Retinal organoids provide a powerful tool to diagnose and study Leber congenital amaurosis

Leber Congenital Amaurosis (LCA) is an inherited retinal disease leading to severe vision impairment from early infancy, affecting 2-3 out of every 100,000 newborns. LCA is caused by variants in certain genes from which proteins essential for retinal cell function and survival are made. Mutations in over 20 different genes can cause LCA and in each of those genes, hundreds of different changes, known as genetic variants, can occur. Importantly, while some of these genetic variants are benign and do not compromise function, other variants cause dysfunction or complete loss of function. Further, for some of these variants, which are called variants of uncertain significance (VUS), it is currently not known if they are disease causing or benign. 

The research team of Robyn Jamieson from Children's Medical Research Institute, University of Sydney, Australia have now set up a lab-based testing platform to classify VUS in retinal organoids, which are small 3D structures of retinal cells resembling the human retina. The work was published recently in Stem Cell Reports. The retinal organoids were grown from immature stem cells taken from a LCA patient with known pathogenic variants in the gene RPGRIP1, and from a second patient who carried a VUS in the same gene. Organoids from both patients had distinct abnormalities such as less light-sensing photoreceptors and altered gene expression. Having identified these "biomarkers" of RPGRIP1-related LCA in the retinal organoids, Jamieson's team went one step further and inserted the RPGRIP1 VUS into healthy retinal organoids. Strikingly, the genetically engineered retinal organoids also developed the disease changes, confirming that the VUS in the RPGRIP1 gene was indeed pathogenic. Further, by reintroducing a healthy RPGRIP1 gene into the retinal organoids these disease-mediated changes were reversed. This new platform can be used to classify new VUS in RPGRIP1 and other LCA genes, enabling clinical genetic diagnosis. Ultimately, the gained knowledge may help to develop targeted therapies for LCA patients and will inform decision-making and genetic counselling for at-risk populations.