Agalsidase Beta (Fabrazyme)

Agalsidase beta is a recombinant enzyme-replacement drug for Fabry disease, a rare inherited disorder in which a missing enzyme lets a fatty substance build up in blood vessels throughout the body, damaging the kidneys, heart and brain. Approved in 2003 as the first treatment for the disease in the US, it went through the same 2009 Genzyme manufacturing crisis this site's imiglucerase page describes — except Fabry patients were rationed to roughly a third of their approved dose for nearly three years, not simply paused. In March 2021, after 18 years on an accelerated approval, the FDA converted it to a full traditional approval, closing off the same expedited pathway competing Fabry gene-therapy candidates had hoped to use.

A missing enzyme, and a disease that damages blood vessels everywhere

Fabry disease is a rare, X-linked inherited disorder caused by deficient activity of alpha-galactosidase A, an enzyme that normally breaks down a fatty molecule called globotriaosylceramide (GL-3, also written Gb3). Without enough of the enzyme, GL-3 accumulates inside the walls of small blood vessels throughout the body, causing progressive kidney damage, thickening of the heart muscle, and a heightened risk of stroke, alongside earlier symptoms such as severe nerve pain in the hands and feet and a distinctive skin rash. Before enzyme-replacement therapy existed, treatment was entirely symptomatic — pain management, dialysis, and eventually kidney transplant — and did nothing to slow the underlying disease. Genzyme developed agalsidase beta, a recombinant form of human alpha-galactosidase A produced in genetically engineered Chinese hamster ovary cells, and the FDA approved it on 24 April 2003 under the brand name Fabrazyme — the first Fabry disease treatment approved in the United States. A related enzyme, agalsidase alfa (Replagal), had already been approved in the European Union in 2001 and remains a mainstay treatment there and in many other countries, but Shire (later Takeda) withdrew its US marketing application in 2012 after the FDA indicated it would require additional controlled trials, so agalsidase alfa has never been approved in the US.

The trial that won accelerated approval

The FDA granted Fabrazyme accelerated approval based on a multicenter, randomized, double-blind, placebo-controlled trial of 58 adults with Fabry disease, who received either agalsidase beta or placebo by infusion every two weeks for 20 weeks (10 doses). The primary endpoint was the percentage of patients whose kidney-biopsy specimens were entirely free of microvascular endothelial GL-3 deposits after treatment: 20 of 29 patients on agalsidase beta (69%) reached that endpoint, versus none of 29 on placebo (P<0.001), and most of the remaining treated patients showed partial clearance rather than none at all (Eng CM, Guffon N, Wilcox WR, et al., "Safety and Efficacy of Recombinant Human alpha-Galactosidase A Replacement Therapy in Fabry's Disease," N Engl J Med 2001;345(1):9-16, PMID 11439963, DOI: 10.1056/NEJM200107053450102).¹ Secondary analyses found similar clearance of GL-3 deposits in heart and skin tissue. Because the endpoint was a tissue-level surrogate marker rather than a hard clinical outcome like kidney failure or death, the FDA approved Fabrazyme on an accelerated basis, with Genzyme required to confirm real clinical benefit in further studies.

2009: the same Genzyme crisis, a harder rationing

Because Fabrazyme had no FDA-approved alternative at the time — agalsidase alfa was never approved in the US, as the previous section describes — Fabry patients had nowhere else to turn during the shortage the way some Gaucher disease patients did. A 2010 consent decree between Genzyme and the FDA, covering the Allston facility's manufacturing of Cerezyme and Fabrazyme (and the fill-finish operations for Thyrogen), required Genzyme to disgorge $175 million in past profits and meet a schedule of remediation milestones backed by per-day fines if missed. Multiple lawsuits from Fabry patients over the prolonged under-dosing followed in the years afterward, with litigation over the episode still working through US courts as recently as 2024.

Eighteen years to a full approval — and what it closed off for rivals

Fabrazyme remained on its original 2003 accelerated approval — based on the GL-3 clearance surrogate endpoint rather than a hard clinical outcome — for far longer than most accelerated approvals stay open before either being confirmed or withdrawn. On 11 March 2021, the FDA converted Fabrazyme to a full, traditional approval, based on the accumulated long-term clinical and real-world evidence Genzyme/Sanofi had generated over nearly two decades of marketed use. The conversion had a genuine, documented consequence beyond Fabrazyme itself: with GL-3 clearance no longer an available accelerated-approval surrogate endpoint specifically because a drug had already used it to reach full approval, at least one company developing a gene-therapy candidate for Fabry disease (Avrobio) publicly said the change forced it to plan a more demanding head-to-head confirmatory trial against Fabrazyme rather than pursue the faster accelerated route.

Current status

Fabrazyme remains FDA-approved and currently marketed by Sanofi (through its Genzyme division). It is no longer the only approved option: migalastat (Galafold), an oral pharmacological chaperone rather than an infused enzyme, was approved in 2018 for patients with a genetically "amenable" GLA mutation, and pegunigalsidase alfa (Elfabrio), a PEGylated enzyme jointly developed by Protalix BioTherapeutics and Chiesi, was approved in 2023. Fabry disease patients today have a wider set of real, FDA-approved treatment choices than existed through the 2009-2012 shortage described above, when Fabrazyme was the only approved option in the country and could not reliably be dosed as approved.