ATP7A and spinal muscular atrophy: Pathogenic variants in ATP7A result in three clinically distinct X-linked inherited disorders: Menkes disease (MD; OMIM #309400), occipital horn syndrome (OHS; OMIM #304150), and distal motor neuropathy spinal muscular atrophy [SMAX3, OMIM #X-linked distal spinal muscular atrophy-3 (SMAX3) X-linked distal spinal muscular atrophy-3 (SMAX3) X-linked distal spinal muscular atrophy-3 (SMAX3) X-linked distal spinal muscular atrophy-3 (SMAX3) 300489].