Novel gene-brain structure relationships in psychotic disorder revealed using parallel independent component analyses

BACKGROUND

Schizophrenia, schizoaffective disorder, and psychotic bipolar disorder overlap with regard to symptoms, structural and functional brain abnormalities, and genetic risk factors. Neurobiological pathways connecting genes to clinical phenotypes across the spectrum from schizophrenia to psychotic bipolar disorder remain largely unknown.

METHODS

We examined the relationship between structural brain changes and risk alleles across the psychosis spectrum in the multi-site Bipolar-Schizophrenia Network for Intermediate Phenotypes (B-SNIP) cohort. Regional MRI brain volumes were examined in 389 subjects with a psychotic disorder (139 schizophrenia, 90 schizoaffective disorder, and 160 psychotic bipolar disorder) and 123 healthy controls. 451,701 single-nucleotide polymorphisms were screened and processed using parallel independent component analysis (para-ICA) to assess associations between genes and structural brain abnormalities in probands.

RESULTS

482 subjects were included after quality control (364 individuals with psychotic disorder and 118 healthy controls). Para-ICA identified four genetic components including several risk genes already known to contribute to schizophrenia and bipolar disorder and revealed three structural components that showed overlapping relationships with the disease risk genes across the three psychotic disorders. Functional ontologies representing these gene clusters included physiological pathways involved in brain development, synaptic transmission, and ion channel activity.

CONCLUSIONS

Heritable brain structural findings such as reduced cortical thickness and surface area in probands across the psychosis spectrum were associated with somewhat distinct genes related to putative disease pathways implicated in psychotic disorders. This suggests that brain structural alterations might represent discrete psychosis intermediate phenotypes along common neurobiological pathways underlying disease expression across the psychosis spectrum.

State dependent cortico-amygdala circuit dysfunction in bipolar disorder

BACKGROUND

Existing models of the pathophysiology of bipolar disorder posit disruption in neural circuits of emotion regulation and reward processing. However, few fMRI studies have compared regional brain activity and connectivity in different mood states in bipolar disorder to determine if manic symptomatology is reflected in specific circuit abnormalities. The purpose of this study was to test the hypothesis that bipolar mania is associated with altered connectivity between cortical regions thought to regulate subcortical structures such as the amygdala and striatum.

METHODS

28 subjects with bipolar disorder in a manic state, 24 different bipolar subjects in a euthymic state, and 23 matched healthy comparison subjects underwent resting state fMRI scans. Several cortical and sub-cortical structures implicated in the pathogenesis of bipolar disorder were selected for study. We conducted a whole-brain analysis of functional connectivity of these regions.

RESULTS

Bipolar mania was differentiated from euthymia by decreased functional connectivity between the amygdala and anterior cingulate cortex (ACC). Mania was also characterized by increased connectivity between amygdala and dorsal frontal cortical structures that are normally anti-correlated in emotion regulation tasks.

LIMITATIONS

Both groups of bipolar subjects were prescribed medications. The study was not longitudinal in design.

CONCLUSIONS

Compared to bipolar subjects in a euthymic state, subjects in the manic state demonstrate disrupted functional connectivity between brain regions involved in the regulation of emotion and the amygdala. This disruption of activity in neural circuits involved in emotion may underlie the emotional dysregulation inherent to a bipolar manic episode.

Impulsivity across the psychosis spectrum: Correlates of cortical volume, suicidal history, and social and global function

Patients with psychotic disorders appear to exhibit greater impulsivity-related behaviors relative to healthy controls. However, the neural underpinning of this impulsivity remains uncertain. Furthermore, it remains unclear how impulsivity might differ or be conserved between psychotic disorder diagnoses in mechanism and manifestation. In this study, self-reported impulsivity, measured by Barratt Impulsiveness Scale (BIS), was compared between 305 controls (HC), 139 patients with schizophrenia (SZ), 100 with schizoaffective disorder (SZA), and 125 with psychotic bipolar disorder (PBP). In each proband group, impulsivity was associated with regional cortical volumes (using FreeSurfer analysis of T1 MRI scans), suicide attempt history, Global Assessment of Functioning (GAF), and Social Functioning Scale (SFS). BIS scores were found to differ significantly between participant groups, with SZA and PBP exhibiting significantly higher impulsivity than SZ, which exhibited significantly higher impulsivity than HC. BIS scores were significantly related to suicide attempt history, and they were inversely associated with GAF, SFS, and bilateral orbitofrontal cortex (OFC) volume in both SZA and PBP, but not SZ. These findings indicate that psychotic disorders, particularly those with prominent affective symptoms, are characterized by elevated self-reported impulsivity measures. Impulsivity's correlations with suicide attempt history, GAF, and SFS suggest that impulsivity may be a mediator of clinical outcome. The observed impulsivity-OFC correlations corroborate the importance of OFC deficits in impulsivity. These correlations' presence in SZA and PBP but not in SZ suggests that impulsivity may have different underlying mechanisms in affective and non-affective psychotic disorders.

Angiogenic and immune signatures in plasma of young relatives at familial high-risk for psychosis and first-episode patients: A preliminary study

Schizophrenia (SZ) is a heterogeneous disorder that presents in adolescence, persists into adulthood, and has many clinical features. Recent evidence suggests that abnormalities in inflammatory, neurotrophic, and angiogenic processes may play a role in the etiology of SZ. The identification of molecular biomarkers early in the course of disease is crucial to transforming diagnostic and therapeutic avenues. We investigated 14 molecular analytes focusing on inflammatory, neurotrophic and angiogenic pathways from the plasma of antipsychotic-naïve familial high risk for SZ (FHR; n=35) and first-episode psychosis (FEP; n=45) subjects, in comparison to healthy controls (HC, n=39). We identified distinct alterations in molecular signatures in young relatives at FHR for SZ prior to psychosis onset and FEP subjects. Firstly, the expression of soluble fms-like tyrosine kinase (sFlt-1), an anti-angiogenic factor that binds vascular endothelial growth factor (VEGF), was significantly increased in the FHR group compared to HC, but not in FEP. Secondly, interferon gamma (IFNγ) was significantly reduced in the FEP group compared to HC. Thirdly, network analysis revealed a positive correlation between sFlt-1 and VEGF, suggesting an activation of the angiogenic cascade in the FHR group, which persists in FEP. Our results indicate an angiogenesis and immunological dysfunction early in the course of disease, shifting the balance towards anti-angiogenesis and inflammation.

Increased cardiometabolic dysfunction in first-degree relatives of patients with psychotic disorders

INTRODUCTION

Elevated prevalence of comorbid cardio-vascular and metabolic dysfunction (CMD) is consistently reported in patients with severe psychotic disorders such as schizophrenia (SZ), schizoaffective (SZA) and bipolar disorder (BP-P). Since both psychosis and CMD are substantively heritable in nature, we attempted to investigate the occurrence of CMD disorders in first-degree relatives of probands with psychosis.

METHODS

Our sample included 861 probands with a diagnosis of SZ (n=354), SZA (n=212) and BP-P (n=295), 776 first-degree relatives of probands and 416 healthy controls. Logistic regression was used to compare prevalence of any CMD disorders (diabetes, hypertension, hyperlipidemia or coronary artery disease) across groups. Post hoc tests of independence checked for CMD prevalence across psychosis diagnosis (SZ, SZA and BP-P), both in relatives of probands and within probands themselves.

RESULTS

After controlling for potential confounders, first-degree relatives with (p<0.001) and without (p=0.03) Axis I non-psychotic or Axis- II cluster disorders were at a significant risk for CMD compared to controls. No significant difference (p=0.42) was observed in prevalence of CMD between relatives of SZ, SZA and BP-P, or between psychosis diagnoses for probands (p=0.25).

DISCUSSION

Prevalence of CMD was increased in the first-degree relatives of psychosis subjects. This finding suggests the possibility of overlapping genetic contributions to CMD and psychosis. Increased somatic disease burden in relatives of psychotic disorder probands points to need for early detection and preventive efforts in this population.

Correlations between brain structure and symptom dimensions of psychosis in schizophrenia, schizoaffective, and psychotic bipolar I disorders

INTRODUCTION

Structural alterations may correlate with symptom severity in psychotic disorders, but the existing literature on this issue is heterogeneous. In addition, it is not known how cortical thickness and cortical surface area correlate with symptom dimensions of psychosis.

METHODS

Subjects included 455 individuals with schizophrenia, schizoaffective, or bipolar I disorders. Data were obtained as part of the Bipolar Schizophrenia Network for Intermediate Phenotypes study. Diagnosis was made through the Structured Clinical Interview for DSM-IV. Positive and negative symptom subscales were assessed using the Positive and Negative Syndrome Scale. Structural brain measurements were extracted from T1-weight structural MRIs using FreeSurfer v5.1 and were correlated with symptom subscales using partial correlations. Exploratory factor analysis was also used to identify factors among those regions correlating with symptom subscales.

RESULTS

The positive symptom subscale correlated inversely with gray matter volume (GMV) and cortical thickness in frontal and temporal regions, whereas the negative symptom subscale correlated inversely with right frontal cortical surface area. Among regions correlating with the positive subscale, factor analysis identified four factors, including a temporal cortical thickness factor and frontal GMV factor. Among regions correlating with the negative subscale, factor analysis identified a frontal GMV-cortical surface area factor. There was no significant diagnosis by structure interactions with symptom severity.

CONCLUSIONS

Structural measures correlate with positive and negative symptom severity in psychotic disorders. Cortical thickness demonstrated more associations with psychopathology than cortical surface area.

Local gyrification index in probands with psychotic disorders and their first-degree relatives

BACKGROUND

Psychotic disorders are characterized by aberrant neural connectivity. Alterations in gyrification, the pattern and degree of cortical folding, may be related to the early development of connectivity. Past gyrification studies have relatively small sample sizes, yield mixed results for schizophrenia, and are scant for psychotic bipolar and schizoaffective (SZA) disorders and for relatives of these conditions. Here, we examine gyrification in psychotic disorder patients and their first-degree relatives as a possible endophenotype.

METHODS

Regional local gyrification index (LGI) values, as measured by FreeSurfer software, were compared between 243 control subjects, 388 psychotic disorder probands, and 300 of their first-degree relatives. For patients, LGI values were examined grouped across psychotic diagnoses and then separately for schizophrenia, SZA, and bipolar disorder. Familiality (heritability) values and correlations with clinical measures were also calculated for regional LGI values.

RESULTS

Probands exhibited significant hypogyria compared with control subjects in three brain regions and relatives with Axis II cluster A disorders showed nearly significant hypogyria in these same regions. Local gyrification index values in these locations were significantly heritable and uncorrelated with any clinical measure. Observations of significant hypogyria were most widespread in SZA.

CONCLUSIONS

Psychotic disorders appear to be characterized by significant regionally localized hypogyria, particularly in cingulate cortex. This abnormality may be a structural endophenotype marking risk for psychotic illness and it may help elucidate etiological underpinnings of psychotic disorders.

Are structural brain abnormalities associated with suicidal behavior in patients with psychotic disorders?

Suicide represents a major health problem world-wide. Nevertheless, the understanding of the neurobiological underpinnings of suicidal behavior remains far from complete. We compared suicide attempters to non-attempters, and high vs. low lethality attempters, to identify brain regions associated with suicidal behavior in patients with psychotic disorders. 489 individuals with schizophrenia, schizoaffective disorder, or psychotic bipolar disorder I and 262 healthy controls enrolled in the B-SNIP study were studied. Groups were compared by attempt history and the highest medical lethality of previous suicide attempts. 97 patients had a history of a high lethality attempt, 51 of a low lethality attempt and 341 had no attempt history. Gray matter volumes were obtained from 3T structural MRI scans using FreeSurfer. ANCOVAs were used to examine differences between groups, followed by Hochberg multiple comparison correction. Compared to non-attempters, attempters had significantly less gray matter volume in bilateral inferior temporal and superior temporal cortices, left superior parietal, thalamus and supramarginal regions, right insula, superior frontal and rostral middle frontal regions. Among attempters, a history of high lethality attempts was associated with significantly smaller volumes in the left lingual gyrus and right cuneus. Compared to non-attempters, low lethality attempters had significant decreases in the left supramarginal gyrus, thalamus and the right insula. Structural brain abnormalities may distinguish suicide attempters from non-attempters and high from low lethality attempters among individuals with psychotic disorders. Regions in which differences were observed are part of neural circuitries that mediate inhibition, impulsivity and emotion, visceral, visual and auditory perception.