ESPE Abstracts

Objectives: Hypophosphatasia (HP) is a rare inherited disorder characterized by defective bone and teeth mineralization, and deficiency of serum and bone alkaline phosphatase activity. The symptoms are highly variable in their clinical expression, which ranges from stillbirth without a mineralized bone to early loss of teeth without bone symptoms. We aimed to report a patient with HP presenting with fibrous dysplasia.

Methods: For genetic analysis, written consent was obtained from the family. Targeted exome sequencing (TES) was carried out using the NextSeq 500 sequencing platform and TruSight One Sequencing panel (Depth 94X) (Illumina, San Diego, CA, USA).

Results: The patient was an 8-year-old boy who was referred to our clinic due to fibrous dysplasia. He was born at full-term by vaginal delivery and weighed 3140 g. There was no perinatal problem. He had suffered from intermittent dizziness and pain in both legs and lower back. His height was 131 cm (50th percentile) and his weight was 26 kg (25-50th percentile). There were no skin lesions such as café-au-lait macules. On laboratory findings, bone ALP was 36.9 µg/l (range: <20.1 µg/L); total calcium was 9.9 mg/dL (range: 8.8 – 10.8 mg/dL); inorganic phosphorus was 5.0 mg/dL (range: 3.7 – 5.6 mg/dL). He was initially suspected of having a monostotic fibrous dysplasia because brain MRI showed fibrous dysplasia involving the left greater wing and body of the sphenoidal bone. TES identified ALPL gene mutation, c.668G>A (P.Arg223Gln), in the patient. The patient was finally diagnosed with HP accompanied by decreased level of ALP (145 IU/l, range: 172 – 437 IU/L) and elevated pyridoxal-5’-phosphate (69.9 µg/l, range: 5.0 – 50.0 µg/L).

Conclusions: This is the first report of HP presenting with fibrous dysplasia. It is necessary to check biochemical findings such as pyridoxal-5'-phosphate and ALP in patients with fibrous dysplasia.