To add a bit to this discussion:
It doesn't matter, if you're dealing with an active alcoholic, it simply makes no difference.
I can say that I know people who knew and had been warned repeatedly that they likely had a genetic predisposition to alcoholism/addiction, and in the majority of cases it didn't make a whit of difference. I've known exactly ONE person who took that information and chose to stay away from alcohol and drugs completely. The others, are in differing stages of recovery, or dead at a young age.