US SMA sizing isn't one number. It's a prevalence estimate and a separate, trackable treated-cohort count, and a launch model needs both.
Two independent methods size the US SMA population, and they answer different commercial questions. The epidemiology method starts from incidence, roughly 1 in 10,000 live births, yielding an estimated 8,000-10,000 prevalent US patients across Types 1 through 4, with SMN2 copy number setting the severity split (Type 1 approximately 60%, Type 2 approximately 27%, Type 3 approximately 13%, Type 4 under 5%). Since all 50 states began universal newborn screening by 2023, roughly 300 additional infants are identified pre-symptomatically each year, a flow the prevalence estimate already assumes but a launch model must isolate separately, since pre-symptomatic infants convert to gene therapy at a materially different rate than symptomatic older patients.
The second method is not epidemiological at all. It is a registry count of a specific treated cohort: an estimated 500-700 US children received Zolgensma between 2019 and 2023 and are now 4 to 7 years old, tracked through the Cure SMA gene therapy registry and post-marketing follow-up. Clinical monitoring suggests 15-20% of this cohort show early motor plateau or functional decline, the basis of the Zolgensma-attenuation hypothesis. This is not a subset of the 8,000-10,000 prevalence estimate to be modelled by percentage; it is a named, trackable population with its own sizing logic, relevant to any pipeline asset targeting attenuation, a booster, or combination therapy. A sizing model that reports only total prevalence misses the single most commercially actionable number in the US SMA market today.
US SMA sizing — prevalence estimate versus the Zolgensma-treated cohort
| Sizing Method | Population Estimate | Source |
|---|---|---|
| Epidemiology-based (total prevalence) | 8,000-10,000 patients, Types 1-4 | CureSMA / Prior TW, Genet Med 2010 |
| Newborn-screening flow (annual) | ~300 pre-symptomatic infants/yr | CureSMA / federal RUSP |
| Registry-based (Zolgensma-treated cohort) | 500-700 patients, aged 4-7 | Cure SMA gene therapy registry; Strauss KA et al., Mol Ther 2023 |
| Estimated attenuation-signal share | 15-20% of treated cohort | Strauss KA et al., Mol Ther 2023 |
Sources: CureSMA; Prior TW, Genetics in Medicine 2010 (PMID 20057317); federal Recommended Uniform Screening Panel (RUSP); Cure SMA gene therapy registry; Strauss KA et al., Molecular Therapy 2023.
What this model answers
Every section answers a named commercial question your team is asking, scoped to your asset.
Delivers
- Type 1-4 prevalence split by SMN2 copy number
- the ~300/yr newborn-screening flow
- pre-symptomatic vs symptomatic segmentation logic
Delivers
- Cure SMA gene therapy registry methodology
- the 15-20% attenuation-signal estimate
- why this cohort doesn't reduce to a percentage of prevalence
Delivers
- Sensitivity ranking of every input
- attenuation-conversion-rate modelling
- scenario ranges tied to Cure SMA registry follow-up data
Custom model delivered in 72 hours.
Commission This ModelWhat's inside
- Why the Zolgensma-treated cohort is a separate sizing question from total prevalence, not a subset of it
- Pressure-tested against the registry-vs-epidemiology gap before the rest of the model is built out
- US incidence (~1:10,000) and the Type 1-4 prevalence split by SMN2 copy number
- The newborn-screening flow this implies (~300/yr)
- Cure SMA gene therapy registry methodology and the 500-700-patient count
- Cross-check against total prevalence
- Where prevalence-based and registry-based sizing answer different commercial questions
- The attenuation-signal estimate as a distinct forward-looking segment
- Attenuation-conversion rate ranked against prevalence rate as the binding assumption
- Scenario ranges tied to Cure SMA registry follow-up data
- The full triangulated model, re-runnable with your own assumptions
- The open sizing questions your team must close before the number is used in planning
Included with every brief
How AXLRx builds this model
Prepared by MoatRx analysts.
Every AXLRx market sizing model triangulates at least two independent methods, epidemiology-based and registry-based, before accepting a patient count. This is explicitly a sizing model (static patient count), distinct from a Patient Flow or forecasting model (dynamic revenue/uptake).
SMA US sizing sources: CureSMA and Prior TW (Genet Med 2010) for prevalence and genetics, the federal Recommended Uniform Screening Panel for newborn-screening coverage, and the Cure SMA gene therapy registry with Strauss KA et al. (Mol Ther 2023) for the Zolgensma-treated cohort.
- US SMA prevalence and Type 1-4 split verified against Prior TW, Genet Med 2010 and CureSMA
- Newborn-screening annual diagnosis rate verified against the federal RUSP and CureSMA
- Zolgensma-treated cohort size and attenuation-signal estimate verified against Strauss KA et al., Mol Ther 2023 and the Cure SMA gene therapy registry
Frequently asked questions
Commission this model
AXLRx delivers rare disease market sizing models built for forecasting and strategy teams sizing the US SMA opportunity, including the emerging Zolgensma-attenuation cohort. Custom model in 72 hours.
Specify your indication, market, and cohort definition.
AXLRx analyst confirms triangulation methods and comparator set before building.
Research-verified sizing model in 72 hours with optional analyst readout.