In mouse models in which the endogenous Smn1 gene has been knocked out and
human versions
of SMN2 have been swapped in, the Isis therapy — a so - called «antisense oligonucleotide» — delivered to the mouse central nervous system (CNS) increased the expression
of full -
length SMN protein in motor neurons, improved muscle strength in behavioral tests and extended the rodents» median
lifespan from 16 days to 26 days3.