Last spring, John Zhang made headlines after his fertility clinic announced that for the first time a baby had been born using a new technique requiring three genetic parents. The baby's mother carried the genes for a fatal nervous system disorder called Leigh syndrome, but Zhang had been able to keep the disease from being inherited by her son by swapping in a donor's mitochondrial DNA, the teeny bit of DNA where Leigh syndrome is housed. Since the technique is illegal in the US, the baby had been born in Mexico, where, as Zhang explained in a comment he might live to regret, "there are no rules."