The baby who was treated, Kyle “KJ” Muldoon Jr., suffers from a rare metabolic condition caused by a particularly unusual gene misspelling. Researchers say their attempt to correct the error demonstrates the high level of precision new types of gene editors offer. “My hope is that someday no rare-disease patients will die prematurely from misspellings in their genes, because we’ll be able to correct them.”The project also highlights what some experts are calling a growing crisis in gene-editing technology. In KJ’s case, the treatment was programmed to correct a single letter of DNA in his cells. That effort involved more than 45 scientists and doctors as well as pro bono assistance from several biotechnology companies.