Liver-Directed Adeno-Associated Virus Serotype 8 Gene Transfer Rescues a Lethal Murine Model of Citrullinemia Type 1

Citrullinemia type 1 (CTLN1) is an autosomal recessive disorder of metabolism caused by a deficiency of argininosuccinate synthetase. Despite optimal management, CTLN1 patients still suffer from lethal metabolic instability and experience life threatening episodes of acute hyperammonemia. A murine model of CTLN1 (fold/fold) that displays lethality within the first 21 days of life was used to determine the efficacy of adeno-associated viral (AAV) gene transfer as a potential therapy. An AAV serotype 8 (AAV8) vector was engineered to express the human ASS1 cDNA under the control of a liver-specific promoter (thyroxine binding globulin, TBG), AAV8-TBG-hASS1, and delivered to 7–10 day old mice via intraperitoneal injection. Greater than 95% of the mice were rescued from lethality and survival was extended beyond 100 days after receiving a single dose of vector. AAV8-TBG-hASS1 treatment resulted in liver specific expression of hASS1, increased ASS1 enzyme activity, reduction in plasma ammonia and citrulline concentrations, and significant phenotypic improvement of the fold/fold growth and skin phenotypes. These experiments highlight a gene transfer approach using AAV8 vector for liver targeted gene therapy that could serve as a treatment for CTLN1.