SMN2 and proximal spinal muscular atrophy: To do so, we carried out immunoprecipitation experiments with anti-Sm antibodies from equal amounts of whole spinal cord extracts from normal (SMN2+/+;mSmn+/+), carrier (SMN2+/+;mSmn+/−) and severe SMA (SMN2+/+;mSmn−/−) mice at postnatal day 3.