According to Fox News:
Britain may allow a controversial technique to create babies using DNA from three people, a move that would help couples avoid passing on rare genetic diseases, the country’s top medical officer says.
The new techniques help women with faulty mitochondria, the energy source in a cell, from passing on to their babies defects that can result in such diseases as muscular dystrophy, epilepsy, heart problems and mental retardation. About one in 200 children is born every year in Britain with a mitochondrial disorder.