SMN2 and proximal spinal muscular atrophy: Another variant of arginine rich CPP with X and B (RXRRBRRXRYQFLI(RXRB)2) called PMO internalizing peptide 6a (Pip6a) conjugated to splice-switching PMO, targeted exon 7 of survival motor neuron 2 (SMN2) pre-mRNA and showed significant distribution to the CNS after systemic administration, and resulted in 38-fold extended life expectancy in a spinal muscular atrophy (SMA) mice model [112].