Research in this area has generated evidence for this way of thinking about how adolescents grow and has investigated the relationship between adolescent problem behavior and cognitive deficits. Life course persistent individuals begin antisocial behavior early in childhood and continue into adulthood, after their adolescence limited counterparts stop. Life course persistent behavior has been correlated with neurological deficits and pathological behaviors, (e.g., impulsivity) which are exacerbated when they are combined with stressful home situations. In one study of 13 year olds, individual differences - such as deficits in sensory, perceptual, and cognitive abilities, including the use of languageC were shown to predict participation in crime five years later. For instance, boys with poorer verbal functioning initiated delinquent behavior at younger ages. It has also been demonstrated that boys with poorer neuropsychological functioning, especially verbal functioning at age 13, were more likely to have committed crimes at age 18 than were their counterparts with better neuropsychological functioning at age 13.

Gender Differences

From about 4 years of age on, boys are more likely than girls to engage in both aggressive and nonaggressive antisocial behavior. Much remains to be learned about the causes of gender differences in antisocial behavior, but based on what is known, it is suspected that antisocial behavior might need to be defined somewhat differently for the two genders. In contrast to overt aggression, which inflicts harm through physical damage or the threat of such damage more common in boys, social aggression by girls harms through damage to peer relationships; study of this form of aggression may be crucial to understanding the aggressive development of girls. The NIMH is currently funding research on the antecedents and consequences of aggression for girls, as well as for boys, knowledge that can be used to develop empirically-based interventions for aggressive children of both sexes.

Antisocial Behavior Co-Occurring with Child Psychopathology

There is strong evidence for the co-occurrence of two or more syndromes or disorders among children with behavioral and emotional problems. Many people think that children either act out or turn their feelings inward, but the truth is more complex. The obviously angry adolescent has other conditions such as anxiety disorders and depression (as seen in the quiet withdrawn young person) more often than would occur by chance. Research in this area indicates that very young children with conduct problems and anxiety disorders or depression display more serious aggression than youths with only conduct problems. It is not known whether depression precipitates acting out, whether impairments and predispositions for acting out lead to depression, or whether there are underlying causal factors that are responsible for the joint display of such problems.

It is very common for youth with conduct problems to also display symptoms of attention deficit hyperactivity disorder (ADHD), the most commonly diagnosed behavioral disorder of childhood. The diagnosis is made by the presence of
persistent age-inappropriate inattention and impulsivity, often coexisting with hyperactivity. This co-occurrence is often associated with an early onset of aggression and impairment in personal, interpersonal, and family functioning. Furthermore, academic underachievement is common in youth with early onset conduct problems, ADHD, and adolescents who display delinquent behavior.

Individual Liability and Genetic Factors

Identifying numerous genes that may play a role in any complex disorder is a formidable task and is only the first step in understanding how a gene or genes affect an individual. Genes act by producing specific proteins that may contribute to a particular biological or behavioral trait. Every human carries between 80,000 and 100,000 genes; the products of these genes S acting together and in combination with the environment B help shape every human characteristic. It has become clear that the genetics of vulnerability to certain behaviors or mental disorders is complex. We still do not know how many different genes might contribute to vulnerability for any personality trait or specific mental disorder, nor do we know the nature of the nongenetic effects (such as environmental factors) that convert vulnerability into illness.

Our understanding of the nature of genetic influences on antisocial behavior is similarly incomplete. However, research on differences in the magnitude of genetic and environmental influences on different kinds of conduct problems is providing a key to understanding the developmental origins of antisocial behavior. Many twin and adoption studies indicate that child and adolescent antisocial behavior is influenced by both genetic and environmental factors, suggesting that genetic factors directly influence cognitive and temperamental predispositions to antisocial behavior. These predisposing child factors and socializing environments, in turn, influence antisocial behavior.

Research suggests that for some youth with early onset behavior problems, genetic factors strongly influence temperamental predisposition, particularly oppositional temperament, which can affect experiences negatively. When antisocial behavior emerges later in childhood or adolescence, it is suspected that genetic factors contribute less, and such youths tend to engage in delinquent behavior primarily because of peer influences and lapses in parenting. The nature of the child's social environment regulates the degree to which heritable early predisposition results in later antisocial behavior. Highly adaptive parenting is likely to help children who may have a predisposition to antisocial behavior. Success in school and good verbal ability tend to protect against the development of antisocial behavior, pointing to the importance of academic achievement.