Belgian pharmaceutical company UCB SA has agreed to buy Zogenix Inc., a U.S. maker of drugs to treat seizures and rare diseases, for as much as $1.9 billion, expanding its portfolio to treat epilepsy.

Investors will get $26 in cash for every Zogenix share, plus a potential $2 per share payment if the U.S. company’s Fintepla drug gets regulatory approval for Lennox-Gastaut syndrome by the end of 2023, UCB said. T

Lennox-Gastaut syndrome is an orphan disease that causes seizures. UCB has been expanding in therapies for rare ailments, like many big rivals including Sanofi, Takeda Pharmaceutical Co. and Roche Holding AG, as they can charge more for unique life-saving drugs than for routine treatments.

Fintepla has already received regulatory approval in the U.S. and European Union for seizures caused by Dravet syndrome, a rare form of epilepsy.

UCB said it will finance the deal with cash and a loan. Lazard and Barclays are the company’s financial advisors, while Bank of America Securities and SVB Leerink advised Zogenix.