SMN1 and proximal spinal muscular atrophy: As SMN-deficient cells we used primary fibroblasts from SMA patients (Fig. S1a), SMA iPSC-derived motoneurons (Fig. S2) and transformed fibroblasts in which SMN was downregulated by lentiviral transfection of 2 independent inducible shRNAs against SMN 3’UTR (Fig. 1c).