662 CHAPTER 14
However, as with most psychological disorders that are infl uenced by genes, a
combination of genes—not a single gene—probably contributes to it (Faraone et al.,
2005). In fact, over a dozen different genes have so far been identifi ed as possibly
contributing to this disorder (Guan et al., in press; Swanson et al., 2007; Waldman &
Gizer, 2006). Many of these genes have been shown to affect the activity of the
neurotransmitters that likely are involved in the disorder. In addition, some of these
genes may also contribute to conduct disorder and oppositional defi ant disorder,
which would, at least in part, account for the high comorbidity among these disor-
ders (Dick et al., 2005; Jain et al., 2007).
Genetic factors do not occur in a vacuum. In fact, such factors often interact
with environmental events, which lead a given individual to be more or less sen-
sitive to teratogens prenatally or to environmental exposure during early child-
hood (Jacobson et al., 2006; Kahn et al. 2003; Pineda et al., 2007; Swanson et al.,
2007). Researchers have identifi ed several environmental risk factors. For example,
children whose mothers smoked while pregnant are much more likely to develop
ADHD than are children whose mothers did not smoke (Braun et al., 2006), and this
relationship appears to be particularly strong for children who have a specifi c gene
(Neuman et al., 2007).Neurological Factors in Conduct and Oppositional Defi ant Disorders
Finally, although ADHD is by far the best-understood of the disruptive disorders,
researchers have begun to investigate the other two. Much of what is known about
neurological factors related to oppositional defi ant disorder and conduct disorder
overlaps with what is known about antisocial personality disorder (see Figure 13.6).
This is not surprising, given the fact that most people with antisocial personality
disorder or psychopathy had oppositional defi ant disorder and/or conduct disor-
der during childhood or adolescence. Moreover, many, if not most, of the partici-
pants in those studies probably also had comorbid ADHD (although most people
with ADHD don’t develop oppositional defi ant disorder, conduct disorder, or anti-
social personality disorder). It is clear that genes play a role (Gelhorn et al., 2006;
Hudziak et al., 2005; Maes et al., 2007): Both oppositional defi ant disorder and
conduct disorder are more common among children whose biological parents were
criminals or had been diagnosed with oppositional defi ant disorder, conduct dis-
order, ADHD, antisocial personality disorder, a substance use disorder, or a mood
disorder (Frick & Muñoz, 2006; Haber, Jacobs, & Heath, 2005). All of these dis-
orders except depression are considered to refl ect externalizing problems, related to
undercontrol (see Chapter 3).
Conduct disorder with callous and unemotional traits is accompanied by decreased
sensitivity to—and arousal by—punishment, which is associated with a temperament
referred to as low harm avoidance (Frick et al., 2003). This temperament in turn
impedes the ability to internalize appropriate social norms and develop a conscience
(Pardini, 2006). Moreover, individuals with this type of conduct disorder are likely
to be high in another aspect of temperament, reward dependence; they are strongly
motivated by the possibility of reward. But at the same time they are also low in persis-
tence; they have a low tolerance for frustration (Gray, 1987; Zuckerman, 1991).Psychological Factors: Recognizing Facial Expressions,
Keeping Track of Time
We’ll fi rst examine the psychological factors of the best understood of the disorders
that involve disruptive behavior—ADHD. In addition to problems with attention
and executive function, people with ADHD may have other, perhaps less obvi-
ous, difficulties. As with autism, one problem is recognizing emotions in facial
expressions—not all emotions, but anger and sadness in particular. Why? The
answer isn’t known, but one suggestion is that these people might have had very
negative experiences with others who are sad or angry, and these unpleasant experi-
ences motivate them to tune out such expressions (Pelc et al., 2006).P SN