MD is an X-linked recessive disease that affects Cu metabolism and is caused by mutations in the ATP7A gene.52 The resulting loss of functional ATP7A in the intestine leads to reduced Cu efflux into the blood, an accumulation of Cu in enterocytes, and generalized severe systemic Cu deficiency.53 MD is a fatal disorder, and affected patients usually die in early childhood. Here, ATP7A is linked to X-linked recessive disease.