BioMarin Pharmaceutical has signed a deal to buy Alesta Therapeutics for up to $490 million, adding a potential treatment for a rare genetic bone disease to its portfolio.

Under the terms of the deal, Alesta shareholders will receive an upfront payment of $275 million. They will receive an additional $215 million in subsequent payments, dependent upon the achievement of certain development and regulatory milestones, BioMarin said Tuesday.

The company plans to fund the transaction with cash on hand.

With the purchase, BioMarin will gain Alesta's lead clinical-stage asset, ALE1, a potential treatment for hypophosphatasia, or HPP, a rare genetic bone disease caused by mutations in the ALPL gene that can affect bone and tooth mineralization, resulting in easy or frequent bone breaks and early tooth loss, as well as muscle weakness, fatigue and pain.

BioMarin said ALE1, which is currently being evaluated in an ongoing Phase 1/2a clinical trial, has the potential to be the first oral therapy for HPP and will meaningfully strengthen the company's early-stage clinical pipeline.

"This is exactly the kind of opportunity to address a significant unmet need that lets us compete in larger rare disease markets," Chief Executive Alexander Hardy said. "We plan to continue to seek these kinds of opportunities as we focus on clinical-stage innovation to drive durable growth for BioMarin."

Alesta plans to spin out all non-ALE1 assets prior to the close of the transaction, which has been approved by both companies' boards and is expected to be completed this quarter. Former Alesta employees will transfer to the spinout entity, and as a result, none will become employees of BioMarin, the companies said.

BioMarin expects the transaction to have "a modestly dilutive impact" on its financial results this year. The company said it would provide an updated full-year forecast following the transaction's close.