In that study, scientists cut a specific target sequence on a mutant gene known to be carried by a sperm donor.
In this new publication, researchers targeted other discrete mutations using donated sperm and eggs, including one mutation known to cause hypertrophic cardiomyopathy, a condition in which the heart muscle becomes abnormally thick, and a different one associated with high cholesterol. In each case an enzyme known as Cas9, used in tandem with CRISPR, induced a double-strand break in DNA at the precise site of the mutation.
Every human being shares two versions, or alleles, of every gene on the human genome—one contributed from each parent. Most of the time, the alleles are identical, given 99.9% of any individual's DNA sequence is shared with the rest of humanity. In some cases, however, one parent will carry a recessive disease-causing mutation that's normally canceled out by the other parent's dominant healthy version of the same gene.