As far as I am aware, it is not a genetic condition. However, I have known "families" of goats which have seemed to be more prone to it. That said, it wouldn't be every animal in the family, just a couple spread over over a big family. We seemed to have a little outbreak of it about 10 years ago in our BT's. I would treat her brother as normal- there is nothing to say he will get the same thing.
Beth