Rationale:

Haemophilia is a rare disease; to improve knowledge international collaboration is needed. Well-defined clinical data will be collected from complete cohorts in order to prevent selection bias.

Objective:

To collect data on bleeding during neonatal period, endogenous (genetic) and exogenous (treatment-related) determinants of inhibitor development and long term outcome.

Design: Multicenter Prospective Observational Birth Cohort Study

Population:

Patients with haemophilia A and B with FVIII/IX levels of <1 to 25% born between 1-1-2000 and 1-1-2040.

Intervention:

No intervention; only documentation of patient characteristics and parameters of routine patient care and outcome

Main outcome parameters:

Outcome: clinically relevant inhibitor development, bleeding pattern and joint status on physical examination and imaging.

Determinants: baseline FVIII/IX levels, measurement of inhibitory antibodies, family history, FVIII/IX gene mutation, details on replacement therapy (according to each infusion for the first 50 treatment days, and annually thereafter) and surgeries.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness:

• No burden for the patients. Well-defined clinical data will be collected from the medical files. Participating in this registry will not change the number of visits to the clinic. All outcome parameters that are collected (including laboratory results) are part of routine clinical care.
• Direct benefit is not to be expected. However, the direct interaction between centres that treat patients with rare diseases improves both clinical care and will result in better guidelines and as such may provide indirect benefit.
• Multicentre participation: haemophilia is a very rare condition. Therefore, collecting data on a multi-centre observational cohort is the only way to study this specific population.
• The registry concerns young boys and girls with haemophilia and cannot be performed in older patients, as >90% of inhibitors occur develop during the first 50 exposure days, and the results of prophylactic replacement therapy are highly dependent on the initiation of this treatment.

Inclusion Criteria:

• Diagnosed with Haemophilia A or B
• Factor VIII/ IX activity of <1 to 25%
• Complete records of Factor treatment and bleeds
• Treated in one of the participating centres

Exclusion Criteria:

• Patients referred because of an inhibitor*
• Informed consent not obtained

Children with mild ( FVIII/IX 6 to 25%), moderate (FVIII/IX 1 to 5%) or severe (FVIII/IX <1%) haemophilia A or B, born from January 1st 2000 until January 1st 2030 who have been or are to be treated in one of the participating centres