Furthermore, individuals at risk of developing bulimia nervosa (BN) have trait abnormalities in the regulation of their brain serotonin function that might increase their vulnerability to dieting-induced decreases in plasma tryptophan.1 The gene responsible for 5-HT synthesis, the tryptophan hydroxylase gene (TPH), is a plausible candidate for susceptibility to eating disorders. The gene discussed is TPH1; the disease is eating disorder.