Often there is a genetic and/or environmental trigger for genes like this to express -- something here is not making a lot of sense.   It's like a piece of the picture is missing on the immune side.  (An immune system problem could trigger expression of the defective gene.)

I sincerely hope that the bone marrow transplant works -- no child should have to go through medical conditions like this.   And, I also hope there isn't another simpler way of turning off the expression of this gene through addressing an immune system problem, which may also have a genetic component and may be a lot less taxing for a small child as well as being less expensive and less risky to treat. 

I really hope they haven't overlooked something.   Patients and their families rely on doctors and researchers to find the best approach that also minimizes risk to the patient.