Low serum alkaline phosphatase activity due to asymptomatic hypophosphatasia in a teenage girl

摘要

ObjectiveThe case report details an unusual presentation of a teenage patient with hypophosphatasia. Patient and methodsA 17?year-old female patient presented to endocrinology for the evaluation of fatigue and possible adrenal insufficiency. In the course of her clinical evaluation she was noted to have a low serum alkaline phosphatase activity. Relatively few conditions are associated with a low serum alkaline phosphatase including Wilson's disease, hypophosphatasia, pernicious anemia and untreated hypothyroidism. ResultsLaboratory testing for hypothyroidism were unrevealing, as were the results for vitamin B12 and vitamin D. Testing for Wilson's disease revealed a ceruloplasmin concentration of 165?mg/L (Reference Interval, 160–450?mg/L), however sequencing of the ATP7B gene revealed no deleterious mutations. Measurement of serum pyridoxal phosphate and urine phosphoethanolamine for the diagnosis of hypophosphatasia revealed concentrations of 541.5?nmol/L (reference interval: 29.6–295.5) and 707?mmol/mol creatinine (reference interval: <778?mmol/mol creatinine), respectively, consistent with a diagnosis of hypophosphatasia. ConclusionsHypophosphatasia was initially considered an unlikely diagnosis for this patient given her lack of characteristic skeletal abnormalities. This diagnosis of hypophosphatasia in this case was complicated by a serum ceruloplasmin concentration at the lower end of the reference interval leading to the genetic testing for Wilson's disease.