The FDA has issued Alexion Pharmaceuticals a priority review voucher for a rare pediatric disease designation.

Approved in October, Strensiq (asfotase alfa) is a long-term enzyme replacement therapy to treat infantile and juvenile onset hypophosphatasia, a rare genetic disorder that affects the development of bones and teeth.

With the approval of the drug for the treatment of a rare pediatric disease, the sponsor of the application is eligible for a voucher that can be used to obtain priority review for a subsequent NDA or BLA for another drug.

The vouchers also can be sold to other companies. For example, United Therapeutics agreed to sell its rare pediatric disease priority review voucher to AbbVie for $350 million in August.

The FDA now has issued five rare pediatric disease priority review vouchers. The other four are:

• BioMarin’s Vimizim (elosulfase alfa) in 2014;
• Asklepion’s Cholbam (cholic acid) in 2015;
• United Therapeutics’ Unituxin (dinutuximab) in 2015; and
• Wellstat’s Xuriden (uridine triacetate) in 2015.

The FDA defines a rare pediatric disease as one that affects fewer than 200,000 individuals under the age of 18.

Alexion spokesperson Kim Diamond says the company expects to use the voucher opportunistically to receive priority review on a future application.