No Tryptophan, Tyrosine and Phenylalanine Abnormalities in Children with Attention-Deficit/Hyperactivity Disorder.

BACKGROUND: The aim of the current study was to explore the role of aromatic amino acids (AAAs) in blood in relation to attention-deficit/hyperactivity disorder (ADHD). Given their impact on the synthesis of serotonin and dopamine, decreased concentrations of the AAAs tryptophan, tyrosine and phenylalanine in blood may contribute to the expression of ADHD symptoms. Decreased AAA blood concentrations, in turn, may be related to lowered dietary protein intake or to abnormal AAA catabolism, as evidenced by increased urinary AAA concentrations. METHODS: Eighty-three children with ADHD (75% males) and 72 typically developing (TD) children (51% males), aged 6 to 13 years, participated in the study. AAA concentrations were assessed in blood spots and an 18-hour urinary sample. A nutritional diary was filled out by parents to calculate dietary protein intake. Parent and teacher questionnaires assessed symptoms of ADHD, oppositional defiant disorder, conduct disorder, and autism spectrum disorder. RESULTS: Children with ADHD showed normal AAA concentrations in blood spots and urine, as well as normal protein intake compared to controls. No associations between AAA concentrations and symptoms of ADHD or comorbid psychiatric disorders were found. CONCLUSIONS: This study is the first to explore AAA metabolism in children with ADHD using a well-defined and relatively large sample. We found that AAA deficiencies are not related to ADHD. The results do not support treatment with AAA supplements in children with ADHD. Future studies regarding the cause of serotonin and dopamine alterations in ADHD should focus on other explanations, such as effects of altered transport of AAAs.

Effects of d,l-fenfluramine on aggressive and impulsive responding in adult males with a history of conduct disorder.

RATIONALE: The role of serotonin in aggression and impulsivity was examined by administering the serotonin-releasing drug, d, l-fenfluramine and measuring effects on aggressive and impulsive responding under controlled laboratory conditions. METHODS: Ten male subjects with a history of conduct disorder and criminal behavior participated in experimental sessions, which measured aggressive and impulsive responses. Aggression was measured using the Point subtraction Aggression paradigm (PSAP), which provides subjects with an aggressive, escape and monetary reinforced response options. Impulsive responses were measured using a paradigm which provided subjects with choices between small rewards after short delays versus larger rewards have long delays. RESULTS: Acute challenge doses (0.2,0.4 and 0.8 mg/kg) of d,l-fenfluramine produced significant dose-dependent decreases in aggressive and impulsive responses. Escape and monetary reinforced responses were not significantly changed. Decreases in aggressive responses were therefore selective, because escape responses were not affected, and could not be attributed to a non-specific sedative action because monetary reinforced responses were slightly increased. CONCLUSIONS: Release of serotonin and/or reuptake blockade by d,l-fenfluramine is the possible mechanism for reductions in aggression and impulsivity. These results are consistent with a large body of data linking reduced serotonin function and aggressive behavior and impulsivity.