Although the SMNΔ7 mouse reproduces the generalized reduction in SMN levels that characterizes human patients, significant divergence from the classical SMA phenotype, such as a pronounced cardiac phenotype and a relatively modest degree of motor neuron cell death have been emphasized [39, 48–50], raising the question as to its reliability as a model for the study of the human disease. This evidence concerns the gene SMN2 and proximal spinal muscular atrophy.