SLC6A4 and Anxiety: An open trial of citalopram in children and adolescents with depressive or anxiety symptoms found that youth who were homozygous for the “short” allele (S/S) of the SLC6A4 gene exhibited poor antidepressant treatment response for depressive symptoms (but not for anxiety symptoms) compared to youth who were homozygous for the “long” allele (L/L) of SLC6A4 [77].