ATP7A and occipital horn syndrome: Presently, we know that genetic defects affecting the copper-transporter P-ATPase, ATP7A, cause three X-linked recessive rare diseases: occipital horn syndrome (OMIM 304150), spinal muscular atrophy, distal, X-linked 3 (SMAX3, OMIM 300489), and Menkes disease (OMIM 309400) (Kaler, 2011).