ESPE Abstracts

Introduction: Osteogenesis imperfecta (OI) is a rare heterozygous disorder of collagen production. It is characterized by low bone mass, bone fragility, blue sclera, and progressive hearing loss. Expanded Sillence Classification divides OI into 7 types with Type I OI as the mildest and commonest form. Hyperplastic callus (HC) is a rare but characteristic complication in patients with OI type V. We report a infant with Type I OI with hyperplastic callus.

Case: A 2-month-old baby girl born via caesarean section at 37 weeks with birth weight of 2.43 kg. After birth, she had bilateral incomplete Moro’s, short limbs with lower limb bowing and blue sclera. Antenatally, mother had seronegative antiphospholipid syndrome secondary to systemic lupus erythematosus and Vitamin D deficiency. Antenatal scan showed shortened lower limbs. Serum investigations revealed hemoglobin 18.2 g/dL, total white cell count 19.7 x 109/L, and platelet 494 x 109/L. Renal profile was normal. Other investigations were calcium 2.14 mmol/L, magnesium 0.71 mmol/L, inorganic phosphate 2.36 mmol/L, total protein 66 g/L, albumin 35 g/L, alkaline phosphatase (ALP) 157U/L, alanine transaminase (ALT) 24 U/L, and bilirubin 75 µmol/L. Her intact parathyroid hormone (iPTH) 5.97 pmol/L and vitamin D level 71.13 nmol/L were within normal reference range. She sustained closed fractures of proximal left humerus, bilateral clavicles, upper third of left ulna, midshaft left femur, proximal third of left tibia, midshaft right femur and multiple ribs bilaterally. U-Slab was applied for the left humerus and removed 6 weeks later. On repeat X-rays, the child developed HC over each fracture site. Whole exome sequencing (WES) test revealed pathogenic heterozygous variant identified in COL1A1, c.1273G>A, p. Gly425Ser COL1A1 which is associated with autosomal dominant OI, type I. She received intravenous Pamidronate at 7 weeks and at 3 months of life.

Conclusion: Hyperplastic callus is a well-described but mysterious feature of osteogenesis imperfecta. In a review of 47 cases of HC in the published literature there was no special tendency as to scleral colour. Although HC occurred more frequently with severe bone fragility, it was also seen with mild bone fragility. Thus, in patients with HC and OI, genetic studies to determine type should be done where available to facilitate counselling.