Case Report: Efficacy of Reduced Doses of Asfotase Alfa Replacement Therapy in an Infant With Hypophosphatasia Who Lacked Severe Clinical Symptoms

Effects of enzyme replacement therapy in sibling cases of hypophosphatasia of varying severities

Hypophosphatasia (HPP) is a hereditary disorder characterized by impaired bone mineralization caused by decreased tissue-nonspecific alkaline phosphatase (TNSALP) activity. Specifically, HPP is caused by a loss-of-function variant in the ALPL gene encoding TNSALP. Although genotype-phenotype correlations have been described, phenotypic differences have been reported in patients with the same variants, even within families. The proband, a girl, was suspected to have in utero fractures of the long bones, suggestive of osteogenesis imperfecta. No respiratory impairment was observed after birth; however, the patient's serum alkaline phosphatase level was low. In addition, the patient's perinatal findings were consistent with those of perinatal benign HPP, although the bone symptoms subsequently worsened. The patient's brother, initially suspected to have odonto-HPP due to the premature loss of primary teeth, later developed compression fractures and extraosseous symptoms. Both patients had the same ALPL variants, c. 572A>G(;)1559del, p. Glu191Gly(;)Leu520ArgfsTer86; however, the severity of their conditions differed. Patients with HPP with identical genotypes in the same family may have varying severity levels of HPP. In this case report, both patients received enzyme replacement therapy (ERT), which improved the clinical symptoms. Therefore, for perinatal benign HPP, ERT should be considered if bone symptoms worsen. In addition, odonto-HPP should be closely monitored, and ERT should be considered if bone and extraosseous symptoms arise.

Enzyme replacement therapy for hypophosphatasia-The current paradigm

Hypophosphatasia (HPP) is a rare, inherited, and systemic disorder characterized by impaired skeletal mineralization and low tissue nonspecific serum alkaline phosphatase (TNSALP) activity. It is caused by either autosomal recessive or dominant-negative mutations in the gene that encodes TNSALP. The phenotype of HPP is very broad including abnormal bone mineralization, disturbances of calcium and phosphate metabolism, pain, recurrent fracture, short stature, respiratory impairment, developmental delay, tooth loss, seizures, and premature death. Other than supportive care, there has been no disease-specific treatment available for those with HPP. Asfotase alfa is a fully humanized, recombinant enzyme replacement therapy for the management of HPP. It is available in several countries for the treatment of the more severe forms of HPP, namely perinatal and infantile HPP. This review will summarize the preclinical data on asfotase alfa and highlight the data from clinical trials and case reports. These data show the transformative nature of asfotase alfa when administered as part of an interdisciplinary treatment model.

Multidisciplinary Management of Infantile Hypophosphatasia Resulting in Radiographic and Clinical Improvement: A Case Report

Hypophosphatasia (HPP) is a rare genetic condition that can manifest from the prenatal period to adulthood. Clinical presentation is characterized by six major forms. HPP can be complex and debilitating. A two-year-old male with a past medical history of HPP presented to our emergency room with a non-displaced supracondylar fracture after minor trauma. Non-accidental trauma was considered in addition to inadequate medical control of his HPP. He was referred to our multidisciplinary clinic and asfotase alfa was increased to an appropriate dose. A multidisciplinary approach is the standard of care for the management of children with HPP, allowing for routine evaluation by tertiary specialists. This includes medication dosing surveillance with serum studies and imaging. Enzyme replacement therapy, appropriately dosed by considering weight and laboratory values, may reduce orthopedic complications. A multidisciplinary team's surveillance of patients with HPP ensures proper medication management, decreases the likelihood of bony injury and encourages continued patient follow-up.