Gray and white matter volumetric and diffusion tensor imaging (DTI) analyses in the early stage of first-episode schizophrenia

The effects of gender on grey matter abnormalities in major psychoses: a comparative voxelwise meta-analysis of schizophrenia and bipolar disorder

BACKGROUND

Recent evidence from genetic and familial studies revitalized the debate concerning the validity of the distinction between schizophrenia and bipolar disorder. Comparing brain imaging findings is an important avenue to examine similarities and differences and, therefore, the validity of the distinction between these conditions. However, in contrast to bipolar disorder, most patient samples in studies of schizophrenia are predominantly male. This a limiting factor for comparing schizophrenia and bipolar disorder since male gender is associated with more severe neurodevelopmental abnormalities, negative symptoms and cognitive deficits in schizophrenia.

METHOD

We used a coordinate-based meta-analysis technique to compare grey matter (GM) abnormalities in male-dominated schizophrenia, gender-balanced schizophrenia and bipolar disorder samples based on published voxel-based morphometry (VBM) studies. In total, 72 English-language, peer reviewed articles published prior to January 2011 were included. All reports used VBM for comparing schizophrenia or bipolar disorder with controls and reported whole-brain analyses in standard stereotactic space.

RESULTS

GM reductions were more extensive in male-dominated schizophrenia compared to gender-balanced bipolar disorder and schizophrenia. In gender-balanced samples, GM reductions were less severe. Compared to controls, GM reductions were restricted to dorsal anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex in schizophrenia and ACC and bilateral fronto-insular cortex in bipolar disorder.

CONCLUSIONS

When gender is controlled, GM abnormalities in bipolar disorder and schizophrenia are mostly restricted to regions that have a role in emotional and cognitive aspects of salience respectively. Dorsomedial and dorsolateral prefrontal cortex were the only regions that showed greater GM reductions in schizophrenia compared to bipolar disorder.

Does the salience network play a cardinal role in psychosis? An emerging hypothesis of insular dysfunction

The insular cortex is one of the brain regions that show consistent abnormalities in both structural and functional neuroimaging studies of schizophrenia. In healthy individuals, the insula has been implicated in a myriad of physiologic functions. The anterior cingulate cortex (ACC) and insula together constitute the salience network, an intrinsic large-scale network showing strong functional connectivity. Considering the insula as a functional unit along with the ACC provides an integrated understanding of the role of the insula in information processing. In this review, we bring together evidence from imaging studies to understand the role of the salience network in schizophrenia and propose a model of insular dysfunction in psychosis.

Putative structural neuroimaging endophenotypes in schizophrenia: a comprehensive review of the current evidence

The genetic contribution to schizophrenia etiopathogenesis is underscored by the fact that the best predictor of developing schizophrenia is having an affected first-degree relative, which increases lifetime risk by tenfold, as well as the observation that when both parents are affected, the risk of schizophrenia increases to approximately 50%, compared with 1% in the general population. The search to elucidate the complex genetic architecture of schizophrenia has employed various approaches, including twin and family studies to examine co-aggregation of brain abnormalities, studies on genetic linkage and studies using genome-wide association to identify genetic variations associated with schizophrenia. ‘Endophenotypes’, or ‘intermediate phenotypes’, are potentially narrower constructs of genetic risk. Hypothetically, they are intermediate in the pathway between genetic variation and clinical phenotypes and can supposedly be implemented to assist in the identification of genetic diathesis for schizophrenia and, possibly, in redefining clinical phenomenology.

Voxel-based morphometry (VBM) studies in schizophrenia-can white matter changes be reliably detected with VBM?

Voxel-based morphometry (VBM) is a hypothesis-free, whole-brain, voxel-by-voxel analytic method that attempts to compare imaging data between populations. Schizophrenia studies have utilized this method to localize differences in diffusion tensor imaging (DTI) derived fractional anisotropy (FA), a measure of white matter integrity, between patients and healthy controls. The number of publications has grown, although it is unclear how reliable and reproducible this method is, given the subtle white matter abnormalities expected in schizophrenia. Here we analyze and combine results from 23 studies published to date that use VBM to study schizophrenia in order to evaluate the reproducibility of this method in DTI analysis. Coordinates of each region reported in DTI VBM studies published thus far in schizophrenia were plotted onto a Montreal Neurological Institute atlas, and their anatomical locations were recorded. Results indicated that the reductions of FA in patients with schizophrenia were scattered across the brain. Moreover, even the most consistently reported regions were reported independently in less than 35% of the articles studied. Other instances of reduced FA were replicated at an even lower rate. Our findings demonstrate striking inconsistency, with none of the regions reported in much more than a third of the published articles. This poor replication rate suggests that the application of VBM to DTI data may not be the optimal way for finding the subtle microstructural abnormalities suggested in schizophrenia.

Putative diffusion tensor neuroimaging endophenotypes in schizophrenia: a review of the early evidence

Although schizophrenia has a high heritability, the genetic effects conferring diathesis to schizophrenia are thought to be complex and underlain by multifactorial polygenic inheritance. ‘Endophenotypes’, or ‘intermediate phenotypes’, are narrowed constructs of genetic risk that are assumed to be more proximal to the gene effects in the disease pathway than clinical phenotypes. A current aim in schizophrenia research is to identify promising putative endophenotypes for use in molecular genetics studies. Recently, much of the focus has been on neurocognitive, conventional T1-weighted structural MRI, functional MRI and electrophysiological endophenotypes. Diffusion tensor imaging has emerged as another important structural neuroimaging modality in the aim to identify abnormalities in brain connectivity and diffusivity in schizophrenia, and abnormalities detected via this method may be promising candidate endophenotypes. In this article, we present the first comprehensive review of the early evidence that qualifies diffusion tensor abnormalities as potentially appropriate endophenotypes of schizophrenia.

Neuroanatomical abnormalities in schizophrenia: a multimodal voxelwise meta-analysis and meta-regression analysis

Despite an increasing number of published voxel based morphometry studies of schizophrenia, there has been no adequate attempt to examine gray (GM) and white matter (WM) abnormalities and the heterogeneity of published findings. In the current article, we used a coordinate based meta-analysis technique to simultaneously examine GM and WM abnormalities in schizophrenia and to assess the effects of gender, chronicity, negative symptoms and other clinical variables. 79 studies meeting our inclusion criteria were included in the meta-analysis. Schizophrenia was associated with GM reductions in the bilateral insula/inferior frontal cortex, superior temporal gyrus, anterior cingulate gyrus/medial frontal cortex, thalamus and left amygdala. In WM analyses of volumetric and diffusion-weighted images, schizophrenia was associated with decreased FA and/or WM in interhemispheric fibers, anterior thalamic radiation, inferior longitudinal fasciculi, inferior frontal occipital fasciculi, cingulum and fornix. Male gender, chronic illness and negative symptoms were associated with more severe GM abnormalities and illness chronicity was associated with more severe WM deficits. The meta-analyses revealed overlapping GM and WM structural findings in schizophrenia, characterized by bilateral anterior cortical, limbic and subcortical GM abnormalities, and WM changes in regions including tracts that connect these structures within and between hemispheres. However, the available findings are biased towards characteristics of schizophrenia samples with poor prognosis.

A schizophrenia risk gene, ZNF804A, influences neuroanatomical and neurocognitive phenotypes

ZNF804A is one of the strongest candidate genes for schizophrenia (SZ), yet its function and role in disease pathophysiology are largely unknown. The only in vivo endophenotype study of the SZ-associated SNP (rs1344706) pointed towards effects on brain functional connectivity. We examined the relationship of this SNP to neuroanatomical and neurocognitive phenotypes that were assessed in healthy individuals. Volunteers with no history of psychiatric illness were assessed with structural magnetic resonance imaging (1.5T GE scanner, standard gradient-echo acquisition). Carriers of the minor allele were compared with homozygotes for the T (SZ-associated) allele on measures of total volume of the white matter (WM), gray matter (GM), and cerebrospinal fluid compartments, as well as on voxel-wise measurements of regional brain volumes. After examining the correlation between genotype-associated regions of interest and neurocognitive performance measures, the effects of rs1344706 genotype on a measure of visuomotor performance speed (trails A) were examined in an independent cohort of volunteers. Among healthy subjects, risk allele homozygotes showed larger total WM volumes than carriers of the other allele. Controlling for WM volumes, these same subjects showed reduced GM volumes in several regions comprising the 'default mode network,' including angular gyrus, parahippocampal gyrus, posterior cingulate, and medial orbitofrontal gyrus/gyrus rectus (FDR-corrected p<0.05). The risk allele dosage also predicted impairments on a timed visuomotor performance task (trails A). Results support a role of ZNF804A in phenotypes reflecting altered neural connectivity.

The efficacy of a voxel-based morphometry on the analysis of imaging in schizophrenia, temporal lobe epilepsy, and Alzheimer's disease/mild cognitive impairment: a review

Voxel-based morphometry (VBM) done by means of MRI have provided new insights into the neuroanatomical basis for subjects with several conditions. Recently, VBM has been applied to investigate not only regional volumetric changes but also voxel-wise maps of fractional anisotropy (FA) computed from diffusion tensor imaging (DTI). The aim of this article is to review the recent work using VBM technique in particular focusing on schizophrenia, temporal lobe epilepsy (TLE), and Alzheimer's disease (AD)/mild cognitive impairment (MCI). In patients with schizophrenia, VBM approach detects the structural brain abnormalities that appear normal on conventional MRI. Moreover, this technique also has the potential to emerge as a useful clinical tool for early detection and monitoring of disease progression and treatment response in patients with schizophrenia or AD/MCI. In TLE, VBM approach may help elucidate some unresolved important research questions such as how recurrent temporal lobe seizures affect hippocampal and extrahippocampal morphology. Thus, in the future, large cohort studies to monitor whole brain changes on a VBM basis will lead to a further understanding of the neuropathology of several conditions.