Any signs of precocious puberty?  That was my daughter's case when she was 5.  Her bone age was well advanced, but bloodwork did not look bad.  Turns out it was CPP.  She was put on a monthly injection of Lupron which we just recently stopped.  I am happy to say that she has just turned 13 and her bone age just came back at 13.  We were able to arrest the rapid advance of the bone age.  Just something to think about.