A technique has been developed in order to prevent damaged DNA from being transferred from the mother's eggs to her children. The treatment creates an embryo using the genetic (DNA) material from three people: the parents and an egg donor. Mitochondrial DNA is only transferred from the mother. Mitochondrial dysfunction has been recognized as a significant cause of a number of serious diseases. This technique, developed to prevent diseases affecting tissue with a high metabolic demand, such as brain, heart, muscle, and central nervous system, has obtained approval only in England.