SUN-742 A Case Of Adult Onset Hypophosphatasia With Convulsions

Abstract Disclosure: H. Shichi: None. T. Kawarai: None. T. Kasamatsu: None. M. Amano: None. Y. Ohnishi: None. M. Watanabe: None. T. Takeuchi: None. H. Komada: None. N. Hashimoto: None. K. Iida: None. Case: A 58-year-old man. Complaint: Lower back pain. History of the present illness: The patient experienced lower back pain after getting up from lying down. The patient was unable to move and transported to another hospital. The patient was diagnosed with multiple thoracic and lumbar vertebral fractures and referred to our hospital for an investigation of the cause. Laboratory results revealed a low serum ALP level of 27 U/L (IFCC, reference range [RR]; 38-113 U/L) despite the acute stage of the fracture. At 39 years of age, laboratory examination showed low serum ALP level of 70 U/L (JSCC, RR; 102-302 U/L). As the patient’s urinary phosphoethanolamine was elevated at 164.8 μmol/day, hypophosphatasia (HPP) was suspected. Genetic testing was considered to confirm the diagnosis. The patient was discharged and referred for genetic counseling. Two days after genetic counseling in the outpatient clinic, the patient was transferred to our hospital with generalized convulsions. The seizures disappeared before arriving at the hospital. Neuroimaging and laboratory investigation demonstrated no potential causes for generalized seizure. Considering the possibility of HPP-associated vitamin B6-dependent epilepsy, vitamin B6 supplementation was initiated. Subsequently, ALPL gene mutations (c.529G>A/p.Ala177Thr and c.1559delT/p.Leu520ArgfsTer86) was identified, leading to the diagnosis of adult-onset HPP. Discussion: Based on the low ALP levels, HPP was suspected to be the cause of the vertebral fracture, and the diagnosis was confirmed by genetic testing. Adult-onset generalized seizure was seen in the case, which might have been associated with underlying the metabolic abnormalities due to HPP. Convulsions in patients should be considered as vitamin B6-dependent epilepsy, but are typically seen in severe perinatal cases. Because of decreased ALP activity, vitamin B6-dependent epilepsy is caused by the impaired conversion of pyridoxal 5-phosphate to pyridoxal, which is permeable to the blood-brain barrier. Although this was an adult-onset case that was believed to be atypical, the existence of a similar pathology was considered. Therefore, vitamin B6 supplementation may be necessary to improve pathogenesis. Presentation: Sunday, July 13, 2025