For arginase 1 deficiency, all you can do is cut protein from the diet
The core idea stands, but key numbers or details have changed.
TaughtArginase 1 deficiency lets the amino acid arginine build to toxic levels, causing stiffness, seizures, and developmental regression. There is no drug for it. Management means a severely protein-restricted diet, for life, and it is rarely enough.
NowOn 23 February 2026 the FDA granted accelerated approval to Loargys (pegzilarginase), an engineered enzyme injected to break down the excess arginine the body cannot clear on its own, the first therapy that directly targets the disease.
What actually happened
The logic is enzyme replacement: the patient is missing working arginase, so Loargys supplies a durable, pegylated version in the bloodstream that chews arginine down to safer levels. In trials it lowered plasma arginine where diet alone had failed, which is why it cleared the bar for accelerated approval.
The hedges are real and worth stating plainly. Accelerated approval means it was cleared on that arginine-lowering marker, with confirmatory evidence on long-term neurological outcomes still owed, and it is used alongside, not instead of, dietary restriction. But 'the only thing you can do is eat less protein' was the whole standard of care for this disease, and now it is not. There is an enzyme for it.
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Who was taught this
Still standard through 2026, so anyone who finished school between 1950 and 2026 learned the earlier version.