Hemochromatosis is one of the most common inherited metabolic diseases among white populations and predominantly originates from a homozygous C282Y mutation in the HFE gene. The G > A transition at position c.845 of the gene causes misfolding of the HFE protein, ultimately resulting in its absence at the cell membrane. Consequently, the lack of interaction with the transferrin receptors 1 and 2 leads to systemic iron overload. We screened potential gRNAs in a highly precise cell culture assay

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... d applied an AAV8 split-vector expressing the adenine base editor ABE7.10 and our candidate gRNA in 129-Hfe tm.1.1Nca mice. Here we show that a single injection of our therapeutic vector leads to a gene correction rate of >10% and improved iron metabolism in the liver. Our study presents a proof-of-concept for a targeted gene correction therapy for one of the most frequent hereditary diseases affecting humans. Hereditary hemochromatosis is caused by mutations in genes involved in the regulation of systemic iron homeostasis. Dysregulation of iron homeostasis leads to the absorption and storage of more iron than required, causing tissue damage and disease. Five genes have been associated with various subtypes of the disorder. The most common gene involved in hereditary hemochromatosis is HFE (OMIM 235200). Homozygosity for a single missense substitution (p.Cys282Tyr) is responsible for most cases among European populations. The G > A transition at position c.845 of the gene causes the disruption of an intrachain disulfide bond, which leads to misfolding of the HFE protein. As a result, the mutated protein cannot associate with beta-2 microglobulin and does not reach the cell membrane, where it interacts with the transferrin receptors 1 and 2 (TFR1,2) 1 . This consequently leads to continuous iron uptake in the intestine and accumulation of iron in various organs such as the liver, pancreas, and heart. Affected patients may exhibit liver cirrhosis, diabetes mellitus as well as cardiomyopathy. The current state-of-the-art treatment of hemochromatosis includes life-long phlebotomy and the application of chelating agents such as deferoxamine. With the rapid emergence of novel CRISPR/Cas-based geneediting tools, proof-of-concept gene therapy strategies were rapidly developed. Metabolic liver diseases such as ornithine transcarbamylase deficiency, tyrosinemia type 1, and alpha-1-antitrypsin deficiency were successfully treated in vivo in various mouse models [2] [3] [4] [5] . Recently, the adenine base editing system ABE7.10 was developed, facilitating the highly efficient conversion of A•T to G•C 6 . This