Proqr Therapeutics NV stock lost three-quarters of its value as word got out that its pivotal phase II/III study of sepofarsen in treating a tough, rare and genetic retinal disease failed to hit the primary endpoint. CEO Daniel de Boer said he was “shocked by the unexpected outcome” based on data from earlier studies. He added that he is unsure if Proqr will continue developing its therapy for treating CEP290-mediated Leber congenital amaurosis 10 until it understands the new results.