Anton, in my family, my father was a heavy drinker but I never saw him "drunk", his brother was called "Nip", due to him going thru a bottle of whisky a day. My sister heads for glass of wine within minutes of getting home from work and easily goes thru 2 bottles or more of wine. I have had years of heavily drinking with my xah, and have recently demolished half a bottle of whisky when so distraught I just didn't think about what I was doing. That was the first wipe-out for me in over 30 years.
My abf's family has 4 generations of alcoholics, that abf knows of. His brother doesn't drink at all, says he realised 10 years ago that he was heading down the same road as his dad and abf, so quit without any help.
I have read lots re alcoholism and using that and personal knowledge, I believe that there is a gene that can be passed down, that predisposes towards alcohol disfunction. Precisely how it does, science is still trying to find out.
God bless