To do so, the 35.5 kb BamHI fragment corresponding to the genomic region encompassing the SMN2 gene (Figure 1A), previously used to generate SMA mice [51], was cloned into a cosmid vector containing a neomycin selection cassette under the control of the SV40 promoter and the resulting construct was transfected into NIH3T3-SmnRNAi cells. Here, SMN2 is linked to proximal spinal muscular atrophy.