Various alterations in corresponding genes affect the levels of serotonin or sensitivity to serotonin and may cause behavioral changes. Changes in serotonin level can affect behavior. The level of serotonin is controlled by multiple mechanisms.Any changes in the genes involved may lead to serious consequences.everal genetic alterations in the gene for tryptophan hydroxylase were reported to be associated with suicidal behavior. This enzyme is involved in biosynthesis of serotonin, and therefore its genetic alterations can easily affect the level of this mediator.