I hope someone who knows more about this answers you.  Is Letrozole the same thing as Arimidex?   My son has been taking Arimidex which supposedly stops bone age advancement.  His growth has been not spectacular but he’s been ahead of the game because his bone age has been steady.  He’s been growing about 1 1/2 to 2 inches a year. When he first started getting treated he was almost 8 and seemed like he was going to go into puberty early.  But it all reversed overnight with good control.    has your son’s CAH been well controlled?  Did you try the circadian dosing?  Isn’t the 10 Testosterone normal for prepubertal boys?  I’m not sure about all this.  Did his testicles get bigger on examination?  I know I shouldn’t second guess your doctor but you never know.