It's now well known and accepted knowledge that "addictions" have heritable elements (specifically in the transition from initial to problematic use). This has been proven by repeated studies of families and twins.
The preponderance of substance abuse addicts in recovery that "swap the witch for the bitch" and adopt behavioural addictions also support the genetic basis for addictability (my word).
I am a behavioural addict in recovery (4442 days today) and when I consider my siblings, parents, their siblings and their children (my first cousins), there's a >50% incidence of addiction to either smoking (>2 packs/day), alcohol, sex, food, gambling, or drug use. Half of that cohort have more than one addiction and among those almost all share a substance addiction with a behavioural addiction.
I appreciate that this is just one family and is statistically irrelevant. However because I've been around people dealing with their addictions for so long and spoken to so many, this is not an uncommon familial pattern among addicts.
I'd also add that in my clan there are many instances where one sibling is an addict and another isn't. This is not learned behaviour (though the introduction to addictive pathways/behaviours etc is often as a result of environmental and psycho-social factors).