Key takeaways
- 100-200K estimated total US gMG prevalence (14-20 per 100,000), the epidemiology-based sizing anchor
- 4,000-6,000 US patients currently on FcRn antagonist therapy, the treated-population sizing anchor
- 30-35% share of on-FcRn-therapy patients inadequately controlled (MG-ADL ≥6 despite treatment), equal to 1,200-2,100 patients
- 490-700 estimated seronegative gMG patients (~7% of gMG), the least-served serostatus subtype and a first-in-class commercial opening
Two sizing methods disagree by 20-50x, and the gap itself, not either number alone, defines the near-term US gMG opportunity: 4,000-6,000 are on FcRn therapy against a 100,000-200,000 epidemiology total, and 1,200-2,100 of the treated group are inadequately controlled.
The epidemiology method starts from population prevalence: US generalised myasthenia gravis is estimated at 100,000-200,000 patients, roughly 14-20 per 100,000, with serology dividing the population into 85% AChR-antibody positive, 5% MuSK-antibody positive, 2% LRP4-positive, and 8-10% seronegative. The treated-population method starts from the opposite end, counting patients currently on an FcRn antagonist: an estimated 4,000-6,000 US patients are on efgartigimod or rozanolixizumab today. Triangulating the two does not average them into one figure. It identifies the diagnosed-to-treated funnel, not measurement error, as the reason a sizing model built only on epidemiology would overstate the near-term addressable population by more than an order of magnitude.
The more commercially decisive number sits inside the treated population, not at either end of the funnel. An estimated 1,200-2,100 US patients, 30 to 35% of those already on FcRn therapy, remain inadequately controlled (MG-ADL score of 6 or higher despite treatment), a population whose disease appears to involve non-IgG mechanisms that IgG-reduction alone does not resolve. Serostatus narrows the opportunity further: seronegative patients, about 7% of gMG and an estimated 490-700 people nationally, are the least mechanistically understood and least studied subtype, with no agent purpose-built for them. Our sensitivity analysis ranks the inadequate-control share above raw prevalence as the assumption most likely to move a near-term forecast, the opposite of what a naive epidemiology-only sizing exercise would assume.
US gMG sizing — epidemiology total versus treated-population count
| Sizing Method | Population Estimate | Source |
|---|---|---|
| Epidemiology-based (total prevalence) | 100,000-200,000 patients (14-20 per 100,000) | MGFA epidemiology estimates; Gilhus NE, NEJM 2016 |
| Treated-population (on FcRn therapy) | 4,000-6,000 patients | IQVIA gMG Rx data by indication |
| Inadequately-controlled subgroup | 1,200-2,100 patients (30-35% of treated) | argenx ADAPT extension MG-ADL non-responder data |
| Seronegative serostatus niche | 490-700 patients (~7% of gMG) | Serostatus segmentation analysis |
Sources: MGFA epidemiology estimates; Gilhus NE, NEJM 2016 (PMID 28029925); IQVIA gMG Rx data by indication; argenx ADAPT extension study MG-ADL non-responder data.
What this model answers
Every section answers a named commercial question your team is asking, scoped to your asset.
- Why does the treated-population count of 4,000-6,000 sit so far below the 100,000-200,000 epidemiology total, and which number should drive a near-term forecast? • Epidemiology-based versus treated-population sizing methodology • the diagnosed-to-treated funnel as the explanation for the gap • guidance on which anchor fits a near-term versus long-run forecast
- How large is the inadequately-controlled cohort inside the treated population, and why does it matter more than raw prevalence for a new entrant? • 1,200-2,100-patient inadequate-control cohort sizing • sensitivity ranking of inadequate-control share versus prevalence rate • the mechanistic rationale (non-IgG pathways) for why this cohort is addressable
- What is the size and commercial opportunity of the underserved serostatus subgroups, particularly seronegative MG? • Seronegative population sizing (490-700 patients) • MuSK+ and LRP4+ subgroup sizing • first-in-class positioning implications by serostatus
What's inside
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1 · The Binding Constraint 2 pp
- Why the inadequate-control share inside the treated population, not raw prevalence, is the assumption that determines whether a near-term forecast holds up
- Pressure-tested against the epidemiology-versus-treated-population gap before the rest of the model is built out
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2 · Epidemiology-Based Sizing 3 pp
- Total US gMG prevalence (100,000-200,000; 14-20 per 100,000)
- Serostatus split: AChR+ 85%, MuSK+ 5%, LRP4+ 2%, seronegative 8-10%
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3 · Treated-Population Sizing 3 pp
- FcRn-therapy population count (4,000-6,000)
- The diagnosed-to-treated funnel and why it explains the epidemiology gap
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4 · Triangulation & Confidence Range 3 pp
- Where the two methods agree and diverge
- The inadequate-control cohort (1,200-2,100 patients) as the near-term addressable population
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5 · Sensitivity Analysis 3 pp
- Inadequate-control share ranked above prevalence rate as the binding assumption
- Seronegative and MuSK+ subgroup sizing (490-700 and ~560-800 patients respectively)
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6 · Editable Excel Model —
- The full triangulated model, re-runnable with your own assumptions
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7 · Client Alignment Questions 2 pp
- The open sizing questions your team must close before the number is used in planning
Appendix and source ledger included · 45-minute analyst readout included with delivery
Custom model delivered in 72 hours.
Assess this reportIncluded with every brief
Get Started
Commission this model
AXLRx delivers rare disease market sizing models built for forecasting and strategy teams sizing the US gMG opportunity. Custom model in 72 hours.
- 1. Submit your requestSpecify your indication, target market, and cohort definition.
- 2. Scoping callAXLRx analyst confirms triangulation methods and comparator set before building.
- 3. DeliveryResearch-verified sizing model in 72 hours with optional analyst readout.
How AXLRx builds this model
Prepared by MoatRx analysts on the AXLRx commercial consulting engine.
Every AXLRx market sizing model triangulates at least two independent methods, epidemiology-based and treated-population/claims-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).
US myasthenia gravis sizing sources: MGFA epidemiology estimates, Gilhus NE (NEJM 2016), IQVIA gMG Rx data by indication, and argenx ADAPT extension study MG-ADL non-responder data.
- Total US gMG prevalence and serostatus split verified against Gilhus NE, NEJM 2016 (PMID 28029925) and MGFA epidemiology estimates
- Treated-population (on-FcRn-therapy) count verified against IQVIA gMG Rx data by indication
- Inadequate-control share and seronegative subgroup sizing verified against argenx ADAPT extension MG-ADL non-responder data
Frequently asked questions
Deliverables What formats are included with every model?
Every commissioned Market Sizing Model includes an editable 5-sheet Excel model (Cover, Model, Research Validation, QC, Sensitivity) and a PDF methodology brief, no PowerPoint deck, since a sizing model is built to be worked in directly rather than presented from. An optional 45-minute analyst readout call is included.
Sources How is the patient count verified?
AXLRx triangulates every sizing estimate across at least two independent methods, epidemiology-based and treated-population/claims-based, no single-source number ships unverified.
Customisation Can I size a specific serostatus subgroup or payer segment?
Yes. The intake form captures your indication, target subgroup, and cohort definition. A scoping call confirms scope before research starts. Commission via the intake form to start.