Gene therapy may be effective against mitochondrial diseases

By Allen Cone
Gene therapy may be effective against mitochondrial diseases
This micrograph shows ragged red fibers, which are seen in various types of mitochondrial diseases. A newly developed gene editing tool potentially can treat these diseases, according to a study with mice. Photo by Nephron/Wikimedia Commons

Sept. 24 (UPI) -- A newly developed gene editing tool can potentially treat mitochondrial diseases, inherited and often fatal conditions that occur when the energy-producing cell structures malfunction.

Researchers successfully targeted and eliminated the damaged DNA in mitochondria by applying an experimental gene therapy treatment in mice. The findings, which were led by researchers at the University of Cambridge in London, were published Monday in the journal Nature Medicine.


The researchers said they developed the first programmable genome engineering tools used inside a living animal.

Besides representing a potentially practical route to treating patients with the diseases, researchers believe one day it can be an alternative to mitochondrial replacement therapy, or "three-parent IVF."

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"Mitochondrial replacement therapy is a promising approach to prevent transmission of mitochondrial diseases, however, as the vast majority of mitochondrial diseases have no family history, this approach might not actually reduce the proportion of mitochondrial disease in the population," first author Dr. Payam Gammage, a postdoctoral researcher in the MRC Mitochondrial Biology Unit, said in a press release.


In the three-parent IVF, affected mitochondria from an egg or embryo are replaced with healthy ones from a donor.

Mitochondria, which produce energy and carry their own DNA, are inherited from a person's mother via the egg, but if they are damaged, it can result in a serious mitochondrial disease.

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Mitochondria create more than 90 percent of the energy needed by the body to sustain life and support organ function.

MELAS Syndrome, which stands for mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes, is a severe multi-system disorder causing progressive loss of mental and movement abilities, and is usually apparent in early childhood.

Other diseases are more complex in adults because detectable changes in mtDNA occur as people age, according to the United Mitochondrial Disease Foundation. Symptoms can include seizures, strokes, severe developmental delays, inability to walk, talk, see and digest food.

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Mitochondrial conditions affect about 1 in 5,000 adults.

Typically there are about 1,000 copies of mitochondrial DNA per cell, with the percentage damaged, or mutated, determining whether a person will suffer from mitochondrial disease. Typically, more than 60 percent of the molecules in a cell need to be mutated for the disease to emerge.


"One idea for treating these devastating diseases is to reduce the amount of mutated mitochondrial DNA by selectively destroying the mutated DNA, and allowing healthy DNA to take its place," senior author Dr. Michal Minczuk, also from the Medical Research Council Mitochondrial Biology Unit.

Having tested the gene therapy method on human cells in petri dishes, the researchers tested the gene therapy -- mitochondrially targeted zinc finger-nuclease, or mtZFN -- in mice with the same mutation as some humans.

The treatment recognizes and eliminates mutant mitochondrial DNA, based on the DNA sequence differences between healthy and mutant mitochondrial DNA.

The treatment was injected into the bloodstream of the mouse using a modified virus in heart cells and specifically eliminated the mutated mitochondrial DNA and heart metabolism improved, the researchers report.

Based on the study, the researchers say they plan to develop a clinical trial to test the treatment in humans.

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