Symptoms of Attention Deficit Hyperactivity Disorder, Oppositional Defiant Disorder and Conduct Disorder in preschool children: comorbidity patterns, functional impairment and perinatal maternal risk factors

Attention Deficit Hyperactivity Disorder (ADHD) is one of the most frequent and debilitating childhood disorders, in which comorbid behaviour disorders considerably worsen the prognosis. Early identification could promote prevention and intervention at an earlier stage, but there is also a need for more knowledge about the presentation of co-occurring patterns of Oppositional Defiant Disorder (ODD) compared to Conduct Disorder (CD), and how symptom patterns impact daily life function at an early stage. Sex differences are shown to vary with sample source, rater source, age and comorbid conditions. A better understanding of the observed sex-distributions of ADHD could benefit from a more systematic examination of the course and putative risk- and protective factors. Although ADHD has been found to be highly heritable, environmental risk and protective factors are also shown to be involved, including antenatal and postnatal maternal anxiety and/or depression. More knowledge is therefore needed from studies examining different types of exposure, time variation during gestation and postnatally, as well as various symptom dimensions or symptom clusters within the same study design. The overall aim of this thesis was to provide more knowledge on young preschool children’s symptom characteristics, clinical presentation and the risk factors associated with ADHD, ODD and CD.!Participants were recruited from a prospective birth cohort, the Norwegian Mother and Child Cohort Study (MoBa), and clinically assessed in the preschool ADHD study, which took place when the children were 3.5 years old. Children who had scores above the 90th percentile on ADHD characteristics from the MoBa questionnaires at 36 months (n = 1048) were included in the first two studies, while a randomly selected control group (n = 147) was also included in the third study (n = 1195). The first objective was to!examine the co-occurrence patterns of ODD and/or CD in children with symptoms of ADHD (Study I). The assessment of DSM-IV-TR symptoms and functional impairment were based on parental ratings and a semi-structured psychiatric interview, “The Preschool Age Psychiatric Assessment” (PAPA). Among children with ADHD, concurrent ODD was present more often than CD (31% vs. 10%), but having ADHD gave an almost three times higher increase in the odds of CD compared with ODD. Among children with co-occurring CD, a greater proportion of children had the combined ADHD subtype and more severe inattentiveness than those with ODD. We discuss these important differences in co-occurring patterns of ODD compared to CD identified in these young preschool children with symptoms of ADHD. The second objective was to investigate the impairment of ADHD by examining which functional domains were affected and how the impairment was related to ADHD subtype, symptom load, co-occurrence ODD and/or CD (Study II). Impairment was assessed in domains of family functioning, peer relationships, play, life quality and areas of learning. All domain scores of impairment were strongly inter-correlated, and added to a total score. Impairment was mainly reported in areas of family functioning, but overall, most of the nonreferred young children with clinical symptoms of ADHD were not severely impaired. The most significantly impaired subgroups were children with combined ADHD symptoms and those with co-occurring ODD symptoms, in which between 80-90% of children were rated as moderately or severely impaired. The findings indicate that assessing the impact of ADHD symptoms and co-existing difficulties in preschoolers may help verify the identification of children and families who are in the greatest need of early intervention efforts. The third aim was to examine the relationships of perinatal maternal symptoms of anxiety or depression to the symptom dimensions of ADHD (i.e. inattentive compared to hyperactive-impulsive symptoms), ODD and CD, and to examine whether the effects varied with the type- or time of exposure. Information about maternal anxiety and depression (SCL- 5) was obtained from the MoBa questionnaires completed at weeks 17 and 30 during gestation and at six months post-partum. Perinatal maternal symptoms of anxiety and depression represented relatively stable, but generally modest risk factors for preschoolers’ symptoms of ADHD and ODD. There was no significant variation with time during earlyand mid-to-late gestation, or postnatally. Covariate adjustments highly attenuated the effects indicating that risk relationships depend on a number of other risk factors and correlates. All the way through this thesis, we intended to examine sex differences of ADHD, co-existing behaviour disorders and functional impairment of ADHD, and whether there were sex differences compared to the potential risk associations of perinatal maternal symptoms of anxiety or depression to child symptoms of ADHD, ODD or CD (Studies I, II, III). A male predominance was seen among children with ADHD alone and among those with the combined subtype (ADHD-C). However, there were no sex differences among the diagnostic groups of children with ADHD and a co-occurrence of ODD and/or CD. Minor sex differences were also shown compared to the impairment of ADHD, but boys with ADHD-C and those with ADHD and concurrent ODD were rated more impaired than girls. Boys whose mothers had symptoms of anxiety during their peripartum period were also found more susceptible than girls for symptoms of ADHD. Conversely, the prediction of child ODD symptoms by perinatal maternal symptoms of anxiety tended to be more marked for girls than boys. These findings contrast with previous results on this topic, and are discussed in terms of methodological differences in the assessment of child psychopathology and possible underlying mechanisms. The implications of the main findings in this thesis are that preschool children with symptoms of ADHD and concurrent ODD and CD present with many of the same clinical features as their older counterparts, but with a few exceptions: inattentive symptoms were not easily identified, and ADHD is far less debilitating in most settings. Furthermore, the increased understanding of how environmental risk factors, and among these, perinatal maternal anxiety and depression, are related to these frequently occurring and often overlapping mental health conditions could help build a theoretical knowledge that has implications for both prevention efforts and future research