Embryo created from one man, two women

A paint white blotch in the tube (right) is DNA that has been removed from a human egg, center

Scientist in the US have created embryos with genes from one man and two women, using a provactive technique that someday could be used to prevent babies from inheriting certain rare incurable diseases. The researchers at Oregon Health & Sciences University said they are not using the embryos to produce children.

     Over the past few years, scientists have reported that such experiments produced healthy monkeys. The US scientists reported that they have produced about dozen early human embryos and found the technique is highly effective in replacing DNA.

     The genes they want to replace aren’t the kind most people think of, which are found in the nucleus of cells. Rather, these genes reside outside the nucleus of cells. Rather, these genes reside outside the nucleus in energy-producing structures called mitochondria. These genes are passed by mothers, not fathers.

    About 1 in every 5,000 children inherits a disease caused by defective mitochondrial genes. The defects can cause many rare diseases with a host of symptoms, including strokes, epilepsy, dementia, blindness, deafness, kidney failure and heart disease.

    The new technique, if approved someday for routine use, would allow a woman to give birth to a baby who inherits her nucleus DNA but not her mitochondrial DNA. Here’s how it would work:

    Doctors would need unfertilized eggs from the patient and a healthy donor. They would remove the nucleus DNA from the donor eggs and replace it with nucleus DNA from the patient’s eggs. So, they would end up with eggs that have the mother’s nucleus DNA, but the donor’s healthy mitochondrial DNA.

    In a report published in Nature, Shoukhrat Mitalipov and others transplanting nucleus DNA into 64 unfertilised  eggs from healthy donors. After fertilization, 13 eggs showed normal development and went on to form early embryos. The researchers also reported that four monkeys born from eggs that had DNA transplants remain healthy.