Neuroanatomical correlates of genetic risk for bipolar disorder: A voxel-based morphometry study in bipolar type I patients and healthy first degree relatives

Larger putamen in individuals at risk and with manifest bipolar disorder

BACKGROUND

Individuals at risk for bipolar disorder (BD) have a wide range of genetic and non-genetic risk factors, like a positive family history of BD or (sub)threshold affective symptoms. Yet, it is unclear whether these individuals at risk and those diagnosed with BD share similar gray matter brain alterations.

METHODS

In 410 male and female participants aged 17-35 years, we compared gray matter volume (3T MRI) between individuals at risk for BD (as assessed using the EPIbipolar scale; n = 208), patients with a DSM-IV-TR diagnosis of BD (n = 87), and healthy controls (n = 115) using voxel-based morphometry in SPM12/CAT12. We applied conjunction analyses to identify similarities in gray matter volume alterations in individuals at risk and BD patients, relative to healthy controls. We also performed exploratory whole-brain analyses to identify differences in gray matter volume among groups. ComBat was used to harmonize imaging data from seven sites.

RESULTS

Both individuals at risk and BD patients showed larger volumes in the right putamen than healthy controls. Furthermore, individuals at risk had smaller volumes in the right inferior occipital gyrus, and BD patients had larger volumes in the left precuneus, compared to healthy controls. These findings were independent of course of illness (number of lifetime manic and depressive episodes, number of hospitalizations), comorbid diagnoses (major depressive disorder, attention-deficit hyperactivity disorder, anxiety disorder, eating disorder), familial risk, current disease severity (global functioning, remission status), and current medication intake.

CONCLUSIONS

Our findings indicate that alterations in the right putamen might constitute a vulnerability marker for BD.

White and gray matter alterations in bipolar I and bipolar II disorder subtypes compared with healthy controls - exploring associations with disease course and polygenic risk

Patients with bipolar disorder (BD) show alterations in both gray matter volume (GMV) and white matter (WM) integrity compared with healthy controls (HC). However, it remains unclear whether the phenotypically distinct BD subtypes (BD-I and BD-II) also exhibit brain structural differences. This study investigated GMV and WM differences between HC, BD-I, and BD-II, along with clinical and genetic associations. N = 73 BD-I, n = 63 BD-II patients and n = 136 matched HC were included. Using voxel-based morphometry and tract-based spatial statistics, main effects of group in GMV and fractional anisotropy (FA) were analyzed. Associations between clinical and genetic features and GMV or FA were calculated using regression models. For FA but not GMV, we found significant differences between groups. BD-I patients showed lower FA compared with BD-II patients (ptfce-FWE = 0.006), primarily in the anterior corpus callosum. Compared with HC, BD-I patients exhibited lower FA in widespread clusters (ptfce-FWE < 0.001), including almost all major projection, association, and commissural fiber tracts. BD-II patients also demonstrated lower FA compared with HC, although less pronounced (ptfce-FWE = 0.049). The results remained unchanged after controlling for clinical and genetic features, for which no independent associations with FA or GMV emerged. Our findings suggest that, at a neurobiological level, BD subtypes may reflect distinct degrees of disease expression, with increasing WM microstructure disruption from BD-II to BD-I. This differential magnitude of microstructural alterations was not clearly linked to clinical and genetic variables. These findings should be considered when discussing the classification of BD subtypes within the spectrum of affective disorders.

Functional Alterations in Patients with Bipolar Disorder and Their Unaffected First-Degree Relatives: Insight from Genetic, Epidemiological, and Neuroimaging Data

Bipolar disorder (BD) profoundly affects cognitive and psychosocial functioning, leading to a significant illness burden on patients and their families. Genetic factors are predominant in the onset of bipolar disorder and functional impairments. This disorder exhibits a strong family aggregation, with heritability estimates reaching up to 80%. Individuals with BD often experience impaired functioning, especially in significant areas such as physical performance, sleep, cognition, interpersonal interactions, socioeconomic status, family and marital relationships, work and school performance, well-being, and life expectancy. However, patients with different subtypes exhibit significant heterogeneity in social functioning, cognition, and creativity levels. There are notable differences in psychosocial and cognitive function in their unaffected first-degree relatives (UFR) who do not suffer but may carry susceptibility genes compared to healthy control (HC) without a family history. The observations indicate common genetic structures between BD patients and their UFR, which results in varying degrees of functional abnormalities. Therefore, this article mainly provides evidence on cognition, creativity, and psychosocial functioning in patients with BD and their UFR to provide a more comprehensive understanding of this critical topic in the field of BD. By integrating various findings, including clinical data and neuroimaging studies, our article aims to provide insights and valuable information for a deeper exploration of the pathogenesis of BD and the development of more targeted therapeutic strategies in the future.

Cerebellar morphological differences and associations with extrinsic factors in bipolar disorder type I

BACKGROUND

The neural underpinnings of bipolar disorder (BD) remain poorly understood. The cerebellum is ideally positioned to modulate emotional regulation circuitry yet has been understudied in BD. Literature suggests differences in cerebellar activity and metabolism in BD, however findings on structural differences remain contradictory. Potential reasons include combining BD subtypes, small sample sizes, and potential moderators such as genetics, adverse childhood experiences (ACEs), and pharmacotherapy.

METHODS

We collected 3 T MRI scans from participants with (N = 131) and without (N = 81) BD type I, as well as blood and questionnaires. We assessed differences in cerebellar volumes and explored potentially influential factors.

RESULTS

The cerebellar cortex was smaller bilaterally in participants with BD. Polygenic propensity score did not predict any cerebellar volumes, suggesting that non-genetic factors may have greater influence on the cerebellar volume difference we observed in BD. Proportionate cerebellar white matter volumes appeared larger with more ACEs, but this may result from reduced ICV. Time from onset and symptom burden were not associated with cerebellar volumes. Finally, taking sedatives was associated with larger cerebellar white matter and non-significantly larger cortical volume.

LIMITATIONS

This study was cross-sectional, limiting interpretation of possible mechanisms. Most of our participants were White, which could limit the generalizability. Additionally, we did not account for potential polypharmacy interactions.

CONCLUSIONS

These findings suggest that external factors, such as sedatives and childhood experiences, may influence cerebellum structure in BD and may mask underlying differences. Accounting for such variables may be critical for consistent findings in future studies.

Neuroanatomical and functional substrates of the hypomanic personality trait and its prediction on aggression

Hypomanic personality manifests a close link with several psychiatric disorders and its abnormality is a risk indicator for developing bipolar disorders. We systematically investigated the potential neuroanatomical and functional substrates underlying hypomanic personality trait (HPT) and its sub-dimensions (i.e., Social Vitality, Mood Volatility, and Excitement) combined with structural and functional imaging data as well as their corresponding brain networks in a large non-clinical sample across two studies (n = 464). Behaviorally, HPT, specifically Mood Volatility and Excitement, was positively associated with aggressive behaviors in both studies. Structurally, sex-specific morphological characteristics were further observed in the motor and top-down control networks especially for Mood Volatility, although HPT was generally positively associated with grey matter volumes (GMVs) in the prefrontal, temporal, visual, and limbic systems. Functionally, brain activations related to immediate or delayed losses were found to predict individual variability in HPT, specifically Social Vitality and Excitement, on the motor and prefrontal-parietal cortices. Topologically, connectome-based prediction model analysis further revealed the predictive role of individual-level morphological and resting-state functional connectivity on HPT and its sub-dimensions, although it did not reveal any links with general brain topological properties. GMVs in the temporal, limbic (e.g., amygdala), and visual cortices mediated the effects of HPT on behavioral aggression. These findings suggest that the imbalance between motor and control circuits may be critical for HPT and provide novel insights into the neuroanatomical, functional, and topological mechanisms underlying the specific temperament and its impacts on aggression.

Frequency and imaging correlates of neuropsychiatric symptoms in Progressive Supranuclear Palsy

Neuropsychiatric symptoms are intrinsic to Progressive Supranuclear Palsy (PSP) and a spoonful of studies investigated their imaging correlates. Describe (I) the frequency and severity of neuropsychiatric symptoms in PSP and (II) their structural imaging correlates. Twenty-six PSP patients underwent Neuropsychiatric Inventory (NPI) and brain 3D T1-weighted MRI. Spearman's rho with Bonferroni correction was used to investigate correlations between NPI scores and volumes of gray matter regions. More than 80% of patients presented at least one behavioral symptom of any severity. The most frequent and severe were depression/dysphoria, apathy, and irritability/lability. Significant relationships were found between the severity of irritability and right pars opercularis volume (p < 0.001) as well as between the frequency of agitation/aggression and left lateral occipital volume (p < 0.001). Depression, apathy, and irritability are the most common neuropsychiatric symptoms in PSP. Moreover, we found a relationship between specific positive symptoms as irritability and agitation/aggression and greater volume of the right pars opercularis cortex and lower volume of the left occipital cortex, respectively, which deserve further investigations.

Mania-related effects on structural brain changes in bipolar disorder - a narrative review of the evidence

Cross-sectional neuroimaging studies show that bipolar disorder is associated with structural brain abnormalities, predominantly observed in prefrontal and temporal cortex, cingulate gyrus, and subcortical regions. However, longitudinal studies are needed to elucidate whether these abnormalities presage disease onset or are consequences of disease processes, and to identify potential contributing factors. Here, we narratively review and summarize longitudinal structural magnetic resonance imaging studies that relate imaging outcomes to manic episodes. First, we conclude that longitudinal brain imaging studies suggest an association of bipolar disorder with aberrant brain changes, including both deviant decreases and increases in morphometric measures. Second, we conclude that manic episodes have been related to accelerated cortical volume and thickness decreases, with the most consistent findings occurring in prefrontal brain areas. Importantly, evidence also suggests that in contrast to healthy controls, who in general show age-related cortical decline, brain metrics remain stable or increase during euthymic periods in bipolar disorder patients, potentially reflecting structural recovering mechanisms. The findings stress the importance of preventing manic episodes. We further propose a model of prefrontal cortical trajectories in relation to the occurrence of manic episodes. Finally, we discuss potential mechanisms at play, remaining limitations, and future directions.

Association of childhood trauma with cognitive impairment and structural brain alterations in remitted patients with bipolar disorder

BACKGROUND

Cognitive impairment affects many patients with bipolar disorder (BD). No pro-cognitive treatment with robust efficacy exists partly due to limited insight into underlying neurobiological abnormalities.

METHODS

This magnetic resonance imaging (MRI) study investigates structural neuronal correlates of cognitive impairment in BD by comparing brain measures in a large sample of cognitively impaired versus cognitively intact patients with BD or cognitively impaired patients with major depressive disorder (MDD) and healthy controls (HC). Participants underwent neuropsychological assessments and MRI scans. The cognitively impaired and - intact BD and MDD patient groups were compared with each other and HC regarding prefrontal cortex measures, hippocampus shape/volume, and total cerebral white (WM) and grey matter (GM).

RESULTS

Cognitively impaired BD patients showed lower total cerebral WM volume than HC, which scaled with poorer global cognitive performance and more childhood trauma. Cognitively impaired BD patients also showed lower adjusted GM volume and thickness in the frontopolar cortex than HC but greater adjusted GM volume in the temporal cortex than cognitively normal BD patients. Cognitively impaired BD patients showed decreased cingulate volume than cognitively impaired MDD patients. Hippocampal measures were similar across all groups.

LIMITATIONS

The cross-sectional study design prevented insights into causal relationships.

CONCLUSIONS

Lower total cerebral WM and regional frontopolar and temporal GM abnormalities may constitute structural neuronal correlates of cognitive impairment in BD, of which the WM deficits scale with the degree of childhood trauma. The results deepen the understanding of cognitive impairment in BD and provide a neuronal target for pro-cognitive treatment development.

Neurocognitive Correlates of Cerebellar Volumetric Alterations in Youth with Pediatric Bipolar Spectrum Disorders and Bipolar Offspring

BACKGROUND

Emerging evidence points towards the involvement of the cerebellum in the processing of emotions and pathophysiology of mood disorders. However, cerebellar and related cognitive alterations in youth with pediatric bipolar disorder (PBD) and those at high risk to develop the disorder, such as bipolar offspring (BD-OFF) are not clearly defined.

OBJECTIVE

To investigate cerebellar gray and white matter volumes, cognition, and their relationship in youth with PBD and BD-OFF.

METHODS

Thirty youth (7 to 17 years, inclusive) with PBD, 30 BD-OFF and 40 healthy controls (HC) were recruited. Study participants underwent a computer-based cognitive battery assessing affective processing, executive function, attention, psychomotor speed, and learning. Three-tesla MRI scan was performed to assess cerebellar white and gray matter volumes. Cerebellar segmentation was performed with FreeSurfer. Statistical analyses include between-group differences in cognitive domains, cerebellar gray, and white matter volumes. Relationships between cerebellar volumes and cognitive domains were examined.

RESULTS

Youth with PBD showed greater cerebellar gray matter volumes than both BD-OFF and HC, whereas no differences were present between BD-OFF and HC. Both youth with PBD and BD-OFF showed altered processing of negative emotions and a bias towards positive emotions. In youth with PBD and BD-OFF, greater impairment in the processing of emotions correlated with greater cerebellar gray matter volumes.

CONCLUSION

The present findings corroborate hypotheses on cerebellar involvement in the processing of emotions and the pathophysiology of PBD. The presence of cerebellar dysfunction in BD-OFF is unclear.

A graph theory neuroimaging approach to distinguish the depression of bipolar disorder from major depressive disorder in adolescents and young adults

BACKGROUND

Markers to differentiate depressions of bipolar disorder (BD-Dep) from depressions of major depressive disorder (MDD-Dep), and for more targeted treatments, are critically needed to decrease current high rates of misdiagnosis that can lead to ineffective or potentially deleterious treatments. Distinguishing, and specifically treating the depressions, during the adolescent/young adult epoch is especially important to decrease illness progression and improve prognosis, and suicide, as it is the epoch when suicide thoughts and behaviors often emerge. With differences in functional connectivity patterns reported when BD-Dep and MDD-Dep have been studied separately, this study used a graph theory approach aimed to identify functional connectivity differences in their direct comparison.

METHODS

Functional magnetic resonance imaging whole-brain functional connectivity (Intrinsic Connectivity Distribution, ICD) measures were compared across adolescents/young adults with BD-Dep (n = 28), MDD-Dep (n = 20) and HC (n = 111). Follow-up seed-based connectivity was conducted on regions of significant ICD differences. Relationships with demographic and clinical measures were assessed.

RESULTS

Compared to the HC group, both the BD-Dep and MDD-Dep groups exhibited left-sided frontal, insular, and medial temporal ICD increases. The BD-Dep group had additional right-sided ICD increases in frontal, basal ganglia, and fusiform areas. In seed-based analyses, the BD-Dep group exhibited increased interhemispheric functional connectivity between frontal areas not seen in the MDD-Dep group.

LIMITATIONS

Modest sample size; medications not studied systematically.

CONCLUSIONS

This study supports bilateral and interhemispheric functional dysconnectivity as features of BD-Dep that may differentiate it from MDD-Dep in adolescents/young adults and serve as a target for early diagnosis and treatment strategies.

The inferior frontal gyrus and familial risk for bipolar disorder

Bipolar disorder (BD) is a familial disorder with high heritability. Genetic factors have been linked to the pathogenesis of BD. Relatives of probands with BD who are at familial risk can exhibit brain abnormalities prior to illness onset. Given its involvement in prefrontal cognitive control and in frontolimbic circuitry that regulates emotional reactivity, the inferior frontal gyrus (IFG) has been a focus of research in studies of BD-related pathology and BD-risk mechanism. In this review, we discuss multimodal neuroimaging findings of the IFG based on studies comparing at-risk relatives and low-risk controls. Review of these studies in at-risk cases suggests the presence of both risk and resilience markers related to the IFG. At-risk individuals exhibited larger gray matter volume and increased functional activities in IFG compared with low-risk controls, which might result from an adaptive brain compensation to support emotion regulation as an aspect of psychological resilience. Functional connectivity between IFG and downstream limbic or striatal areas was typically decreased in at-risk individuals relative to controls, which could contribute to risk-related problems of cognitive and emotional control. Large-scale and longitudinal investigations on at-risk individuals will further elucidate the role of IFG and other brain regions in relation to familial risk for BD, and together guide identification of at-risk individuals for primary prevention.

A comparative study of gray matter volumetric alterations in adults with attention deficit hyperactivity disorder and bipolar disorder type I

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) and bipolar disorder type I (BD-Ι) share great overlapping symptoms and are highly comorbid. We aimed to compare and obtain the common and distinct gray matter volume (GMV) patterns in adult patients.

METHOD

We searched four databases to include whole-brain voxel-based morphometry studies and compared the GMV patterns between ADHD and healthy controls (HCs), between BD-I and HCs, and between ADHD and BD-I using anisotropic effect-size signed differential mapping software.

RESULTS

We included 677 ADHD and 452 BD-Ι patients. Compared with HCs, ADHD patients showed smaller GMV in the anterior cingulate cortex (ACC) and supramarginal gyrus but a larger caudate nucleus. Compared with HCs, BD-Ι patients showed smaller GMV in the orbitofrontal cortex, parahippocampal gyrus, and amygdala. No common GMV alterations were found, whereas ADHD showed the smaller ACC and larger amygdala relative to BD-Ι. Subgroup analyses revealed the larger insula in manic patients, which was positively associated with the Young Mania Rating Scale. The decreased median cingulate cortex (MCC) was positively associated with the ages in ADHD, whereas the MCC was negatively associated with the ages in BD-Ι.

LIMITATIONS

All included data were cross-sectional; Potential effects of medication and disease course were not analyzed due to the limited data.

CONCLUSIONS

ADHD showed altered GMV in the frontal-striatal frontal-parietal circuits, and BD-Ι showed altered GMV in the prefrontal-amygdala circuit. These findings could contribute to a better understanding of the neuropathology of the two disorders.

Correlations between peripheral levels of inflammatory mediators and frontolimbic structures in bipolar disorder: an exploratory analysis

BACKGROUND

Altered peripheral immune/inflammatory system and brain volumetric changes have been implicated in the pathophysiology of bipolar disorder (BD). This study aimed to evaluate how peripheral levels of cytokines are related to volumetric brain changes in euthymic patients with BD.

METHODS

Euthymic patients with BD (n = 21) and healthy controls (n = 22) were enrolled in this exploratory study. Blood samples were collected on the same day of clinical assessment and neuroimaging. Cytokines were measured through cytometric bead array method. Neuroimaging data were acquired using a sagittal three-dimensional magnetic resonance imaging T1-weighted fast field echo sequence and was processed using FreeSurfer.

RESULTS

Compared to controls, BD patients had significantly lower volumes in the cingulate, medial-orbitofrontal (MOF) and parahippocampal regions. We found a negative correlation between right MOF volume and interferon-gamma levels (β = -0.431, P = .049) and a positive correlation between interleukin-10 levels and left posterior cingulate volume (β = 0.457, P = .048).

CONCLUSION

Our results support the involvement of inflammatory pathways in structural brain changes in BD.

Gray matter abnormalities and associated familial risk endophenotype in individuals with first-episode bipolar disorder: Evidence from whole-brain voxel-wise meta-analysis

Gray matter abnormalities have been widely reported in individuals with and at familial risk for bipolar disorder (BD). However, inconsistent findings were reported, and whether shared abnormalities exist between at-risk individuals and patients which can represent an endophenotype remained unclear. This meta-analysis aimed at identifying robust patterns of gray matter changes in patients with first-episode BD (FEBD) and associated risk endophenotype of BD. A systematic literature search was performed to identify eligible voxel-based morphometry studies comparing FEBD patients and healthy controls. Findings of included studies were integrated using the Seed-based d Mapping toolbox. Common and distinct patterns of gray matter abnormalities between FEBD patients and unaffected at-risk individuals were explored. A total of 16 VBM studies comparing 411 FEBD patients and 521 controls were included. FEBD patients showed increased gray matter volume in the cerebellum, posterior cingulate cortex and striatum, and decreased gray matter volume in the medial superior frontal gyrus and gyrus rectus. No common abnormalities were identified between FEBD patients and unaffected at-risk individuals. More gray matter loss in the medial superior frontal gyrus and insula were found in FEBD patients relative to unaffected at-risk individuals. These findings revealed robust gray matter abnormalities in the cortico-striato-cerebellar and default mode network regions in FEBD, and implicated that gray matter deficits may not represent a familial risk endophenotype of BD.

Accelerated cortical thinning and volume reduction over time in young people at high genetic risk for bipolar disorder

BACKGROUND

Bipolar disorder (BD) is a familial psychiatric disorder associated with frontotemporal and subcortical brain abnormalities. It is unclear whether such abnormalities are present in relatives without BD, and little is known about structural brain trajectories in those at risk.

METHOD

Neuroimaging was conducted at baseline and at 2-year follow-up interval in 90 high-risk individuals with a first-degree BD relative (HR), and 56 participants with no family history of mental illness who could have non-BD diagnoses. All 146 subjects were aged 12-30 years at baseline. We examined longitudinal change in gray and white matter volume, cortical thickness, and surface area in the frontotemporal cortex and subcortical regions.

RESULTS

Compared to controls, HR participants showed accelerated cortical thinning and volume reduction in right lateralised frontal regions, including the inferior frontal gyrus, lateral orbitofrontal cortex, frontal pole and rostral middle frontal gyrus. Independent of time, the HR group had greater cortical thickness in the left caudal anterior cingulate cortex, larger volume in the right medial orbitofrontal cortex and greater area of right accumbens, compared to controls. This pattern was evident even in those without the new onset of psychopathology during the inter-scan interval.

CONCLUSIONS

This study suggests that differences previously observed in BD are developing prior to the onset of the disorder. The pattern of pathological acceleration of cortical thinning is likely consistent with a disturbance of molecular mechanisms responsible for normal cortical thinning. We also demonstrate that neuroanatomical differences in HR individuals may be progressive in some regions and stable in others.

Cortical mediation of relationships between dopamine receptor D2 and cognition is absent in youth at risk of bipolar disorder

Bipolar disorder is associated with cognitive deficits and cortical changes for which the developmental dynamics are not well understood. The dopamine D2 receptor (DRD2) gene has been associated with both psychiatric disorders and cognitive variability. Here we examined the mediating role of brain structure in the relationship between DRD2 genomic variation and cognitive performance, with target cortical regions selected based on evidence of association with DRD2, bipolar disorder and/or cognition from prior literature. Participants (n = 143) were aged 12-30 years and comprised 62 first-degree relatives of bipolar patients (deemed 'at-risk'), 55 controls, and 26 patients with established bipolar disorder; all were unrelated Caucasian individuals with complete data across the three required modalities (structural magnetic resonance imaging, neuropsychological and genetic data). A DRD2 haplotype was derived from three functional polymorphisms (rs1800497, rs1076560, rs2283265) associated with alternative splicing (i.e., D2-short/-long isoforms). Moderated mediation analyses explored group differences in relationships between this DRD2 haplotype, three structural brain networks which subsume the identified cortical regions of interest (frontoparietal, dorsal-attention, and ventral-attention), and three cognitive indices (intelligence, attention, and immediate memory). Controls who were homozygous for the DRD2 major haplotype demonstrated greater cognitive performance as a result of dorsal-attention network mediation. However, this association was absent in the 'at-risk' group. This study provides the first evidence of a functional DRD2-brain-cognition pathway. The absence of typical brain-cognition relationships in young 'at-risk' individuals may reflect biological differences that precede illness onset. Further insight into early pathogenic processes may facilitate targeted early interventions.

Identification of bipolar disorder using a combination of multimodality magnetic resonance imaging and machine learning techniques

BACKGROUND

Bipolar disorder (BPD) is a common mood disorder that is often goes misdiagnosed or undiagnosed. Recently, machine learning techniques have been combined with neuroimaging methods to aid in the diagnosis of BPD. However, most studies have focused on the construction of classifiers based on single-modality MRI. Hence, in this study, we aimed to construct a support vector machine (SVM) model using a combination of structural and functional MRI, which could be used to accurately identify patients with BPD.

METHODS

In total, 44 patients with BPD and 36 healthy controls were enrolled in the study. Clinical evaluation and MRI scans were performed for each subject. Next, image pre-processing, VBM and ReHo analyses were performed. The ReHo values of each subject in the clusters showing significant differences were extracted. Further, LASSO approach was recruited to screen features. Based on selected features, the SVM model was established, and discriminant analysis was performed.

RESULTS

After using the two-sample t-test with multiple comparisons, a total of 8 clusters were extracted from the data (VBM = 6; ReHo = 2). Next, we used both VBM and ReHo data to construct the new SVM classifier, which could effectively identify patients with BPD at an accuracy of 87.5% (95%CI: 72.5-95.3%), sensitivity of 86.4% (95%CI: 64.0-96.4%), and specificity of 88.9% (95%CI: 63.9-98.0%) in the test data (p = 0.0022).

CONCLUSIONS

A combination of structural and functional MRI can be of added value in the construction of SVM classifiers to aid in the accurate identification of BPD in the clinic.

Brain structural correlates of familial risk for mental illness: a meta-analysis of voxel-based morphometry studies in relatives of patients with psychotic or mood disorders

Schizophrenia (SCZ), bipolar disorder (BD), and major depressive disorder (MDD) are heritable psychiatric disorders with partially overlapping genetic liability. Shared and disorder-specific neurobiological abnormalities associated with familial risk for developing mental illnesses are largely unknown. We performed a meta-analysis of structural brain imaging studies in relatives of patients with SCZ, BD, and MDD to identify overlapping and discrete brain structural correlates of familial risk for mental disorders. Search for voxel-based morphometry studies in relatives of patients with SCZ, BD, and MDD in PubMed and Embase identified 33 studies with 2292 relatives and 2052 healthy controls (HC). Seed-based d Mapping software was used to investigate global differences in gray matter volumes between relatives as a group versus HC, and between those of each psychiatric disorder and HC. As a group, relatives exhibited gray matter abnormalities in left supramarginal gyrus, right striatum, right inferior frontal gyrus, left thalamus, bilateral insula, right cerebellum, and right superior frontal gyrus, compared with HC. Decreased right cerebellar gray matter was the only abnormality common to relatives of all three conditions. Subgroup analyses showed disorder-specific gray matter abnormalities in left thalamus and bilateral insula associated with risk for SCZ, in left supramarginal gyrus and right frontal regions with risk for BD, and in right striatum with risk for MDD. While decreased gray matter in right cerebellum might be a common brain structural abnormality associated with shared risk for SCZ, BD, and MDD, regional gray matter abnormalities in neocortex, thalamus, and striatum appear to be disorder-specific.

The Association Between Familial Risk and Brain Abnormalities Is Disease Specific: An ENIGMA-Relatives Study of Schizophrenia and Bipolar Disorder

BACKGROUND

Schizophrenia and bipolar disorder share genetic liability, and some structural brain abnormalities are common to both conditions. First-degree relatives of patients with schizophrenia (FDRs-SZ) show similar brain abnormalities to patients, albeit with smaller effect sizes. Imaging findings in first-degree relatives of patients with bipolar disorder (FDRs-BD) have been inconsistent in the past, but recent studies report regionally greater volumes compared with control subjects.

METHODS

We performed a meta-analysis of global and subcortical brain measures of 6008 individuals (1228 FDRs-SZ, 852 FDRs-BD, 2246 control subjects, 1016 patients with schizophrenia, 666 patients with bipolar disorder) from 34 schizophrenia and/or bipolar disorder family cohorts with standardized methods. Analyses were repeated with a correction for intracranial volume (ICV) and for the presence of any psychopathology in the relatives and control subjects.

RESULTS

FDRs-BD had significantly larger ICV (d = +0.16, q < .05 corrected), whereas FDRs-SZ showed smaller thalamic volumes than control subjects (d = -0.12, q < .05 corrected). ICV explained the enlargements in the brain measures in FDRs-BD. In FDRs-SZ, after correction for ICV, total brain, cortical gray matter, cerebral white matter, cerebellar gray and white matter, and thalamus volumes were significantly smaller; the cortex was thinner (d < -0.09, q < .05 corrected); and third ventricle was larger (d = +0.15, q < .05 corrected). The findings were not explained by psychopathology in the relatives or control subjects.

CONCLUSIONS

Despite shared genetic liability, FDRs-SZ and FDRs-BD show a differential pattern of structural brain abnormalities, specifically a divergent effect in ICV. This may imply that the neurodevelopmental trajectories leading to brain anomalies in schizophrenia or bipolar disorder are distinct.

Larger right inferior frontal gyrus volume and surface area in participants at genetic risk for bipolar disorders

BACKGROUND

Larger grey matter volume of the inferior frontal gyrus (IFG) is among the most replicated biomarkers of genetic risk for bipolar disorders (BD). However, the IFG is a heterogeneous prefrontal region, and volumetric findings can be attributable to changes in cortical thickness (CT), surface area (SA) or gyrification. Here, we investigated the morphometry of IFG in participants at genetic risk for BD.

METHODS

We quantified the IFG cortical grey matter volume in 29 affected, 32 unaffected relatives of BD probands, and 42 controls. We then examined SA, CT, and cortical folding in subregions of the IFG.

RESULTS

We found volumetric group differences in the right IFG, with the largest volumes in unaffected high-risk and smallest in control participants (F2,192 = 3.07, p = 0.01). The volume alterations were localized to the pars triangularis of the IFG (F2,97 = 4.05, p = 0.02), with no differences in pars opercularis or pars orbitalis. Pars triangularis volume was highly correlated with its SA [Pearson r(101) = 0.88, p &lt; 0.001], which significantly differed between the groups (F2,97 = 4.45, p = 0.01). As with volume, the mean SA of the pars triangularis was greater in unaffected (corrected p = 0.02) and affected relatives (corrected p = 0.05) compared with controls. We did not find group differences in pars triangularis CT or gyrification.

CONCLUSIONS

These findings strengthen prior knowledge about the volumetric findings in this region and provide a new insight into the localization and topology of IFG alterations. The unique nature of rIFG morphology in BD, with larger volume and SA early in the course of illness, could have practical implications for detection of participants at risk for BD.

Structural imaging biomarkers for bipolar disorder: Meta-analyses of whole-brain voxel-based morphometry studies

BACKGROUND

Bipolar disorder (BD) is a common and destructive psychiatric illness worldwide. Although it is known that BD is associated with morphological abnormalities of the brain, the regions implicated in BD remain unclear. Therefore, we aimed to update current knowledge on potential structural imaging biomarkers of BD.

METHODS

Studies published up to January 31, 2018, were identified by a comprehensive literature search of PubMed, EBSCO, and BrainMap voxel-based morphometry (VBM) database. Whole-brain VBM studies that examined gray matter (GM) abnormalities of group comparisons between BD and healthy controls (HC) and reported results as coordinates in a standard reference space were included. Different meta-analyses were performed by activation likelihood estimation (ALE) algorithm.

RESULTS

A total of 46 studies with 56 experiments, including 1720 subjects and 268 foci were included. Seven different meta-analyses were calculated separately across experiments reporting decreased or increased GM volume among BD, BDΙ, BD-adults, and BD-youths groups. Fifteen regions of significantly different GM volume between four groups and HC were identified. There were extensive GM deficits in the prefrontal and temporal cortex, and enlargements in the putamen, cingulate cortex, and precuneus.

CONCLUSIONS

The results revealed that the thinning of prefrontal cortex was a key region in the pathophysiology of BD. The enlargement of the cingulate cortex may be implicated in a compensatory mechanism. It underscored important differences between BD-adults and BD-youths and specific biomarkers of three subgroups.

Reduced cerebrovascular reactivity among adolescents with bipolar disorder

OBJECTIVES

Cardiovascular disease (CVD) is excessive and premature among individuals with bipolar disorder (BD). Cerebrovascular reactivity (CVR), reflecting vasodilatory capacity of cerebral blood vessels in response to vasoactive substances, is a marker of cerebrovascular health. Despite informative findings in other diseases, CVR has not previously been examined in BD.

METHODS

Twenty-five adolescents with BD and 25 age and sex-matched psychiatrically healthy controls (HCs) completed six 15-second breath-holds (BHs) during functional magnetic resonance imaging (fMRI) at 3-Tesla. CVR was determined by comparing blood-oxygenation-level dependent (BOLD) signal changes. Voxel-wise contrasts were analyzed. Body mass index (BMI) was examined as a potential confound.

RESULTS

CVR in the posterior cingulate gyrus and periventricular white matter was lower in BD vs HC. After controlling for differences in BMI, additional between-group CVR differences were observed in the temporal poles, supramarginal gyrus, and lingual gyrus. There were no regions in which CVR was significantly greater in BD vs HC. CVR was not associated with mood symptoms.

CONCLUSIONS

This preliminary study provides evidence of cerebrovascular dysfunction in BD, including regions known to be susceptible to cerebrovascular dysfunction and/or disease. These findings warrant additional research on the causes and consequences of cerebrovascular dysfunction in early-onset BD.

Correlation of proinflammatory cytokines levels and reduced gray matter volumes between patients with bipolar disorder and unipolar depression

BACKGROUND

Gray matter volume reduction in specific brain regions, such as the prefrontal cortex, was found in patients with bipolar disorder and those with unipolar depression. However, few studies have directly compared gray matter volumes between bipolar disorder and unipolar depression. In addition, it is unknown whether proinflammatory cytokines play a role in the gray matter volume difference between bipolar disorder and unipolar depression.

METHODS

Twenty-three patients with bipolar disorder and 23 with unipolar depression in a mildly ill state (Clinical Global Impression-Severity ≤ 3) were enrolled in our study. Each participant underwent structural magnetic resonance imaging and proinflammatory cytokines examination. Voxel-based morphometry was performed to investigate the gray matter volume difference between bipolar disorder and unipolar depression. Correlations of the proinflammatory cytokines and the gray matter volume difference were analyzed.

RESULTS

Several brain regions, including the orbitofrontal cortex, lingual gyrus, inferior frontal cortex, middle frontal cortex, and planum polare, were significantly smaller in patients with bipolar disorder than in those with unipolar depression. These gray matter volume differences between bipolar disorder and unipolar depression were negatively correlated with soluble IL-6 receptor levels.

DISCUSSION

Proinflammatory cytokines, especially IL-6, were associated with the gray matter volumes in bipolar disorder and unipolar depression. However, the complicated associations between proinflammatory cytokines, neurocognitive function, and gray matter volumes require further investigation.

Cortical thickness and surface area as an endophenotype in bipolar disorder type I patients and their first-degree relatives

OBJECTIVES

So far, few studies have investigated cortical thickness (CT) and surface area (SA) measures in bipolar disorder type I (BDI) in comparison to a high genetic risk group such as first-degree relatives (FR). This study aimed to examine CT and SA differences between BDI, FR and healthy controls (HC).

METHODS

3D T1 magnetic resonance images were acquired from 27 euthymic BDI patients, 24 unaffected FR and 29 HC. CT and SA measures were obtained with FreeSurfer version 5.3.0. Generalized estimating equations were used to compare CT and SA between groups. Group comparisons were repeated with restricting the FR group to 17 siblings (FR-SB) only.

RESULTS

\Mean age in years was 36.3 ± 9.5 for BDI, 32.1 ± 10.9 for FR, 34.7 ± 9.8 for FR-SB and 33.1 ± 9.0 for HC group respectively. BDI patients revealed larger SA of left pars triangularis (LPT) compared to HC (p = .001). In addition, increased SA in superior temporal cortex (STC) in FR-SB group compared to HC was identified (p = .0001).

CONCLUSIONS

Our result of increased SA in LPT of BDI could be a disease marker and increased SA in STC of FR-SB could be a marker related with resilience to illness.

Brain Age in Early Stages of Bipolar Disorders or Schizophrenia

BACKGROUND

The greater presence of neurodevelopmental antecedants may differentiate schizophrenia from bipolar disorders (BD). Machine learning/pattern recognition allows us to estimate the biological age of the brain from structural magnetic resonance imaging scans (MRI). The discrepancy between brain and chronological age could contribute to early detection and differentiation of BD and schizophrenia.

METHODS

We estimated brain age in 2 studies focusing on early stages of schizophrenia or BD. In the first study, we recruited 43 participants with first episode of schizophrenia-spectrum disorders (FES) and 43 controls. In the second study, we included 96 offspring of bipolar parents (48 unaffected, 48 affected) and 60 controls. We used relevance vector regression trained on an independent sample of 504 controls to estimate the brain age of study participants from structural MRI. We calculated the brain-age gap estimate (BrainAGE) score by subtracting the chronological age from the brain age.

RESULTS

Participants with FES had higher BrainAGE scores than controls (F(1, 83) = 8.79, corrected P = .008, Cohen's d = 0.64). Their brain age was on average 2.64 ± 4.15 years greater than their chronological age (matched t(42) = 4.36, P < .001). In contrast, participants at risk or in the early stages of BD showed comparable BrainAGE scores to controls (F(2,149) = 1.04, corrected P = .70, η2 = 0.01) and comparable brain and chronological age.

CONCLUSIONS

Early stages of schizophrenia, but not early stages of BD, were associated with advanced BrainAGE scores. Participants with FES showed neurostructural alterations, which made their brains appear 2.64 years older than their chronological age. BrainAGE scores could aid in early differential diagnosis between BD and schizophrenia.

Pattern recognition of magnetic resonance imaging-based gray matter volume measurements classifies bipolar disorder and major depressive disorder

BACKGROUND

Bipolar Disorder (BD) cannot be reliably distinguished from Major Depressive Disorder (MDD) until the first manic or hypomanic episode. Consequently, many patients with BD are treated with antidepressants without mood stabilizers, a strategy that is often ineffective and carries a risk of inducing a manic episode. We previously reported reduced cortical thickness in right precuneus, right caudal middle-frontal cortex and left inferior parietal cortex in BD compared with MDD.

METHODS

This study extends our previous work by performing individual level classification of BD or MDD in an expanded, currently unmedicated, cohort using gray matter volume (GMV) based on Magnetic Resonance Imaging and a Support Vector Machine. All patients were in a Major Depressive Episode and a leave-two-out analysis was performed.

RESULTS

Nineteen out of 26 BD subjects and 20 out of 26 MDD subjects were correctly identified, for a combined accuracy of 75%. The three brain regions contributing to the classification were higher GMV in bilateral supramarginal gyrus and occipital cortex indicating MDD, and higher GMV in right dorsolateral prefrontal cortex indicating BD.

LIMITATIONS

This analysis included scans performed with two different headcoils and scan sequences, which limited the interpretability of results in an independent cohort analysis.

CONCLUSIONS

Our results add to previously published data which suggest that regional gray matter volume should be investigated further as a clinical diagnostic tool to predict BD before the appearance of a manic or hypomanic episode.

Obesity and frontal-striatal brain structures in offspring of individuals with bipolar disorder: Results from the global mood and brain science initiative

OBJECTIVES

To compare frontal-striatal brain volumes between offspring of individuals with bipolar disorder (BD) and healthy controls; to investigate the associations of body mass index (BMI) and age with brain volumes; and to assess the moderating effects of BMI and age on the relationship between risk status and structural brain differences.

METHODS

We cross-sectionally assessed structural regional and global brain volumes using magnetic resonance imaging and BMI among 53 BD offspring subjects, stratified by risk status, and 23 non-BD offspring controls (aged 8-28 years). Analyses of variance and covariance and linear regression analyses were conducted to investigate the associations between BMI and measures of brain volume, as well as the interaction effects between age, BMI, and risk status on brain volumes.

RESULTS

After adjusting for age, sex, and intracranial volume, higher BD risk status was associated with lower bilateral cerebellar cortical and right pars orbitalis volumes. Higher BMI was significantly associated with greater brain volumes in frontal and subcortical structures. A significant interaction effect between BMI and risk status was observed in right middle frontal volume. The moderating effect of BMI on brain volume was most robustly observed among subjects aged 14-19 years and less robustly observed among those aged 20-28 years; BMI and brain volumes were negatively correlated among subjects aged 8-13 years.

CONCLUSIONS

Alterations in brain structures in individuals at risk for BD may be moderated by BMI. Obesity among individuals with a family history of BD may confer additional risk, particularly in mid-adolescence.

Aberrant cerebellar connectivity in bipolar disorder with psychosis

BACKGROUND

The cerebellum, which modulates affect and cognition in addition to motor functions, may contribute substantially to the pathophysiology of mood and psychotic disorders, such as bipolar disorder. A growing literature points to cerebellar abnormalities in bipolar disorder. However, no studies have investigated the topographic representations of resting state cerebellar networks in bipolar disorder, specifically their functional connectivity to cerebral cortical networks.

METHODS

Using a well-defined cerebral cortical parcellation scheme as functional connectivity seeds, we compared ten cerebellar resting state networks in 49 patients with bipolar disorder and a lifetime history of psychotic features and 55 healthy control participants matched for age, sex, and image signal-to-noise ratio.

RESULTS

Patients with psychotic bipolar disorder showed reduced cerebro-cerebellar functional connectivity in somatomotor A, ventral attention, salience, and frontoparietal control A and B networks relative to healthy control participants. These findings were not significantly correlated with current symptoms.

CONCLUSIONS

Patients with psychotic bipolar disorder showed evidence of cerebro-cerebellar dysconnectivity in selective networks. These disease-related changes were substantial and not explained by medication exposure or substance use. Therefore, they may be mechanistically relevant to the underlying susceptibility to mood dysregulation and psychosis. Cerebellar mechanisms deserve further exploration in psychiatric conditions, and this study's findings may have value in guiding future studies on pathophysiology and treatment of mood and psychotic disorders, in particular.

Manual motor speed dysfunction as a neurocognitive endophenotype in euthymic bipolar disorder patients and their healthy relatives. Evidence from a 5-year follow-up study

BACKGROUND

Few studies have examined Manual Motor Speed (MMS) in bipolar disorder (BD). The aim of this longitudinal, family study was to explore whether dysfunctional MMS represents a neurocognitive endophenotype of BD.

METHODS

A sample of 291 subjects, including 131 BD patients, 77 healthy first-degree relatives (BD-Rel), and 83 genetically-unrelated healthy controls (HC), was assessed with the Finger-Tapping Test (FTT) on three occasions over a 5-year period. Dependence of FTT on participants´ age was removed by means of a lineal model of HC samples, while correcting simultaneously the time and learning effect. Differences between groups were evaluated with an ANOVA test.

RESULTS

The patients' performance was significantly worse than that of HC over time (p≤0.006), and these deficits remained when non-euthymic BD patients (n=9) were excluded from analysis. Some significant differences between BD patients and BD-Rel (p≤0.037) and between BD-Rel and HC (p≤0.033) were found, but they tended to disappear as time progressed (p≥0.057). Performance of the BD-Rel group was intermediate to that of BD and HC. Most sociodemographic and clinical variables did not affect these results in patients. (p≥0.1). However, treatment with carbamazepine and benzodiazepines may exert a iatrogenic effect on MMS performance (p≤0.006).

LIMITATIONS

Only right-handed subjects were included in this study. Substantial attrition over time was detected.

CONCLUSIONS

There were significant differences between the patients´ MMS performance and that of healthy relatives and controls, regardless of most clinical and sociodemographic variables. Dysfunctional MMS could be considered an endophenotype of BD. Further studies are needed to rule out possible iatrogenic effects of some psychopharmacological treatments.

Cortical complexity in bipolar disorder applying a spherical harmonics approach

Recent studies using surface-based morphometry of structural magnetic resonance imaging data have suggested that some changes in bipolar disorder (BP) might be neurodevelopmental in origin. We applied a novel analysis of cortical complexity based on fractal dimensions in high-resolution structural MRI scans of 18 bipolar disorder patients and 26 healthy controls. Our region-of-interest based analysis revealed increases in fractal dimensions (in patients relative to controls) in left lateral orbitofrontal cortex and right precuneus, and decreases in right caudal middle frontal, entorhinal cortex, and right pars orbitalis, and left fusiform and posterior cingulate cortices. While our analysis is preliminary, it suggests that early neurodevelopmental pathologies might contribute to bipolar disorder, possibly through genetic mechanisms.

Voxel-based morphometry meta-analysis of gray and white matter finds significant areas of differences in bipolar patients from healthy controls

OBJECTIVE

We present a retrospective meta-analysis of voxel-based morphometry (VBM) of gray (GM) and white matter (WM) differences between patients with bipolar disorder (BD) and behaviorally healthy controls.

METHODS

We used the activation likelihood estimation and Sleuth software for our meta-analysis, considering P-value maps at the cluster level inference of .05 with uncorrected P<.001. Results were visualized with the software MANGO.

RESULTS

We included twenty-five articles in the analysis, and separated the comparisons where BD patients had lower GM or WM concentrations than controls (573 subjects, 21 experiments, and 117 locations/180 subjects, five experiments, and 15 locations, respectively) and the comparisons where BD patients had greater GM concentrations than controls (217 subjects, nine experiments, and 49 locations). Higher WM concentrations in BD patients were not detected. We observed for BD reduced GM concentrations in the left medial frontal gyrus and right inferior/precentral gyri encompassing the insular cortex, and greater GM concentrations in the left putamen. Further, lower WM concentrations were detected in the left inferior longitudinal fasciculus, left superior corona radiata, and left posterior cingulum.

CONCLUSIONS

This meta-analysis confirms deterioration of frontal and insular regions as already found in previous meta-analysis. GM reductions in these regions could be related to emotional processing and decision making, which are typically impaired in BD. Moreover, we found abnormalities in precentral frontal areas and putamen that have been linked to more basic functions, which could point to sensory and specific cognitive deficits. Finally, WM reductions involved circuitry that may contribute to emotional dysregulation in BD.

Neurobiology of Risk for Bipolar Disorder

Bipolar disorder (BD) is a chronic mental illness which follows a relapsing and remitting course and requires lifetime treatment. The lack of biological markers for BD is a major difficulty in clinical practice. Exploring multiple endophenotypes to fit in multivariate genetic models for BD is an important element in the process of finding tools to facilitate early diagnosis, early intervention, prevention of new episodes, and follow-up of treatment response in BD. Reviewing of studies on neuroimaging, neurocognition, and biochemical parameters in populations with high genetic risk for the illness can yield an integrative perspective on the neurobiology of risk for BD. The most up-to-date data reveals consistent deficits in executive function, response inhibition, verbal memory/learning, verbal fluency, and processing speed in risk groups for BD. Functional magnetic resonance imaging (fMRI) studies report alterations in the activity of the inferior frontal gyrus, medial prefrontal cortex, and limbic areas, particularly in the amygdala in unaffected first-degree relatives (FDR) of BD compared to healthy controls. Risk groups for BD also present altered immune and neurochemical modulation. Despite inconsistencies, accumulating data reveals cognitive and imaging markers for risk and to a less extent resilience of BD. Findings on neural modulation markers are preliminary and require further studies. Although the knowledge on the neurobiology of risk for BD has been inadequate to provide benefits for clinical practice, further studies on structural and functional changes in the brain, neurocognitive functioning, and neurochemical modulation have a potential to reveal biomarkers for risk and resilience for BD. Multimodal, multicenter, population-based studies with large sample size allowing for homogeneous subgroup analyses will immensely contribute to the elucidation of biological markers for risk for BD in an integrative model.

Abnormalities in left inferior frontal gyral thickness and parahippocampal gyral volume in young people at high genetic risk for bipolar disorder

BACKGROUND

Fronto-limbic structural brain abnormalities have been reported in patients with bipolar disorder (BD), but findings in individuals at increased genetic risk of developing BD have been inconsistent. We conducted a study in adolescents and young adults (12-30 years) comparing measures of fronto-limbic cortical and subcortical brain structure between individuals at increased familial risk of BD (at risk; AR), subjects with BD and controls (CON). We separately examined cortical volume, thickness and surface area as these have distinct neurodevelopmental origins and thus may reflect differential effects of genetic risk.

METHOD

We compared fronto-limbic measures of grey and white matter volume, cortical thickness and surface area in 72 unaffected-risk individuals with at least one first-degree relative with bipolar disorder (AR), 38 BD subjects and 72 participants with no family history of mental illness (CON).

RESULTS

The AR group had significantly reduced cortical thickness in the left pars orbitalis of the inferior frontal gyrus (IFG) compared with the CON group, and significantly increased left parahippocampal gyral volume compared with those with BD.

CONCLUSIONS

The finding of reduced cortical thickness of the left pars orbitalis in AR subjects is consistent with other evidence supporting the IFG as a key region associated with genetic liability for BD. The greater volume of the left parahippocampal gyrus in those at high risk is in line with some prior reports of regional increases in grey matter volume in at-risk subjects. Assessing multiple complementary morphometric measures may assist in the better understanding of abnormal developmental processes in BD.