Three Parents – One Baby

In vitro fertilization technology has been used for many years to help couples conceive a child. The process involves taking an egg from the mother and fertilizing it with paternal sperm to create embryos that are then implanted into the mother (or a surrogate) to carry the child to term. A new technique has been proposed that allows for a donor egg to be used in cases where the mother’s cells contain defective genes in the mitochondria.

Mitochondria are organelles inside a cell that generates ATP energy the cell required for everyday metabolism. These organelles contain genetic material (DNA) which codes for 37 genes, 14 of which are related to specific proteins related to efficient ATP production. Any defect in these genes leads to serious conditions like Alpers disease and various mitochondrial myopathies (muscle disorders). While there are numerous other genes found in the nucleus related to mitochondria, it is this smaller set of genes found in the mitochondria themselves that have become a matter of controversy. At issue is an innovative therapy to prevent genetic diseases directly tied to these mitochondrial genes.

A new form of in vitro fertilization creates what is sometimes called a “three-parent baby” because a third party donates an egg to be fertilized with a maternal nucleus and paternal sperm. The donor’s nuclear genes are removed but the genes inside the mitochondria remain behind. The resulting baby has all of the nuclear genes of the mother and father but the 37 genes found in the mitochondria belong to the donor of the original egg cell.

There are two basic methods used to accomplish this. These are paternal spindle transfer and pronuclear transfer. The short video above that explains the differences between these two techniques.

This procedure is up for review by the FDA to be approved for clinical studies. This has been a source of controversy by many parties interested in reproductive issues. However, while popularized in the media as 3-parent babies, the genes in question amount to just 37 out of  the estimated 25,000 total genes in a human cell.Therefore, many argue that this does not justify calling it a third parent baby since the donated mitochondrial genes are insignificant in number compared to the rest of the genome derived from the parents.

References:

  •  Amato P., Tachibana M., Sparman M. & Mitalipov S. (2014). Three-parent in vitro fertilization: gene replacement for the prevention of inherited mitochondrial diseases, Fertility and Sterility, 101 (1) 31-35. DOI:

Article and animation concepts contributed by Michael Troyan. Michael has spent 20 years teaching non-majors biology and microbiology and currently works as an online instructor at Penn State University. He can be reached at mbt102@psu.edu

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