Association between clozapine response and allelic variation in the 5-HT2C receptor gene

A cysteine to serine substitution at amino acid 23 in the 5-HT 2C receptor gene alters the pharmacological properties of the protein. We investigated this polymorphism in subjects with schizophrenia resistant to conventional neuroleptic drugs, and analysed our data for allelic association between the disease state or clinical response to the atypical antipsychotic drug, clozapine. Ninety percent of subjects who had one or more 5-HT 2C ser alleles (19/21) were classified as clozapine responders compared with 59% (84/141) without this allele (χ 2 = 7.7, p = 0.005), suggesting that this mutation is a predictor of good response to clozapine. There was no association between schizophrenia and the 5-HT 2C ser allele, but our results indicate that the 5-HT 2C receptor may contain the major site of action through which clozapine mediates its antipsychotic effects.