Asfotase alfa has a limited effect in improving the bowed limbs in perinatal benign hypophosphatasia: A case report

Hypophosphatasia (HPP) is a rare skeletal dysplasia characterized by impaired bone mineralization, caused by loss-of-function mutations in the tissue-nonspecific alkaline phosphatase (TNSALP) gene. Enzyme replacement therapy (ERT) by administration of asfotase alfa was reported to improve the survival rate, bone mineralization, and short stature in the severe form of HPP. However, the effect of asfotase alfa in improving the skeletal phenotypes for the mild form of HPP has not been elucidated. We report a case with perinatal benign HPP who had compound heterozygous mutations of p.F327L and p.R30X in the TNSALP gene. No hypomineralization was seen in the radiographs from the neonatal period, but bowing of the femurs and ulnares bilaterally was persistent. ERT was administered during the age of 7.8 to 10.8 yr, although there was an interruption in the treatment for one year. The bowed femurs and ulnares were not improved by the treatment with asfotase alfa at the age of 10.8 yr. Bone mineral density of the lumbar spine was between -0.5 and -1.0 of the z-score, and the patient's height was about -2.0 SD during the treatment. Asfotase alfa might have a limited effect in improving the bowed limbs in perinatal benign hypophosphatasia.