Parenting Quality, DRD4, and the Prediction of Externalizing and Internalizing Behaviors in Early Childhood C. Propper Center for Developmental Science University of North Carolina-Chapel Hill CB# 8115, 100 East Franklin Street Chapel Hill, NC 27599-811 E-mail: propper@email.unc.edu M. Willoughby Frank Porter Graham Child Development Institute UNC-Chapel Hill, CB#8180 Chapel Hill, NC 27599-8180 C.T. Halpern Maternal and Child Health University of North Carolina-Chapel Hill CB # 7445, Chapel Hill, NC 27599-7445 M.A. Carbone Department of Genetics North Carolina State University Box 7614, Raleigh, NC 27695-7614 M. Cox Center for Developmental Science University of North Carolina-Chapel Hill CB# 8115, 100 East Franklin Street Chapel Hill, NC 27599-811 ABSTRACT: Recent research has found that the dopamine D4 receptor (DRD4) gene and maternal insensitivity may interact to predict externalizing behavior in preschoolers. The current study attempted to replicate and extend this finding in a sample of 18–30-month-old children. The current study examined two distinct dimensions of parenting (warm-responsive and negative-intrusive) as predictors of childhood externalizing and internalizing behavior. Further, race was investigated as a moderator of gene–environment relationships. Results revealed that high warm-responsive parenting was associated with decreased externalizing behavior only for African American children possessing the short polymorphism of DRD4. The data indicate that children may be differentially susceptible to different aspects of parenting depending on their genotype, and it is important to consider differences in racial composition when studying these relationships. ß 2007 Wiley Periodicals, Inc. Dev Psychobiol 49: 619–632, 2007. Keywords: dopamine; externalizing behavior; internalizing behavior; maternal sensitivity; parenting; gene–environment interactions INTRODUCTION Behavior genetics studies have frequently examined the heritability of childhood behavior problems using twin and adoption designs (Gjone, Stevenson, Sundet, & Eilertsen, 1996; Schmitz, Cherny, Fulker, & Mrazek, 1994; van der Valk, Verhulst, Neale, & Boomsma, 1998). More recently, researchers have begun to examine the molecular genetics of childhood behavior problems. This emerging body of research has associated specific poly- morphisms of the D4 dopamine receptor (DRD4) gene with externalizing behaviors, as well as related infant temperament and adult personality characteristics. The current study investigated DRD4 both alone, and in combination with parenting, as a risk factor for the emergence of internalizing and externalizing behaviors in early childhood. Dopamine has been suggested as an underlying neurotransmitter influencing the behavioral system of approach in adults (Cloninger, 1987; Gray, 1982; Zukerman, 1994). More specifically, it has been associ- ated with active exploration and approach toward novel stimuli as well as activation and intensity of response in reward situations (Panskepp, 1986). DRD4 is primarily expressed in the limbic areas of the brain that are involved in cognition and emotion. This gene contains a repeated sequence polymorphism (i.e., variations in DNA) within its coding sequences that changes the length of the receptor protein that has been shown to have functional significance (Asgahari et al., 1994). There is a long polymorphism (L-DRD4; 6–8 repeats or presence of 7-repeat allele) and a short polymorphism (S-DRD4; 2–5 repeats or absence of 7-repeat allele); the shorter the allele, the more efficient the receptor is in binding dopamine (Plomin & Rutter, 1998). The relationship between the DRD4 gene and behavioral characteristics has also been examined in both Received 27 September 2006; Accepted 22 May 2007 Correspondence to: C. Propper Contract grant sponsor: The National Science Foundation (The North Carolina Child Development Research Collaborative) Contract grant number: #BCS-0126475 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/dev.20249 ß 2007 Wiley Periodicals, Inc.