This seems a newsworthy story by Ian Sample at the Guardian: "Britain ponders 'three-person embryos' to combat genetic diseases".
If ministers and MPs give the procedures the green light, Britain would become the first country to offer treatments that lead to children being born with DNA from three people: their parents and a woman donor. The amount of DNA from the donor is tiny compared with the parents.
About one in 6,000 people is born with a disease caused by genetic glitches in their mitochondria, the biological batteries that power the cells in our bodies. Mitochondria are inherited only from mothers and contain just 37 genes, held separately to the 23,000 genes that shape our appearance and define much of who we are.
Nuclear transfer is in principle one of the easiest methods of genetic engineering. In this case, they are talking about taking a donor egg and then transferring the nuclear genetic material from the parents' fertilized egg into that donor egg. It's taking the cytoplasm from one woman (including all the mitochondria in that cell) and grafting on a whole diploid genome from a cell with two other parents. It is a cloning technique, although interestingly the Guardian article does not use the word "clone" anywhere.
This technique would really only be useful to parents where the mother has a heritable mitochondrial disorder, so that's a small population. But it's possibly a growing population as genetic tests become more widespread, as some disease-linked mitochondrial variants go without noticeable effects in younger adults.