New CRISPR-based gene therapy for single-gene conditions

A new genome editing approach that inserts a new functional gene in front of a copy carrying a mutation has the potential to treat diseases caused by a variation on a single gene.

The 'Co-opting Regulation Bypass Repair' (CRBR) method was devised to address the current limitations of CRISPR/Cas9 genome editing: that it can only be used when a cell is dividing – a rare event in adult tissues – and that a wide spectrum of disease-causing mutations can occur in a single gene, so strategies that address only the mutation are limited in how many patients they will be applicable to. 

'This approach is especially promising for rare genetic diseases caused by a single gene, where limited time and resources typically preclude design and testing for the many possible disease-causing mutations,' said Professor Douglas Cavener who lead the research at Pennsylvania State University. 

CRBR allows the insertion of a condensed version of a normal gene between the promoter region, (a genetic sequence that drives gene expression), and the mutated gene sequence. The mutated gene is not removed from the genome, but is not expressed as the newly inserted DNA concludes with a terminator (like a stop sign) that prevents any downstream gene expression. 

'Our approach co-opts the native promoter for a gene. This means that the newly inserted gene will be expressed at the same times and at appropriate levels within the cell as the gene it is replacing. This is an advantage to other types of gene therapies, which rely on an external promoter to drive high levels of expression of the gene that could lead to negative effects if too much is produced or if essential regulation response is missing under certain physiological conditions,' said first author Jingjie Hu.

In a series of experiments, the research team showed that CRBR can effectively prevent disease-causing mutations from being manifested. In a mouse model of Wolcott-Rallison syndrome associated with neonatal diabetes and skeletal problems, the researchers inserted a normal copy of the PERK gene in healthy mice and bred those mice with a defective PERK gene. The resulting progeny did not suffer from the abnormalities associated with the syndrome. Further experiments were also successful in human cell cultures.

The research findings are yet to be peer-reviewed and published in the journal Molecular Therapy.