University of Connecticut Health Center, Farmington, CT, Associate Professor, Genetics and Genome Sciences
Associate Director, Graduate Program in Genetics and Developmental Biology
CRISPR is an exciting technology that has already revolutionized laboratory science and will likely revolutionize medicine in the future. CRISPR-based approaches can be divided into two major themes: genome editing, which changes the actual DNA base pairs in the genome of a cell and alteration of gene expression, which changes how much of a gene or protein is produced, but does not change the sequence of the DNA itself.
In the lab, we are using the genome editing version of CRISPR to mutate individual genes, to delete an entire copy of the 15q11-q13 region, or to get rid of the isodicentric chromosome in Dup15q induced pluripotent stem cell lines. These are terrific lab tools, but the technology is not efficient enough or safe enough to use as a therapeutic approach just yet.
We are also using the other version of CRISPR to activate or repress genes specifically. In this version, the Cas9 protein, which usually cuts DNA is changed so that it cannot cut the DNA. However, this protein can still be targeted to a specific place in the genome. Groups have attached different cargo to this protein to activate silent or quiet genes or to dampen highly expressed (loud) genes. We have been developing this approach to turn UBE3A up or down in our induced pluripotent stem cell lines. We haven’t yet applied this to Dup15q cells, but if it works well, we will look to do that in the future.
Therapeutic approaches using CRISPR are still a ways out in the future. While some groups have used them therapeutically, this has thus far been limited to blood cells, where they can take a cell out, use CRISPR in a dish, and then return the cell to the patient. This is not really feasible for disorders involving the central nervous system. For therapeutic approaches, the CRISPR components will have to be delivered using a virus, such as AAV. Labs are working on this, but the CRISPR machinery is a little too big for the current approaches. There are also worries about off-target effects—CRISPR can edit the DNA in places that it is not supposed to—which can increase risk of cancer and other issues. Finally, some worry about accidentally editing the germline—eggs and sperm—which could make unintended changes to future generations. This is a major ethical dilemma facing CRISPR therapeutics.
Nonetheless, progress will continue to be made to develop therapeutics using both types of CRISPR approaches. They will likely take longer to develop and vet than some other promising therapeutic approaches. For instance, antisense oligonucleotides (ASOs) and short hairpin RNAs (shRNAs) can all currently be used to alter gene expression in a targeted and reversible fashion. Both of these types of approaches are already used in the clinic for other disorders. If we know which gene(s) to focus on, these might be more promising approaches for Dup15q syndrome.