Phenylketonuria (PKU) is an autosomal recessive liver disease in which phenylalanine hydroxylase (PAH) enzyme deficiency results in decreased phenylalanine metabolism, causing hyperphenylalaninemia.262 Repair of mutated bases using a single-base editor that converts C-G base pairs to T-A base pairs restores PAH expression and increases the reduced level of phenylalanine in blood. This evidence concerns the gene PAH and phenylketonuria.