Is schizophrenia an HLA-associated disease?

Contribution from MHC-Mediated Risk in Schizophrenia Can Reflect a More Ethnic-Specific Genetic and Comorbid Background

The immune system seems to play a significant role in the development of schizophrenia. This becomes more evident with the emerging role of MHC complex and cytokines in schizophrenia. In the recent past, several GWAS have implied that the 6p21 region was associated with schizophrenia. However, the majority of these studies were performed in European populations. Considering tremendous variations in this region and the probability of South Indian populations being quite different from the European gene-pool from an immunogenetic point, the present study was initiated to screen SNPs in the 2.28 MB region, spanning the extended MHC locus, in 492 cases and controls from a South Indian population. We found a very strong association of rs3815087 with schizophrenia at both allelic and genotypic levels with a 7.3-fold increased risk in the recessive model. Interestingly, the association of none of the earlier reported GWAS hits, such as rs3130375, rs3131296, rs9272219, or rs3130297 were found to be replicable in our study population. rs3815087 lies in the 5′UTR region of the psoriasis susceptibility 1 candidate 1 (PSORS1C1) gene, which further suggests that inflammatory processes might be an important common pathogenic pathway leading to both schizophrenia and psoriasis. The study hints at ethnic specific gene–environment interaction in determining the critical threshold for disease initiation and progression.

Microglia Activation and Schizophrenia: Lessons From the Effects of Minocycline on Postnatal Neurogenesis, Neuronal Survival and Synaptic Pruning

The implication of neuroinflammation in schizophrenia, sustained by recent genetic evidence, represents one of the most exciting topics in schizophrenia research. Drugs which inhibit microglia activation, especially the classical tetracycline antibiotic minocycline are currently under investigation as alternative antipsychotics. However, recent studies demonstrated that microglia activation is not only a hallmark of neuroinflammation, but plays important roles during brain development. Inhibition of microglia activation by minocycline was shown to induce extensive neuronal cell death and to impair subventricular zone (SVZ) neurogenesis and synaptic pruning in the early postnatal and adolescent rodent brain, respectively. These deleterious effects contrast with the neuroprotective actions of minocycline at adult stages. They are of potential importance for schizophrenia, since minocycline triggers similar pro-apoptotic effects in the developing brain as NMDA receptor (NMDAR) antagonists, known to induce long-term schizophrenia-like abnormalities. Moreover, altered postnatal neurogenesis, recently described in the human striatum, was proposed to induce striatal dopamine dysregulation associated with schizophrenia. Finally, the effect of minocycline on synapse remodeling is of interest considering the recently reported strong genetic association of the pruning-regulating complement factor gene C4A with schizophrenia. This raises the exciting possibility that in conditions of hyperactive synaptic pruning, as supposed in schizophrenia, the inhibitory action of minocycline turns into a beneficial effect, with relevance for early therapeutic interventions. Altogether, these data support a differential view on microglia activation and its inhibition. Further studies are needed to clarify the relevance of these results for the pathogenesis of schizophrenia and the use of minocycline as antipsychotic drug.

Recent genetic findings in schizophrenia and their therapeutic relevance

Over 100 loci are now associated with schizophrenia risk as identified by single nucleotide polymorphisms (SNPs) in genome-wide association studies. These findings mean that 'genes for schizophrenia' have unquestionably been found. However, many questions remain unanswered, including several which affect their therapeutic significance. The SNPs individually have minor effects, and even cumulatively explain only a modest fraction of the genetic predisposition. The remainder likely results from many more loci, from rare variants, and from gene-gene and gene-environment interactions. The risk SNPs are almost all non-coding, meaning that their biological significance is unclear; probably their effects are mediated via an influence on gene regulation, and emerging evidence suggests that some key molecular events occur during early brain development. The loci include novel genes of unknown function as well as genes and pathways previously implicated in the pathophysiology of schizophrenia, e.g. NMDA receptor signalling. Genes in the latter category have the clearer therapeutic potential, although even this will be a challenging process because of the many complexities concerning the genetic architecture and mediating mechanisms. This review summarises recent schizophrenia genetic findings and some key issues they raise, particularly with regard to their implications for identifying and validating novel drug targets.

Analysis of the role of human leukocyte antigen class-I genes to understand the etiopathology of schizophrenia

BACKGROUND

Schizophrenia is the paradigmatic illness of psychiatry. The involvement of immunological and immunopathological mechanisms in the etiopathogenesis of schizophrenia has been a matter of research, with recently increasing effort.

AIMS

In this study, we investigated the incidence of human leukocyte antigen (HLA) Class I antigens to understand the role of HLA genes in schizophrenia.

MATERIALS AND METHODS

India born schizophrenic patients in and around Siliguri who attended outpatient department (OPD) of Department of Psychiatry, North Bengal Medical College and Hospital were considered for the present study. After the longitudinal follow up, 50 patients were enrolled for the study. The same number of age, sex and ethnically matched healthy subjects were considered as control. Low resolution polymerase chain reaction-sequence specific primer method was applied for typing the HLA antigens.

STATISTICS

The phenotype frequencies were calculated by direct count. chi(2) test was done to compare the frequency of each antigen among the patients and control group and it was followed by Fisher's exact test. Relative risk was estimated by using Haldane's method.

RESULTS

The result showed that some of the HLA antigens are associated with the schizophrenia and significant increase were observed for HLA A*03 antigen along with the significant decrease for HLA A*25, A*31 and HLA B*51.

CONCLUSIONS

The study provides the evidence for the possible existence of susceptibility locus for schizophrenia within the HLA region. This preliminary observation may help to understand the etiological basis of this disorder and the study may further strengthen the HLA antigens as the marker for schizophrenia.

Genetic associations between delusional disorder and paranoid schizophrenia: A novel etiologic approach

OBJECTIVES

Genetic associations between delusional disorder and paranoid schizophrenia are not well understood, although involvement of biological factors has been suspected. We investigated the incidence of human leukocyte antigen (HLA) class I alleles in patients with delusional disorder and paranoid schizophrenia, first, to explore a possible immunogenetic etiology of these paranoid disorders and, second, to determine whether they share similar etiologic mechanisms.

METHOD

We employed a nested case-control study design. Psychiatric reference data were available for 38,500 patients attending a hospital-based psychiatric outpatient department between 1998 and 2005. We enrolled 100 patients with delusional disorder and 50 patients with paranoid schizophrenia as the subject cases, using DSM-IV criteria. We considered equivalent numbers of healthy volunteers matched for age and ethnic background as control subjects. All subjects came from an India-born Bengali population. We applied the polymerase chain reaction-based molecular typing method to all patients and healthy subjects.

RESULTS

The HLA-A*03 gene is significantly associated with delusional disorder as well as with paranoid schizophrenia. This HLA gene alone or in linkage disequilibrium with other HLA genes or other closely linked non-HLA genes may influence susceptibility to delusional disorder and paranoid schizophrenia.

CONCLUSIONS

The study reveals important associations between HLA genes and paranoid disorders. Delusional disorder and paranoid schizophrenia may share similar etiologic mechanisms. This preliminary observation may help our understanding of the genetic basis of these paranoid disorders.

Human leukocyte antigen DR1 in Japanese and Turkish patients with schizophrenia

The main focus of this review has been to discuss the probable causes of the higher frequency of HLA DR1 antigen in patients with schizophrenia from Japan and Turkey, and also to see whether there was an impact of belonging to the Ural-Altaic language group. A general medline search on the terms HLA and schizophrenia was used as the method to determine HLA studies in patients with schizophrenia. Most of the findings were inconsistent regarding the increased or decreased frequencies of different Class I and II antigens. However, there were interesting results, which have been consistently repeated in several Japanese studies and in a Turkish study. HLA DR1 antigen was statistically significantly increased in Japanese and Turkish patients with schizophrenia. As Japanese and Turkish languages belong to the Ural-Altaic language group, HLA DR1 antigen might have a specific association with schizophrenia in Japanese and Turkish patients. Searching the frequency of HLA DR1 antigen in patients with schizophrenia in other members of Ural-Altaic language group is necessary to support this hypothesis. Other language groups (e.g. Indo-European) should be assessed as well.

Schizophrenia and HLA: a review

A number of reports of genetic association of human leucocyte antigens (HLA) and alleles with schizophrenia have recently been published. A schizophrenia locus on chromosome 6p near the HLA region has also been reported, on the basis of linkage studies. We have therefore reviewed the investigations of association of HLA with schizophrenia published from 1974 to date, and have also briefly reviewed the chromosome 6p linkage studies. Two or more groups of investigators have reported association of each of the following HLA antigens or alleles with schizophrenia - A9 or its A24 subspecificity, A28, A10, DRB1*01 and DRw6. However, these results may represent Type I errors caused by small sample size, inappropriate diagnostic, laboratory and/or statistical methodology, and/or incorrectly chosen comparison subjects. Hypothesis-driven negative associations of DRB1*04 and DQB1*0602 with schizophrenia have also been reported. Taken together, however, HLA association investigations provide only weak evidence for the existence of either resistance or susceptibility loci for schizophrenia close to the HLA region at the 6p21.3 band and, indeed, recently reported investigations that controlled for most of these confounders found no evidence of association. Linkage studies suggest that a susceptibility locus may exist and that it may be within the HLA region, but again the evidence is far from conclusive. Further HLA association investigations should employ operational diagnostic criteria, comparison subjects screened for illness and HLA genotyping, and should include both association studies of candidate alleles and transmission disequilibrium and haplotype relative risk studies.

Association between HLA-A1 allele and schizophrenia gene(s) in patients refractory to conventional neuroleptics but responsive to clozapine medication

We report an association between HLA-A1 allele and a subgroup of schizophrenic patients refractory to conventional neuroleptic treatment but responsive to clozapine. The frequency of HLA-A1 was 58% among the schizophrenic patients not responding to conventional treatment but responsive to clozapine but only 10.5% among the patients responding to conventional neuroleptics. The HLA-A1 occurs in 20% of the random Finnish population. Our results indicate that HLA-A1 defines a subgroup of schizophrenic patients with a selective response to neuroleptics.

Failure to find interference between anti-HLA antibodies and chlorpromazine

Chlorpromazine has been reported to interfere with the action of alloantibodies directed against HLA-A1. We attempted to replicate this finding using peripheral blood lymphocytes from 3 healthy donors in a complement-mediated lymphocytotoxicity assay. We were unable to find evidence of interference between chlorpromazine and the anti-HLA sera tested. Possible reasons for the difference between our finding and the previous report, as well as the implications for schizophrenia, are discussed.

Blood groups and affective disorders

Distributions of seven blood groups (ABO, MNSs, P, Rh, Duffy, Kidd and Xg) were studied in a total of 118 Japanese patients with affective disorders. The patients were diagnosed according to the DSM-III: (1) Major Depression (= Unipolar Disorder, UP) (2) Bipolar Disorder (BP) and (3) Other Affective Disorders. The following results were found: (1) a high frequency of the B blood group in all patients with affective disorders compared with controls; (2) a high frequency of the Fy(a+b+) and a low frequency of the Fy(a+b-) in all patients with affective disorders, UP and BP compared with controls; (3) a low frequency of the Jk(a+b+) and a high frequency of the Jk(a+b-) in BP compared with controls and with UP.

Is there really a split in schizophrenia? The genetic evidence

Although the clinical presentation and course of schizophrenia is highly variable, it is unclear whether this reflects heterogeneity at an aetiological level. The genetic evidence is reviewed concerning 'traditional' clinical subtypes as more novel categories derived from multivariate statistical methods and Crow's type I-type II classification. Recent data based on a twin series and re-analysis of older published family material suggest that attempts to divide up schizophrenia have resulted in splits between two or more categories of disorder which occupy different positions on the same continuum of liability. Thus, apparent heterogeneity is more likely to be due to quantitative difference in familial-genetic loading rather than qualitative differences. Similarly, the hypothesis that schizophrenia can be broadly divided into two groups, one genetic and the other non-genetic has little to support it. It seems improbable that any further useful and genetically relevant subdivision of schizophrenia can be effected on purely clinical grounds. Further progress awaits developments in the discovery of endophenotypes and the application of molecular genetic marker strategies.

Affective disorders and ABO blood groups: new data and a reanalysis of the literature using the logistic transformation of proportions

No statistically significant associations were found between ABO blood group distributions and RDC subtype diagnoses in 79 subjects with unipolar (single episode and recurrent) and bipolar major depressive disorder using data from our sample. We discuss methodological issues related to the control samples and choice of statistical methods in the reported studies which have looked for associations between ABO blood types and patients diagnosed as having an affective disorder. After presenting our rationale for employing the logarithm of the cross product ratio (lambda) in place of the more traditionally utilized chi-squared, we used lambda to reanalyze the original data from nine studies in the literature. The individual studies are equivocal on the basic issue of an association between type O blood and bipolar I illness, either compared to controls or to recurrent unipolar patients. The combined (weighted average) measure of association indicates a small but definite association, but statistical analysis of the dispersion of the individual estimates around this combined estimate reveals that the studies have a higher degree of heterogeneity in results than expected by chance. The consequences of this finding are discussed, and possible explanations are offered.

Immunoglobulin allotypes Gm and Km in chronic schizophrenia: no apparent association

The distribution of the immunoglobulin allotypic markers G1m(1), G1m(2), G1m(3), G3m(5) and Km(1) was determined in 168 hospitalized Caucasian chronic schizophrenic patients and compared with that in healthy controls. No association between Gm or Km phenotypes and chronic schizophrenia is apparent.

A family study of HLA antigens and other genetic markers in schizophrenia

HLA antigens and 19 other genetic marker systems were studied in 12 families containing 2 or more members diagnosed as schizophrenic. In contrast with previous reports we could exclude linkage between the disorder and HLA, and we found no evidence of linkage with Gm or Gc. The disagreement between our results and those of a previous study, which suggested linkage between HLA and schizophrenia, could not be explained on the basis of genetic heterogeneity within the disorder. The problems of performing a linkage study in the face of diagnostic uncertainty and an unknown mode of inheritance of the main trait are discussed, and the measures taken in attempts to overcome these difficulties are described. Despite present drawbacks, genetic marker studies hold future promise as a means of detecting major gene effects in schizophrenia and other familial psychiatric disorders.

HLA antigens and subtypes of schizophrenia

Studies on HLA antigens in schizophrenia have produced conflicting results, but there has been greater agreement when clinical subtypes of the disorder have been separated. In view of this, we reassessed 68 previously studied patients with hospital diagnoses of schizophrenia and, while blind to their HLA types, used operational criteria to define clinical subtypes. We compared and combined the results with those from all available similar studies. Those of our patients who fulfilled operational criteria for paranoid schizophrenia showed a nonsignificant increase in HLA A9 as compared with controls. The magnitude of the increase was similar to that from all previous reports, and when data from all sources were combined, the evidence for an association between HLA A9 and paranoid schizophrenia was consistent and highly significant. Patients who were diagnosed as suffering from hebephrenic schizophrenia showed significant increases in HLA A1 and B8 compared with controls. An association between hebephrenia and A1, but not B8, remained on combining the results with those of other studies.