Orphan Drug Gets FDA Nod for Genetic Enzyme Disease

The FDA approved vestronidase alfa-vjbk (Mepsevii) for the treatment of patients with the inherited disease mucopolysaccharidosis type VII (MPS VII). This extremely rare metabolic condition is also known as Sly syndrome and affects tissues and organs, according to a press release.

MPS VII is rare lysosomal storage disorder and affects less than 150 patients. While symptoms vary among patients, a majority have skeletal abnormalities that progress with age, including short height, according to the FDA. The condition is also characterized by heart valve problems, enlarged liver and spleen, narrow airways, developmental delay, and progressive intellectual disability.

The FDA reports that the life expectancy varies based on symptoms, with some patients not living past infancy and others surviving to adulthood. A majority of patients with MPS VII die from heart disease and airway obstruction, according to the release.

The condition is the result of a deficiency of the beta-glucuronidase enzyme, which results in a build-up of toxic substances in cells. Vestronidase alfa-vjbk works by replacing missing beta-glucuronidase.

The safety and efficacy of the drug was explored in a clinical trial of 23 patients with MPS VII aged 5 months to 25 years who were treated with vestronidase alfa-vjbk once every 2 weeks for up to 164 weeks.

The investigators evaluated efficacy based on a 6-minute walking test in 10 patients with the ability to walk. After 24 weeks of treatment, the mean difference in distance walked between the drug and placebo was 18 meters, according to the FDA. At 120 weeks, these results continued in 3 patients and stabilized in other patients treated with vestronidase alfa-vjbk.

The researchers also noted that vestronidase alfa-vjbk was observed to significantly increase lung function.

Overall, these findings suggest that the treatment can improve walking ability and lung function, which are hallmarks of the condition, according to the release.

The FDA warns that common adverse events include infusion site reactions, diarrhea, rash, and anaphylaxis.

Previously, vestronidase alfa-vjbk was granted fast track and orphan drug designations.

“This approval underscores the agency’s commitment to making treatments available to patients with rare diseases,” said Julie Beitz, MD, director of the Office of Drug Evaluation III in the FDA’s Center for Drug Evaluation and Research. “Prior to today’s approval, patients with this rare, inherited condition had no approved treatment options.”