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EDITORIALS |
Department of Forensic Mental Health Science, Institute of Psychiatry, King's College London SE5 8AF, UK. Email: s.hodgins{at}iop.kcl.ac.uk
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ABSTRACT |
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INTRODUCTION |
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SUBGROUPS OF PERSISTENT VIOLENT OFFENDERS |
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During the past 25 years, evidence has accumulated that men within this population with psychopathy diagnosed according to PCLR differ markedly from the others. They commit more violent offences, engage in both instrumental and reactive aggression and more quickly reoffend when released. They display a profound emotional dysfunction characterised by impaired recognition of fear and sadness in faces and voices, low levels of stress reactivity indexed by heart rate, skin conductance and cortisol, and a cognitive style dominated by reward and a failure to recognise punishment. Performance on IQ and standard neuropsychological tests is within normal limits (Patrick, 2006).
Among children with early-onset conduct disorder, there is a subgroup with stable, callousunemotional traits that are thought to represent the antecedents of the psychopathic traits. There are as yet no studies that have followed such children into adulthood, but the available evidence suggests that boys who present both conduct disorder and callousunemotional traits share many features with adult psychopathy. Compared with boys with conduct disorder alone, boys with both conduct disorder and such traits present more severe conduct problems, more aggressive behaviour and violent crimes at an earlier age. They demonstrate a preference for risky behaviours that are novel and exciting to them, less reactivity to threatening and emotionally distressing stimuli and a muted cortisol stress response. They show less ability to recognise sadness in faces and vocalisations and are more impaired on tests of moral reasoning and empathy. In addition, these boys have difficulty changing behaviours that are initially rewarded and subsequently punished and emphasise the positive consequences of aggressive behaviour but fail to appreciate the negative consequences. Not surprisingly given these characteristics, the boys with both conduct disorder and callousunemotional traits are less responsive to parenting practices and most particularly to punishment. In addition to the emotional deficits, children with callousunemotional traits also display cognitive abnormalities similar to those observed among adult men with psychopathy, and have higher IQ scores than other boys with conduct disorder (Blair, 2003; Frick & Marsee, 2006).
Boys with conduct problems who do not present callousunemotional traits display aggressive behaviour that is emotionally charged in response to provocations that may be real or result from their tendency to perceive hostility in others, even in neutral faces (Dadds et al, 2006). These children report emotional distress, are more reactive to distress and especially to negative emotional stimuli. They are, however, responsive to good parenting practices and benefit when their parents complete parent training programmes (Hawes & Dadds, 2005). These boys present high levels of impulsivity, a tendency towards anger and like children with anxiety disorders have lower than average verbal abilities (Frick & Marsee, 2006).
The place of attention-deficit hyperactivity disorder (ADHD) in persistent violent offending and in the characterisation of the proposed subgroups remains unclear (Waschbusch, 2002). This is often comorbid with conduct disorder and the combination is predictive of criminality in adulthood. Among boys with conduct disorder and ADHD, it is callousunemotional traits and not ADHD symptoms that are associated with aggression and delinquency. Further, boys with such traits without ADHD have been shown to have the highest rates of aggressive behaviour and delinquency (Frick & Marsee, 2006). Recent evidence demonstrates that both the genotype and the phenotype of ADHD are heterogeneous, and that IQ mediates, at least in part, psychosocial functioning, including violent offending, in adulthood (Mill et al, 2006). Boys with conduct disorder and ADHD obtain lower IQ scores and are more impulsive than boys with only conduct disorder. Inattention precedes the onset of conduct disorder, allowing for the possibility that early intervention could interrupt the development of conduct disorder (Simonoff, 2000; Waschbusch, 2002).
Available evidence suggests that the aetiology in the three subgroups of males with early-onset stable antisocial behaviour differs. A meta-analysis of twin and family studies reported a modest genetic contribution (0.41 heritability) to the development of early-onset and stable antisocial behaviour, including substance misuse (Rhee & Waldman, 2002), but depending on the definition of the phenotype other studies report much higher heritability coefficients (Young et al, 2000). Recent evidence suggests that callousunemotional traits are also heritable. For example, a recent study of young twins in the UK has shown that the combination of conduct problems and callousunemotional traits is much more heritable (heritability coefficient 0.81) than conduct problems alone (heritability coefficient 0.30) (Viding et al, 2005). This is consistent with studies of older participants showing high heritability for psychopathic traits (Blonigen et al, 2003; Taylor et al, 2003; Larsson et al, 2006). These results indicate that from conception onwards individuals who display early-onset stable antisocial behaviour differ from the rest of the population and that the subgroup who will develop callousunemotional traits differ from the others. Genes modify the individual's interaction with their environment, hence each of the subtypes would be reacting to and selecting environments differently from conception onwards. Interestingly, this would mean that the subgroups would react differently during the prenatal period when individual thresholds for stress reactivity of the hypothalamicpituitaryadrenal axis are set (Susman, 2006). This could be one of the reasons why one sub-group displays high anxiety levels and another presents abnormally low levels.
As is hypothesised for other complex disorders, each of the genes involved in antisocial and aggressive behaviour may interact with a specific environmental factor to determine outcome. For example, a functional polymorphism in the promoter of the monoamine oxidase A gene had previously been associated with persistent aggressive behaviour in animals and in one human pedigree. In a birth cohort, neither the low nor high activity allele was associated with violent behaviour in adulthood. The males in the cohort who carried the low activity allele and who experienced physical abuse during childhood were three times more likely than the men with the same allele who had not experienced abuse to present conduct disorder and ten times more likely to commit violent criminal offences. Physical abuse in the absence of the gene did not increase the risk of conduct disorder or violent crime (Caspi et al, 2002). Two studies have replicated this finding in White males (Foley et al, 2004; Widom & Brzustowicz, 2006). Thus, individuals who differed in genetic profile reacted differently to their environments, and even to a severe event such as physical abuse.
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IMPLICATIONS OF THE FAILURE TO IDENTIFY SUBTYPES |
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The failure to characterise subtypes within this population may also lead to difficulty in interpreting the evaluations of treatment programmes. It has been known for a number of years that parent training programmes reduce conduct problems among young children (Farmer et al, 2002). A recent study showed that children with conduct disorder but without callousunemotional traits benefited most, whereas those with such traits only learned when reward was used. Time-out, although an effective intervention for the children without callousunemotional traits, failed to reduce inappropriate behaviours displayed by the children with such traits (Dadds et al, 2005). Insensitivity to punishment is a key feature of psychopathy and of children with conduct disorder and callousunemotional traits, but not of the other subgroups (Dadds & Salmon, 2003). Taking account of the presence or absence of such characteristics when developing treatment programmes will increase their specificity and thereby effectiveness.
Although several offender rehabilitation programmes have been shown to be as effective as most accepted medical treatments, there is little evidence about the characteristics of offenders who benefit and those that do not (Welsh et al, 2002). Richer and more complete characterisations of the subtypes of persistent violent offenders would lead to the development of treatments that directly target deficits. For example, one of the characteristics of boys with conduct disorder and callousunemotional traits and offenders with psychopathy is their altered perception of reward and punishment. Both in neuropsychological tests and in real-life situations, they focus on rewards and ignore punishments. Consequently, they persistently miss the signal the punishment that a behaviour is inappropriate. As children, this may be one of the key mechanisms that promotes their antisocial behaviour and that limits their access to the usual socialising experiences such as sports and other community activities, and eventually even to school. The problem persists into adulthood and is present, for example, later in life when they are incarcerated and enrolled in an offender rehabilitation programme. Many of these programmes include a module designed to develop problem-solving skills. Problem-solving is divided into four steps. Step one involves identifying the problem, step two generating as many responses as possible, step three assessing the likely positive and negative consequences of each possible response, and the final step selecting the best response. At step three, men with psychopathy and boys with conduct disorder and callousunemotional traits would focus on rewards and be less able than others to identify possible negative outcomes. To help them learn to solve problems would first require teaching them to identify negative outcomes. For the adults, this may be particularly difficult as they have had so many years without this skill.
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