Disentangling the effects of Tourette syndrome and attention deficit hyperactivity disorder on cognitive and behavioral phenotypes
Eighty participants (62 males; 18 females; age range: 6-16 years) took part in the study, comprising four groups of 20 subjects each: TS-only, ADHD-only, TS+ADHD, controls. The age distributions, did not differ significantly among the four groups. The severity of symptoms, assessed by the TSGS, did not differ significantly between the two TS groups. Standardised measures were used throughout. The "cases" (i.e. TS-only, TS+ADHD, ADHD-only) were significantly different from controls on most measures of behavior. There were also differences amongst the various clinical subgroups, with, in general, TS-only participants being similar to controls with regards to both "total behavior" ratings and cognitive testing results. A diagnosis of ADHD, either or its own or in association with TS, was associated with greater maladaptive behavior and worse cognitive functioning. With regards to affective symptoms and anxiety, the three clinical groups did not differ from each other, but each of them was more affected than the control group. One finding in our study which differed from previous literature was that TS-only patients were rated as more "delinquent" than controls by their parents: possible reasons for this are discussed. Oppositional defiant disorder (ODD) was seen in a few (2,3,3 ODD patients in each clinical group), but as numbers were small no statistics were undertaken. Family histories were in accord with both TS and ADHD being genetic disorders, but sharing an overlap in only some cases. The "additive effect" hypothesis is discussed in detail in the light of our results and recent literature.