Congenital blindness refers to newborns that are visually impaired at birth. Blindness currently represents an enormous disease burden in terms of human suffering and economic cost. The CNIB (Canadian National Institute for the Blind) reports that more than one million Canadians are living with blindness or a significant loss of vision. Furthermore, developmental defects in the embryonic eye are a significant cause of blindness in Canada. These defects, which include Aniridia, often have a very strong genetic link.
The eye is leading the way for gene therapy of the nervous system. Currently, there are 24 clinical trials of rAAV (recombinant adeno-associated virus)-based therapies ongoing in the USA for: Leber congenital amaurosis, choroideremia, and age-related macular degeneration (www.clinicaltrials.gov). Most advanced in clinical trials is gene therapy for the rare vision-threatening disorder Leber’s Congenital Amaurosis, resulting from mutations in the RPE65 gene. The plethora of ocular trials is due in part to the relatively lower risk, ease of accessibility, and at least partially immunoprivileged status of the eye (Dalkara and Sahel, 2014).
Our goal is to develop an rAAV-based gene therapy for aniridia. Our experiments are the first towards AAV-based gene therapy for aniridia in mouse.
Currently we are taking a two-pronged approach to gene therapy for the congenital blindness aniridia: augmentation gene therapy, and genome editing using CRISPR (clustered regularly interspaced short palindromic repeats) /cas9 (CRISPR-associated nuclease 9). For augmentation gene therapy, we are delivering to the eye additional PAX6, the gene mutated in aniridia, encoded in rAAV. Because PAX6 may need to be carefully regulated, we have designed MiniPromoters from the human PAX6 gene and tested them in the mouse eye (Hickmott et al., 2016 in revision). For genome-editing therapy, we are using the bacterial CRISPR/cas9 system. It will be delivered in rAAV to edit out the genomic mutation in vivo in a mouse model of aniridia.
Corso-Díaz, X., Borrie, A.E., Bonaguro, R.J., Schuetz, J.M., Rosenberg, T., Jensen, H., Brooks, B.P., MacDonald, I., Pasutto, F., Walter, M., Gronskov, K., Brooks-Wilson, A.R., and Simpson, E.M. (2012). Absence of NR2E1 mutations in Patients with Aniridia. Molecular vision 18, 2770-2782, PMID 23213277