Unexpected Risks Found In Editing Genes To Prevent Inherited Disorders

The genes in mitochondria, which are the powerhouses in human cells,

can cause fatal inherited disease.

But replacing the bad genes may cause other health problems.

Uknown to many is the fact that DNA is present not only in the nuclei of cells, but also in the cell's power generation organelle, the mitochondria.

There the mitochondria generates it's power generating ATP and also contains DNA and RNA. The hidden risk is that during meiosis and later fertilization of the female egg, the new zygote contains cytoplasm from the mother as well as nuclear DNA. The male sperm contains little, if any cytoplasm.

Thus the female contributes cellular mitochondria (containing DNA) to the fertilization. So the new oocyte contains not only nuclear DNA formed by meiosis it also contains cellular DNA from mother. Therein lies a new risk factor.

Some genetic diseases are caused by mutations or defects in mitochondrial DNA.

There are several neuro-muscular diseases caused by mitochondrial defects.

In September, reproductive endocrinologist John Zhang and his team at the New Hope Fertility Center in New York City captured the world's attention when they announced the birth of a child to a mother carrying a fatal genetic defect.

Using a technique called mitochondrial replacement therapy, the researchers combined DNA from two women and one man to bypass the defect and produce a healthy baby boy — one with, quite literally, three genetic parents.

It was heralded as a stunning technological leap for in vitro fertilization, albeit one that the team was forced to perform in Mexico, because the technique has not been approved in the United States.

But for all the accolades, the method also has scientists concerned that the fatally flawed mitochondria can resurface to threaten a child's health.

Earlier this month, a study published in Nature by Shoukhrat Mitalipov, head of the Center for Embryonic Cell and Gene Therapy at the Oregon Health and Science University in Portland, suggested that in roughly 15 percent of cases, the mitochondrial replacement could fail and allow fatal defects to return, or even increase a child's vulnerability to new ailments.

"This study shows the potential as well as the risks of gene therapy in the germline," Mitalipov says. This is especially true of mitochondria, because its genomes are so different than the genomes in the nucleus of cells. Slight variations between mitochondrial genomes, he adds, "turn out to matter a great deal."

Gene Therapy To Prevent Inherited Diseases May Cause Other Ills : Shots - Health News : NPR