I only this week became aware of this.
The article is extremely technical, but makes clear in no uncertain terms that Delta FosB is the genetic risk factor for addiction. All addicts have it, regardless whether the addiction is chemical or behavioral.
It also helps me understand how, without having been born with the specific genes for alcoholism, they came to be present for me in middle age; how, after decades of consuming alcohol no differently than any normal person, I abruptly became a “drunk” at about age 32.
Related: Alcoholism basics