An external genetic analysis of the SMA cases detected in our laboratory has identified two children with one SMN2 copy, fifty-two children with two SMN2 copies, thirty-one children with three SMN2 copies, thirty children with four SMN2 copies, five children with five SMN2 copies and one child with six SMN2 copies (personal communication, state authorities). The gene discussed is SMN2; the disease is proximal spinal muscular atrophy.