Glutamate NMDA receptor antagonism is associated with increased amphetamine-induced dopamine release in healthy humans [96], indicating the importance of glutamatergic control over subcortical dopamine. Regional specificity to the head of caudate is consistent with extensive connection of this striatal subregion with the prefrontal cortex [80]. Prefrontal pathology as a genetically mediated trait in schizophrenia is supported by findings of reduced gray matter volume [97] and deficits are frontally mediated cognitive functioning [98] in unaffected co twins of patients with schizophrenia. Increased striatal D2 receptors may be more readily detected in individuals at genetic risk, because they probably lack the higher synaptic dopamine concentration that occurs in schizophrenia [35,36] and that may occupy D2 receptors [99]. This hypothesis predicts that striatal dopamine D2 receptor may be a viable biomarker of vulnerability to schizophrenia. Whether this biomarker is useful for genetic association studies or clinical studies on early interventions remains to be seen.
If dopaminergic abnormalities in schizophrenia are genetically determined, which genes are involved? The gene for D2 receptors has many polymorphisms, some of which affect receptor binding in vivo. A recent meta-analysis identified over-representation of the C allele of the C957T polymorphism in schizophrenia