Marked motor function improvement in a 32-year-old woman with childhood-onset hypophosphatasia by asfotase alfa therapy: Evaluation based on standardized testing batteries used in Duchenne muscular dystrophy clinical trials

Hypophosphatasia (HPP) is a rare disorder resulting from biallelic loss-of-function variants or monoallelic dominant negative variants in the ALPL gene. We herein describe the clinical outcome of a 32-year-old woman with childhood-onset HPP caused by compound heterozygous variants in ALPL. Her chief complaints were severe musculoskeletal pain, muscle weakness, and impaired daily activities necessitating assistance in housework and child-rearing in addition to a history of early tooth loss and mildly short stature. Asfotase alfa therapy produced a remarkable increase in muscle strength and daily activities and markedly reduced musculoskeletal pain. Drug efficacy was clearly demonstrated through multiple test batteries (muscle strength test using microFET®2, six-minute walking test, Stair Climb Test, rising-from-floor-time test, and number-of-steps test using Actigraph®) currently adopted as standardized evaluations in Duchenne muscular dystrophy clinical trials since no test batteries for HPP have been established to date. These tests may also be promising for the assessment of HPP.