Recently, Bock et al, using an engineered PE lacking an RNAse H domain is able to revert disease-causing mutation targeting liver in a mouse model of phenylketonuria (PKU) (74) Moreover, by combining two PE pegRNAs with a Cas9-RT conjugate, Xue and coworkers developed a novel PE-Cas9 based deletion and repair method (PEDAR) that precisely removed a 1.38-kb pathogenic insertion within the tyrosinemia causing Fah gene (Fumarylacetoacetate hydrolase) to restore its expression in the liver of a mouse model of tyrosinemia (75). Here, FAH is linked to phenylketonuria.