MicroRNAs are smaller than the small interfering RNA (siRNA) drugs now reaching the market, such as Alnylam’s Onpattro (patisiran), Givlaari (givosiran) and Oxlumo (lumasiran) for rare diseases.

Since then, Alnylam has claimed approval for two more RNAis, Givlaari (givosiran) for acute hepatic porphyria (AHP) and Oxlumo (lumasiran) for primary hyperoxaluria type 1 (PH1). RNAi uses small ...