Curing Mitochondrial-Based Genetic Diseases

As you may know, 37 of our roughly 22,000 genes are located within mitochondria, rather than in the nucleus. Consequently these 37 genes are inherited entirely from the mother, since the female provides the egg (with its haploid number of chromosomes) and all of the egg’s organelles including the mitochondria. The male provides a haploid number of nuclear chromosomes.

A few inherited diseases are due to defects in those 37 mitochondrial genes. In fact the chance is about 1 in 4,000 that a child will develop a mitochondrial-based disease. Researchers think that these diseases could be among the first heritable diseases that could be permanently cured, according to a news report in Nature. How? The potential mother (with the mitochondrial-based genetic disease) and a healthy female donor would each provide an egg. The nucleus of the potential mother’s egg would be removed and inserted into the healthy mother’s enucleated egg. The egg would be fertilized by the potential father’s sperm, allowed to develop into a zygote (an early stage of development), and then inserted into the potential mother for development.

The child would have genes from two women, of course, but not very many from the donor woman - only 37 out of 22,000. And the child and all of its future descendants would be forever free of the disease.

So far, this has not yet been attempted beyond the zygote development stage. For one, genetically engineering a child is currently illegal. For another, the researchers who carried out the experiment to the zygote stage found a disturbing number of abnormalities in the zygotes they created. The researchers believe, however, that with further experimentation these problems could be overcome. The fact that we’re so close to curing a whole class of heritable diseases is likely to stimulate debate over whether such experiments should ever be conducted.