Arginase 1 deficiency (ARG1-D) is a rare condition in which the body cannot properly break down a substance called arginine. This leads to high levels of arginine and related substances in the blood, which can cause serious health problems and reduce quality of life.

Loargys is a new treatment designed to lower arginine levels in people with ARG1-D. It works by providing a modified version of a natural enzyme that breaks down arginine in the blood. The dose of Loargys is adjusted for each patient based on their arginine levels.

Because Loargys continues to break down arginine even after a blood sample has been taken, to ensure accurate results, a special substance (called nor-NOHA) is added to the blood collection tubes to stop this process after the sample is taken. The arginine levels are then measured using a standard laboratory test.

The Loargys Arginine Test System used in this study includes both the special blood collection tubes and the laboratory test used to measure arginine.

The purpose of this study is to evaluate the safety of this test system when used to measure arginine levels in patients receiving Loargys.

Inclusion Criteria:

• Participant receiving treatment with commercialized Loargys for ARG1-D
• Participant is willing to sign the Informed Consent Form

Exclusion Criteria:

• None