Delusional misidentification and platelet monoamine oxidase.

Recently, reduced platelet monoamine oxidase (MAO) activity was demonstrated in two cases of paranoid schizophrenia exhibiting Capgras' syndrome. The present authors report platelet MAO studies in an additional patient with the Delusion of Doubles. In this case, one of delusional hyperidentification (false recognition), decreased platelet MAO activity compared with normal controls was detected. The patient, while not schizophrenic, showed platelet MAO activity comparable with that of a chronic schizophrenic control group. The possible significance of the findings are discussed.