The primary objective of the study is to assess the efficacy of FACTOR X in the prevention of bleeding when given as routine prophylaxis over 12 months.

The secondary objectives of the study are:

1. To assess the pharmacokinetics of FACTOR X after a single dose of 50 IU/kg.
2. To assess the safety of FACTOR X when given as routine prophylaxis over 6 months (26 weeks).

Inclusion Criteria

1. Children with hereditary severe or moderate FX deficiency (FX:C <5 IU/dL), based on their lowest reliable FX:C recorded.
2. Children under 12 years old, whose parent/guardian has given informed consent.
3. Children with a history of severe bleeding e.g.: intracranial haemorrhage, before starting prophylactic therapy, OR a mutation in the F10 gene causing a documented severe bleeding phenotype.

Exclusion Criteria

1. Children must not suffer from clinically significant liver disease, renal disease, or other coagulopathy or thrombophilia
2. Children must have no history or suspicion of inhibitors to factor X.
3. Children who have known or suspected hypersensitivity to the investigational medicinal product or its excipients.
4. Children with a history of unreliability or non-cooperation.
5. Children who are participating or have taken part in another trial within the last 30 days.
6. Children planning more than 4 weeks' continuous absence from the locality of the investigational site, between the Screening Visit and the End of Study Visit at approximately 6 months (26 weeks) post-Baseline.

From signing of informed consent form until 28 days post-last dose. For subjects who had received FACTOR X on compassionate use prior to study entry, retrospective adverse events data was collected as part of medical history.

2 subjects completed less than 26 weeks in the study. The subjects were re-enrolled and data from their first treatment cycle was excluded from the Per-Protocol analysis. 9 unique subjects were enrolled even though there were 11 treatment cycles