Tobacco addiction as a marker of age at onset of schizophrenia.

Schizophrenia is a heterogenous disorder, with diversity in symptoms, course, prognosis, and probably etiology. The timing of its onset (i.e., early vs. late) not only predicts outcome of illness, but also corresponds to fundamental neurochemical and neuroendocrine distinctions. There is recent evidence that early age at onset of schizophrenia is associated with more prominent negative symptoms, which are associated with decreased dopaminergic functions in the limbic system. Since addictive behaviour may be related to decreased dopamine activity in the mesolimbic reward circuitry, we predict a higher prevalence of tobacco addiction in patients with an earlier age at onset of schizophrenia. To investigate this hypothesis, we studied the association of cigarette smoking to age at onset of illness in a sample of 142 chronic schizophrenic inpatients, 73 of whom were smokers. We found that patients who smoked had a significantly earlier age at onset of psychiatric illness as compared to the nonsmokers (p less than .01). Since damage to dopaminergic systems at the lateral hypothalamic level of the medial forebrain bundle and in the ventral tegmental reward system produces the strongest indication of reward, our data suggest that alterations in dopaminergic functions in these systems may be linked to the timing of onset of schizophrenic symptoms.