Arginase 1 Deficiency

Arginase 1 Deficiency (ARG1-D) is a little-known disease with a big impact on patients’ lives.

ARG1-D is a debilitating and progressive inherited metabolic disorder affecting children, teens, and adults that can significantly impact a patient’s health over time. ARG1-D is one of the Urea Cycle Disorders (UCDs). It is a rare autosomal recessive metabolic disorder caused by abnormalities in the arginase 1 gene resulting in the failure of the body to break down arginine causing its accumulation. This accumulation of arginine is what separates ARG1-D from the other UCDs. Arginase 1 Deficiency can cause spasticity, mobility difficulties, seizures and intellectual delays.

Symptoms typically begin in childhood and include lower limb spasticity, which is tight or stiff muscles, intellectual disability and/or seizures as well as complain of stomach aches or nausea. Aversion to high protein foods is not uncommon as well as irritability, clumsiness, poor concentration and slowing down in development. Those affected with ARG1-D may also not attain as much speech as other children their age as well as may struggle to follow commands. Untreated high levels of arginine in childhood may lead to debilitating complications into adulthood.

If you or someone you know has been diagnosed with Arginase 1 Deficiency, please download the patient brochure using the link below or visit for more information.

Living with ARG1-D deficiency? Watch our video

Download our patient brochure: English | Spanish | Arabic

Diet & Nutrition
Current treatment for ARG1-D includes dietary protein restrictions to limit the amount of argine consumed. While protein restriction is effective, it is limited in its ability to reduce arginine levels to the normal range.

The normal range of protein intake amount varies by age and weight. If a protein-restricted diet is needed, consider working with a dietitian for guidance.

Managing a low-protein diet can be challenging, particularly for children. You can learn more about low-protein diet options, including recipes and meal planning resources, on our Diet & Nutrition page.

Ongoing Clinical Trials
We are conducting a Phase 3 clinical trial, called PEACE [link to:], to study the effects of an investigational drug, pegzilarginase, as a treatment for ARG1-D. The trial began in 2019 and the initial results from the trial are expected before the end of 2021. More information about the trial can be found on (NCT03921541).

If you wish to learn more about how clinical trials work, visit our FAQs page.

ARG1-D Advocacy Organizations
While ARG1-D is a rare condition, patients and families do not have to face this disorder alone. There is an established community of patients, caregivers, doctors, nurses, genetic counselors and dietitians who are ready to lend help and support.


Meet the patients and caregivers living with ARG1-D and inspiring us each day. They are true heroes!

Isaiah’s Story


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Read Isaiah’s story in Spanish – Lea la historia de Isaías en español.

Four-year-old Isaiah is living with Arginase 1 Deficiency. He is bright and full of life and loves to talk, to run around and play like any healthy child. But his mother, Angela, worries about what might happen if one day that all changes and he is no longer able to live his life to the fullest.

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For Angela and Isaiah, the most difficult part of their day is managing food. Angela struggles with not knowing what she can give him for a meal without jeopardizing his health and his future. She knows that high levels of the arginine building up in the body can cause numerous things: muscle spasticity, developmental or intellectual delay, and seizures. And she works hard to help control Isaiah’s arginine levels with the limited treatment options available to them.

Sometimes Isaiah has pain in his legs. Although Angela knows there’s a lot of different things that may cause this, even normal growing pains, she still worries about it because she knows that it could be a sign of the Arginase 1 Deficiency getting worse. Although Isaiah is only four and, so far, is living a fairly normal life, she can already see the toll Arginase 1 Deficiency is taking on the whole family – she sees her children worry. Angela believes the most difficult thing about living with Arginase 1 Deficiency is that it doesn’t only affect you as a parent, but it affects the other siblings as well.

Her major wish for Isaiah and his future would be for him to continue to live like he’s living and thriving, to be a successful young man.

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