A high prevalence of depressive symptoms, hypothetically related to serotonergic dysfunction, have been reported among adults with celiac disease[32] Adolescent celiac disease patients with depression have significantly lower pre-diet tryptophan/competing amino-acid (CAA) ratios and free tryptophan concentrations, and significantly higher biopsy morning prolactin levels compared to those without depression[33]. This evidence concerns the gene PRL and depressive disorder.