Safety and efficacy of treatment with asfotase alfa in patients with hypophosphatasia: Results from a Japanese clinical trial

Objective: Hypophosphatasia (HPP) is a rare skeletal disease characterized by hypomineralization and low alkaline phosphatase activity. Asfotase alfa (AA) has been recently developed to treat HPP complications. This study evaluated its safety and efficacy in Japan. Design: Open-label, multicentre, prospective trial. Patients were enrolled in 11 hospitals from June 2014 to July 2015. Patients: Thirteen patients (9 females, 4 males) ages 0 days to 34 years at baseline were enrolled and treated with AA (2 mg/kg three times weekly subcutaneously in all but one patient). All had ALPL gene mutations. HPP forms were perinatal (n=6), infantile (n=5), childhood (n=1) and adult (n=1). Measurements: Safety determined from adverse events (AEs) and laboratory data was the primary outcome measure. Efficacy was assessed as a secondary outcome measure from overall survival, respiratory status, rickets severity and gross motor development. Results: Injection site reactions were the most frequent AEs. Serious AEs possibly related to treatment were convulsion and hypocalcaemia observed in a patient with the perinatal form. In addition, hypercalcaemia and/or hyperphosphatemia was observed in three patients with the infantile form and a low-calcium and/or low-phosphate formula was given to these patients. With respect to efficacy, all patients survived and the radiographic findings, developmental milestones and respiratory function improved. Conclusion: Asfotase alfa therapy improved skeletal, respiratory and physical symptoms with a few serious AEs in patients with HPP. Our results add support to the safety and efficacy of AA therapy for HPP patients.