I am aware of it. I read about it on a blog. What about it?. What are you gonna do, tell people they can't associate with each other? It's not caused by underage sex. And it's not caused by incest, it's genetic. Although it might be spread in a closed situations such as these compounds over time. Here's a bit more.
Until 1990 Tarby says he knew of only 13 cases of Fumarase Deficiency worldwide. Since, it has taken hold in the FLDS community because of intermarriage. "If you have two parents with the gene," Tarby says, "you are going to have a one-in-four chance of having a child afflicted with it." Depending on the severity of the disorder, children may die in childhood or may survive into early adulthood; if a person who has developed the disorder goes on to have a child, his or her chances of passing it on are one in two. But diagnosing the condition is difficult and requires extremely careful testing, the doctor says. His research, published in 2006, identified 20 cases within the Hildale-Colorado City enclave. "I would expect there are going to be Fumarase Deficiency cases there in Texas," he said.

Don't forget the Jews have genetic diseases too. For closed breeding I bet.

And if we find 13 year old girls that have, then do something about that particular case, but we have 400 kids and 200 adults so far. Can't blame the entire group for the actions of that couple of people. And if they are 14, which is obviously an arbitrary number since they just raised it on a whim, I have no problem with it.

Where is the evidence of sexual abuse and neglect? I haven't seen any report of it. Only the contrived illegal kind. Which ain't abuse, just illegal.