Traits of alcoholism, as related to Glass Castle
Alcohol addicts in the study displayed higher "harm avoidance" levels, which fits very much with the character of Rex Walls, who didn't really solve any of his problems, he just tried to get out of or around them. They also have lower levels of self-transcendence, or ability to see beyond their present circumstances. For a family always moving around, there would be little hope if you were unable to see beyond the problems facing your immediate family, because that is all you have.
Interestingly, as a child, Walls' younger sister also seems to fulfill characteristics that match up with alcoholism. This seems almost to foreshadow her downfall in New York. She goes to her friends' house instead of living at home, just like Rex Walls leaves for days at a time, unable to transcend self. Her ultimate move- traveling to California instead of trying to live in New York with her family- also shows harm avoidance.
It seems clear that the tendency of alcohol addiction to run in families is due not only to genetics and family situations, but also to character, because none of the other Walls children has this much trouble functioning as an adult.