Evidence of association between smoking and alpha7 nicotinic receptor subunit gene in schizophrenia patients.

A number of studies have suggested that the alpha-7-nicotinic receptor D15S1360 polymorphism is associated with schizophrenia and a deficiency in the normal inhibition of the P50 auditory-evoked response. Schizophrenia patients and some of their unaffected relatives show a failure of inhibition in their 50-ms response to the second of a pair of tones. Biochemical studies have suggested that the alpha7 nicotinic acetylcholine receptor is involved in this sensory gating deficit. Furthermore, high-dose nicotine transiently normalizes the abnormality in P50 inhibition in schizophrenic patients and in their relatives. Schizophrenic patients are unusually heavy smokers, and up to 85% of hospitalized schizophrenic patients smoke. This rate is three times higher than the general population, and may represent an attempt to self-medicate through this pathophysiologic mechanism. Despite schizophrenics' extremely heavy nicotine use, nicotinic receptor genes have not been previously investigated in relation to smoking in schizophrenia. In this study, we hypothesized that the D15S1360 marker is associated with smoking in patients with schizophrenia. We found an association between the homozygous 113 bp allele and smoking risk (chi2=10.37, 3 df, p=0.015). Although this novel finding requires replication, it suggests that further study into the relationship between schizophrenia and nicotine system genes is warranted.