"There is no specific addiction gene but there are genetic variations that can confidently predict a tendency for addiction."

Well there is definitely a genetic component to alcoholism. I won't speak for other addictions,, which can be based on intermittent reward more than on substances, but the evidence for alcoholism being genetic is very strong. For one thing it is attenuated over time (millennia); Chinese have had alcohol longer than anyone and you won't see a lot of Chinese in drunk tanks. Alcoholics tend to have fewer children and so pass on the genes less.

In those societies most recently introduced to alcohol like native Americans it can be so bad that the stuff is banned in some places, with a majority of adults who have tried it end up being hooked.