Improvement of bone microarchitecture parameters after 12 months of treatment with asfotase alfa in adult patient with hypophosphatasia: Case report

RATIONALE: Hypophosphatasia is an inborn error of metabolism that can appear any time in life, mainly with bone manifestations due to low alkaline phosphatase activity. Asfotase alfa is a specific enzyme reposition treatment that has shown promising results in children; however, there are few reports about the outcomes in adult patients. PATIENT CONCERNS: A 36-year-old male presented with an early history of craniosynostosis, short stature, and multiple fractures since the age of 13 years—which needed numerous surgical corrections. He was admitted with a previous diagnosis of osteogenesis imperfecta, taking alendronate, calcium carbonate, cholecalciferol, and calcitriol. Bone mineral density was low (lumbar spine Z-score = −3.0 SD), with impairment of all parameters of high-resolution peripheral quantitative computed tomography (HR-pQCT). Kidney impairment was also observed with reduced creatinine clearance, nephrolithiasis, and nephrocalcinosis. DIAGNOSIS: Alkaline phosphatase was unexpectedly low (6 U/L, reference value: 30–120 U/L), with high serum vitamin B6 (260 mcg/L, reference value: 5.2–34.1). Genetic testing showed a homozygous missense mutation in ALPL gene c.443 C>T: p.Thr148Ile. INTERVENTION: Asfotase alfa was requested due to important bone deterioration, ambulatory disability, and kidney impairment. It was given subcutaneously 2 mg/kg per dose, 3 times a week, for 12 months before reassessment. OUTCOMES: Bone mineral densities of the lumbar spine and whole body, besides almost all HR-pQCT microstructural parameters of the distal tibia, showed improvements and the patient was able to walk without assistant device. Kidney function did not further deteriorate. LESSONS: Hypophosphatasia should be considered as a differential diagnosis in young patients with multiple fractures and kidney impairment, since the use of antiresorptive drugs, calcium and vitamin D, commonly used to treat fractures, worsen its symptoms and prognosis. A 12-month asfotase alfa treatment improved bone density and structural parameters even in an adult patient with late diagnosis.