US Pompe Disease Launch Readiness

Nexviazyme (avalglucosidase alfa, Sanofi, approved 2021) is the growing leader in newly-diagnosed late-onset Pompe disease (LOPD), capturing an estimated 35–40% of new starts on the strength of its COMET trial result — a 23.5-metre six-minute-walk-test (6MWT) advantage over first-generation alglucosidase alfa. Pombiliti+Opfolda (cipaglucosidase alfa plus the miglustat chaperone, Amicus Therapeutics, approved 2023) entered the market with a switch-population claim from PROPEL (a 20.8-metre 6MWT gain in ERT-experienced patients), but on a different evidence base than Nexviazyme's, so head-to-head comparison is not available and prescribers are choosing on indirect evidence and individual anti-drug-antibody (ADA) risk. WAC for both next-gen ERTs runs $600,000–800,000/year, roughly 50–60% above first-generation alglucosidase alfa.

The clinical fact both incumbents have to answer for is ADA: 30–40% of Pompe ERT patients develop high-titre neutralising anti-drug antibodies that measurably reduce enzyme efficacy, and this is the single question US Pompe KOLs ask first about any new agent. An estimated 25–30% of the roughly 2,000 US LOPD patients on ERT (375–600 patients) are inadequate responders (FVC decline of 5% or more per year, or a 6MWT decline of 10% or more over 12 months, despite 12-plus months of ERT), most often driven by that high-titre ADA. This inadequate-responder cohort is the only clean pre-launch opening in a market already served by two next-generation ERTs; a third agent competing broadly, without an ADA advantage, has no differentiated claim to make.

Most US payers require a documented alglucosidase step-edit (6–12 months of prior ERT plus evidence of inadequate response or high-titre ADA) before authorising a next-generation switch; a new entrant either clears that step-edit with ADA data in hand or pursues a first-line (ERT-naive) label modelled on COMET to bypass it altogether. ICER has not yet assessed avalglucosidase alfa (a review is expected in 2025), and at the current WAC gap the implied cost per QALY for an incremental 6MWT gain runs into the millions — a genuinely difficult ICER profile unless net pricing or an ADA-driven efficacy advantage is demonstrated. Pompe ERT is billed under Medicare Part B as a medical benefit, so a new entrant needs to begin its HCPCS J-code application roughly 12 months before approval, with a temporary Q-code bridging the first two quarters post-launch.

This assessment synthesises three independently-verified research angles into one pre-launch view: competitive standard-of-care positioning, target-population epidemiology, and anticipated payer posture. Every factual claim traces to a primary source: FDA approval records, peer-reviewed trial publications, and US Pompe registry data.

Pompe sources: FDA Drugs@FDA, COMET (Nexviazyme), PROPEL (Pombiliti+Opfolda), LOTS (alglucosidase alfa), COMET/PROPEL ADA sub-analyses, IQVIA Pompe Rx data 2024, and SPK-3006/RGX-202 gene-therapy trial registrations on ClinicalTrials.gov.