I think the medical term is 'Alcohol Use Disorder', and you won't find 'alcoholic' or 'alcoholism' in the 'The Diagnostic and Statistical Manual of Mental Disorders'. As far as a gene goes, I have not heard that they have identified one gene or gene sequence that makes one an alcoholic. Some people it seems have a higher disposition to become alcoholic, but that may be the nature of person's with addictive personalities, pleasure/reward seekers if you will. Other people may abuse alcohol to treat mental or physical disorders.
Alcohol dependence is both physical and mental, worse over time and age. If your friend is suffering health and life consequences from his/her alcohol use, the sane reaction would be to take a long hiatus from drinking. I would start there, encouraging him to take a break. A visit with his primary care physician is recommended. A few good nights of hard to come by sleep is usually a sign of of being on the safe side of detox. A couple of weeks may be needed for the primary cravings to subside. I've heard it said that, medically speaking, after 6 months there are no more cravings.
For some this fork in the road becomes problematic. Self awareness of the dilemma and all that is worth holding on to, but the insanity of trying to control their drinking over and over again. Some may not be able to stop at all and needi medical intervention. Others might put in a year here or years there, but when they return they quickly rediscover that have no chill zone when it comes to their drug of choice.
When it comes to the Big Book, the foreward Dr.'s Opinion on xxviii states
For me it's important to think of the allergy not from a medical immune sense, but in a colloquial having a peculiar reaction.
The short nuts and bolts of it can be found on Ch.3 More about alcoholism pg. 30
Bolded first sentence is a pretty simple and fundamental definition of an alcoholic. Some in the rooms will pronounce themselves "Real Alcoholic". At first it can be a little off putting, but almost all in AA is out of love and acceptance, even in the hardest of biker rooms.
Later on in the chapter 'To Wives', page 108, Bill, err I mean Bill's Wife, describes 4 types of progressive drinkers, but it's too long to copy past here. It begins with heavy and ends with completely despaired. Good news is this book and way of living works for all types. And for those that can quit drinking on their own or by other means, the program tips their hat.
Sorry for the slow and long winded response. Maybe it will help someone.