In September 2016, Dr. John Zhang announced the birth of the first baby using mitochondrial replacement therapy (MRT), colloquially called “three-parent IVF,” born in Mexico to Jordanian parents. The technique prevented transmission of the mother’s mitochondrial disease (Leigh syndrome, which had killed her first two children) by combining her nuclear DNA and the father’s sperm with a donor woman’s healthy mitochondria—creating a baby with genetic material from three people, though 99.8% from the parents and just 0.2% (37 genes) from the mitochondrial donor.

The Procedure

Zhang’s team used spindle transfer: they removed the nucleus from the mother’s egg, inserted it into a donor egg with healthy mitochondria (whose nucleus had been removed), then fertilized it with the father’s sperm. The resulting embryo had the parents’ nuclear DNA (determining appearance, personality, intelligence) but the donor’s mitochondrial DNA (responsible only for cellular energy production). The procedure was performed in Mexico because it was illegal in the US and the family’s home country.

Ethical Firestorm

The announcement ignited debates about “designer babies” and germline genetic modification. Unlike gene therapy that affects only the treated individual, MRT changes create heritable modifications—the donor’s mitochondrial DNA would pass to all future generations. UK legalized MRT in 2015 under strict oversight; the US maintained a ban on clinical use (research only). Critics warned of slippery slopes toward genetic enhancement, while supporters argued preventing devastating diseases justified the technique. Some religious groups opposed creating and destroying embryos; others objected to “playing God” with inheritance.

Current Status

By 2023, the UK had approved over 30 MRT cases under regulatory supervision. Australia legalized it in 2022. The technique remains banned for clinical use in the US, though research continues. Follow-up studies on the first three-parent children show normal development so far, but long-term multi-generational effects remain unknown. The term “three-parent baby” is controversial—advocates prefer “mitochondrial donation” to emphasize that mitochondrial DNA doesn’t affect identity traits, though the genetic reality remains: DNA from three people contributed to the child.

Sources: New Scientist September 2016 report, Dr. John Zhang interviews, UK HFEA regulatory approvals, Nature Medicine MRT research, bioethics journal debates