NORADRENERGIC MECHANISMS IN ADHD CHILDREN WITH AND WITHOUT READING DISABILITIES - A REPLICATION AND EXTENSION

Objective: To examine noradrenergic (NA) function in children with att ention-deficit hyperactivity disorder (ADHD) by replicating and expand ing upon a previous finding that ADHD children with and without readin g disabilities (Raj differ in plasma levels of the NA metabolite 3-met hoxy-4-hydroxyphenylglycol (MHPG). Method: Plasma levels of MHPG were compared in ADHD children who were subdivided on the basis of the pres ence or absence oi RD. Subsequently, this replication sample was combi ned with a previously studied sample to further explore the relationsh ip between plasma MHPG levels and measures of cognitive function in ch ildren with ADHD. Results: Plasma levels of MHPG were significantly lo wer in ADHD children without RD, compared with those with RD, replicat ing a previously published finding, Analyses in the combined sample in dicated that, among children with ADHD, plasma MHPG levels were invers ely associated with measures of academic achievement and verbal proces sing, but not parent or teacher ratings of behavior or continuous perf ormance test measures of attention and impulsivity. Conclusions: These data indicate that children with ADHD are not homogeneous with regard to NA function and that neurochemical variation is closely associated with differences in clinical characteristics of the children.