SMN1 and proximal spinal muscular atrophy: To this end, expression of human SMN2 and SMNΔ7 in the Smn1 null background in transgenic mice is shown to rescue the embryo-lethal phenotype, with transgenic rescue mice showing spinal cord and skeletal muscle abnormalities similar to phenotypes seen in SMA patients (Hsieh-Li et al., 2000).