Global Patient Numbers for ARG1 Deficiency Remain Unclear Despite Pegzilarginase Progress

These numbers highlight just how uncommon the disorder is compared with most genetic diseases.

Country-Level Patient Estimates

Because ARG1‑D is so rare, many countries only have rough estimates of patient numbers.

• In the United States, about 250 people are estimated to be living with ARG1‑D. ^[7]
• In the United Kingdom, the estimated prevalence is about 0.58 cases per million people. ^[6][8]

Such figures reflect diagnosed and surviving patients rather than theoretical cases predicted by birth statistics.

Why a Global Patient Number Is Hard to Define

Even though prevalence ranges are available, translating them into a single worldwide patient figure is difficult for several reasons:

• Underdiagnosis: Newborn screening programs do not consistently detect ARG1‑D, and arginine levels can appear normal shortly after birth. ^[6]
• Differences in screening coverage: Some countries routinely screen metabolic disorders, while others do not.
• Survival variability: The disease can cause progressive neurological damage and early mortality without effective treatment. ^[2]

Because of these factors, theoretical estimates derived from population statistics can differ significantly from the number of patients actually identified and eligible for therapy.

Bottom Line

Based on currently available public sources, pegzilarginase documentation does not publish a definitive global patient count for ARG1‑D. What researchers and policy agencies provide instead are prevalence estimates and country‑specific patient numbers, which can be used to approximate the potential treatment population but cannot precisely define it worldwide. ^{[1][2][6][7][8]}

For analysts or market observers, global estimates typically rely on applying the disease’s birth prevalence range (roughly 1 in 300,000 to 1 in 1,000,000 births) to population data and then adjusting for diagnosis rates and survival—an approach that provides only rough projections rather than confirmed patient counts. ^[6][7]