So, in experiments that began a few years ago, Dr. Cohen and his colleagues began injecting cytoplasm from the eggs of fertile women into the eggs of the infertile women. The group has treated 30 women, Dr. Cohen said, and they have given birth to 15 babies. About 30 babies have been born worldwide as a result of this technique, he added. But the cytoplasm of an egg contains more than just proteins to help an embryo grow. It also contains mitochondria, which are self-contained tiny structures that use oxygen and nutrients to create energy for the cells.
Mitochondria have their own genetic material.
That gave rise to a question. The answer, Dr. Cohen and his colleagues reported, is yes. They tracked the one region of the mitochondrial genetic material that normally varies from person to person, a region, Dr. Cohen said, in which genes are inactive. This is a fingerprinting difference. But in an editorial published in the journal Science on April 20, two ethicists, Erik Parens of the Hastings Center in Garrison, N.Y., and Eric Juengst of Case Western Reserve University in Cleveland, suggested that such treatments, because they result in permanent genetic alterations that in turn will be passed on to the babies' children, might not have been approved by a federal committee that oversees experiments that involve gene transfer.