Differences in the neural correlates of schizophrenia with positive and negative formal thought disorder in patients with schizophrenia in the ENIGMA dataset

The human cerebral cortex morphology in neuropsychiatric disorders: A causal inference based on Mendelian Randomization

BACKGROUND

Neuropsychiatric disorders, including Alzheimer's disease (AD), major depressive disorder (MDD), anxiety disorders, attention-deficit/hyperactivity disorder (ADHD), bipolar disorder, insomnia, and schizophrenia (SCZ), are prevalent and impose substantial morbidity and mortality worldwide. Brain morphometry, is increasingly recognized for its relevance to cognitive, emotional, and behavioral functions, yet its causal links to neuropsychiatric pathologies are not well established.

OBJECTIVE

This study aimed to explore the causal relationships between cortical thickness (TH) and surface area (SA) with 7 neuropsychiatric disorders using Mendelian randomization (MR) analyses.

METHODS

We employed data from genome-wide association studies (GWAS) comprising 51,665 individuals to evaluate cortical SA and TH. We selected single nucleotide polymorphisms (SNPs) as instrumental variables for MR analyses to investigate the causal associations with neuropsychiatric disorders.

RESULTS

Increased TH in the paracentral cortex was associated with a reduced risk of ADHD. Similarly, a thicker temporal pole was linked to a lower risk of MDD. The TH of the lingual region showed an inverse association with anxiety disorders. The SA of the fusiform gyrus was associated with AD risk, and morphological variations in the caudal middle frontal cortex, isthmus cingulate cortex, and temporal pole were correlated with bipolar disorder risk. An increased TH of the posterior cingulate cortex was associated with higher insomnia risk, and the TH of the pericalcarine region negatively correlated with SCZ risk.

CONCLUSION

This research provided novel evidence for the causal role of cerebral cortex morphology in neuropsychiatric disorders, suggesting potential targets for therapeutic intervention.

Cerebellum as a neural substrate for impoverishment in early psychosis

BACKGROUND

Formal Thought Disorder and includes both positive (i.e., disorganized speech) and negative (i.e., impoverished speech) symptoms. Emerging evidence suggests that the cerebellum plays a critical role in cognitive functions, including language processing. This study leverages Natural Language Processing to objectively measure language disturbances in patients with first-episode psychosis and investigates the relationship between these disturbances and cerebellar structure.

METHODS

Fifty-four patients with schizophrenia, either drug-naïve or minimally medicated, were recruited from an early psychosis program. Impoverished thought was assessed using the Thought Language Index while lexico-semantic features (affect, cognitive, linguistic, perception, time) were identified from speech samples analyzed using the Linguistic Inquiry Word Count-22 software. Structural cerebellar analysis was completed on 7.0 Tesla MRI scans using voxel-based morphometry (VBM) to measure global and regional grey matter volume changes.

RESULTS

Linear regression analysis revealed that reduced perceptual word usage was the strongest predictor of impoverished thinking. Correlational analysis identified reduced cerebellar volumes in patients with lower LIWC-based perception scores. VBM localized this relationship to a cluster in the right posterolateral cerebellar hemisphere, an area related to executive demand and verb generation function.

CONCLUSION

The cerebellum contributes to impoverished thinking in early psychosis, likely by influencing the lexical expression of perceptual experiences. This underscores the cerebellum's role in higher-order cognitive processes relevant to psychotic disorders and its potential as a therapeutic target for language and cognitive deficits in schizophrenia.

Meta‐Analysis of Brain Structure in Magnetic Resonance Imaging Studies of Adolescents With Schizophrenia

Background: Adolescence is a critical stage for neurobiological development, including the formulation of advanced cognitive functions. It is also a period of immense susceptibility to psychiatric disorders, meaning that there may be cortical structural abnormalities in adolescents with these conditions, including schizophrenia. Adolescents with schizophrenia also tend to have symptoms that are common to a variety of psychiatric disorders, leading to diagnostic challenges. Thus, we meta‐analyzed MRI data to study the structural brain characteristics of adolescent with schizophrenia.

Methods: We used “early onset schizophrenia, child/children/childhood onset schizophrenia, adolescent/adolescence onset schizophrenia, and magnetic resonance imaging (MRI)” as keywords for searches in the PubMed, Web of Science, EBSCO databases, and ClincalTrial.gov to find English‐language articles publicly available before March 31, 2023. This meta‐analysis was registered on PROSPERO (CRD42023404619) and followed the guidelines of PRISMA.

Results: Twenty‐nine publications were included in the final meta‐analysis, involving 726 patients and 1039 healthy controls. We found data available only in structural brain volume for meta‐analysis. Gray matter (GM) structures in the frontal, occipital, and parietal areas, as well as the thalamus, were significantly reduced, while the lateral ventricles were significantly increased. In patients with childhood‐onset schizophrenia (COS), total GM, frontal, parietal, and lateral ventricle volume were significantly altered. Patients with first‐episode drug‐naïve (FEDN) schizophrenia had a significant atrophy in the frontal and parietal, occipital, and thalamus, along with enlarged lateral ventricles. Additionally, in the sum of GM and white matter, total brain volume, temporal, and left temporal were significantly decreased, but putamen was increased. In COS patients, total brain volume was reduced considerably, but putamen volumes were significantly increased.

Conclusions: Our study indicates that there are extensive structural abnormalities in the brain regions of adolescent schizophrenics, especially within cortical structures. Patients with either COS or non‐first‐episode schizophrenia who may have received antipsychotic medication also exhibited extensive structural brain abnormalities. The thalamus, lateral ventricles, and putamen may be crucial biological markers of structural brain abnormalities in adolescent schizophrenia, providing a basis for exploring the pathological mechanisms underlying the disease, as well as essential targets for early diagnosis and treatments.

Current Findings and Potential Mechanisms of KarXT (Xanomeline-Trospium) in Schizophrenia Treatment

Standard schizophrenia treatment involves antipsychotic medications that target D2 dopamine receptors. However, these drugs have limitations in addressing all symptoms and can lead to adverse effects such as motor impairments, metabolic effects, sedation, sexual dysfunction, cognitive impairment, and tardive dyskinesia. Recently, KarXT has emerged as a novel drug for schizophrenia. KarXT combines xanomeline, a muscarinic receptor M1 and M4 agonist, with trospium, a nonselective antimuscarinic agent. Of note, xanomeline can readily cross blood-brain barrier (BBB) and, thus, enter into the brain, thereby stimulating muscarinic receptors (M1 and M4). By doing so, xanomeline has been shown to target negative symptoms and potentially improve positive symptoms. Trospium, on the other hand, is not able to cross BBB, thereby not affecting M1 and M4 receptors; instead, it acts as an antimuscarinic agent and, hence, diminishes peripheral activity of muscarinic receptors to minimize side effects probably stemming from xanomeline in other organs. Accordingly, ongoing clinical trials investigating KarXT's efficacy in schizophrenia have demonstrated positive outcomes, including significant improvements in the Positive and Negative Syndrome Scale (PANSS) total score and cognitive function compared with placebo. These findings emphasize the potential of KarXT as a promising treatment for schizophrenia, providing symptom relief while minimizing side effects associated with xanomeline monotherapy. Despite such promising evidence, further research is needed to confirm the efficacy, safety, and tolerability of KarXT in managing schizophrenia. This review article explores the current findings and potential mechanisms of KarXT in the treatment of schizophrenia.