The changes are bone related which is a direct result of inflated levels of IGF-1. Though GH will create sectretion of IGF-1, it in itself (GH) is not the direct cause.
"Overproduction of growth hormone leads to increase in insulin-like growth factor 1 (IGF-1) by the liver and other tissues. IGF-1 causes such symptoms as soft tissue swelling, joint disorders, enlargements of hands, feet, and jaw, visceral overgrowth,..."
I also believe aas alone can make your jaw grow just like any other muscle group..lord knows mine has