MSX1 and tooth agenesis: Its inactivation leads to the formation of supernumerary teeth, and its excessive activation results in tooth agenesis.91,93 Animal studies have revealed that blocking USAG-1 function via USAG-1 knockout or using anti-USAG-1 antibodies can treat tooth agenesis caused by genetic factors such as Msx1, EDA1 and Runx2.19,20