Arginase 1 Deficiency Treatments
The treatment landscape for Arginase 1 Deficiency (ARG1-D) is changing in ways that were unimaginable just a few years ago. For decades, individuals living with this ultra-rare metabolic disorder relied primarily on strict dietary management, specialized medical formulas, and supportive therapies to help control symptoms and slow disease progression. While these approaches remain important components of care, advances in research have led to the development of therapies that directly target the underlying biochemical causes of ARG1-D.
Today, the ARG1-D community is witnessing a new era of treatment options. The approval of Loargys® (pegzilarginase), the first therapy specifically developed for ARG1-D, represents a historic milestone and offers a new way to manage elevated arginine levels, the hallmark of the disorder. At the same time, researchers continue to explore innovative approaches such as gene therapy, with the goal of addressing the root cause of ARG1-D and potentially providing long-lasting benefits through a one-time treatment.
Loargys® (Pegzilarginase)
Loargys® (pegzilarginase) is the first approved therapy specifically developed to address the underlying biochemical cause of Arginase 1 Deficiency (ARG1-D). Developed by Immedica Pharma AB, Loargys is a recombinant human arginase-1 enzyme replacement therapy designed to rapidly and sustainably reduce elevated blood arginine levels, the hallmark of ARG1-D. It represents a major milestone for the ARG1-D community and the first approved treatment shown to directly target hyperargininemia, the primary driver of disease progression.
For decades, treatment for ARG1-D relied on strict dietary protein restriction, specialized medical formulas, and medications aimed at managing symptoms and reducing ammonia levels. While these approaches remain important components of care, they do not replace the missing arginase enzyme. Loargys provides a new treatment option by supplying a functional form of the arginase-1 enzyme, allowing excess arginine to be metabolized and helping restore balance within the urea cycle.
Clinical studies have demonstrated that Loargys can rapidly lower plasma arginine levels and maintain those reductions over time. In the Phase 3 PEACE study, patients receiving Loargys experienced significant reductions in plasma arginine compared with placebo, along with improvements in important clinical measures. Long-term data have further supported the sustained biochemical benefits of treatment and its potential to positively impact disease outcomes.
Loargys is administered as a once-weekly intravenous infusion (or with physician approval subcutaneous injection) and is approved for adults and children aged 2 years and older with ARG1-D, in conjunction with dietary protein restriction. The therapy has received regulatory approvals in multiple regions, including the European Union, United Kingdom, Oman, Canada and the United States. In February 2026, the U.S. Food and Drug Administration granted accelerated approval of Loargys for the treatment of hyperargininemia in patients with ARG1-D, marking a historic achievement for families who have waited decades for an approved treatment.
For many families, the journey to Loargys has been years in the making. Patients, caregivers, advocacy organizations, clinicians, researchers, and industry partners worked together to advance the development of pegzilarginase through clinical trials, regulatory review, and ultimately approval. Today, Loargys offers new hope for individuals living with ARG1-D and represents a significant step forward in transforming the treatment landscape for this ultra-rare disorder.
Loargys® (pegzilarginase) is a prescription medication. Treatment decisions should always be made in consultation with a qualified metabolic specialist or healthcare provider. Approved indications, availability, and prescribing information may vary by country.
Investigational Gene Therapy for Arginase 1 Deficiency
The Arginase 1 Deficiency Foundation is encouraged by the ongoing progress being made toward a potential one-time gene therapy treatment for Arginase 1 Deficiency (ARG1-D) under the leadership of Gerry Lipshutz and his team at the University of California, Los Angeles (UCLA).
Gene therapy is designed to address the underlying cause of ARG1-D by delivering a functional copy of the ARG1 gene to the liver, with the goal of restoring arginase enzyme activity and improving the body’s ability to process arginine through the urea cycle. Unlike current therapies that require lifelong management, this investigational approach is being developed as a potential one-time treatment.
The Lipshutz Laboratory continues to make significant progress in the studies required before seeking approval to begin human clinical trials. Current research is focused on generating the data needed for a pre-Investigational New Drug Application (pre-IND) submission to the U.S. Food and Drug Administration (FDA), which is anticipated later this year.
Preclinical studies using a near-clinical-grade gene therapy product in arginase-deficient mice have demonstrated promising results. Researchers have observed long-term control of blood arginine levels, improvement in urea cycle function, and the absence of abnormal elevations in guanidino compounds—important markers associated with disease progression. In addition, the manufacturing process for the gene therapy product has been fully developed and defined, representing another critical milestone toward clinical development.
The laboratory team has expressed optimism regarding the findings to date and believes the results provide strong support for advancing this treatment approach for individuals living with ARG1-D. Community participation has also played an important role in the program’s progress. Responses from the ARG1-D patient and caregiver survey have demonstrated meaningful interest in this innovative therapeutic strategy and will help inform future development plans.
The next major milestone for the program will be the submission of the pre-IND package to the FDA. While additional studies and regulatory review will be required before human clinical trials can begin, these advances represent an important step toward a future where a one-time treatment may become a reality for individuals and families affected by Arginase 1 Deficiency.
Gene therapy for ARG1-D remains investigational and has not been approved by the U.S. Food and Drug Administration. Safety and effectiveness have not yet been established in human clinical trials.