Friedreich's Ataxia or FRDA is the most prevalent form of hereditary ataxia. Most
individuals with FRDA have large expansions of “GAA/TTC” triplets in the first intron of
the FRATAXIN (FXN) gene. These repeat expansions repress FXN transcription resulting in
reduced levels of mature FXN protein when compared with unaffected individuals. It has
been proposed that the presence of expanded GAA/TTC repeats is associated with
heterochromatin-like changes at the FXN locus.
With no cure for the disease, currently patients with FRDA undergo symptom management.
Number of approaches have been reported thus far to mitigate the loss of FXN expression to
improve the disease condition. Most prominent amongst them are use of HDAC inhibitors or
transcription elongation factors to reverse the repressive epigenetic histone modifications,
gene replacement therapy by delivery of frataxin expressing AAV, deletion of trinucleotide
expansion using ZFNs/ CRISPR to restore FXN levels. However, none of the above methods
had promising outcomes suggesting missing links in the molecular aetiology of the disease.
A growth defect in the model plant Arabidopsis thaliana was shown to be caused by an
intronic GAA/TTC repeat expansion, which leads to downregulation of gene expression like
what is known in FRDA. Studies in plants reveal a role of small RNA and SUMOylation
and/or deSUMOylation pathway in repeat expansion-induced epigenetic silencing.
Taking cues from these studies, we seek to identify novel candidate genes that can increase
FXN levels to normal physiological levels. We carried out genetic screening using CRISPR
library in patient derived lymphoblast cell line. Candidate genes from our study will be used
to test restoration of chromatin status at the FXN locus and its expression at RNA and protein
level.
This genome wide perturbation study using CRISPR library in FRDA cell lines would
potentially lead to a significant advancement towards addressing FRDA disease.