UK Dravet Syndrome Market Sizing Model

The clinical-population method counts everyone currently managed under NICE's Dravet treatment algorithm. Of an estimated 2,000-2,500 UK Dravet patients, 1,500-2,000 are on cannabidiol (Epidiolex, NICE TA614) and 400-600 have stepped up to the combined cannabidiol-plus-fenfluramine regimen (Fintepla, NICE TA808). The genetic-registry method counts differently: the NHS Genomic Medicine Service offers free SCN1A testing to any patient presenting with febrile-seizure-onset epilepsy, and clinical molecular confirmation runs at roughly 75% of tested cases, but the registry itself logs only 400-500 patients with a formally recorded SCN1A-positive result. Triangulating the two methods does not average them into a single figure. It identifies the gap as a scope difference: the treatment-algorithm population includes long-standing patients diagnosed clinically before national genomic testing became routine, alongside newly tested cases, while the genetic registry reflects only patients whose molecular confirmation has been logged in the current testing infrastructure.

That gap matters directly for how a NICE submission or NHS budget-impact model should be built. NICE's own TA614 and TA808 assessments, and the payer-and-HTA cost modelling built on them, use the 400-500 figure as their population base, since HTA cost-effectiveness modelling requires a molecularly documented cohort. A launch or forecasting model built only on the 400-500 registry count would understate the addressable clinical population by the 1,500-2,000-patient margin sitting outside current genetic documentation, while a model built only on the 2,000-2,500 treatment-algorithm total would overstate the population any near-term genetic-registry-gated intervention could actually reach. Within the treatment-algorithm total, an estimated 600-900 patients are inadequately controlled despite combined cannabidiol-plus-fenfluramine therapy — the addressable refractory segment for a new entrant, and the population any competitive trial design should target as its comparator background.

Every AXLRx market sizing model triangulates at least two independent methods, clinical-population-based and genetic-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).

Dravet syndrome UK sizing sources: NHS Genomic Medicine Service epilepsy gene panel data, Dravet UK Society patient data (2023), and NICE TA614 and TA808 appraisal documentation.