Those with germline-modified mitochondria walk among usSunday, 2 March, 2008
A news article on the mitochondrial transplants I blogged about previously has the headline: “First disease-free babies could be born in three years as doctors create embryo from THREE parents”
But, and I kick myself for not remembering (or, more accurately, rediscovering) a certain fact earlier – that babies have been born with genetic material from three parents over ten years ago. Let me tell you the story of the real first baby (technically, an embryo, although a healthy baby did result – see below) created from three parents. This story comes from the following source: J. Cohen et al “Birth of Infant after Transfer of Anucleate Donor Oocyte Cytoplasm into Recipient Eggs” The Lancet 350(9072): pp186-187, July 1997
In 1996-7, Jacques Cohen and his team from the Institute for Reproductive Medicine and Science at the Saint Barnabas Medical Center in Livingston, New Jersey (in the USA) were treating a 39-year old, whose efforts as assisted reproduction had all failed. She was offered, and consented to, a cytoplasm transfer. Ooplasm, containing mitochondria and all the other organelles and chemicals present in the cytoplasm of an oocyte, from the eggs of a 27-year old donor was extracted with a pipette and inserted into the eggs of the patient. The patient’s eggs were fertilised with her husband’s sperm, and four embryos were implanted. A single impregnation resulted, and a healthy baby girl (weighing 4356g) was born as a result.
The thing is, the researchers report the following:
We compared nuclear and mitochondrial DNA fingerprinting profiles from aspirated amniocytes with those from both parents and the egg donor, […] Donor mitochondria had been displaced by homologous mitochondria before 16 weeks’ gestation.
So, technically this wasn’t germline engineering, or at least wasn’t a ‘successful’ example of it. The now 11-year old girl currently contains none of the donor mitochondria, so can’t pass any but her own mitochondria to any children she may have. But the same is not the case in the other children (17 of them, I believe) born as a result of the same technique in that medical centre and others across America (as far as I know, it hasn’t happened outside of the US, but I could easily be wrong). According to the following article: Barritt et al “Mitochondria in human offspring derived from ooplasmic transplantation: A brief communication” Human Reproduction 16(3):pp513-516, March 2001
mtDNA fingerprinting analysis performed on blood samples from 1 year old children following ooplasmic transfer detected mitochondrial polymorphisms in which both alleles were present in the hypervariable region of the mitochondrial genome. […] These are the first reported cases of germline mtDNA genetic modification which have led to the inheritance of two mtDNA populations in the children resulting from ooplasmic transplantation. These mtDNA fingerprints demonstrate that the transferred mitochondria can be replicated and maintained in the offspring, therefore being a genetic modification without potentially altering mitochondrial function.
So, these children are actually the first germline-modified children to be born, as far as I know. But I shouldn’t use the words ‘germline genetically modified’, because since these words were used, the FDA tightened their restrictions on the procedure. In a meeting of the Biological Response Modifiers Advisory Commitee on May 9,2002, the FDA changed regulations to require each procedure to gain approval from the FDA before going ahead (read the minutes of the meeting here, or the full transcript here).
The only difference here between what I blogged about previously and the procedure discussed above is that the latter uses cytoplasmic transfer rather than nuclear transfer as in the former, but as I said in my previous blog on this, it is all relative to what is the defining characteristic of a cell – if a nucleus is the defining feature of a cell, then picking that up and putting in a different cell is actually a full cytoplasm transplant rather than nuclear transfer. (An analogy would be brain transplants vs body transplants – if personhood is localised in the brain, then a brain transplant is actually a body transplant).
Anyway, the point remains that the embryo created by British researchers is not the first to be created with three genetic parents. Let us hope that those members of the House of Commons in the UK are considering this fact when deciding whether to allow it in Britain.