ATTENTION-DEFICIT HYPERACTIVITY DISORDER AND WHOLE-BLOOD SEROTONIN LEVELS - EFFECTS OF COMORBIDITY

Whole-blood serotonin (5-hydrdxytryptamine, 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 (r(s) = 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. However, children with comorbid CD or ODD who had elevated whole-blood 5-HT levels may represent a more clinically homogeneous subgroup of children with ADHD. As in previous studies of autistic disorder, these data suggest that whole-blood 5-HT levels are familial in ADHD.