Date of Award


Degree Name

Master of Arts



First Advisor

DiLalla, Lisabeth


The goal of this thesis was to determine the influence of genetic and environmental effects on the development of internalizing problems. Internalizing problems affect millions of children and include problems such as depression, anxiety, and somatization. Temperament is a genetically-based factor that has been shown to influence the development of internalizing problems; specifically reactive temperaments. 5-HTTLPR is a serotonin transcription gene that has also been shown to affect internalizing problems. Parenting is an environmental factor that may influence many factors in children’s lives, including internalizing problems. This thesis examined the effects of parenting, reactivity, and 5-HTTLPR, alone and in interactions with one another, on internalizing problems in preschool-aged children. Further, this thesis proposed that the differential susceptibility model might fit the data, in that children with reactive temperaments or the 5-HTTLPR risk allele might show a differential response to parenting. This study was conducted using a sample of 220 twins and triplets who had previously participated in the Southern Illinois Twins/Triplets and Siblings Study (SITSS). The children’s parents completed the Child Behavior Checklist (CBCL) to determine internalizing symptoms at age 5. Buccal cells were collected at two ages, and a parent-child interaction was conducted at age 5 to assess parenting behaviors. Temperament was also examined via parent-completed questionnaire at age 4, using the Child Behavior Questionnaire (CBQ). One important finding of this study was the significant effect of reactivity on internalizing problems. Further, non-positivity in parenting interacted significantly with 5-HTTLPR risk sum. There was a trend toward significance for the interaction between ineffective parenting and 5-HTTLPR risk allele presence or absence. These interactions indicated that the children without the risk allele actually showed the most differential response to parenting, with fewer internalizing problems when parenting was more positive and more internalizing problems when parenting was less positive. Children with the risk allele had a minimal response to parenting in terms of internalizing behaviors. Overall, the results of this study indicate that reactivity is a significant predictor of internalizing problems, and that the 5-HTTLPR gene may moderate this effect. Further studies should be conducted on this subject to further examine the effects parenting and genes have on the development of internalizing problems.




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