US researchers raise hopes on genetic therapy to prevent inherited diseases

PUBLISHED : Sunday, 26 April, 2015, 6:45am
UPDATED : Sunday, 26 April, 2015, 6:45am

Researchers in the US have raised hopes for a simple genetic therapy that could prevent devastating diseases being passed on from mothers to their children.

A team at the Salk Institute in California demonstrated in mice that a single injection into embryos could rewrite faults in the DNA of mitochondria, the biological batteries that are needed to keep tissues healthy.

Most cells in the body carry hundreds or thousands of mitochondria, which are inherited only from mothers. Harmful mutations in mitochondrial DNA cause progressive and often fatal diseases that typically affect the heart, brain and muscles.

The US researchers showed that simple and widely available genome editing procedures could correct faulty mitochondria in the mouse embryos and then dramatically reduce the number they then passed down to future generations.

Many mitochondrial diseases only take hold if the person, or their specific organs, carry a sufficiently high proportion of the faulty mitochondria, said Juan Carlos Izpisua Belmonte, who led the work.

"This technology is not perfect; it cannot eliminate all the bad DNA, but by eliminating some, it'll be enough to prevent the transmission of these diseases to the kids of affected mothers," said Belmonte.

They first injected freshly fertilised mouse embryos with enzymes that cut DNA at specific points. The mice had two types of mitochondria that differed by one letter of the genetic code.

When the enzymes were injected, they behaved sort of like molecular scissors that cut out the target letter in one type of mitochondria, leaving the rest largely untouched.

In a second series of experiments, the scientists inserted faulty human mitochondria into mouse eggs and then tried to correct the mutations.

This time, the researchers created bespoke enzymes in the lab that targeted the harmful mutations without damaging DNA elsewhere in the cells. These were less effective than those used in the first experiments, but still reduced mitochondrial mutations by around half, the scientists write in the journal Cell.

Buoyed by their findings, the US group has begun tests on surplus human eggs donated by fertility clinics.