A flock of gene-edited sheep has been used by scientists to pinpoint a promising treatment for a lethal inherited brain disease that afflicts young children. The researchers, based in the UK and US, say their work could lead to the development of drugs to alleviate infantile Batten disease.
In the UK, Batten disease affects between 100 and 150 children and young adults and is inherited from two symptomless parents who each carry a rare recessive gene mutation.
Children who carry two copies of this faulty gene begin to suffer loss of vision, impaired cognition and mobility problems. Seizures and early death follow. “The effect on families is devastating,” said Professor Jonathan Cooper of Washington University School of Medicine in St Louis, one of the project’s leaders.
Researchers first began experiments, working with colleagues at Collaborations Pharmaceuticals, which showed mice affected by one form of Batten disease, known as CLN1 disease, could be treated with a missing enzyme.
“That was encouraging but we needed to test the treatment in larger brains with a structure more like those of a child,” said another project leader, Professor Tom Wishart, of Edinburgh University’s Roslin Institute, where cloning techniques were used to create Dolly the Sheep in 1996. “You cannot extrapolate straight from mouse experiments to humans. Having an intermediate larger model is important.”
The project scientists used the gene-editing technique Crispr-Cas9 to create a version of the faulty gene responsible for CLN1 in sheep. “Sheep ovaries were collected from abattoirs, eggs were removed and fertilised. Crispr reagents were added to make the required changes in CLN1 and the eggs were then implanted into surrogate sheep.” The scientists were able to create a small flock of sheep, each engineered to carry a single functional copy of the CLN1 gene.
“These are symptomless carriers, like the parents of Batten disease children,” added Wishart. “From these we could then breed sheep that have two faulty copies. These go on to develop a disease like those children, and became the subjects of our therapy trials.”
Children succumb to this version of Batten disease because they lack an enzyme made by healthy CLN1 genes. Without it the performance of their bodies’ lysosomes, which recycle waste material that builds up in cells, is impaired. This process is impeded in Batten disease.
The research on mice revealed that injecting the missing enzyme into the brain produced noticeable improvements. But jumping straight to trials on humans was not practical or safe, the group reasoned.
“You can miss two crucial issues,” added Cooper. “How to deliver the drug to the right place in a bigger brain and how to scale up dosing.”
Answers were provided by experiments on a half-dozen sheep bred from the Roslin flock with two faulty CLN1 genes. These showed many hallmarks of the disease that affects humans. By calculating an appropriate dose and the route to deliver it to brains of sheep, improvements in their disease could be observed by the team, whose research is published by the Journal of Clinical Investigation.
The results are promising, say the scientists, but they stress several years’ research will still be needed to optimise treatment.
“We have gained enormous insights that will help in the development of therapies for children one day,” said Wishart. His point was backed by Cooper. “We have still some way to go but we have taken a very important step.”
