Three main patterns emerged. First, in line with prior twin studies, we observed a positive rg between problem alcohol use (i.e., AUD) and AN diagnosis. Second, we estimated positive rgs between cannabis initiation and AN diagnosis, as well as cannabis initiation and the AN with binge-eating subtype. This is a novel finding not previously examined in twin research. The positive genetic associations suggest that some genetic loci are influencing these traits in the same direction. Second, negative genetic correlations emerged between the three smoking phenotypes from the GWAS & Sequencing Consortium of Alcohol and Nicotine use (GSCAN) cohort and AN without binge-eating, but not with the other three eating disorder phenotypes. These negative genetic correlations indicate that some of the loci influencing the liability to these eating disorder and smoking phenotypes are shared, but are affecting the liability to these traits in opposite directions. Indeed, genetic correlations cannot identify specific loci or underlying mechanisms that contribute to the shared risk. Nevertheless, the results provide initial evidence for differential genetic associations between the liability to varying eating disorder and substance use-related phenotypes.
