Study of LNP.UCD.ABE in Patients With Urea Cycle Disorders

Humans ingest protein to support growth and the synthesis of a number of key macromolecules. Nitrogen waste generated from protein catabolism is converted to ammonia, which under normal physiologic conditions is converted to urea via the urea cycle. Urea is then excreted in urine to maintain whole-body nitrogen homeostasis. Loss of function of any of the six enzymes of the urea cycle-encoded by CPS1 (carbamoyl phosphate synthetase 1), OTC (ornithine transcarbamylase), ASS1 (argininosuccinate synthetase), ASL (argininosuccinate lyase), ARG (arginase), and NAGS (N-acetylglutamate synthetase)-results in a urea cycle disorder (UCD). In addition loss of the ornithine transporter, ORNT1 (encoded by SLC25A15), can also lead to disease. Severe UCD patients typically present as neonates and have a profound decrease in function in any one of the six enzymes of the urea cycle or a lack of function of the ornithine transporter that carries urea cycle intermediates. This results in toxic accumulation of ammonia in the blood and accumulation of specific urea cycle amino acids that aid in diagnoses and therapeutic monitoring. Patients are at risk of developing extremely elevated blood ammonia levels (hyperammonemia) that can lead acutely to coma and death and chronically to profound neurologic dysfunction. LNP.UCD.ABE is an investigational in vivo gene editing product proposed for the treatment of hyperammonemia in patients under 5 years of age with deficiencies in enzymes or a related transporter of the urea cycle who are homozygous or compound heterozygous for a pathogenic variant in any UCD gene, including CPS1, OTC, ASS1, ASL, ARG, NAGS, and SLC25A15, that can be efficiently corrected by an adenine base editor (ABE). Each subject will have a personalized variant-specific LNP.UCD.ABE developed and evaluated during the Screening period, which may last up to 8 months. Subjects will eligible for a lead in period to establish a stable diet. After the subject's drug is developed and lead in has been completed, the subject will be administered LNP.UCD.ABE via a single intravenous infusion. After LNP.UCD.ABE administration, participants will be followed for safety and efficacy for 52 weeks.