Dopamine Psychosis in Schizophrenia? Molecular Genetic Study on Delusional Disorder

Delusional disorder is characterized by mono-symptomatic paranoid symptoms without other schizophrenic symptoms. Thus, delusional disorder can be a good clinical model for investigating the molecular genetic mechanisms for paranoid symptoms. In this study, we hypothesized that a hyperdopaminergic state in the brain is responsible for producing paranoid symptoms. To test this hypothesis, we (1) compared neuroleptic responses between patients with delusional disorder and schizophrenia, (2) measured plasma levels of homovanillic acid (pHVA), an indicator of brain dopamine activity, in patients with delusional disorder, and (3) analysed the polymorphism of dopamine receptors (DRs) and its synthesizing enzyme gene.