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54. Shared genetic effects between schizophrenia and substance abuse: A multiplex extended pedigree study
Substance abuse is a serious public health issue and is increased among those with schizophrenia (28-47% versus 14.6% in the general population). In an attempt to better understand this comorbidity, the current study used an extended pedigree sample ascertained through schizophrenia probands (total sample N=1307, with N=852 relatives and N=455 unrelated controls) to examine the degree to which genetic effects influence shared liability for schizophrenia (N=123) and three different categorizations of DSM-IV substance use diagnoses: any substance dependence or abuse diagnosis (N=251), cannabis dependence or abuse (N=106) and alcohol dependence or abuse (N=179). The univariate heritabilities of any substance dependence/abuse diagnosis (h2=0.597, p=2.83e-08), cannabis dependence/abuse (h2=0.926, p=2.08e-09), and alcohol dependence/abuse (h2=0.433, p=1.00e-4) were all significant. The genetic correlations between schizophrenia and any substance dependence/abuse (Rg=0.300, p=0.040) and schizophrenia and alcohol dependence/abuse (Rg=0.388, p=0.025) were both significant; however, the genetic relationship between schizophrenia and cannabis dependence/abuse was not significant (Rg=0.190, p=0.124). Environmental correlations were all non-significant. Results indicate that genetic effects play a significant role in both unique and shared variance between schizophrenia and multiple measures of substance abuse. Future research will evaluate the mediating effects of MRI brain structure volumes on schizophrenia and substance abuse.