Elosulfase Alfa (Vimizim)

Elosulfase alfa is a recombinant enzyme-replacement drug for Morquio A syndrome (mucopolysaccharidosis type IVA, or MPS IVA), a rare inherited disorder in which a missing enzyme lets sugar molecules build up mainly in cartilage and bone, causing severe skeletal disease while usually sparing intelligence. Approved in 2014 as the first disease-specific treatment for MPS IVA anywhere, its pivotal trial actually tested two dosing schedules side by side — and only one of them worked. The drug's UK story took even longer to resolve: a list price of roughly $380,000 a year drew an initial "minded to reject" verdict from NICE before a five-year, real-world-data-collecting Managed Access Agreement broke the deadlock in November 2015.

A skeletal MPS that usually spares intelligence, and no treatment before 2014

Morquio A syndrome (mucopolysaccharidosis type IVA, or MPS IVA) is a rare inherited disorder caused by deficient activity of N-acetylgalactosamine-6-sulfatase (GALNS), an enzyme that normally breaks down two glycosaminoglycans, keratan sulfate and chondroitin-6-sulfate. Without it, these sugar chains accumulate largely in cartilage, bone and connective tissue rather than spreading as broadly through the brain and organs as in the MPS I and MPS II diseases covered elsewhere on this site (see this site's laronidase and idursulfase pages) — the result is a severe skeletal dysplasia (short trunk, chest and joint deformities), corneal clouding, cardiac valve disease and restrictive lung disease, alongside a real and serious risk of cervical spinal cord compression from odontoid bone hypoplasia at the top of the spine, while intelligence is usually preserved. Contemporary estimates put global birth prevalence at roughly 1 in 200,000 to 300,000, and classical, severely affected patients have historically had a life expectancy in their 20s to 30s, dying most often of respiratory failure, spinal cord compromise or heart valve disease, with milder cases surviving into their 60s or beyond. Before 2014, no disease-specific drug existed for MPS IVA of any severity — treatment was limited to managing individual complications: spinal surgery, joint replacement, cardiac valve repair and respiratory support. BioMarin Pharmaceutical, already the developer of laronidase for MPS I, brought recombinant GALNS (elosulfase alfa, internally BMN 110) through development, and the FDA approved it on 14 February 2014 under the brand name Vimizim — the first treatment specifically for MPS IVA approved anywhere.

The trial that won approval — and the dose that didn't work

The pivotal evidence was MOR-004, a randomized, double-blind, placebo-controlled, multinational trial of 176 patients with MPS IVA aged 5 and older, randomized roughly evenly to elosulfase alfa 2.0 mg/kg once weekly, the same 2.0 mg/kg dose given every other week instead, or placebo, for 24 weeks. The primary endpoint was change in six-minute walk test (6MWT) distance. At week 24, the estimated mean effect on 6MWT versus placebo was 22.5 meters for the weekly-dosing group (95% CI 4.0 to 40.9; P=.017) — a real, statistically significant result — but only 0.5 meters for the every-other-week group (95% CI −17.8 to 18.9; P=.954), indistinguishable from placebo (Hendriksz CJ, Giugliani R, Harmatz P, Mengel E, Guffon N, Valayannopoulos V, et al., "Efficacy and safety of enzyme replacement therapy with BMN 110 (elosulfase alfa) for Morquio A syndrome (mucopolysaccharidosis IVA): a phase 3 randomised placebo-controlled study," J Inherit Metab Dis 2014;37(6):979-990, PMID 24810369).¹ Urinary keratan sulfate excretion fell significantly in both dosing groups, showing the drug reached its biological target at either schedule, but only the weekly regimen translated that biomarker change into a walking-distance benefit large enough to clear placebo. The 3-minute stair-climb test, a secondary endpoint, did not reach statistical significance in either group. The FDA approved only the once-weekly, 2.0 mg/kg regimen for market — a genuinely uncommon case among the drugs on this site of a pivotal trial testing two real dosing schedules head-to-head, with one of them clearly failing rather than simply being un-tested.

A boxed warning, and a disease complication that can look just like it

Vimizim carries an FDA boxed warning for hypersensitivity reactions, including anaphylaxis: in clinical trials, reactions occurred as early as 30 minutes into an infusion and as late as 3 hours after one ended, and at least one case occurred as late as a patient's 47th infusion — meaning tolerating the drug for months is not a guarantee against a later reaction. The FDA-approved label requires administration in a setting equipped to manage anaphylaxis, with medical supervision and access to resuscitation equipment.

Five years to a UK yes, by way of a managed access deal

BioMarin priced Vimizim at roughly $380,000 per patient per year in the US, and just under £395,000 in the UK before any discount — pricing the company defended at the time as broadly consistent with other enzyme-replacement therapies for similarly rare diseases, including its own laronidase. England's National Institute for Health and Care Excellence (NICE) evaluated the drug under its Highly Specialised Technologies (HST) process, reserved for treatments for very rare conditions; in an initial 2015 consultation, the evaluation committee was minded to reject funding, citing substantial uncertainty about the clinical evidence and unresolved questions about whether the price was justified. Rather than a straight rejection or approval, NICE, NHS England and BioMarin instead negotiated a Managed Access Agreement, announced in November 2015 and formalized in final guidance (HST2) published 16 December 2015: a confidential patient access scheme discount, explicit clinical criteria for starting and stopping treatment, and — the more unusual feature — a five-year commitment to collect UK-specific real-world outcomes data to inform a future review of the guidance, rather than NICE relying solely on the original trial evidence indefinitely.

Current status

Vimizim remains FDA-approved and currently marketed by BioMarin in the US, EU and other markets, and remains the only FDA-approved disease-specific treatment for MPS IVA of any severity, over a decade after its original approval. It remains a core part of BioMarin's enzyme-therapies business: the company reported $210.2 million in Vimizim revenue in the first quarter of 2026 alone, up from $188.3 million in the same quarter of 2025, alongside continued growth in Naglazyme and its other enzyme-replacement products. No FDA-approved generic, biosimilar or competing disease-specific therapy for MPS IVA exists as of 2026; management of the disease's skeletal, cardiac and respiratory complications through surgery and supportive care continues alongside weekly enzyme replacement rather than in place of it.