Today the British House of Commons passed a law that would create a regulatory framework for a in vitro fertilization procedure that would create an embryo containing DNA from three individuals. The procedure is designed to prevent children from inheriting one of the many serious metabolic disorders caused by defects in the genome of the mitochondria.
Mitochondria are small compartments in the cell that do most of the work of converting molecules such as sugars and fats into ATP, which the cell uses to power most of its basic functions. Mitochondria are the evolutionary descendants of bacteria that got trapped in eukaryotic cells like ours, and they still retain some essential genes in a small genome. The mitochondria are delivered along with their genome to new embryos in the egg. Thus, all genetic defects in the mitochondrial genome are passed directly from a mother to all of her offspring.
The National Institutes of Health has a list of some of the disorders that are inherited with the mitochondrial genome. These include various forms of deafness, neuromuscular disorders and diseases that cause blindness, among others.
Researchers in the UK have developed a technique that allows a woman carrying mitochondrial disease to have children with normal mitochondria. The woman with the disease donates an egg which is then fertilized in a test tube. The resulting chromosomes are then transferred to a healthy donor’s egg after that donor’s own genome has been eliminated. The resulting fertilized egg now has the chromosomes of two parents (the mother and father) and the normal mitochondrial genome of the healthy donor. (An alternative approach involves transferring an egg’s chromosomes prior to fertilization and fertilizing it afterwards; the end result is the same.)
Essentially, the technique allows a woman who carries a mitochondrial disease to give birth to offspring that are largely genetically hers.
The UK is the first country to formally adopt this process and impose restrictions on its use; The debate in parliament has largely focused on whether it could open a way for something more akin to designer babies. Still, the measure went from 382 to 128. In the US, the Food and Drug Administration is currently holding advisory committee meetings on the procedure.