For SMN1 c.347T>C (p.Ile116Thr), nusinersen/risdiplam retains the clearest RNA-therapy fit

For SMN1 c.347T>C (p.Ile116Thr), a pathogenic missense allele that destabilizes SMN protein folding, antisense oligonucleotides like nusinersen and small-molecule splicing modulators like risdiplam remain the clearest RNA-therapy fits because they increase functional SMN isoforms irrespective of the specific coding substitution.

ClinVar classifies c.347T>C (p.Ile116Thr) as likely pathogenic for SMA type 1. Nusinersen (Spinraza) demonstrated durable motor gains and survival benefit in the pivotal ENDEAR trial, establishing intrathecal ASO-mediated SMN2 exon 7 inclusion as the reference RNA-therapy modality (PMID:29374173). Risdiplam (Evrysdi), a systemic splicing modulator, produced clinically meaningful motor improvements and increased SMN protein in the FIREFISH and SUNFISH studies, reinforcing the platform’s ability to treat even patients with early truncating or destabilizing variants by boosting SMN quantity rather than correcting the allele itself (PMID:33052932).

This summary relies on disease-level outcome data rather than allele-specific cohorts. Response still depends heavily on age at first dose, disease stage, ventilation status, and SMN2 copy number. ASOs require intrathecal access and repeated dosing, while systemic small molecules carry off-target risk despite broader distribution. Treat this as a modality-fit argument rather than proven efficacy for p.Ile116Thr alone.