Nusinersen: antisense oligonucleotide to increase SMN protein production in spinal muscular atrophy

Patients with spinal muscular atrophy (SMA) have an autosomal recessive disease that limits their ability to produce survival motor neuron (SMN) protein in the CNS resulting in progressive wasting of voluntary muscles. Detailed studies over several years have demonstrated that phosphorothioate and 2'-O-methoxyethyl- modified antisense oligonucleotides (ASOs) targeting the ISS-N1 site increase SMN2 exon 7 inclusion, thus increasing levels of SMN protein in a dose- and time-dependent manner in liver, kidney and skeletal muscle, and CNS tissues only when administered intrathecally. On a dose basis, nusinersen was found to be the most potent ASO for SMN2 splicing correction in the CNS of adult mice. After nusinersen was found to increase levels of SMN protein in the CNS of mice and subhuman primates without causing significant adverse events, it was advanced into clinical studies in patients with SMA. These trials in SMA patients have demonstrated significant improvements in various measures of motor function and in progression to movement developments not normally seen in SMA patients. In addition, there have been significant extensions in life expectancy. These findings led to the U.S. and European approval of nusinersen for use in SMA patients of all ages.