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.
Delivers
- 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
Delivers
- 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
Delivers
- Seronegative population sizing (490-700 patients)
- MuSK+ and LRP4+ subgroup sizing
- first-in-class positioning implications by serostatus
Custom model delivered in 72 hours.
Commission This ModelWhat's inside
- 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
- Total US gMG prevalence (100,000-200,000; 14-20 per 100,000)
- Serostatus split: AChR+ 85%, MuSK+ 5%, LRP4+ 2%, seronegative 8-10%
- FcRn-therapy population count (4,000-6,000)
- The diagnosed-to-treated funnel and why it explains the epidemiology gap
- Where the two methods agree and diverge
- The inadequate-control cohort (1,200-2,100 patients) as the near-term addressable population
- Inadequate-control share ranked above prevalence rate as the binding assumption
- Seronegative and MuSK+ subgroup sizing (490-700 and ~560-800 patients respectively)
- 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 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
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.
Specify your indication, target 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.