The copper efflux transporters ATP7A and ATP7B sequester intracellular copper into the vesicular secretory pathway for export from the cell. 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, characterized by neurological symptoms and hepatic damage.