March 25 (Reuters) - The U.S. Food and Drug Administration has approved Denali Therapeutics' therapy to treat children ⁠with a rare genetic disorder, marking the first regulatory green light for the drugmaker in the country. 

However, continued approval for the treatment ⁠may be contingent upon verification of clinical benefit in a confirmatory trial, the company said on Wednesday.

Denali's ⁠shares were up 8.4% at $22.74.

Marketed as Avlayah, ‌the enzyme replacement therapy is aimed at treating Hunter syndrome, a rare genetic disorder that affects about 500 people in the U.S., almost exclusively males, and leads to the buildup of certain sugar molecules in the brain and body.

Symptoms include developmental delays, cognitive decline and behavioral abnormalities. 

Given as a ‌once-weekly infusion, Avlayah has been approved to treat the neurologic symptoms of the ​condition in ‌presymptomatic or symptomatic pediatric patients.

The list price of ‌a single-use vial has been set at $5,200 per 150 milligrams, Denali said, adding that the therapy will be available in ⁠the U.S. shortly.  

SURROGATE ENDPOINTS  

The accelerated approval was based on a surrogate ‌endpoint, or a substitute measure, ⁠that tracked the reduction of heparan ​sulfate, a sugar molecule that accumulates due ‌to the disorder and is linked to organ damage.

The endpoint was reasonably likely to predict Avlayah’s clinical benefit, the agency said, though Denali is now also conducting a trial for the ​same.

Wedbush analyst Laura Chico said the approval bodes well for other ‌programs ‌incorporating surrogate endpoints. 

The FDA under Vinay Prasad, known for his skepticism toward surrogate endpoints, had adopted ‌a tougher stance on approvals ​for rare-disease treatments. 

However, Prasad will leave the agency at the end of April.

Avlayah's approval includes a boxed warning, the agency's most serious kind, for severe allergic reactions. 

Takeda Pharmaceuticals' ⁠Elaprase has been the only FDA-approved enzyme replacement therapy for the condition ‌in the U.S. since 2006, but it addressed only the physical symptoms. 

(Reporting by Kunal Das and ​Sneha S K; Editing by Jonathan Ananda)