Abstract: A method of treating a subject for a serotonergic neurotransmission dysregulation disorder, comprises administering the subject a serotonin enhancer (e.g., a serotonin reuptake inhibitor) in an amount effective to treat the disorder; and concurrently administering the subject 5-hydroxytryptophan in an amount effective to enhance the activity of the serotonin enahancer, (e.g., serotonin reuptake inhibitor). In preferred embodiments the disorder is depression, anxiety, or substance abuse.

Abstract: A method of screening a subject for a serotonergic neurotransmission dysregulation disorder comprises detecting the presence or absence of an Tph2 mutation in the subject; and then determining that the subject is at increased risk of a serotonergic neurotransmission dysregulation disorder due to the presence or absence of the Tph2 mutation.