MYOD1 and proximal spinal muscular atrophy: 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).