COMT and Atypical behavior: Furthermore, this study showed that Hp increased monoamine oxidase (MAO-B) and catechol-O-methyltransferase (COMT) gene expression, the enzymes involved in the catabolism of catecholamines and serotonin, and decreased norepinephrine, dopamine and serotonin levels, downregulating the monoaminergic system, which may be a cause of behavioral disorders (Leone et al., 2017).