RNA Editing for Programmable A to I Replacement (REPAIR) was developed by Feng Zhang at the Broad Institute at MIT and Harvard based on CRISPR-Cas13 was developed by Zhang’s lab to edit RNA transcripts with pathogenic mutations . The Cas13b ortholog from the bacterium Prevotella sp. P5–125 was engineered to not cleave RNA (dCas13b) and fused to an adensosine deaminase enzyme which changes A to I in targeted spot on an RNA transcript as determined by the user supplied guide RNA. Zhang’s team used REPAIR to correct RNA transcripts in cell lines from patients with mutations causing Fanconi anemia and X-linked Nephrogenic diabetes insipidus. The REPAIR system is engineered for viral delivery into cells. There are less sequence constraints for CRISPR-Cas13 RNA editing than for CRISPR-Cas9 DNA editing, making it more flexible. However since the REPAIR system targets RNA not DNA, effects are temporary. Zheng's group suggests it would be suitable to treat diseases with acute phases like inflammation or modify proteins in the disease pathway to slow disease progression.