Menkes disease and occipital horn syndrome are allelic X-linked recessive disorders caused by defects in a gene that encodes an evolutionarily conserved copper-transporting ATPase. In mammals, this gene product functions as an intracellular pump to transport copper into the trans-Golgi network for incorporation into copper-requiring enzymes including dopamine-beta-hydroxylase, and also mediates copper exodus from cells.
In the small intestine, ATP7A is needed for passage of copper from duodenal mucosal cells into blood, and is also expressed in cells that comprise the blood-brain barrier, brain capillary endothelial cells and astrocytes,where it is required for delivery of copper to neurons within the central nervous system.
In human beings, mutations in this copper-transporting ATPase can cause classical severe Menkes disease or a much milder condition called the occipital horn syndrome. The type of mutation, different in each family, seems to determine which form occurs.
Above image is a visual representation of a child with Menkes disease.
Image on the right is an image of a teenager diagnosed with Occipital Horn Syndrome.