Schizophrenia and bipolar disorder are distinguished mainly by differences in neurodevelopment

A comparison of neighbourhood level variation and risk factors for affective versus non-affective psychosis

BACKGROUND

Studies typically highlight area level variation in the incidence of non-affective but not affective psychoses. We compared neighbourhood-level variation for both types of disorder, and the specific effects of neighbourhood urbanicity and ethnic density, using Danish national registry data.

METHODS

Population based cohort (2,224,464 people) followed from 1980 to 2013 with neighbourhood exposure measured at age 15 and incidence modelled using multilevel Poisson regression.

RESULTS

Neighbourhood variation was similar for both disorders with an adjusted median risk ratio of 1.37 (95% CI 1.34-1.39) for non-affective psychosis and 1.43 (1.38-1.49) for affective psychosis. Associations with neighbourhood urbanicity differed: living in the most compared to the least urban quintile at age 15 was associated with a minimal increase in subsequent affective psychosis, IRR 1.13 (1.01-1.27) but a substantial increase in rates of non-affective psychosis, IRR 1.66 (1.57-1.75). Mixed results were found for neighbourhood ethnic density: for Middle Eastern migrants there was an increased average incidence of both affective, IRR 1.54 (1.19-1.99), and non-affective psychoses, 1.13 (1.04-1.23) associated with each decrease in ethnic density quintile, with a similar pattern for African migrants, but for European migrants ethnic density appeared to be associated with non-affective psychosis only.

CONCLUSIONS

While overall variation and the effect of neighbourhood ethnic density were similar for both types of disorder, associations with urbanicity were largely confined to non-affective psychosis. This may reflect differences in aetiological pathways although the mechanism behind these differences remains unknown.

Schizophrenia and Bipolar Polygenic Risk Scores in Relation to Intracranial Volume

Schizophrenia and bipolar disorder are neurodevelopmental disorders with overlapping symptoms and a shared genetic background. Deviations in intracranial volume (ICV)—a marker for neurodevelopment—differ between schizophrenia and bipolar disorder. Here, we investigated whether genetic risk for schizophrenia and bipolar disorder is related to ICV in the general population by using the UK Biobank data (n = 20,196). Polygenic risk scores for schizophrenia (SZ-PRS) and bipolar disorder (BD-PRS) were computed for 12 genome wide association study P-value thresholds (PT) for each individual and correlations with ICV were investigated. Partial correlations were performed at each PT to investigate whether disease specific genetic risk variants for schizophrenia and bipolar disorder show different relationships with ICV. ICV showed a negative correlation with SZ-PRS at PT ≥ 0.005 (r < −0.02, p < 0.005). ICV was not associated with BD-PRS; however, a positive correlation between BD-PRS and ICV at PT = 0.2 and PT = 0.4 (r = +0.02, p < 0.005) appeared when the genetic overlap between schizophrenia and bipolar disorder was accounted for. Despite small effect sizes, a higher load of schizophrenia risk genes is associated with a smaller ICV in the general population, while risk genes specific for bipolar disorder are correlated with a larger ICV. These findings suggest that schizophrenia and bipolar disorder risk genes, when accounting for the genetic overlap between both disorders, have opposite effects on early brain development.

Mapping multimorbidity in individuals with schizophrenia and bipolar disorders: evidence from the South London and Maudsley NHS Foundation Trust Biomedical Research Centre (SLAM BRC) case register

OBJECTIVES

The first aim of this study was to design and develop a valid and replicable strategy to extract physical health conditions from clinical notes which are common in mental health services. Then, we examined the prevalence of these conditions in individuals with severe mental illness (SMI) and compared their individual and combined prevalence in individuals with bipolar (BD) and schizophrenia spectrum disorders (SSD).

DESIGN

Observational study.

SETTING

Secondary mental healthcare services from South London PARTICIPANTS: Our maximal sample comprised 17 500 individuals aged 15 years or older who had received a primary or secondary SMI diagnosis (International Classification of Diseases, 10th edition, F20-31) between 2007 and 2018.

MEASURES

We designed and implemented a data extraction strategy for 21 common physical comorbidities using a natural language processing pipeline, MedCAT. Associations were investigated with sex, age at SMI diagnosis, ethnicity and social deprivation for the whole cohort and the BD and SSD subgroups. Linear regression models were used to examine associations with disability measured by the Health of Nations Outcome Scale.

RESULTS

Physical health data were extracted, achieving precision rates (F1) above 0.90 for all conditions. The 10 most prevalent conditions were diabetes, hypertension, asthma, arthritis, epilepsy, cerebrovascular accident, eczema, migraine, ischaemic heart disease and chronic obstructive pulmonary disease. The most prevalent combination in this population included diabetes, hypertension and asthma, regardless of their SMI diagnoses.

CONCLUSIONS

Our data extraction strategy was found to be adequate to extract physical health data from clinical notes, which is essential for future multimorbidity research using text records. We found that around 40% of our cohort had multimorbidity from which 20% had complex multimorbidity (two or more physical conditions besides SMI). Sex, age, ethnicity and social deprivation were found to be key to understand their heterogeneity and their differential contribution to disability levels in this population. These outputs have direct implications for researchers and clinicians.

Neurodevelopmental pathways in bipolar disorder

Aberrations in neurodevelopmental trajectories have been implicated in the neurobiology of several mental disorders and evidence indicates a pathophysiological and genetic overlap of schizophrenia and bipolar disorder (BD). In this narrative review, we summarize findings related to developmental and perinatal factors as well as epidemiological, clinical, neuropsychological, brain imaging, postmortem brain and genomic studies that provide evidence for a putative neurodevelopmental pathogenesis and etiology of BD. Overall, aberrations in neurodevelopmental pathways have been more consistently implicated in the pathophysiology of schizophrenia compared to BD. Nevertheless, an accumulating body of evidence indicates that dysfunctional neurodevelopmental pathways may be implicated in the underlying pathophysiology of at least a subset of individuals with BD particularly those with an early age of illness onset and those exhibiting psychotic symptoms. A heuristic neurodevelopmental model for the pathophysiology of BD based on the findings of this review is proposed. Furthermore, we critically discuss clinical and research implications of this model. Finally, further research directions for this emerging field are provided.

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.

Intra-individual variability and psychotic-like experiences in adolescents: Findings from the ALSPAC cohort

Clinical and epidemiological studies have demonstrated associations between elevated intra-individual variability (IIV) of reaction time and psychotic disorders. However, little attention has been paid to the relationship between performance stability and psychotic-like experiences (PLE) in adolescence, before psychotic disorder onset. Data from 6702 children from the Avon Longitudinal Study of Parents and Children (ALSPAC) were used to address this issue. Children took part in a semi-structured clinical interview regarding psychotic symptoms at age 12 and 18, and reaction time variability was assessed at age 13 and 15. Children who had elevated IIV at age 15 were more likely to report suspected or definite PLE at age 18, with larger associations being found for more frequent or bizarre symptoms. Elevated IIV at age 15 was also associated with persistent PLE between age 12 and 18. These findings tentatively suggest that elevated IIV in early adolescence may be predictive of later PLE, and offer some support for the notion of a psychosis continuum.

Minor physical anomalies in schizophrenia and bipolar I disorder and the neurodevelopmental continuum of psychosis

OBJECTIVES

Minor physical anomalies (MPAs) have been investigated by numerous studies in patients with schizophrenia in support of the neurodevelopmental hypothesis of the disorder, but have rarely been examined in patients with bipolar disorder or in direct comparisons between the two conditions. The main objective of the present study was to compare the prevalence of MPAs in psychiatrically healthy controls, patients with bipolar I disorder, and patients with schizophrenia.

METHODS

A slightly modified version of the Waldrop Physical Anomaly Scale was used to assess MPAs in psychiatrically healthy controls (n = 103), patients with bipolar I disorder (n = 61), and patients with schizophrenia (n = 128).

RESULTS

In five out of six topographic regions (mouth, feet, head, eyes, and ears) there was a pattern of lowest regional MPA scores in controls, intermediate in bipolar I disorder, and highest in schizophrenia. The cephalofacial composite score and the total MPA score showed the same pattern, with all between-group differences being statistically significant. Seven individual MPAs in the discriminant analysis model contributed independently to the prediction of the triple-dependent status of 'psychiatrically healthy control, bipolar I disorder patient, schizophrenia patient': high/arched palate, fine electric hair, large gap between first and second toes, third toe ≥ second toe, epicanthus, malformed ears, and furrowed tongue.

CONCLUSIONS

Our findings support the existence of a continuum of neurodevelopmental adversity within the clinical spectrum of psychosis, with bipolar I disorder occupying an intermediate position between psychiatric health and schizophrenia.

Neurobehavioral Mechanisms of Traumatic Stress in Post-traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a debilitating psychiatric disorder that develops following trauma exposure. It is characterized by four symptom clusters: intrusion, avoidance, negative alteration in cognitions and mood, and alterations in arousal and reactivity. Several risk factors have been associated with PTSD, including trauma type and severity, gender and sexual orientation, race and ethnicity, cognitive reserve, pretrauma psychopathology, familial psychiatric history, and genetics. Great strides have been made in understanding the neurobiology of PTSD through animal models and human imaging studies. Most of the animal models have face validity, but they have limitations in the generalization to the human model of PTSD. Newer animal models, such as the "CBC" model, have better validity for PTSD, which takes into account the different components of its diagnostic criteria. To date, fear conditioning and fear extinction animal models have provided support for the hypothesis that PTSD is a dysregulation of the processes related to fear regulation and, especially, fear extinction. More research is needed to further understand these processes as they relate not only to PTSD but also to resilience. Further, this research could be instrumental in the development of novel effective treatments for PTSD.

Detection of an immature dentate gyrus feature in human schizophrenia/bipolar patients

Hippocampus-associated cognitive impairments are a common, highly conserved symptom of both schizophrenia (SCZ) and bipolar disorder (BPD). Although the hippocampus is likely an impacted region in SCZ/BPD patients, the molecular and cellular underpinnings of these impairments are difficult to identify. An emerging class of mouse models for these psychiatric diseases display similar cognitive impairments to those observed in human patients. The hippocampi of these mice possess a conserved pathophysiological alteration; we term the 'immature dentate gyrus' (iDG), characterized by increased numbers of calretinin-positive immature neuronal progenitors, a dearth of calbindin-positive mature neurons and (often) constitutively increased neurogenesis. Although these models provide a link between cellular dysfunction and behavioral alteration, limited translational validity exists linking the iDG to human pathophysiology. In this study, we report the initial identification of an iDG-like phenotype in the hippocampi of human SCZ/BPD patients. These findings suggest a new motif for the etiology of these diseases and link an emerging class of mouse models to the human disease condition.

Cortical volume, surface area, and thickness in schizophrenia and bipolar disorder

BACKGROUND

Magnetic resonance imaging studies have shown that structural brain abnormalities are present in both schizophrenia and bipolar disorder. Most previous studies have focused on brain tissue volumes, but advances in neuroimaging data processing have made it possible to separate cortical area and cortical thickness. The purpose of the present study was to provide a more complete picture of cortical morphometric differences in schizophrenia and bipolar disorder, decomposing cortical volume into its constituent parts, cortical thickness and cortical area.

METHODS

We analyzed magnetic resonance imaging images from a sample of 173 patients with schizophrenia, 139 patients with bipolar disorder, and 207 healthy control subjects. Maps of cortical volume, area, and thickness across the continuous cortical surface were generated within groups and compared between the groups.

RESULTS

There were widespread reductions in cortical volume in schizophrenia relative to healthy control subjects and patients with bipolar disorder type I. These reductions were mainly driven by cortical thinning, but there were also cortical area reductions in more circumscribed regions, which contributed to the observed volume reductions.

CONCLUSIONS

The current surface-based methodology allows for a distinction between cortical thinning and reduction in cortical area and reveals that cortical thinning is the most important factor in volume reduction in schizophrenia. Cortical area reduction was not observed in bipolar disorder type I and may be unique to schizophrenia.

Association of symptoms and executive function in schizophrenia and bipolar disorder

The extent to which cognitive impairment in psychosis is related to the particular disorder or the pattern of symptoms is unclear. We examined executive function in two groups of schizophrenia patients with predominant symptoms of disorganisation (n=15) and psychomotor poverty (n=15), respectively, two groups of bipolar I disorder patients with predominant symptoms of mania (n=15) and depression (n=15), respectively, and 30 healthy controls. We predicted that the pattern of symptoms ('excess' [disorganisation/mania] or 'deficiency' [negative symptoms/depression]) would be more related to executive ability than the underlying disorder. The patient groups showed partially overlapping executive dysfunctions relative to the control group. There were no significant differences between groups with 'excess' symptoms (schizophrenia patients with thought disorder and bipolar patients with mania), or between groups with 'deficiency' symptoms (schizophrenia patients with negative symptoms and bipolar patients with depression). In contrast, differences were noted between groups with the same diagnosis: Schizophrenia patients with disorganisation were less accurate in semantic verbal fluency than those with negative symptoms; and bipolar patients with mania tended to be faster, but less accurate, in sentence completion than those with depression. A statistical comparison of the associations of 'diagnosis' and the 'excess-deficiency' dimension with executive function revealed a trend for a greater association of the latter with two measures of performance accuracy. Executive dysfunction in patients with psychotic disorders may be more related to their symptom profile than their diagnosis.

Perinatal risk factors for schizophrenia: how specific are they?

The association between exposure to perinatal risk factors and increased vulnerability for schizophrenia is now documented by a large body of epidemiologic studies. However, the diagnostic specificity of this association may be questioned, because subjects with a history of exposure to early environmental risk factors are at an increased risk for other psychiatric disorders with childhood or adult onset, such as autism, anorexia nervosa, or affective disorders. Because a given risk factor may be associated with several adverse health outcomes, these findings do not preclude the existence of a causal relationship between perinatal risk factors and schizophrenia. This lack of diagnostic specificity suggests that the clinical expression of the vulnerability induced by early risk factors depends on gene-environment interactions or interaction between this prenatally determined vulnerability and exposure to later environmental risk factors.

Neurodevelopmental liabilities in schizophrenia and affective disorders

There is now considerable evidence that both schizophrenia and affective disorders have their origin at least in part in events that occur during early pre- and post-natal development. In the case of schizophrenia, many observations, for example, increased risk for schizophrenia in the offspring of mothers who had influenza A during their second trimester of pregnancy and evidence for abnormal neuronal migration in the cerebral cortex of post mortem tissue from schizophrenic patients, suggest that a second trimester insult may have occurred and that this insult may have increased the risk for the development of schizophrenia in late adolescence or early adulthood. Animal studies have found that rats that undergo exocitotoxic damage to the ventral hippocampus on postnatal day 7 develop exaggerated sensitivity to dopamine-stimulating drugs or to stressful stimuli that becomes apparent after sexual maturity but not before, providing a neurodevelopmental model of schizophrenia. Similarly, post-weaning social isolation leads to enhanced responses to dopaminergic drugs and to stress that emerges after sexual maturity. These animal models are proving to be valuable tools to study the neurobiological mechanisms mediating the influence of early insults to the nervous system on later behavioural functions. In the case of affective disorders, although the evidence is not as strong, a number of the same observations have been made suggesting that an insult during early ontogeny may lead to the development of affective disorders later in life. For example, retrospective studies of people with affective disorders showed that they were more likely to have attained motor milestones at a later age and to have had poorer academic performance as children. There is a wealth of evidence suggesting hyperfunctioning of the hypothalamic-pituitary-adrenal (HPA) axis in affective disorders. Animal studies have shown that early maternal deprivation can lead to lasting changes in the reactivity of the HPA axis to stressful stimuli, providing another link from early experience to adult psychopathology. Continued studies of the effects of pre- and early post-natal events on the development of the nervous system and the relationships of these events to schizophrenia or affective disorder will provide new insights into the mechanisms underlying these common neuropsychiatric illnesses.