Late-stage clinical trials fail to meet primary goals for rare disease treatments

Two significant late-stage clinical trials failed to meet their primary objectives, impacting research for rare diseases.

In a large international study presented at ESC Congress 2026, the drug eplontersen failed to significantly reduce cardiovascular deaths and repeat cardiovascular events in patients with transthyretin amyloid cardiomyopathy (ATTR-CM). While the RNA-targeted therapy successfully lowered circulating transthyretin protein levels, the biological effect did not translate into clinical benefits for the 1,432 participants across 20 countries. Researchers noted that the trial design may have been complicated by the existence of existing effective treatments for the condition.

Separately, Ultragenyx Pharmaceutical reported that its late-stage Aspire study of apazunersen (GTX-102) failed to meet its primary or key backup goals for treating Angelman syndrome. The study, which involved 129 children, showed no significant improvement in cognitive or daily functioning scores compared to a control group. Following this and a previous failure with a brittle-bone drug, Ultragenyx shares fell 46% in after-hours trading. The company is currently reviewing the program and plans to cut spending.