How does Evrysdi (risdiplam) work in the body?
Evrysdi contains risdiplam, a small molecule that changes how a gene’s instructions are processed in cells. It works by increasing the production of the SMN protein from the SMN2 gene. People with spinal muscular atrophy (SMA) typically have reduced SMN protein because of how SMN2 is spliced in their cells. Risdiplam shifts that splicing so more SMN2 transcripts include the needed exon, which leads to higher levels of functional SMN protein. [1]
How is that different from other SMA treatments?
Many SMA therapies aim to replace or deliver SMN1 function (for example, gene therapies) or directly help motor neurons survive. Risdiplam instead acts at the RNA-processing level, boosting SMN production from SMN2 throughout the body (including the nervous system), depending on where it reaches cells. [1]
What happens at the RNA level (the “splicing” part)?
The key step is splicing: cells edit pre-mRNA by cutting and joining segments. With SMA, SMN2 usually gets spliced in a way that produces mostly a shorter, less useful SMN protein. Risdiplam promotes the splice pattern that generates more full-length SMN2 mRNA, which then produces more functional SMN protein. [1]
Why does increasing SMN protein help SMA symptoms?
SMN protein is critical for maintaining motor neuron function. By raising SMN protein levels, risdiplam helps support motor neurons, which can translate into improved muscle strength and better motor outcomes in people with SMA. [1]
Quick check: is Evrysdi a gene therapy?
No. Evrysdi does not change DNA or deliver a new gene. It changes how SMN2 RNA is spliced so that cells make more functional SMN protein. [1]
Sources:
[1] https://www.evrysdi.com/about/what-is-evrysdi.html