PRX-ASS1

PRX-ASS1 is a preclinical mRNA-based intracellular enzyme replacement therapy being developed by PhaseRx to treat argininosuccinate synthase 1 (ASS1) deficiency, a rare urea cycle disorder characterized by impaired conversion of citrulline and aspartate to argininosuccinate, leading to hyperammonemia and associated neurotoxicity.[2][9] Using PhaseRx’s Hybrid mRNA Technology, PRX-ASS1 delivers synthetic mRNA to hepatocytes via a GalNAc-targeted polymer system, enabling de novo intracellular synthesis of functional ASS1 enzyme in liver cells to restore urea cycle function and normalize blood ammonia levels.[2] The program is part of a portfolio of liver-directed mRNA therapeutics for urea cycle disorders and has been described as in preclinical development, with plans for IND-enabling studies but no reported human trials or approvals to date.[2][9]