A single pivotal phase III trial of an enzyme engineered to treat a rare urea cycle disorder, arginase 1 deficiency (ARG1-D), could potentially support U.S. and European approvals of the therapy, according to Aeglea Biotherapeutics Inc. The Austin, Texas-based biotech expects to start dosing a small group of patients with the enzyme, its lead candidate pegzilarginase, during the second quarter of 2019 and to make top-line data available in the first quarter of 2021.