed patients between Jan 2000 and August 2020. Ten studies were included, representing 234 BD and 296 MDD patients. The meta-analysis found increased activity in the left insula and adjacent area in MDD compared to BD. The finding suggests that the insula is involved in neural activity patterns during resting-state that can be potentially used as a biomarker differentiating both disorders.

Characteristics of temporal dynamics of intrinsic brain activity in unmedicated bipolar disorder with suicidality

BACKGROUND

Bipolar disorder is associated with a high risk of suicide. Routine neuroimaging examination exhibited that bipolar disorder with suicidality was associated with brain structural and functional changes. However, the alterations of brain dynamics have still remained elusive.

PURPOSE

To investigate the alterations of brain dynamics in unmedicated bipolar disorder II depression with suicidality and predict the severity of suicidality.

MATERIALS AND METHODS

This prospective study included 106 bipolar disorder II participants (20 with suicidal attempt, 35 with suicidal ideation, 51 without suicidal ideation) and 50 healthy controls who underwent resting-state functional magnetic resonance imaging between February 2016 and December 2017. We first used sliding window analysis to evaluate the dynamic amplitude of low-frequency fluctuations. Then, we predicted the severity of suicidality using a multivariate regression model.

RESULTS

One-way analysis of covariance revealed that the dynamic amplitude of low-frequency fluctuations in the right temporal pole, inferior temporal gyrus, superior temporal gyrus and the bilateral precuneus/posterior cingulate cortex was significantly different among the four groups. Post hoc pairwise comparisons revealed that dynamic amplitude of low-frequency fluctuations was remarkably decreased in the bilateral precuneus/posterior cingulate cortex in the three bipolar disorder II groups compared with that in healthy controls group. Increased dynamic amplitude of low-frequency fluctuations was found in the right superior temporal gyrus and inferior temporal gyrus in the suicidal attempt group compared with that in the other groups, and in the right temporal pole in the suicidal attempt group compared with that in the suicidal ideation and healthy controls groups. Importantly, these temporal variabilities could be used to predict the severity of suicidality (r = 0.330, p = 0.036), whereas static amplitude of low-frequency fluctuations couldn't (r = -0.050, p = 0.532).

CONCLUSION

Our findings indicated that alterations of temporal variability in the precuneus/posterior cingulate cortex are such a common feature of bipolar disorder patients. Besides, the severity of suicidality could be predicted by the dynamic amplitude of low-frequency fluctuations abnormalities rather than static amplitude of low-frequency fluctuations abnormalities, which is the first evidence of dynamic brain alterations in bipolar disorder patients with suicidality. The proposed predictive model may be advantageous for clinical applications.

Altered ethanolamine plasmalogen and phosphatidylethanolamine levels in blood plasma of patients with bipolar disorder

AIM

Ethanolamine-containing phospholipids are synthesized in endoplasmic reticulum (ER) and mitochondria. ER stress and mitochondrial dysfunction have been implicated in bipolar disorder (BP). In this study, we aimed to examine the relationship of ethanolamine plasmalogen (PLE) and phosphatidylethanolamine (PTE) levels in blood plasma with BP.

METHODS

Plasma PLE and PTE levels were compared between 34 patients with BP (DSM-IV) and 38 healthy control participants matched for age, sex, and ethnicity (Japanese). Furthermore, the relationships of plasma PLE and PTE levels with clinical variables were explored.

RESULTS

Plasma PLE levels were significantly lower in patients with BP than in healthy controls (P = 0.0033). In subgroup analyses, plasma PLE levels were significantly lower in patients with BP type I (BP I) than in healthy controls (P = 0.0047); furthermore, plasma PTE levels were significantly lower in patients with BP I than in controls (P = 0.016) and patients with BP type II (BP II) (P = 0.010). Receiver-operating characteristic curve analysis revealed that the discriminatory power of plasma PTE levels for distinguishing between BP I and II was fair (area under the curve = 0.78; P = 0.0095). There were no significant correlations of plasma PLE or PTE levels with depression or manic symptoms in patients.

CONCLUSIONS

Plasma PLE and PTE levels were associated with BP I, but not with BP II. Moreover, plasma PTE levels differed between patients with BP I and II. Our findings highlight the importance of ethanolamine phospholipids in the pathophysiology of BP, especially BP I.

Abnormal resting-state regional homogeneity in unmedicated bipolar II disorder

BACKGROUND

Previous studies demonstrated that patients with bipolar disorder (BD) exhibited abnormal neural activity in multiple brain regions. However, no study has been conducted to identify regional intrinsic neural activity changes in BD II. In the present study, we used the regional homogeneity (ReHo) approach to explore the regional abnormal neural activity in bipolar II disorder METHODS: One hundred unmedicated patients with BD II depression and 100 healthy controls (HC) underwent the resting-state functional magnetic resonance imaging. The ReHo values of each voxel was calculated in the whole brain. The two-sample t-test and threshold-free cluster enhancement (TFCE) correction were applied for the ReHo analysis.

RESULTS

Compared with the HC group, the BD II group showed significantly decreased ReHo in the left orbitofrontal cortex, and increased ReHo in the right precentral gyrus, right supplementary motor area and bilateral middle occipital gyrus (P < .05, TFCE corrected).

LIMITATIONS

This study lacks the evidence of brain structural changes, and used the cross-sectional design which did not explore local alterations of remitted and manic patients.

CONCLUSION

Our findings revealed abnormal local intrinsic neural activity during resting state which may contribute to the pathophysiology of bipolar II disorder. Particularly the disrupted balance between the prefrontal cortex and primary sensorimotor regions provides evidence for the unique pathological mechanism underlying BD.

Disrupted functional connectivity within the default mode network and salience network in unmedicated bipolar II disorder

BACKGROUND

Recent studies demonstrate that functional disruption in resting-state networks contributes to cognitive and affective symptoms of bipolar disorder (BD), however, the functional connectivity (FC) pattern underlying BD II depression within the default mode network (DMN), salience network (SN), and frontoparietal network (FPN) is still not well understood. The primary aim of this study was to explore whether the pathophysiology of BD II derived from the pattern of FC within the DMN, SN, and FPN by using seed-based FC approach of resting-state functional magnetic resonance imaging (rs-fMRI).

METHODS

Ninety-six BD II patients and 100 HCs underwent rs-fMRI and three-dimensional structural data acquisition. All patients were either drug naive or unmedicated for at least 6 months. The following four regions of interest were used to conduct seed-based FC: the left posterior cingulate cortex (PCC) seed to probe the DMN, the left subgenual anterior cingulate cortex (sgACC) and amygdala seeds to probe the SN, the left dorsal lateral prefrontal cortex (dlPFC) seed to probe the FPN.

RESULTS

Compared with HCs, patients with BD II demonstrated hypoconnectivity of the left PCC to the bilateral medial prefrontal cortex (mPFC) and bilateral precuneus/PCC, and of the left sgACC to the right inferior temporal gyrus (ITG); nevertheless, the left amygdala and dlPFC had no within-network hypo- or hyperconnectivity to any other SN and FPN regions.

CONCLUSION

Our findings suggest that disrupted FC is located in the DMN and SN, especially in the PCC-mPFC and precuneus/PCC, and sgACC-ITG connectivity in BD II patients.

Neurochemical differences between bipolar disorder type I and II in superior temporal cortices: A proton magnetic resonance spectroscopy study

BACKGROUND

Despite the diagnostic challenges in categorizing bipolar disorder subtypes, bipolar I and II disorders (BD-I and BD-II respectively) are valid indices for researchers. Subtle neurobiological differences may underlie clinical differences between mood disorder subtypes. The aims of this study were to investigate neurochemical differences between bipolar disorder subtypes.

METHODS

Euthymic BD-II patients (n = 21) are compared with BD-I (n = 28) and healthy comparison subjects (HCs, n = 30). Magnetic Resonance Imaging (MRI) and proton spectroscopy (¹H MRS) were performed on a 3T Siemens Tim Trio system. MRS voxels were located in the left/right superior temporal cortices, and spectra acquired with the single voxel Point REsolved Spectroscopy Sequence (PRESS). The spectroscopic data were analyzed with LCModel (Version 6.3.0) software.

RESULTS

There were significant differences between groups in terms of glutamate [F = 6.27, p = 0.003], glutamate + glutamine [F = 6.08, p = 0.004], inositol containing compounds (Ino) (F = 9.25, p < 0.001), NAA [F = 7.63, p = 0.001] and creatine + phosphocreatine [F = 11.06, p < 0.001] in the left hemisphere and Ino [F = 5.65, p = 0.005] in the right hemisphere. Post-hoc comparisons showed that the BD-I disorder group had significantly lower metabolite levels in comparison to the BD-II and the HC groups.

LIMITATIONS

This was a cross-sectional study with a small sample size. In addition, patients were on various psychotropic medications, which may have impacted the results.

CONCLUSIONS

Neurochemical levels, in the superior temporal cortices, measured with ¹H-MRS discriminated between BD-II and BD-I. Although further studies are needed, one may speculate that the superior temporal cortices (particularly left hemispheric) play a critical role, whose pathology may be related to subtyping bipolar disorder.

Disrupted Cerebellar Connectivity With the Central Executive Network and the Default-Mode Network in Unmedicated Bipolar II Disorder

Objective: Bipolar disorder (BD) is a common psychiatric disease. Although structural and functional abnormalities of the cerebellum in BD patients have been reported by recent neuroimaging studies, the cerebellar-cerebral functional connectivity (FC) has not yet been examined. The present study aims to investigate the FC between the cerebellum and cerebrum, particularly the central executive network (CEN) and the default-mode network (DMN) in bipolar II disorder (BD II). Methods: Ninety-four patients with unmedicated BD II depression and 100 healthy controls (HCs) underwent the resting-state functional magnetic resonance imaging. Seed-based connectivity analyses were performed using cerebellar seeds previously identified as being involved in the CEN (bilateral Crus Ia) and DMN (bilateral Crus Ib). Results: Compared with HCs, BD II depression patients appeared decreased FC in the right Crus Ia-left dorsal lateral prefrontal cortex (dlPFC) and -left anterior cingulate cortex (ACC), the right Crus Ib-left medial prefrontal cortex (mPFC), -left middle temporal gyrus (MTG), and -left inferior temporal gyrus (ITG). No altered FC between the left Crus Ia or Crus Ib and the cerebral regions was found. Conclusions: Patients with BD II depression showed disrupted FC between the cerebellum and the CEN (mainly in the left dlPFC and ACC) and DMN (mainly in the left mPFC and temporal lobe), suggesting the significant role of the cerebellum-CEN and -DMN connectivity in the pathogenesis of BD.

Blink reflex under external emotional-stimuli in bipolar I and II disorders

Bipolar disorder types I (BD I) and II (BD II) might present different cortico-brainstem circuit dysfunctions under external emotions, which might be reflected by the blink reflex. We therefore invited 32 BD I and 23 BD II patients, and 46 healthy volunteers to answer the Mood Disorder Questionnaire, the Hypomania Checklist-32, and the Plutchik - van Praag Depression inventory, and to undergo the blink reflex test under external emotions (emotional pictures plus sounds) of Disgust, Erotica, Fear, Happiness, and Sadness. Compared to healthy controls, BD I showed prolonged R2/R2' latencies under most emotions, and their PVP scores were negatively correlated with the areas under curve (AUCs) of R2 and R2' under Erotica; and BD II showed reduced R2/R2' AUCs under all emotions. Moreover, R2' AUCs under Disgust, Fear, and Happiness were significantly reduced in BD II than those in BD I. Our results have shown that, irrespective of patients' on-going affective states, the R2/R2' components were delayed in BD I but suppressed in BD II under most external emotions. Our study provides some hints to distinguish the two types of bipolar disorder, referring to the cortico-brainstem circuit dysfunctions under external emotions.

Inhibitory brainstem reflexes under external emotional-stimuli in bipolar I and II disorders

BACKGROUND

Bipolar disorder types I (BD I) and II (BD II) might present different dysfunctions of the cortex and brainstem, as reflected by the second exteroceptive suppression period of temporalis muscle activity (ES2) under different stimuli of external emotions.

METHODS

This study included 30 BD I and 20 BD II patients, and 40 healthy volunteers. All participants were invited to answer the Mood Disorder Questionnaire, the Hypomania Checklist-32, and the Plutchik-van Praag Depression inventory, as well as to undergo the ES2 test under external emotional-stimuli (emotional pictures plus sounds) of Disgust, Erotica, Fear, Happiness, and Sadness.

RESULTS

The scale scores were elevated in both patient groups, but were not correlated with ES2 parameters. Compared to healthy controls, BD I showed prolonged ES2 latency under Erotica, and their perceived happiness and sadness intensities were negatively correlated with the respective ES2 durations, while BD II showed prolonged ES2 latencies under Disgust and Happiness, and shortened ES2 durations under Disgust, Happiness and Sadness. Moreover, ES2 duration under Sadness was significantly shorter in BD II than that in BD I.

CONCLUSIONS

The cortico-brainstem inhibitory dysfunctions in BD I and BD II was different, and this difference was independent of the patient's ongoing emotions. Our study thus provides some hints to distinguish the two types of bipolar disorders.

Relationship between personality disorder functioning styles and the emotional states in bipolar I and II disorders

Background

Bipolar disorder types I (BD I) and II (BD II) behave differently in clinical manifestations, normal personality traits, responses to pharmacotherapies, biochemical backgrounds and neuroimaging activations. How the varied emotional states of BD I and II are related to the comorbid personality disorders remains to be settled.

Methods

We therefore administered the Plutchick – van Praag Depression Inventory (PVP), the Mood Disorder Questionnaire (MDQ), the Hypomanic Checklist-32 (HCL-32), and the Parker Personality Measure (PERM) in 37 patients with BD I, 34 BD II, and in 76 healthy volunteers.

Results

Compared to the healthy volunteers, patients with BD I and II scored higher on some PERM styles, PVP, MDQ and HCL-32 scales. In BD I, the PERM Borderline style predicted the PVP scale; and Antisocial predicted HCL-32. In BD II, Borderline, Dependant, Paranoid (-) and Schizoid (-) predicted PVP; Borderline predicted MDQ; Passive-Aggressive and Schizoid (-) predicted HCL-32. In controls, Borderline and Narcissistic (-) predicted PVP; Borderline and Dependant (-) predicted MDQ.

Conclusion

Besides confirming the different predictability of the 11 functioning styles of personality disorder to BD I and II, we found that the prediction was more common in BD II, which might underlie its higher risk of suicide and poorer treatment outcome.

The neurobiology of bipolar disorder: identifying targets for specific agents and synergies for combination treatment

Bipolar disorder (BD) is a chronic psychiatric illness described by severe changes in mood. Extensive research has been carried out to understand the aetiology and pathophysiology of BD. Several hypotheses have been postulated, including alteration in genetic factors, protein expression, calcium signalling, neuropathological alteration, mitochondrial dysfunction and oxidative stress in BD. In the following paper, we will attempt to integrate these data in a manner which is to understand targets of treatment and how they may be, in particular, relevant to combination treatment. In summary, the data suggested that BD might be associated with neuronal and glial cellular impairment in specific brain areas, including the prefrontal cortex. From molecular and genetics: (1) alterations in dopaminergic system, through catechol-O-aminotransferase; (2) decreased expression and polymorphism on brain-derived neurotrophic factor; (3) alterations cyclic-AMP responsive element binding; (4) dysregulation of calcium signalling, including genome-wide finding for voltage-dependent calcium channel α-1 subunit are relevant findings in BD. Future studies are now necessary to understand how these molecular pathways interact and their connection to the complex clinical manifestations observed in BD.

Exploring the associations between genetic variants in genes encoding for subunits of calcium channel and subtypes of bipolar disorder

BACKGROUND

Associations of two voltage-gated calcium channel (Cav) genes, CACNA1C and CACNB2, were identified for bipolar disorder (BP) in different ethnic groups in recent genome-wide association studies. The current study aimed to evaluate the associations of several Cav genes and subtypes of BP in genetically more homogeneous Taiwanese samples. Additionally, we tested interaction effects among genes that encode for α1, β and γ-subunits of calcium channel.

METHODS

8 Cav genes were selected based on evidence in prior association studies and significant linkage regions for BP. 280 BP patients and 200 controls were recruited. Multifactor dimensionality reduction was performed for interaction testing in these discovery samples. Replication was conducted for two markers using additional 495 Taiwanese cases and 1341 controls.

RESULTS

Weak associations for CACNA1C (rs10848635), CACNA1E (rs10848635), CACNB2 (rs11013860), and CACNG2 (rs2284018) genes were observed. Joint analysis of four markers revealed higher accumulative risk with increasing numbers of risk genotypes an individual endorsed for BP-I (Ptrend=0.006) and BP-II (Ptrend=0.017) disorders. Combined analysis with independent replication samples further supported the association of rs11013860 in CACNB2 with BP subtype I (P=1×10(-6)). Suggestive interactions were found between genes encoded for different subunits of calcium channel (α1, β, and γ).

LIMITATIONS

Moderate sample size and incomplete markers coverage for the chosen Cav genes.

CONCLUSIONS

Our results support the involvement of different calcium channel genes in bipolar illness, in particular the beta-subunit in the Asian population. Further investigation of functional property of these genes can contribute on understanding the etiological mechanisms of bipolar illness.

Gender-specific association of the SLC6A4 and DRD2 gene variants in bipolar disorder

Findings on the association between the risk for developing bipolar disorder and the functions of the serotonin transporter-linked polymorphic region gene (5-HTTLPR) and dopamine D2 receptor gene (DRD2) variants are contradictory. One explanation for this is that a gender difference may exist for genetic contributions. We compared the gender-related main effects and the gene-to-gene interaction between serotonin transporter gene (SLC6A4) and DRD2 in adult male and female patients with bipolar I (BP-I) and bipolar II (BP-II) disorder. Patients with BP-I (n = 400) and BP-II (n = 493), and healthy controls (n = 442) were recruited from Taiwan's Han Chinese population. The genotypes of the 5-HTTLPR and DRD2 Taq-IA polymorphisms were determined using polymerase chain reaction-restriction fragment length polymorphism analysis. Logistic regression analysis showed a significant gender-specific association of the DRD2 A1/A1 and the 5-HTTLPR S/S, S/LG , and LG/LG (S+) (p = 0.01) genotypes in men with BP-I (p = 0.002 and 0.01, respectively) and BP-II (p = 0.001 and 0.007, respectively), but not in women. A significant interaction for the DRD2 A1/A1 and 5-HTTLPR S+ polymorphisms was also found only in men with BP-I and BP-II (p = 0.003 and 0.001, respectively). We provide preliminary evidence for a gender-specific effect of the SLC6A4 and DRD2 gene variants for the risk of BP-I and of BP-II. We also found gender-specific interaction between 5-HTTLPR and DRD2 Taq-IA polymorphisms in patients with bipolar disorder.

P50 sensory gating is a trait marker of the bipolar spectrum

Sensory gating deficit, assessed by a paired auditory stimulus paradigm (P50), has been reported as a stable marker of schizophrenia. The aim of this study was to explore if this neurophysiological disturbance also fulfilled stability criteria in the bipolar disorder (BD) spectrum bipolar, as state independence is one of the main points to be considered as a potential endophenotype of the illness. The P50 evoked potential was studied in 95 healthy controls and 126 bipolar euthymic patients. Euthymia was established according to Van Gorp's criteria. Bipolar I and II subtypes were analyzed separately. The influence of a lifetime history of psychoses was also evaluated in the clinical sample. P50 gating was deficitary in all the subsamples of patients relative to healthy comparison subjects. Bipolar I patients with and without a history of psychosis showed higher P50 ratios than the other subgroups of patients, although these differences were not significant. P50 alterations were mainly due to a deficit in the inhibition of the second wave (test wave or S2) amplitude.

CONCLUSIONS

The findings suggest that this inhibitory deficit can be considered characteristic of the illness and that the intensity of the gating abnormality varies according to the severity of BD.

Genetic and neurocognitive foundations of emotion abnormalities in bipolar disorder

INTRODUCTION

Bipolar Disorder (BD) is a serious mood disorder, the aetiology of which is still unclear. The disorder is characterised by extreme mood variability in which patients fluctuate between markedly euphoric, irritable, and elevated states to periods of severe depression. The current research literature shows that BD patients demonstrate compromised neurocognitive ability in addition to these mood symptoms. Viable candidate genes implicated in neurocognitive and socioemotional processes may explain the development of these core emotion abnormalities. Additionally, links between faulty neurocognition and impaired socioemotional ability complement genetic explanations of BD pathogenesis. This review examines associations between cognition indexing prefrontal neural regions and socioemotional impairments including emotion processing and regulation. A review of the effect of COMT and TPH2 on these functions is also explored.

METHODS

Major computer databases including PsycINFO, Google Scholar, and Medline were consulted in order to conduct a comprehensive review of the genetic and cognitive literature in BD.

RESULTS

This review determines that COMT and TPH2 genetic variants contribute susceptibility to abnormal prefrontal neurocognitive function which oversees the processing and regulation of emotion. This provides for greater understanding of some of the emotional and cognitive symptoms in BD.

CONCLUSIONS

Current findings in this direction show promise, although the literature is still in its infancy and further empirical research is required to investigate these links explicitly.

COMT and BDNF interacted in bipolar II disorder not comorbid with anxiety disorder

Bipolar disorder (BP), especially bipolar II disorder (BP-II), is highly comorbid with anxiety disorder (AD). Monoaminergic dysfunction has been implicated in the pathogenesis of BP, it may be important to investigate genes such as the catechol-O-methyltransferase (COMT), involved in monoamine metabolism and brain-derived neurotrophic factor (BDNF) genes, modulating the monoamine system. We therefore examined the association of the COMT Val158Met and BDNF Val66Met polymorphisms with BP-II with and without comorbidity of AD, and possible interactions between these genes. Seven hundred and seventy-one participants were recruited: 314 with bipolar-II without AD, 117 with bipolar-II with AD, and 340 healthy controls. The genotypes of the COMT and BDNF polymorphisms were determined using polymerase chain reactions plus restriction fragment length polymorphism analysis. Logistic regression analysis showed a significant effect of the COMT and the BDNF polymorphisms, and a significant interaction effect for the Val/Val genotypes of the BDNF Val66Met polymorphism and the COMsT Val158Met Val/Met and Met/Met genotypes (P=0.007, 0.048) discriminated between BP-II without AD patients and controls. Our findings provide initial evidence that the COMT and BDNF genes interact in bipolar-II without AD. Our findings suggest the involvement of dopaminergic pathway in the pathogenesis of bipolar-II.

A mutation in CLOCK leads to altered dopamine receptor function

Mice with a mutation in the Clock gene (ClockΔ19) have a number of behavioral phenotypes that suggest alterations in dopaminergic transmission. These include hyperactivity, increased exploratory behavior, and increased reward value for drugs of abuse. However, the complex changes in dopaminergic transmission that underlie the behavioral abnormalities in these mice remain unclear. Here we find that a loss of CLOCK function increases dopamine release and turnover in striatum as indicated by increased levels of metabolites HVA and DOPAC, and enhances sensitivity to dopamine receptor antagonists. Interestingly, this enlarged dopaminergic tone results in downstream changes in dopamine receptor (DR) levels with a surprising augmentation of both D1- and D2-type DR protein, but a significant shift in the ratio of D1 : D2 receptors in favor of D2 receptor signaling. These effects have functional consequences for both behavior and intracellular signaling, with alterations in locomotor responses to both D1-type and D2-type specific agonists and a blunted response to cAMP activation in the ClockΔ19 mutants. Taken together, these studies further elucidate the abnormalities in dopaminergic transmission that underlie mood, activity, and addictive behaviors.

Dopamine receptor DRD3 codes for trait aggression as Mendelian recessive

The dopamine receptor gene DRD3 and in particular the single nucleotide polymorphism Ser9Gly has been extensively investigated and found to have potential association with a wide variety of conditions. These include essential tremor, unipolar and bipolar depression, as well as a loose association with schizophrenia. Evaluation of (1) these known associations with DRD3, (2) the recent finding of Costas and colleagues that a haplotype containing Ser-9 is associated with protection from schizophrenia, and (3) an extant trait model of personality, leads to the hypothesis that an allele DRD3/Ser codes for trait aggression by Mendelian recessive inheritance. The implications of this hypothesis are that (1) DRD3 is a pleiotropic gene having allelic polymorphism related to both behavior and disease, and (2) models of personality based on genetic traits hold promise. In the area of schizophrenia, the hypothesis implies that schizophrenic patients can be divided into two broad classes: those having genotype DRD3/Ser/Ser and those who lack this homozygosity. The hypothesis of the association of DRD3 with trait aggression could be readily evaluated by testing groups of healthy individuals by personality inventory focused on aggression and by biochemical assay of neurotransmitter levels.