The world's first in-human gene editing treatment will attempt to conquer hemophilia, a common blood disease that could cause people to spontaneously bleed to death internally. The rare genetic disorder has been the target of a number of medical treatments, though none as ambitious as the upcoming gene-editing program developed by Michael Holmes and Thomas Wechsler of California's Sangamo biopharmaceuticals. The procedure involves CRISPR-9 gene editing techniques, in which scientists cut out a portion of DNA and replace it with other strands in its place. While exciting, many scientists are worried that DNA-splicing could lead to unforeseen and potentially disastrous side effects.