The Food and Drug Administration (FDA) has warned a US fertility doctor to stop marketing mitochondrial replacement therapy (MRT) – a technique involving the creation of an embryo with DNA from three people.

Dr John Zhang, chief executive of New Hope Fertility Clinic and research company Darwin Life, made news last October when the world's first MRT baby was born in Mexico. Since then, Dr Zhang has been marketing MRT as a 'cure for mitochondrial disease' which can also '[prolong] natural fertility' and is a 'successful solution to age-related infertility'.

MRT was developed specifically to prevent transmission of mitochondrial disease, where the mother's eggs contain mitochondria with harmful mutations which can cause devastating disease in her children. The nuclear DNA from the patient's egg or embryo is removed, and transferred it to a donor egg or embryo with healthy mitochondria and its own nuclear material removed.

The procedure is currently not approved under US law, and Congress has banned its consideration by prohibiting funds for clinical investigations involving a 'human embryo being intentionally created or modified to include a heritable genetic modification.'

Dr Zhang had previously informed the FDA, following the success of the MRT therapy, that his centre would not 'use its spindle transfer technology again within the United States to support ex-US studies or procedures' until a suitable legal framework was in place.

However, the FDA has written a letter to Dr Zhang expressing its concerns over his company's continued marketing and promotion of the technique.

Mary Malarkey, the director for the Office of Compliance and Biologics Quality at the FDA's Centre for Biologics Evaluation and Research, explains in the letter to Dr Zhang how he had not met federal regulations when creating the embryo, and how by continuing to market the technology, he is compromising his commitment to stopping the use of MRT until approved.

The letter explores the multiple violations Dr Zhang and his team conducted in his 2016 work, including a lack of written notification to the FDA concerning export of the embryo to Mexico and manipulation of cells more than the minimal permitted allowance. While the use of MRT was not forbidden in Mexico, the treatment was still conducted unlawfully as the embryo did not meet US export licence exemptions. Malarkey continues that the 'letter is not intended to be an all-inclusive list of violations' and Dr Zhang must take full responsibility to 'ensure full compliance with the FD&C Act and the PHS Act and their implementing regulations'.

The FDA has requested Dr Zhang to notify it of the steps his centre has taken and will take to 'address [its] violation …and to prevent recurrence'.

'Darwin Life takes FDA's letter seriously', the company told the New York Daily News. 'We are fully committed to complying with all applicable requirements.'

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