Furthermore, as no absolute measures of brain activity are provided with BOLD, the relative change needs to be interpreted with caution. Pharmacologic fMRI is a potentially powerful methodology when integrated with well-designed
and informative pharmacologic paradigms. Neuroimaging genomics The application of fMRI in genetic paradigms is growing rapidly. Initial studies have examined Inhibitors,research,lifescience,medical genetic effects indirectly by comparing activation patterns in probands with schizophrenia, unaffected siblings, and healthy comparison subjects with no family history of schizophrenia. Such studies have demonstrated, for Paclitaxel clinical trial example, that there were abnormalities in siblings that were less severe than those seen in affected individuals. This supports the Inhibitors,research,lifescience,medical application of fMRI as a quantitative phenotypic marker of schizophrenia.4,15,26,27 The draft sequence of the human genome offers unprecedented opportunities for direct evaluation of the effects of genetic variability on brain activity. Early work exploiting this potential has demonstrated such effects in healthy people
by comparing activation patterns between genotypically characterized groups. Studies Inhibitors,research,lifescience,medical applying genetic strategies used functional polymorphisms to group individuals for comparisons. For example, a common Val108/158Met substitution in the gene for catechol-O-methyltransferase (COMT) leads to decreased activity of this enzyme in dopamine catabolism and has been linked to decreased prefrontal cortical activity. Studies therefore examined COMT val/met polymorphism and prefrontal cortex Inhibitors,research,lifescience,medical activation.28,29 Individuals homozygous for the met allele had diminished prefrontal and hippocampal engagement while performing episodic Inhibitors,research,lifescience,medical memory encoding and retrieval compared with val/val subjects. In schizophrenia, where disease risk is likely conferred by multiple interacting susceptibility genes, it is necessary to study convergent potential pathways from gene effects to clinical manifestations. Several at-risk genes implicated in schizophrenia are related
to neuronal function including COMT, dysbindin, neuregulin 1 (NRG1), BDNF, RGS4, and DISC-L Initial work in schizophrenia demonstrated effects of the COMT polymorphism on cognition and prefrontal function and risk for schizophrenia. Using a similar approach about a risk haplotype was examined in GRM3, a gene encoding a metabotropic glutamate receptor. The findings were of reduced neuronal function in prefrontal cortex and impaired activation in the hippocampus during performance of a verbal memory task. The risk allele in the NRG 1 promoter region was associated with decreased activation of prefrontal and temporal lobe cortex. This research has great potential for constructing mechanistic models for the pathophysiology of schizophrenia.