Conduct disorder is one of the most difficult and burdensome mental health problem in children and adolescents. It is defined as a persistent pattern of behavior in which the basic rights of others or major age-appropriate societal norms or rules are violated . Conduct disorder symptoms are most common presenting complaints about psychiatric referral among the youth in the United States . Children with conduct disorder show impairment in virtually all domains of life as compared to any other childhood mental illness . The estimated lifetime prevalence of conduct disorder in the United States is 9.5% (12% in males and 7.1% in females) with 11.6 years median age of onset .
Few studies in the past have shown that conduct problems are associated with increased risk of other mental disorders . Many children with conduct disorder have a coexisting condition such as ADHD, depression, anxiety disorder and schizophrenia . Although schizophrenia has been associated with conduct disorder; it is unclear if schizophrenia is a comorbid condition or a sequel to conduct disorder. On the aetiological basis, possible explanation for why conduct disorder is more common in people with schizophrenia is that the factors which inﬂuence the risk of developing both disorders are common . One such proposed pathway includes the risk factor of childhood adversity which increases the risk conduct disorder and schizophrenia, which indirectly increases the risk of substance abuse . Hence, at a critical stage of brain development these matrices of disorders, further increase the risk of schizophrenia  in children.
Men with schizophrenia and conduct disorder (relative to the schizophrenia patients without conduct disorder) and only conduct disorder patients displayed increased grey matter volumes of the hypothalamus and the inferior and superior parietal lobes . An alternate hypothesis suggests that there are increased rates of assortative mating between women with schizophrenia and men with antisocial behavior. Offspring of such is likely to inherit susceptibility genes for both schizophrenia and conduct disorder. Also, such children are more likely to be exposed to specific environmental events such as physical abuse and other childhood adversities . Thus, schizophrenia and conduct disorder shares causative risk factors, possibly a distinct pattern of neural development  and genetic susceptibility . More longitudinal studies are needed to confirm if there is a common developmental pathway from childhood adversity, through conduct disorder, and drug use to schizophrenia.
Another contrasting view is that conduct disorder is a distinct form of schizophrenia. Conduct disorder is not a comorbidity but represents a sub-group of individuals who are developing schizophrenia. Considering this postulate, it is reasonable to suggest that individuals who presented with CD may have a different presentation than those without a history of conduct problem . This alternate view is further supported with the idea that after the onset of schizophrenia, conduct disorder is associated with aggressive behavior, positive symptoms, noncompliance with medication, lack of care, and substance misuse .
Despite, there is no clear-cut explanation for the association of conduct disorder with schizophrenia both disorders pose a great burden on the society, economy, and healthcare either independently or as comorbidity or sequel. Conduct disorder by itself predisposes to early onset of schizophrenia, first hospitalization, and longer stay in hospital [11, 13]. Studies have shown that patients with onset of conduct disorder before the age of 15 is associated with an increased propensity to violence in adulthood . In addition, about 40% of the children with conduct disorder have an increased risk of persistent aggressive behavior . Other studies have shown that history of conduct disorder in childhood, antisocial personality disorder and a high score of psychopathy in Psychopathy Checklist-Revised (PCL-R) were more prevalent in schizophrenic patients with criminal history compared with non-criminal schizophrenic patients . The association between cumulative childhood adversities and propensity to violence and psychopathy may be mediated by conduct disorder . Thus, further work is needed to advance our understanding of the complex interplay between a variety of childhood risk factors that may be aetiologically important to the future risk of both violence and schizophrenia.
Thus, conduct disorder during childhood has negative consequences during later life, either by leading to schizophrenia, contributing to the severity of mental illness, persistent criminality or to other serious forms of maladjustment. Little is known about the consequences of conduct disorder among individuals who develop schizophrenia. Further studies are needed to determine the prevalence of schizophrenia in adolescents with conduct disorder and demographic predictors & risk of inpatient outcomes of comorbid schizophrenia in conduct disorder.
Monitoring Editor: Rikinkumar S. Patel MD, MPH
Author: Dr. Harinder Gill, MD
Author Affiliation: Healthy Mind Behavioral Health Services (NY)
Correspondence on Email: firstname.lastname@example.org
References are available on request