Clinical data
Participant clinical data including age at first blood transfusion, frequency and volume of each blood transfusion, pre-transfusion Hb, endocrine complications and medications were retrieved from the electronic medical record. We also collected concentrations of serum 25-hydroxy vitamin D (25OHD) and ferritin (assessed every 3-4 months) and liver iron concentration (LIC) measured by MRI (annually). Fracture history was acquired through an interview.