LAUSR

BACKGROUND Hypophosphatasia (HPP), an inherited, metabolic disorder caused by loss-of-function mutations in the ALPL gene, affects not only bone and tooth mineralization but also central nervous system (CNS) function, resulting in vitamin B6/pyridoxine-responsive seizures. Asfotase alfa treatment mainly improves the skeletal manifestations of HPP. As of yet, there are no reports demonstrating seizure exacerbation caused by asfotase alfa interruption. CASE The patient was a 2-year and 8-month-old female with clinical and genetic diagnosis of perinatal severe HPP. Genetic analysis of ALPL identified compound heterozygous variants. Asfotase alfa and pyridoxine administration begun on postnatal day 2 restored normal development and suppressed seizures except for simple febrile seizures. From age 2 years when her asfotase alfa injections became irregular, she began experiencing seizure exacerbation, including status epilepticus, leading to acute encephalopathy and severe sequelae. The seizure exacerbations always coincided with low alkaline phosphatase (ALP) activity caused by the interruption of asfotase alfa administration. DISCUSSION The clinical course of the present case demonstrated the effect of asfotase alfa on CNS symptoms and a clear correlation between low serum ALP activity and seizure exacerbation. Serum ALP activity measurements were useful as a therapeutic marker in the present case. Furthermore, the risk of seizure exacerbation in the patient could have been predicted, given the genotype-phenotype correlation related to the ALPL gene in the Japanese population. CONCLUSION Regular asfotase alfa injections are needed to prevent seizure exacerbation in patients with HPP. Educating patients and their family about the need for regular asfotase alfa treatment is crucial to preventing disease exacerbation.