I'm not quite ready to jump on the "it's in the family" bandwagon. Although there is certainly evidence pointing that way, and there probably is something to it on some level. From my point of view, I don't think it's as much "genetic" as "environmental".
There are cases where heredity has nothing to do with it at all. It's no big secret that I have had my share of addictions/appetites, for a number of reasons FAR to large to go into here. However, it doesn't really run in my family much to speak of. In fact, it's quite the opposite. My grandmother smoked for 52 years...one day just "decided" she didn't want to smoke anymore. She never had another, went through maybe one freakin' day of being a little edgy, and that was that. My mom did the same thing. No real alcoholism to speak of in my family, or drug addiction. Yeah, a couple people here and there...around the general population average. But no "traits" of it.
So, I do believe that environment might be more to blame than a gene. Your parents drank a lot, theirs did...well, I'm pretty sure that imprints on a young impressionable mind. You grow up in a certain "way of life". It can lead to addictions, but doesn't have to be because of it directly. Like I said, no one in my family had any substance issues, but I still grew up with basically enough lunatics, headcases and assholes to drive one into an abyss of his own comfy blankets. 😉