The human gene ATP7B encodes the copper-transporting ATPase 2 (ATP7B, ATPase2, Wilson's protein) which is expressed mainly in the liver, brain and kidneys (Bull et al, 1993). ATP7B resides on the trans-Golgi membrane where it it thought to sequester copper from the cytosol into the golgi (Yang et al, 1997). Defects in ATP7B are the cause of Wilson disease (WD), an autosomal recessive disorder of copper metabolism characterized by the toxic accumulation of copper in a number of organs, particularly the liver and brain (Thomas et al, 1995).