The U.S. Food and Drug Administration has approved Mepsevii (vestronidase alfa-vjbk) to treat pediatric and adult patients with an inherited metabolic condition called mucopolysaccharidosis type VII (MPS VII), also known as Sly syndrome. MPS VII is an extremely rare, progressive condition that affects most tissues and organs.
MPS VII is an inherited, rare genetic condition and impacts less than 150 patients worldwide. The features of MPS VII vary widely from patient to patient, but most patients have various skeletal abnormalities that become more pronounced with age, including short stature. Affected individuals can 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. Heart disease and airway obstruction are major causes of death in people with MPS VII. Affected individuals may have developmental delay and progressive intellectual disability.
The safety and efficacy of Mepsevii were established in clinical trial and expanded access protocols enrolling a total of 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 two weeks for up to 164 weeks. Efficacy was primarily assessed via the six-minute walk test in ten patients who could perform the test. After 24 weeks of treatment, the mean difference in distance walked relative to placebo was 18 meters.
Additional follow-up for up to 120 weeks suggested continued improvement in three patients and stabilization in the others. Two patients in the Mepsevii development program experienced marked improvement in pulmonary function. Overall, the results observed would not have been anticipated in the absence of treatment. The most common side effects after treatment with Mepsevii include infusion site reactions, diarrhea, rash and anaphylaxis.
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