If Wilson's disease is due to too much copper, why are serum copper levels low?

In Wilson's disease, the defect is in Ceruloplasmin, the copper binding protein, its deficiency causes the copper to be free, so it's precipitating in large amounts in organs causing failure, and freely filtered in urine so its urinary level is

in wilsons defect is in atp7b gene .
normally copper was taken by the cmt1 carrier protein from the intestine, and some bound to metallathion and some goes to trans golgi network there (regulated by atox1)the increase in the copper is sensed by the