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Abstract Phenylketonuria (PKU), an autosomal recessive disorder caused by pathogenic variants in the phenylalanine hydroxylase (PAH) gene, results in the accumulation of blood phenylalanine (Phe) to neurotoxic levels. Current dietary and medical treatments are chronic and reduce, rather than normalize, blood Phe levels. Among the most frequently occurring PAH variants in PKU patients is the P281L (c.842C>T) variant. Using a CRISPR prime-edited hepatocyte cell line and a humanized PKU mouse model, we demonstrate efficient in vitro and in vivo correction of the P281L variant with adenine base editing. With the delivery of ABE8.8 mRNA and either of two guide RNAs in vivo using lipid nanoparticles (LNPs) in humanized PKU mice, we observe complete and durable normalization of blood Phe levels within 48 h of treatment, resulting from corrective PAH editing in the liver. These studies nominate a drug candidate for further development as a definitive treatment for a subset of PKU patients.

Lysosomal storage diseases like mucopolysaccharidosis type I (MPS I) cause pathology before birth and result in early morbidity and mortality. Here, the authors show that in utero base editing mediates multi-organ phenotypic and survival benefits in a mouse model recapitulating a common human MPSI mutation.

The ability to support the development of a premature fetus in the form of an extracorporeal system has had limited success. Here, the authors show that an extra-uterine device that mimics the intra-uterine environment can provide physiologic support for the extreme premature lamb fetus for four weeks.

Nature Communications 8: Article number: 15112 (2017); Published 25 April 2017; Updated 23 May 2017 A patent based on the work reported in this Article was inadvertently omitted from the Competing interests section of this article. The Competing interests statement should read: E.M., A.F. and M.D. are co-authors on a patent entitled ‘Extracorporeal life support system and methods of use thereof’ (Patent no.