A gene expression and systems pathway analysis of the effects of clozapine compared to haloperidol in the mouse brain implicates susceptibility genes for schizophrenia.

Clozapine has markedly superior clinical properties compared to other antipsychotic drugs but the side effects of agranulocytosis, weight gain and diabetes limit its use. The reason why clozapine is more effective is not well understood. We studied messenger RNA (mRNA) gene expression in the mouse brain to identify pathways changed by clozapine compared to those changed by haloperidol so that we could identify which changes were specific to clozapine. Data interpretation was performed using an over-representation analysis (ORA) of gene ontology (GO), pathways and gene-by-gene differences. Clozapine significantly changed gene expression in pathways related to neuronal growth and differentiation to a greater extent than haloperidol; including the microtubule-associated protein kinase (MAPK) signalling and GO terms related to axonogenesis and neuroblast proliferation. Several genes implicated genetically or functionally in schizophrenia such as frizzled homolog 3 (FZD3), U2AF homology motif kinase 1 (UHMK1), pericentriolar material 1 (PCM1) and brain-derived neurotrophic factor (BDNF) were changed by clozapine but not by haloperidol. Furthermore, when compared to untreated controls clozapine specifically regulated transcripts related to the glutamate system, microtubule function, presynaptic proteins and pathways associated with synaptic transmission such as clathrin cage assembly. Compared to untreated controls haloperidol modulated expression of neurotoxic and apoptotic responses such as NF-kappa B and caspase pathways, whilst clozapine did not. Pathways involving lipid and carbohydrate metabolism and appetite regulation were also more affected by clozapine than by haloperidol.

Failure to confirm genetic association between schizophrenia and markers on chromosome 1q23.3 in the region of the gene encoding the regulator of G-protein signaling 4 protein (RGS4).

The chromosome 1q23.3 region, which includes the RGS4 gene has been implicated in genetic susceptibility to schizophrenia by two linkage studies with lod scores of 6.35 and 3.20 and with positive lod between 2.00 and 3.00 scores in several other studies. Reduced post mortem RGS4 gene expression in the brain of schizophrenics was reported as well as positive allelic association between markers at the RGS4 gene locus and schizophrenia. We have attempted to replicate the finding of allelic association with schizophrenia in a UK based sample of 450 subjects with schizophrenia and 450 supernormal controls. We genotyped the same SNP marker alleles investigated in the earlier studies and also a di-nucleotide (GT)14 repeat microsatellite marker, which was 7 kb distal to RGS4. In the new UK sample there was no evidence for allelic or haplotypic association between RGS4 markers and schizophrenia. This might reflect genetic heterogeneity between the population samples, genotyping or other methodological problems. The finding weakens the evidence that mutations or variation in the RGS4 gene have an effect on schizophrenia susceptibility.