The paper at the heart of the debate, published online 18 April in Protein & Cell, an obscure Chinese online journal published by an affiliate of China’s Ministry of Education, drew widespread attention only after Nature News reported it online on 22 April. Junjiu Huang and colleagues at Sun Yat-sen University in Guangzhou described how they attempted to use the CRISPR/Cas-9 system, a new technology that makes it easy to modify genes in cells, to edit the hemoglobin-B gene (HBB) in 86 human embryos donated for research by couples at an in vitro fertilization clinic. In theory, this could be a way to prevent beta-thalassemia, a blood disorder which results when that gene is mutated, but the embryos experimented on were selected because they were not viable; they had an extra set of chromosomes as a result of being fertilized by two sperm.