The most common form of intellectual impairment in men is known as the fragile X syndrome and affects 1 out of 3,600 boys. 

Scientists at the Whitehead Institute used CRISPR/Cas9 gene editing method to restore activity to the fragile X syndrome gene in affected neurons. The study has been published in the journal Cell

Demethylation at work. Photo Credit: Cell

The work, performed on human brain cells in a dish, paves the way for trying the technique on the brain, with the hope that it could treat a number of genetic conditions. The research was led by the Institute’s founding member Rudolf Jaenisch. The team produced the first evidence that removing methylation, which are molecular tags that keep a mutant gene shut off, can reactivate the gene and restore the fragile X syndrome neurons. 

A normal version of the FMR1 gene sequence, where the fragile X syndrome can develop, contains 5-55 nucleotide (CGG) repeats. Nucleotides are the basic structural units and building blocks for DNA. The scientists concluded that version of the FMR1 sequence with over 200 nucleotide repeats can result in the syndrome’s production. 

The researchers concluded that methylation can blanket the nucleotide repeats and shut down the gene’s expression. In order to test this, postdoctoral researchers Shawn Li and Hao Wu from Jaenisch’s lab developed a CRISPR/Cas9-based technique which can add or delete methylation tags from a specific stretch of the DNA. Removing the tags renewed the FMR1 gene expression, turning it back into a normal gene. 

“These results are quite surprising-this work produced almost a full restoration of wild-type expression levels of the FMR1 gene,” said Jaenisch. “Often when scientists test therapeutic interventions, they only achieve partial restoration, so these results are substantial.”

The team was also able to reverse the abnormal electrical activity associated with the fragile X syndrome. Neurons rescued by this procedure were grafted into the brains of mice, with the FMR1 gene remaining active for at least three months. This promises that correcting methylation can lead to a sustained remedy for the disease.

“This work validates the approach of targeting the methylation on genes, and it will be a paradigm for scientists to follow this approach for other diseases,” added Jaenisch. 

The syndrome can cause mild to severe intellectual disability, with symptoms like delays in talking, hyperactive behaviour and anxiety. In addition, it might also result in physical features like large ears, a long face with prominent jaw and forehead, as well as flat feet. The disorder has been linked to autism.