The ATP7A gene encodes the Menkes copper-translocating P-type ATPase, a ubiquitous protein that regulates the absorption of copper in the gastrointestinal tract. Inside cells, this protein has a dual function: it delivers copper to cuproenzymes in the Golgi compartment and effluxes excess copper. The trafficking mechanism and catalytic activity combine to facilitate absorption and intercellular transport of copper. Menkes disease, a systemic copper deficiency disorder, is caused by mutations in the ATP7A gene.