Investing.com -- Denali Therapeutics Inc. shares are trading 11.8% higher midday on Wednesday after the U.S. Food and Drug Administration granted accelerated approval for AVLAYAH (tividenofusp alfa-eknm), an enzyme replacement therapy for treating neurologic manifestations of Hunter syndrome in pediatric patients weighing at least 5 kg.

The approval represents the first new FDA-approved treatment for Hunter syndrome in nearly 20 years and marks the first approved medicine designed to cross the blood-brain barrier using transferrin receptor technology. AVLAYAH targets mucopolysaccharidosis type II (MPS II) when initiated in presymptomatic or symptomatic patients prior to advanced neurologic impairment.

Hunter syndrome affects approximately 500 individuals in the United States and is caused by a deficiency in the iduronate 2-sulfatase enzyme. The condition leads to accumulation of glycosaminoglycans in cells throughout the body, including the brain, resulting in progressive organ and tissue damage.

The FDA approval was based on a Phase 1/2 clinical trial showing a 91% reduction in cerebrospinal fluid heparan sulfate levels from baseline by week 24 of treatment. At week 24, 93% of treated patients had cerebrospinal fluid heparan sulfate levels within the range of individuals without Hunter syndrome.

AVLAYAH uses Denali's TransportVehicle platform, which binds to the transferrin receptor to deliver the IDS enzyme to peripheral tissues and the central nervous system through receptor-mediated transcytosis across the blood-brain barrier. The therapy is administered once weekly.