The rare disease drug market is getting a new heavyweight. BioMarin Pharmaceutical announced a definitive agreement to acquire Amicus Therapeutics for $4.8 billion in cash, valued at $14.50 per share—a significant premium to Amicus's recent trading levels. The deal, expected to close in the first half of 2026, will create a dominant force in the treatment of lysosomal storage disorders (LSDs).

The acquisition caps a year of dramatic activity in the biopharmaceutical sector and underscores the strategic value of rare disease franchises, where limited competition and strong pricing power can generate outsized returns.

The Strategic Logic

BioMarin has built its reputation on treating rare genetic conditions, with approved drugs for phenylketonuria, hemophilia A, and several lysosomal storage disorders. The Amicus acquisition extends that franchise considerably:

  • Galafold (migalastat): Amicus's flagship drug for Fabry disease, which generated approximately $450 million in 2024 revenue. Fabry disease affects an estimated 1 in 40,000 people globally
  • Pombiliti + Opfolda: A recently approved treatment for Pompe disease, a debilitating condition that affects muscle function
  • Gene therapy pipeline: Amicus has multiple gene therapy candidates in development that could eventually cure, rather than merely treat, certain LSDs

For BioMarin, the deal diversifies its revenue base beyond hemophilia—where competition is intensifying—and adds proven commercial assets alongside promising pipeline programs.

The Premium Debate

At $14.50 per share, BioMarin is paying roughly a 40% premium to Amicus's unaffected trading price before deal speculation began. Some analysts questioned whether the valuation was justified:

"The premium reflects strategic value rather than standalone fundamentals. Amicus was struggling to achieve profitability on its own, but combined with BioMarin's infrastructure, the math changes considerably."

— Healthcare analyst at Morgan Stanley

Amicus has been a perennial takeover target, with its stock swinging wildly based on clinical data and regulatory decisions. The company's gene therapy programs, while promising, require significant capital investment that strained its balance sheet. Joining BioMarin provides access to the resources needed to see those programs through.

The Rare Disease Model

The deal highlights the unique economics of rare disease drug development:

High Prices, Small Populations

Drugs for lysosomal storage disorders typically cost $300,000 to $500,000 per patient per year. While patient populations are small—often measured in the thousands globally—the pricing power and minimal competition generate substantial revenues.

Regulatory Advantages

Rare disease drugs benefit from expedited FDA review pathways, extended market exclusivity, and reduced clinical trial requirements due to limited patient availability. These advantages make the category attractive despite the scientific challenges.

Payer Acceptance

Insurers and healthcare systems have generally accepted high prices for rare disease drugs, recognizing that the alternative—leaving patients untreated—carries its own costs. However, this dynamic faces increasing scrutiny as drug spending rises.

M&A Wave in Biopharma

The BioMarin-Amicus deal is part of a broader surge in biopharma M&A in 2025. After a slow 2024, dealmaking has accelerated dramatically:

  • Johnson & Johnson's $3 billion Halda Therapeutics acquisition for cancer drug development
  • Merck's $10 billion Prometheus Biosciences deal (closed earlier this year)
  • Multiple AI drug discovery partnerships worth billions in potential milestone payments

Large pharma companies, facing patent cliffs on blockbuster drugs, have turned to acquisitions to replenish their pipelines. Rare disease specialists like Amicus are attractive targets because of their differentiated assets and growth potential.

What It Means for Patients

For patients with Fabry disease, Pompe disease, and other conditions treated by Amicus drugs, the acquisition raises questions about access and pricing:

  • Continuity of supply: BioMarin has committed to maintaining uninterrupted access to all current Amicus products
  • Pipeline investment: The combined company's stronger financial position should accelerate development of gene therapy candidates that could offer one-time cures
  • Pricing pressure: With a larger rare disease portfolio, BioMarin may face intensified scrutiny from payers and policymakers concerned about cumulative spending

Market Reaction

Amicus shares surged on the announcement, closing near the deal price as investors anticipated regulatory approval. BioMarin shares dipped modestly, a typical pattern when acquirers announce large deals, as investors weigh integration risks and capital deployment.

The transaction requires customary regulatory approvals and Amicus shareholder approval. Antitrust review is expected to be straightforward given the limited overlap in the companies' product portfolios.

BioMarin Pharmaceutical (BMRN) closed at $89.42, down 1.8%. Amicus Therapeutics (FOLD) closed at $14.22, up 38%.