Mutations in the copper (Cu)-transporting P-type ATPase ATP7A gene cause three distinct human diseases: Menkes disease (MD) (Mercer et al., 1993; Chelly et al., 1993; Vulpe et al., 1993), its milder allelic variant occipital horn syndrome (OHS) (Kaler et al., 1994) and a form of X-linked hereditary distal motor neuropathy (dHMNX) (Kennerson et al., 2010). The gene discussed is ATP7A; the disease is occipital horn syndrome.