The fact that CSA remained a significant predictor of early initiation of use after accounting for familial influences on early use indicates that the association between CSA and early substance use is only partially accounted for by common risk factors such as genetic liability to substance use disorders, parental separation, and depression. The significant association between co-twin early use and respondent substance use onset found for each of the three substances provides further support for the contribution of genetic and shared environmental influences to initiation of alcohol, cigarette, and cannabis use reported in the larger literature (40–42).
