Attention deficit hyperactivity disorder and whole-blood serotonin levels: effects of comorbidity

Whole-blood serotonin (5-hydroxytryptamine, 5-HT) levels were measured in children with attention deficit hyperactivity disorder (ADHD) with and without comorbid conduct disorder (CD) or oppositional-defiant disorder (ODD). It was hypothesized that the whole-blood 5-HT levels of ADHD probands would be significantly correlated with the whole-blood 5-HT levels of their mothers. Fifty-two children who met DSM-III-R criteria for ADHD were selected consecutively from an ADHD clinic (47 males--35 Caucasians, 10 African-Americans, and 2 Hispanics; 10 females--all Caucasians). Whole-blood 5-HT was assayed by high performance liquid chromatography and compared between ADHD children with and without comorbid CD or ODD. The familiality of whole-blood 5-HT levels was studied by Spearman's rank-order correlation. There were no significant age, race, or sex effects. There was no significant difference in whole-blood 5-HT levels between children with ADHD only (n = 22; 190 +/- 45 ng/ml) and ADHD with CD or ODD (n = 30; 212 +/- 67). However, 7 out of 30 (23%) children with ADHD+CD/ODD had whole-blood 5-HT levels > 270 ng/ml, while none of the ADHD-only children had whole-blood 5-HT levels > 270 ng/ml, a statistically significant difference. Whole-blood 5-HT levels showed significant positive correlations between 36 children with disruptive behavior disorders and their biological mothers (rs = 0.47). There was no difference in mean levels of whole-blood 5-HT between subgroups of children with ADHD with or without comorbid CD or ODD.(ABSTRACT TRUNCATED AT 250 WORDS)