How many children become addicts because their parents were also addicts?

[The Captain]

my brother in law ((Lets call him JOE)) was adopted when he was less than two years old. His "father" was an alcoholic who was shot by a prostitute outside a bar. He never knew the guy. He was raised by my wifes parents who were churchgoing teetotalers (never drank). JOE became a drug addict and committed suicide four years after graduating highschool and moving out of the in laws house to another town.