The US Food and Drug Administration (FDA) has granted Rare Paediatric Disease Designation to Orchard Therapeutics’ metachromatic leukodystrophy (MLD) gene therapy candidate, OTL-200.

The announcement marks the biotech’s fourth designation of this kind for its autologous ex vivo gene therapy.

A Rare Paediatric Disease Designation is given in instances of serious or life-threatening conditions which manifest themselves in patients from the ages of birth to 18 years. The classification will give the treatment access to the FDA’s expedited review and approval process and will make it eligible for a Rare Paediatric Disease Priority Review voucher following FDA approval.

MLD is a rare neurodegenerative, inherited metabolic disease that is often fatal. More than 110 mutations known to cause MLD have been linked to the ARSA gene, which is integral in the production of the arylsulfatase A enzyme. The disruption to arylsulfatase A production as seen in cases of MLD causes sulfatides to breakdown and accumulate in the nervous system, gradually destroying cells that produce myelin, the protective coating around nerves. Damaged myelin leads to a loss of white matter (leukodystrophy) and the erosion of nervous system function.

Late infantile and juvenile forms represent the majority of MLD patients, with mortality at five years estimated at 75% and 30%, respectively.

OTL-200 began as a collaboration between GSK, the Hospital San Raffaele and the Telethon Foundation. Orchard Therapeutics acquired the therapy from GSK in April this year, and hopes to file the therapy for market authorisation with regulatory authorities in 2019.

“This is the fourth Rare Paediatric Disease Designation awarded by the FDA to one of Orchard’s autologous ex vivo gene therapy candidates, providing significant incentives to continue expanding our pipeline,” Orchard CEO Mark Rothera said.

“MLD is a devastating disease in which most patients do not survive the first decade of life. In clinical trials, early treatment with OTL-200 has demonstrated preservation of cognitive and motor development to levels comparable with healthy individuals. We look forward to working with Telethon / Ospedale San Raffaele to bring this potentially life-changing treatment to patients as rapidly as possible.”

Orchard’s portfolio of gene therapy programmes includes Strimvelis, the first autologous ex vivo gene therapy to be EMA-approved in 2016, as well as three programmes for Wiskott Aldrich syndrome (WAS) and adenosine deaminase severe combined immunodeficiency (ADA-SCID).