Biogen's tau-lowering diranersen slows Alzheimer's decline 26% at the lowest dose in Phase 2, but an inverse dose response and a missed endpoint cloud the data.

The study provides the clearest evidence yet that medicines like BIIB080 might improve cognition, but leaves unclear why higher doses didn’t perform better.

An experimental drug might help slow early Alzheimer's disease in a markedly different way than current treatments — by lowering the brain's production of a protein called tau.