The epidemiology says one thing and the treated population says another. The gap between them is the whole commercial question.
Generalised myasthenia gravis has a substantial diagnosed population, but only a small fraction is on a modern biologic. Sizing has to triangulate two independent methods rather than trust either: an epidemiological base gives one figure, and a count of patients actually on therapy today gives a far smaller one. The addressable pool is the inadequately controlled, antibody-positive subset, not the diagnosed population, and forecasts anchored on the larger number consistently overstate the opportunity.
Growth comes from switches and add-ons rather than from new patients, so the model has to describe flows between mechanisms rather than a static share of a fixed pool. Inadequately controlled patients route from conventional immunosuppression onto FcRn or complement agents, and between those classes, and the timing of those flows is what determines a launch curve.
With several agents across two mechanism classes and no head-to-head trials, any positioning comparison is cross-trial and has to be caveated explicitly rather than presented as a direct readout. The defensible approach assembles each asset's placebo-anchored effect on a common scale and is candid about the differences in trial population that make the comparison imperfect. Anything more confident than that will not survive a medical review.
AXLRx myasthenia gravis reports size the inadequately controlled pool by triangulation, model switch and add-on flows between mechanisms, and build a geography-specific value case on that basis.
ICER priced efgartigimod's value at $18,300–28,400 a year, under half its ~$418,400 launch cost. That gap is hardening into a three-tier FcRn-to-C5 step-edit across US commercial plans.
Neuromuscular-junction autoantibody biology, the AChR/MuSK/seronegative split, and the crisis burden that defines US gMG.
Three novel mechanisms in 24 months — FcRn antagonists vs C5 inhibitors, and the AChR+ vs MuSK+ line that segments the market.
NICE's terminated eculizumab appraisal for gMG remains the price precedent every new asset must clear. 2,000-3,000 refractory patients have no NICE-commissioned biologic option, and the IVIg-offset economics decide whether a launch is viable.
100,000-200,000 US gMG patients narrow to a 4,000-6,000 on-FcRn-therapy pool, and 1,200-2,100 of them remain inadequately controlled despite treatment.
6,000-10,000 GCC gMG patients on the epidemiology estimate, of whom 200-300 are refractory and fewer than 50 are currently on biologic therapy.
A ~4,000-patient UK gMG treatment gap remains unresolved. Efgartigimod's June 2025 NICE rejection (TA1069) left it open, against NHS neuromuscular network diagnostics.
Binding constraint: address FcRn-inadequate responders or claim a serostatus niche — efgartigimod sets both the clinical and ICER pricing bar.
NICE has never modelled a cost-per-QALY for a myasthenia gravis biologic. Eculizumab's appraisal (TA636) closed before a dossier was submitted; efgartigimod's (TA1069) closed on evidence gaps, not a quantified ICER breach. A new entrant inherits no reusable comparator or price benchmark from either.
The thyroid-disease diagnostic confounder, specialist neurologist concentration, and the FcRn antagonist access pathway across GCC neurology practice.
NICE's June 2025 rejection of efgartigimod (TA1069) leaves UK myasthenia gravis with no NICE-recommended novel agent. Eculizumab's own appraisal (TA636) was withdrawn by the manufacturer in 2020 without a cost-effectiveness verdict, and the NHS IVIg cost-offset argument is now the strongest lever for a future resubmission.
The broader estimate puts 12,000-15,000 UK patients with generalised myasthenia gravis. About 4,000 have moderate-severe disease and 2,000-3,000 are refractory, with no NICE-recommended novel agent for any of them.
Just 10-15 neuromuscular neurologists across six named GCC referral centres manage 70-80% of confirmed generalised myasthenia gravis. That concentration is exactly what this workbook sizes before any individual name enters it.
Refractory gMG in the GCC is a 200-300 patient market concentrated at fewer than 15 named neurologists. The constraint is building a specialist key-account relationship, not clinical proof.
GCC gMG sizing treats the 6,000-10,000-patient disease-landscape prevalence estimate as the authoritative broad base. A 200-300-patient refractory subgroup, fewer than 50 currently on a biologic, is the narrower actionable segment inside it, not a competing total.
Two UK gMG estimates disagree by 3-4x on purpose. A narrower moderate-severe subgroup of roughly 4,000 from the MGA UK survey sits inside a broader 12,000-15,000 total prevalence figure that also counts mild, well-controlled cases the narrower estimate excludes.
Generalised myasthenia gravis has no formal NPHC programme. Efgartigimod access runs through private insurance, fastest at 1-4 weeks, or hospital pharmacy committees, with NPHC engagement targeted for 2025-2026.
ICER priced efgartigimod's value at $18,300-28,400 a year, under half its ~$418,400 assumed launch price. That gap is hardening into a three-tier step-edit staircase across US commercial and Part B plans.
No UK gMG biologic has ever cleared NICE at any price. Eculizumab's manufacturer withdrew before submitting an ICER, and efgartigimod's June 2025 rejection means a future entrant's price ladder starts from zero precedent, not a benchmark.
No novel biologic is yet NHS-commissioned for generalised MG. Eculizumab's manufacturer withdrew its 2020 NICE appraisal before a verdict, and NICE rejected efgartigimod outright in 2025 — leaving rozanolixizumab as the FcRn class's last untested NICE bid.
A 30-centre NHS neuromuscular network coordinated through Muscular Dystrophy UK carries UK myasthenia care. That network, plus a 3,000-member Myasthenia Gravis Association UK patient registry, is the institutional signal this workbook sizes before any individual name enters it.
GCC gMG has no single price. Efgartigimod costs SAR 300,000-600,000/yr through private VHI, a different figure through hospital pharmacy committees, and a third through NPHC exceptional access, with a unified formulary price still 12-18 months out.
US gMG prevalence runs 100,000-200,000, but only 4,000-6,000 patients are on FcRn therapy today. 1,200-2,100 of those remain inadequately controlled. The near-term opportunity is the funnel gap, not the epidemiology total.
NPHC formulary criteria for the FcRn class don't yet exist, so pyridostigmine and steroids still treat 85%+ of GCC patients. Efgartigimod reached GCC neurology centres via SFDA and MOH UAE registration in 2023.
gMG is a rare autoimmune neuromuscular disease. US prevalence is estimated at 100,000 to 200,000 patients, roughly 14 to 20 per 100,000. The UK carries an estimated 7,000 to 10,000 patients, of whom about 4,000 have moderate-to-severe disease, while the GCC holds an estimated 6,000 to 10,000. An estimated 15 to 20% experience a myasthenic crisis in their lifetime at roughly 4% mortality per episode. The commercially decisive figure is not the prevalence total but the far smaller treated pool.
Diagnosis is confirmed by autoantibody serology, and serostatus segments the market more than severity does. Roughly 85% of patients are AChR-antibody positive, about 5% MuSK-antibody positive, around 2% LRP4-positive, and 8 to 10% seronegative. Serology is the eligibility gate, since only AChR-positive patients qualify for the complement class while FcRn antagonists carry broader labels. In the GCC an estimated 30 to 40% are first misdiagnosed as thyroid myopathy, delaying confirmation and pushing many to a more severe presentation.
Five biologics are FDA-approved across two mechanisms. The FcRn antagonists are efgartigimod (Vyvgart, argenx; IV December 2021, subcutaneous June 2023) and rozanolixizumab (Rystiggo, UCB; June 2023), which lower pathogenic IgG. The C5 complement inhibitors are eculizumab (Soliris, AstraZeneca/Alexion; October 2017), ravulizumab (Ultomiris, AstraZeneca/Alexion; April 2022), and zilucoplan (Zilbrysq, UCB; October 2023). FcRn agents carry broad serology-agnostic labels, whereas the complement class is restricted to AChR-antibody-positive disease, so mechanism and serology jointly define eligibility.
In gMG, serostatus rather than severity sets the ceiling on each mechanism's reachable market, so subtype segmentation is the first modelling step. We split the prevalence base into AChR-positive (about 85%), MuSK-positive (about 5%), LRP4-positive (about 2%), and seronegative (8 to 10%) cohorts, then map each mechanism onto the subtypes it can legally treat. The complement class reaches only AChR-positive patients, capping its pool near 85% of prevalence, while FcRn antagonists span all subtypes. This exposes structural white space, since a MuSK-specific or seronegative-specific asset, covering an estimated 490 to 700 US patients, could claim first-in-class positioning where no mechanism is well-served today.
We triangulate two independent methods rather than trust one. The epidemiology base gives 100,000 to 200,000 US patients, but the treated-population count shows only 4,000 to 6,000 on FcRn therapy today, so the gap is a diagnosed-to-treated funnel, not measurement error. Inside the treated pool we isolate the inadequately-controlled cohort, an estimated 1,200 to 2,100 patients or 30 to 35%, using MG-ADL non-responder rates, then layer serostatus and refractory filters. The refined near-term pool, not the prevalence headline, anchors the value case, which we then rebuild per geography against each market's HTA and access logic.
With five agents and no head-to-head trials, any comparison has to be cross-trial and explicitly caveated, never presented as a direct readout. We assemble each asset's placebo-anchored effect on a common scale, efgartigimod's 68% versus 30% MG-ADL responder rate in ADAPT alongside the other pivotal trials, then flag the differences in populations, endpoints, and dosing that block a clean comparison. On top of that we map the emerging sequence of immunosuppression, then FcRn antagonists, then AChR-restricted complement inhibitors, and model where UCB's dual FcRn-plus-C5 position lets it participate on both tiers. Positioning becomes a defensible argument, not a spurious ranking.
New biologics grow by capturing switches and add-ons, so we model flows between mechanisms rather than a static share. Starting from the treated pool, we route inadequately-controlled patients, the 30 to 35% cohort, into switch and add-on scenarios, testing step-edit sequences and cycle-dosing economics that keep efgartigimod's typical US net cost near $225,000 a year. Each scenario then meets its market's access reality: a hardening three-tier step-edit in the US, an IVIg cost-offset logic in the UK where no novel agent has yet cleared HTA review, and a three-channel private and hospital route across the GCC. The output is a switch-adjusted, geography-specific value case.
Each answer above is a compressed output of AXLRx's gMG research stack, spanning disease landscape, competitive intelligence, market sizing, patient flow, payer and HTA, pricing, and launch-readiness reports across the US, UK, and GCC. The through-line is a single thesis: in gMG the strategy is identification and segmentation, since the opportunity sits in the funnel between prevalence and the treated, antibody-typed, inadequately-controlled pool, not in the epidemiology headline. Explore the full report set to see the methods, sources, and geography-specific models behind each figure.