Protocol amendment 1 included the following changes: Removal of references to user kits as they are not to be provided for this study. Site will use their own administration supplies.

Protocol Amendment 2 included a re-write of the study protocol to reduce the study duration, reduce the number of subjects, and reduce the number of sample collection: Administrative changes to BPL personnel, reduced length of study duration from 12 months to 6 months. Inclusion of the term 'retrospective' to the study to enable collection of retrospective FACTOR X use. Adjustment to study design with respect to blood sampling at the baseline visit as follows; 'sample for inhibitor assessment will be collected and only tested if a later sample is positive for inhibitors. Blood samples for factor x activity analysis will be collected pre-dose and at 30 min (+5 min) post-dose for an incremental recovery assessment'. Reduction of the maximum number of children enrolled from 16 to 12.

Protocol Amendment 3 included the following changes: Additional detail to be collected in the CRF for surgical procedures as follows; name of surgical procedure and surgical technique whether it is a planned or an emergency surgery indication for surgery surgery start and end dates and times extubation date and time date and time post-operative bleeding stabilised discharge date date of last dose of FACTOR X to treat post-operative bleeding number of swabs and pads used whether there were any unusual features of the surgery or complications which might influence bleeding at the time of surgery or later blood loss compared to a patient without a haemostatic disorder undergoing the same type of surgery (more than, equal to, or less than) whether there was excessive bleeding during surgery relevant laboratory assessments FACTOR X infusions administered Deletion of the following text 'For children who turn 6 years old during the study, an assent form is expected to be completed to confirm the child’s continued eligibility for the trial' and instead replaced with 'The child will be provided with written information. If considered appropriate by the investigator, an assent will be obtained using the 8-11 year old Assent Form' and 'For children aged 4-7 years if considered appropriate by the investigator, assent will be obtained using the 4-7 year old Assent Form'. Deletion of the following test relating to additional testing if subjects test positive for Parvovirus 'In addition, children who are negative for Parvovirus B19 IgG and IgM at the Baseline Visit will attend the hospital or a local clinic for an additional blood test 7 days after the Baseline Visit.' Text was deleted as there is no strong scientific rationale or regulatory requirement for children to have this additional test. Text added to clarify when an SAE report needs to be completed in case of a planned surgery e.g. if the underlying condition caused the prolonged hospitalisation.

Protocol Amendment 4 included the following changes: I. Redefinition of factor X severity II. Clarify reporting of laboratory results as adverse events III. Updated Appendix VIII – Trial Plan Flow Chart IV. Clarification of bleeding assessments V. Administrative changes

Protocol Amendment 5 included the following changes: Addition to the protocol title to include 'Prophylaxis of Bleeding in'. Additional text regarding re-enrollment of subjects who have completed the study early as follows 'Children may be re-consented and re-enrolled in to the study following case by case evaluation and agreement between the Sponsor and the Co-ordinating Investigator. In such cases, children will be assigned a new patient number and treated as new subjects who must repeat all trial procedures from Screening Visit to End of Study Visit'. Additional wording to the primary objective to include 'reduction' as well as 'prevention' of bleeding. Additional text on laboratory sampling to state that a sample for inhibitor assessment will be collected and only tested if, for example, there is a clinical suspicion of inhibitor development or a later sample is positive for inhibitors.