ATP7b is an important protein for copper transport and elimination of excess copper from the body. ATP7b transports metals in and out of cells using ATP. There are 3 known isoforms of the ATP7b gene; A is found in the liver, kidney, and brain, the shorter form B is found in brain tissue, and the third isoform, known as WND/140 KDA is found in mitochondria. Mutations in the ATP7b gene can cause Wilson's disease, an inherited disorder causing copper poisoning in the brain and liver.