90 patients. Again, we hypothesize that the reduction and/or abnormal production of collagen type 1 may lead to increased fibrinolysis and, as such, is more likely to be observed in patients with OI. However, the moderately elevated fibrinolysis does not fit with a bleeding score of 0. The questionnaires might possibly have been influenced by a recall bias. Some crucial questions about duration of bleeds and bruise counts are difficult to recall, especially when a number of years have passed since a bleeding event. Intriguingly, Patient 1, with an elevated BS, is the mother of Patient 6, who had a BS of 0 and moderately elevated fibrinolysis. Although, the younger age of Patient 6 might have affected his BS, we would have expected his mother to have abnormalities on fibrinolysis. It remains a possibility that the ISTH-BAT and fibrinolysis are good tools for identifying and/or excluding coagulopathies, but simply not suitable for diagnosing and/or excluding inherited connective tissue disorders, such as OI. We hypothesize that a frequently reported feature, such as easy bruising, might be due to capillary fragility following abnormal and/or reduced collagen type 1 production in OI patients 4,30. Conclusions This is the second largest study to date addressing bleeding tendency in OI and the first study to use ISTH-BAT and elaborate laboratory testing for coagulopathies. In our cohort, 74% reported easy bruising, 18% had an elevated BS on ISTH-BAT without coagulation abnormalities and 9% demonstrated slight hyperfibrinolysis with a BS of 0. We observed no extensive bleeding disorders or evidence of abnormal coagulation in this cohort. Interestingly, two patients were found to have a slight hyperfibrinolysis, which may point to capillary fragility due to abnormal and or reduced collagen type 1 production. Another patient was diagnosed with VWD type 1, which has a high prevalence and is most likely unrelated to OI. There is, however, no correlation between the bleeding tendency according to the BS and hyperfibrinolysis, and it is possible that the ISTH-BAT and hyperfibrinolysis are not good tools for assessing bleeding tendency in patients with OI. Considering the rarity OI is a rare disorder, this study represents the assessment of a large group of patients. However, it is still a limited number of patients from which conclusions can be drawn. As such, it would be important to repeat the same study set-up in a large group of patients with mo-
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