The literature I've read on this question suggests there's definitely at least a genetic component.
Which isn't the same thing as saying "genetics cause alcoholism" or "drinking is hereditary" - such statements are, while not 'wrong', too broad, too general, and not allowing for nuance.
While it definitely does "run in the family" in many cases, it's not necessarily so - the current state of research suggests that there are genes that predispose people to developing alcoholism - doesn't mean that if you have those genes, you definitely will become an alcoholic- just that your risk of developing a drink problem is elevated compared to that of the general public.
After all, most severe cases didn't happen in a flash - it takes many, many years between having your first drink or pissed up night out as a first year uni student, not particularly standing out from anyone else, to getting to the stage where you're not only drinking every evening, and sneaking out between classes to chug a beer, but literally can't go the time it takes to walk between your house and the laundrette without a drink in your hand, and telling yourself that's normal (as was the case with another teacher I knew when I was living in Lop Buri).