Delusional disorder in a boy with phenylketonuria and amine metabolites in the cerebrospinal fluid after treatment with neuroleptics.

A case report of a 16-year-old boy with the classical form of phenylketonuria (PKU) and suffering from a delusional disorder is presented. He did not respond to a traditional antipsychotic medication but improved on an atypical antipsychotic, risperidone. The cerebrospinal fluid metabolites of the biogenic amines were measured and are also reported in the context of a recent interest in the ratios of these amine metabolites in schizophrenia. It is proposed that such dually diagnosed patients with PKU may provide a model in which to test the prevalent biogenic amine theories in psychiatric disorders.