Whereas one (28) reported reduced Pax7, MyoD, and myogenin expression in muscle from symptomatic mutants of a commonly employed SMA mouse model that expresses two SMN2 copies in an Smn-null background (29), another employing SV40 large T antigen–transformed myoblasts from the same line of mice demonstrated reduced Pax7 expression accompanied by an increase in MyoD and myogenin (27). This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.