Merck KGaA buys UK biotech Silence for $1.3 billion

Some diseases come from a gene being too active, not broken. Silence Therapeutics built a drug, divesiran, to quiet one such gene. It treats polycythemia vera, a rare disorder. The disorder makes the body overproduce red blood cells. Divesiran just posted positive results in a mid-stage trial. On Monday, Germany's Merck KGaA agreed to buy the London biotech. The price: about $1.3 billion in cash.

'Gene silencing' sounds complicated, but the idea is simple. The drug attaches to the instructions for one specific protein. It blocks the body from reading them, so the protein never gets made. In polycythemia vera, that protein drives the body to overmake red blood cells. That thickens the blood and raises the risk of dangerous clots. Merck is paying for a drug still in mid-stage testing, not an approved one. That's a real bet. Most drugs at this stage still fail before reaching patients.

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Will divesiran actually reach approval? Mid-stage success is encouraging, not a guarantee. Plenty of promising rare-disease drugs stumble in later, larger trials. The deal itself still needs sign-off from Silence's shareholders and regulators. This is the start of the process, not the finish.