Date of Award

Summer 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

Committee Chair

Dr. Sara Jordan

Committee Chair Department

Psychology

Committee Member 2

Dr. Tammy D. Barry

Committee Member 2 Department

Psychology

Committee Member 3

Dr. Christopher Barry

Committee Member 3 Department

Psychology

Committee Member 4

Dr. D. Joe Olmi

Committee Member 4 Department

Psychology

Abstract

ADHD is a heritable condition, with unknown etiologies and different phenotypic expressions in affected individuals. Its genetic vulnerability may be expressed only when specific environmental conditions are present. Endophenotypes stand in the causal path between genes and disease and are found in children diagnosed with ADHD as well as unaffected relatives. This study investigated the link between ADHD endophenotypes and the heterogeneous expression of ADHD symptoms in 84 children aged 11 to 17 years and explored whether this relation depends on family functioning and resilience of the child (i.e., grit). It was hypothesized that (1) ADHD endophenotypes would be moderately positively related to ADHD symptoms, (2) poorer family functioning would be positively related to ADHD symptoms, (3) grit would be negatively related to ADHD symptoms, (4) poorer family functioning would exacerbate the relation between ADHD endophenotypes and child ADHD symptoms, (5) grit would attenuate the relation between ADHD endophenotypes and ADHD symptoms, (6) grit would attenuate the relation between family functioning and ADHD symptoms, and (7) the influence of family functioning on endophenotypes’ effect on ADHD symptoms would depend on grit so that the magnitude of the effect of endophenotypes on ADHD symptoms in families with poorer functioning would be smaller for children with higher levels of grit. There was partial support for the first five hypotheses. Expected significant correlations between ADHD endophenotypes and parent- and teacher-rated ADHD domains were found. Results indicated a positive relation between family dysfunction and teacher-rated ADHD symptoms, whereas child grit was negatively associated with parent-rated ADHD domains. Some significant interactions emerged. Family dysfunction exacerbated the relation between response disinhibition and parent-rated ADHD domains. Child grit moderated the relation between response disinhibition and teacher-rated ADHD domains, albeit in a way somewhat contrary to predictions. There was a trend toward child grit attenuating the relation between deficits in working memory and parent-rated hyperactivity/impulsivity. The three-way interaction between response disinhibition, family dysfunction, and child grit was significant indicating that the effect of higher family dysfunction on the relation between response disinhibition and teacher-rated inattention was stronger for grittier children. Limitations and conclusions of this study are discussed.

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