The results presented here do not support the hypothesis that DSM-IV OCD diagnosis is associated with MAO-A or COMT. Results were also negative in the additional analyses performed: 1) one that examined a strictly defined phenotype that consisted of individuals with OCD and tic disorders; 2) one that examined a broadly defined phenotype that included OCD, subclinical OCD; 3) one that included other OCD spectrum disorders; and 4) one COMT-MAOA epistasis analysis. This evidence concerns the gene MAOA and tic disorder.