Genes help determine which kids thrive despite abuse

While abused children are at heightened risk for conduct disorder, not all children who suffer abuse develop behavior problems. A new study suggests that genes can be the key to why one maltreated child "goes bad" while another thrives.

Evaluating data from more than a thousand British twin pairs, Sara Jaffee and colleagues identified children who had definitely or possibly suffered abuse. The researchers used parent and teacher evaluations to determine which of the maltreated children showed symptoms of conduct disorder, such as persistent lying, bullying, violence, physical cruelty, and stealing. They then compared monozygotic (identical) twins, who share 100% of their genes, to dizygotic (fraternal) twins, who are no more alike genetically than non-twin siblings. This allowed the researchers to determine what role genes played in determining which children developed conduct disorder and which did not. A substantial role of genes would be indicated, they note, if the identical twins whose co-twins exhibited conduct disorder had a significantly elevated rate of CD, while identical twins whose co-twins had no symptoms of conduct disorder had a low rate, with fraternal twins exhibiting similar but weaker patterns.

In line with previous studies, Jaffee and colleagues detected a strong genetic influence on conduct disorder. Moreover, they report, "The experience of maltreatment was associated with an increase of 2% in the probability of a conduct disorder diagnosis among children at low genetic risk for conduct disorder but an increase of 24% among children at high genetic risk."

The researchers say these findings are consistent with their earlier research (see related article, Crime Times, 2002, Vol. 8, No. 4, Page 1), which found that 85% of severely abused subjects with a low-activity variant of a gene that affects activity of monoamine oxidase (MAOA) developed some form of antisocial behavior. In contrast, participants with the high-activity variant of the gene almost never exhibited aggressive or criminal behavior in adulthood, even if they had been severely abused as children.

"Nature x nurture: genetic vulnerabilities interact with physical maltreatment to promote conduct problems," Sara R. Jaffee, Avshalom Caspi, Terrie B. Moffitt, Kenneth A. Dodge, Michael Rutter, Alan Taylor, and Lucy A. Tully, Development and Psychopathology, Vol. 17, 2005, 67-84. Address: Sara Jaffee, Department of Psychology, University of Pennsylvania, 3720 Walnut Street, Philadelphia, PA 19104, srjaffee@psych.upenn.edu.