Hypophosphatasia: presentation and response to asfotase alfa.

Abstract

Hypophosphatasia (HPP) is a rare inherited metabolic bone disorder characterized by a deficiency in the tissue non-specific alkaline phosphatase (TNSALP) due to loss of function mutation in the ALPL gene. HPP is associated with impaired skeletal mineralization due to elevations in inorganic pyrophosphate and altered phosphate : pyrophosphate ratio. Asfotase alfa (AA) "enzyme replacement" was approved for treatment of HPP in 2015. We present 7 patients with HPP, 5 with pediatric-onset, and 2 with adult-onset, who have been treated with AA and describe the efficacy and safety in these patients. 7 patients (4 females, 3 males) aged 19-68 years with HPP were included in this study. Diagnosis of HPP was confirmed by DNA analysis. AA was administered in doses of 6mg/kg/week with a mean follow-up of 6 months (SD= 5). Subjective improvement in muscle strength, muscle pain, walking ability, and walking distance with a reduction in the use of gait aids was seen "with AA in HPP patients." Muscle strength and pain improved by up to 70% from baseline as quantified subjectively by patients. Walking distance improved by up to 100%. Patients also reported improved cognition, mood, and energy levels, with up to 90% improvement in mood and 75% improvement in energy levels. 4 out of 6 patients first noted clinical signs of improvement after 3 months of being on therapy. 1 out of the 7 patients sustained a toe fracture 10 months from being on AA. AA was well-tolerated with injection site reactions being the most reported adverse effect. HPP treatment with AA in individuals with both pediatric and adult-onset forms resulted in significant subjective improvement in musculoskeletal and cognitive manifestations in addition to patients' quality of life. The drug was well tolerated in 6 patients. 1 patient discontinued therapy because of minor adverse effects with myalgias.