GRM3, a metabotropic glutamate receptor-modulating synaptic glutamate, is a promising schizophrenia candidate gene. In a familybased association study, a common GRM3 haplotype was strongly associated with schizophrenia (P ‫؍‬ 0.0001). Within this haplotype, the A allele of single-nucleotide polymorphism (SNP) 4 (hCV11245618) in intron 2 was slightly overtransmitted to probands (P ‫؍‬ 0.02). We studied the effects of this SNP on neurobiological traits related to risk for schizophrenia and glutamate neurotransmission. The SNP4 A allele was associated with poorer performance on several cognitive tests of prefrontal and hippocampal function. The physiological basis of this effect was assessed with functional MRI, which showed relatively deleterious activation patterns in both cortical regions in control subjects homozygous for the SNP4 A allele. We next looked at SNP4's effects on two indirect measures of prefrontal glutamate neurotransmission. Prefrontal N-acetylaspartate, an in vivo MRI measure related to synaptic activity and closely correlated with tissue glutamate, was lower in SNP4 AA homozygotes. In postmortem human prefrontal cortex, AA homozygotes had lower mRNA levels of the glial glutamate transporter EAAT2, a protein regulated by GRM3 that critically modulates synaptic glutamate. Effects of SNP4 on prefrontal GRM3 mRNA and protein levels were marginal. Resequencing revealed no missense or splice-site SNPs, suggesting that the intronic SNP4 or related haplotypes may exert subtle regulatory effects on GRM3 transcription. These convergent data point to a specific molecular pathway by which GRM3 genotype alters glutamate neurotransmission, prefrontal and hippocampal physiology and cognition, and thereby increased risk for schizophrenia.

Context The CACNA1C gene (alpha 1C subunit of the L-type voltage-gated calcium channel) has been identified as a risk gene for both bipolar disorder and schizophrenia but the mechanism of association has not been explored. Objective To identify the neural system mechanism that explains the genetic association between the CACNA1C gene and psychiatric illness, using neuroimaging and human brain expression. Design We used BOLD fMRI to measure brain activation in circuitries related to bipolar disorder and schizophrenia by comparing CACNA1C genotype groups in healthy subjects. We tested the effect of genotype on mRNA levels of CACNA1C in post-mortem human brain. A case-control analysis was used to determine the association of CACNA1C genotype and schizophrenia. Setting National Institutes of Health Clinical Center Patients Healthy Caucasian men and women participated in the fMRI study. Post-mortem samples from normal human brains were used for the brain expression study. Patients with schizophrenia and healthy subjects were used in the case-control analysis. Main Outcome Measures BOLD fMRI, mRNA levels in post-mortem brain samples, and genetic association with schizophrenia Results The risk associated single nucleotide polymorphism (SNP rs1006737) in CACNA1C predicted increased hippocampal activity during emotional processing (puncorr=0.001, pFDR=0.052, Z=3.20) and increased prefrontal activity during executive cognition (puncorr=2.8e-05, pFDR=0.011, Z=4.03). The risk SNP also predicted increased expression of CACNA1C mRNA in human brain (p=0.0017). CACNA1C was associated with schizophrenia in our case-control sample (OR 1.77, p=0.026). Conclusions The risk associated SNP in CACNA1C maps to circuitries implicated in genetic risk for both bipolar disorder and schizophrenia. Its effects in human brain expression implicate a molecular and neural systems mechanism for the clinical genetic association.

Cortical GABAergic dysfunction has been implicated as a key component of the pathophysiology of schizophrenia and decreased expression of the gamma-aminobutyric acid (GABA) synthetic enzyme glutamic acid decarboxylase 67 (GAD 67 ), encoded by GAD1, is found in schizophrenic post-mortem brain. We report evidence of distorted transmission of single-nucleotide polymorphism (SNP) alleles in two independent schizophrenia family-based samples. In both samples, allelic association was dependent on the gender of the affected offspring, and in the Clinical Brain Disorders Branch/National Institute of Mental Health (CBDB/NIMH) sample it was also dependent on catechol-O-methyltransferase (COMT) Val158Met genotype. Quantitative transmission disequilibrium test analyses revealed that variation in GAD1 influenced multiple domains of cognition, including declarative memory, attention and working memory. A 5 0 flanking SNP affecting cognition in the families was also associated in unrelated healthy individuals with inefficient BOLD functional magnetic resonance imaging activation of dorsal prefrontal cortex (PFC) during a working memory task, a physiologic phenotype associated with schizophrenia and altered cortical inhibition. In addition, a SNP in the 5 0 untranslated (and predicted promoter) region that also influenced cognition was associated with decreased expression of GAD1 mRNA in the PFC of schizophrenic brain. Finally, we observed evidence of statistical epistasis between two SNPs in COMT and SNPs in GAD1, suggesting a potential biological synergism leading to increased risk. These coincident results implicate GAD1 in the etiology of schizophrenia and suggest that the mechanism involves altered cortical GABA inhibitory activity, perhaps modulated by dopaminergic function.