FDA OKs Therapy for Rare Genetic Enzyme Disorder

Megan Brooks

November 16, 2017

The US Food and Drug Administration (FDA) has approved vestronidase alfa-vjbk (Mepsevii, Ultragenyx Pharmaceutical) to treat children and adults with the rare genetic condition mucopolysaccharidosis type VII (MPS VII), also known as Sly syndrome.

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

MPS VII is extremely rare, affecting fewer than 150 patients worldwide, according to the FDA. The progressive condition affects most tissues and organs. Although the features of MPS VII vary widely between patients, most patients have various skeletal abnormalities that become more pronounced with age, including short stature. Affected individuals may also develop heart valve abnormalities, enlarged liver and spleen, and narrowed airways, which can lead to lung infections and trouble breathing.

The life expectancy of individuals with MPS VII depends on the severity of symptoms. Some affected individuals do not survive infancy, while others may live into adolescence or adulthood.

MPS VII is a lysosomal storage disorder caused by deficiency of the enzyme beta-glucuronidase, which causes an abnormal buildup of toxic materials in the body's cells. Mepsevii is an enzyme replacement therapy that works by replacing the missing enzyme.

The safety and efficacy of Mepsevii were demonstrated in 23 patients ranging from 5 months to 25 years of age. Patients received treatment with Mepsevii at doses up to 4 mg/kg once every 2 weeks for up to 164 weeks.

Efficacy was primarily assessed via the 6-minute-walk test in 10 patients who could perform the test. After 24 weeks of treatment, the mean difference in distance walked relative to placebo was 18 meters, the FDA said.

Additional follow-up for up to 120 weeks suggested continued improvement in three patients and stabilization in the others. Two patients experienced marked improvement in pulmonary function.

"Overall, the results observed would not have been anticipated in the absence of treatment," the FDA said. The effect of Mepsevii on the central nervous system manifestations of MPS VII has not been determined, they note.

The most common side effects with Mepsevii include infusion site reactions, diarrhea, rash, and anaphylaxis. The FDA is requiring the manufacturer to conduct a postmarketing study to evaluate the long-term safety of Mepsevii.

Mepsevii was given fast-track designation and priority review by the FDA. The drug also received orphan drug designation, which provides incentives to assist and encourage the development of drugs for rare diseases.

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