How common is conduct disorder?

Conduct disorder is relatively common in the general population with reported rates varying between 1.8% and 16% in boys and 1.2% and 8% in girls (Loeber et al. Reference Loeber, Burke, Lahey, Winters and Zera2000). Hodgins et al. (Reference Hodgins, Cree, Alderton and Mak2007) found that 42% of the males and 22% of the females in a mentally ill in-patient sample from a deprived urban catchment area fulfilled criteria for conduct disorder prior to age 15. These rates are higher than general population rates but direct comparisons are difficult as the diagnoses by Hodgins et al. (Reference Hodgins, Cree, Alderton and Mak2007) were made retrospectively with little access to childhood collateral histories, and the interviewers do not appear to have been blinded to the hypotheses under study. However, Kim-Cohen et al. (Reference Kim-Cohen, Caspi, Moffitt, Harrington, Milne and Poulton2003) found similar rates of childhood conduct disorder (40%) among individuals with an adult schizophrenia-spectrum diagnosis in a longitudinal birth cohort study.

Can we predict poor outcomes?

The prognosis for conduct disorder is gloomy but it is not hopeless. Adverse outcomes are common but not inevitable. On average about 30–40% of children with conduct disorder will continue to exhibit antisocial behaviours in adulthood (Robins, Reference Robins1966; Storm-Mathisen & Vaglum, Reference Storm-Mathisen and Vaglum1994). One key question that remains to be answered is: how can we predict persistence? Individuals whose antisocial behaviours persist into adulthood have more compromised childhood histories, higher rates of parental criminality, lower socioeconomic status, lower IQ and higher rates of childhood maltreatment, than those whose antisocial behaviours resolve in childhood (Odgers et al. Reference Odgers, Caspi, Broadbent, Dickson, Hancox, Harrington, Poulton, Sears, Murray Thompson and Moffitt2007). Internalizing disorders in childhood, such as depression, have also been linked with increased risk of adult offending (Kasen et al. Reference Kasen, Cohen, Skodol, Johnson, Smailes and Brook2001; Copeland et al. Reference Copeland, Miller-Johnson, Keeler and Angold2007). Although internalizing and externalizing disorders are independently associated with antisocial outcomes in adulthood, results from a recent Finnish study suggest that the two interact to produce the most adverse outcomes (Sourander et al. Reference Sourander, Jensen, Davies, Niemelä, Elonheimo, Ristkari, Helenius, Sillanmäki, Piha, Kumpulainen, Tamminen, Moilanen and Almqvist2007). Study of protective factors or resilience is very relevant to a developmental epidemiology approach to antisocial behaviour but has been relatively neglected to date (Cannon et al. Reference Cannon, Huttunen, Murray, Tsuang and Tohen2002).

Can we prevent poor outcomes?

Hodgins and colleagues propose that ‘by identifying this [antisocial] subgroup of patients with severe mental illness at first contact with services and providing them with an intensive and structured package of interventions it might be possible to reduce their criminal activities …’. Unfortunately, by the time an individual has reached adulthood with a long history of conduct disorder, earned a criminal record and developed, in addition, a severe mental illness, successful intervention is very difficult. While it may be useful to be able to predict which seriously mentally ill patients are likely to commit violent crimes, this population are only responsible for a very small proportion of violent crime in society overall. A more fruitful strategy would involve primary prevention, i.e. interventions early in the course of childhood emotional and behavioural problems with proven effectiveness in preventing the development of childhood conduct disorder. Research has shown that targeted interventions in young children at risk can help to reduce antisocial behaviour (Webster-Stratton et al. Reference Webster-Stratton, Reid and Hammond2004, Conduct Problems Prevention Research Group, 2007).

What causes conduct disorder?

Conduct disorder is a heterogeneous disorder that can be considered as the final common pathway of the interaction between a variety of different types of intrinsic/psychobiological vulnerabilities and environmental stressors rather than as a single diagnostic category (Lewis, Reference Lewis1992; Yeager & Lewis, Reference Yeager and Lewis2000). Early childhood trauma in the form of abuse, particularly physical abuse, or neglect has been shown to increase risk of conduct disorder (Fergusson et al. Reference Fergusson, Horwood and Lynskey1996; Kaplan et al. Reference Kaplan, Pelcovitz and Labruna1999; McCabe et al. Reference McCabe, Lucchini, Hough, Yeh and Hazen2005), perpetuating the so-called ‘cycle of abuse’. However the ‘cycle of abuse’ is, in itself, not deterministic (Cannon, Reference Cannon2001). For instance, other factors, such as genes, have been shown to interact with childhood maltreatment to influence adult antisocial outcomes (Kim-Cohen et al. Reference Kim-Cohen, Caspi, Taylor, Williams, Newcombe, Craig and Moffitt2006; Young et al. Reference Young, Smolen, Hewitt, Haberstick, Stallings, Corley and Crowley2006). Once established, conduct disorder is difficult to treat, so that intervening early in the course of the disorder, or even before it develops (Hutchings et al. Reference Hutchings, Bywater, Daley, Gardner, Whitaker, Jones, Eames and Edwards2007; NICE, 2006) offers the best hope of altering the risk of antisocial outcomes in later life. It is particularly worrying to note that rates of psychosocial disorders in young people, particularly serious conduct disorder, have increased over the past few decades (Rutter & Smith, Reference Rutter and Smith1995; Fombonne, Reference Fombonne1998).

Prevention of conduct disorder is a mission not just for psychiatry or psychology but for society. A major investment in parenting-skills training, and measures to reduce social disadvantage and maltreatment in childhood will ultimately translate into lower rates of conduct disorder and a happier, safer society for all. Surely a worthwhile goal!