This lack of full rescue fits with observations recently seen in an SMA mouse model where base editors were used to correct the SMN2 C6-to-T nucleotide change,96 and, in our model, may be caused by additional mutations other than SMN1 in the donors of the SMA lines contributing to SMA pathogenesis97,98 or by epigenetic changes caused by early SMN deficiency99,100,101,102,103 not erased during dedifferentiation protocols. The gene discussed is SMN2; the disease is proximal spinal muscular atrophy.