Assessing bleeding risk in 18 children with Osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a genetic disorder of connective tissue affecting bone formation and strength, resulting in susceptibility to spontaneous fracture. Diagnosis is based on clinical presentation, family history, radiographic features and genetic analysis. A 10–30% incidence of bleeding diathesis is reported in patients with OI undergoing surgery. Bleeding may occur despite normal haemostatic tests, making intraoperative bleeding difficult to predict. Moreover, a standardized evaluation of the degree and severity of the bleeding diathesis has never been attempted in those patients. In the present study, we assessed for the first time the bleeding diathesis in a cohort of 18 children with OI using a validated bleeding score (BS) and exploring coagulation, platelet function and endothelial activation markers. Based on Elbatarny’s study, OI patients were classified according to their BS. BS < 3 correspond to patients with no evidence of bleeding history (OI NB for OI non-bleeders) and a BS ≥ 3 corresponds to patients with features of bleeding (OI B for OI bleeders). There was no significant statistical difference between the OI NB and OI B subgroups regarding age, gender or O Rh-positive blood group. Nevertheless, among OI B patients two experienced spontaneous central nervous system (CNS) bleeding (Table SI). A family history with a first-degree relative affected by OI was present in six patients and patients OINB3 and OINB4 are brother and sister. A pathogenic or probably pathogenic variant in the COL1A1 gene was identified in the 13 remaining OI patients (Table I). Almost all patients showed normal ranges for plasmatic coagulation tests, FXIII, a2-AP and PAP levels. Von Willebrand disease was ruled out based on FVIII, von Willebrand factor (VWF) and blood group analysis (Table SII). Taken together, these observations indicate that bleeding symptoms in patients with OI are not associated with von Willebrand disease, plasmatic coagulation or antifibrinolytic factor deficiencies predisposing to bleeding. Platelet count showed normal ranges for almost all participants (Table SII). On platelets in resting conditions, a2b1, GPVI, GPIb and P-selectin quantification exhibited normal ranges for almost all patients and no significant statistical difference between OI subgroups was observed (Figure S1A, B, D, E; Table SII), except for aIIbb3 quantification (Figure S1C). Regarding intrinsic platelet function, both OI subgroups presented normal aggregations for all the agonists tested (Figure S2). Altogether, our data show that patients had a normal platelet count, normal expression of platelet glycoproteins and a normal platelet response to tested agonists, suggesting that bleeding in those patients is not related to intrinsic platelet dysfunction. We examined VWF as a marker of endothelial dysfunction in vascular diseases. VWF antigen and activity levels were normal for almost all participants (Table SII). Neither pro-inflammatory state nor correlation between VWF and fibrinogen or C-reactive protein (CRP) levels were observed. The difference observed between OI subgroups for both VWF antigen and activity was statistically significant (Fig 1). Moreover, BS correlated weakly with VWF level (r = 0 50, P < 0 05). Finally, we investigated soluble thrombomodulin (sTM) and soluble E-selectin levels, two markers of endothelial cell activation (Fig 1; Table SII). Interestingly, sTM level was significantly higher in the OI B compared to the OI NB subgroup. The same trend was found for sE-selectin level, but no significant difference was observed. Taken together, our data show that the OI B subgroup exhibited higher levels of endothelial activation markers than the OI NB subgroup. Thus, bleeding tendency in OI B patients may be partly related to vascular endothelial dysfunction. Bleeding diathesis is a common feature in OI, particularly in childhood. By using the ISTH-BAT BS, it was possible to discriminate between children with and without defined bleeding disorders and like others, we suggest this could be used to highlight potential predictive markers of bleeding risk. According to their BS, nine children with OI were classified as bleeders and nine as non-bleeders. Coagulation, fibrinolysis and platelet function tests were normal in all patients investigated. Hyperfibrinolysis, previously identified as a possible cause for mild bleeding disorders in adults with OI, was not confirmed in our study. VWF, soluble E-selectin and sTM were also explored as markers of endothelial activation in vascular disorders. In the absence of a pro-inflammatory state, VWF (antigen or activity) and sTM levels were significantly higher in the OI B subgroup suggesting an association between those markers and the severity of the vascular disorder. It is worth noting that increased levels of sTM were associated with increased bleeding and with bleeding-related complications. Thus, we hypothesized that collagen impairment in patients with OI may affect the structure and function of blood vessels leading to vascular fragility and to a physical stress correspondence