SMN2 and proximal spinal muscular atrophy: This is supported by in vivo and in vitro findings showing RBM10 expression to be: (1) regulated during rat skeletal and cardiac muscle cell differentiation61; (2) regulated both temporally and spatially during murine midgestation embryo development6; (3) a regulator of mouse embryonic stem cell proliferation and differentiation22; and (4) able to influence the alternative splicing of SMN2. 32 The latter could be of clinical relevance to patients with spinal muscular atrophy who have a homozygous deletion of SMN1, and thus rely on their SMN2 gene for all SMN protein.