It is of interest that in the CDP, we genotyped the same SNPs as were genotyped in the COGA project. The main effect detected in the COGA project mapped onto the ordering of genotypes observed at the low end of parental monitoring in the CDP sample. The COGA families are densely affected with alcohol dependence, and alcohol dependence in the family is known to be adversely related to family relations (Zhou, King, & Chassin, 2006). Accordingly, one might expect that these families would disproportionately be characterized by low parental monitoring, and the genetic effects observed for the low-monitoring families from the community-based CDP sample exactly map onto the genetic main effects observed in the COGA.
