In 40 out of 45 families, the sporadic case resulted from a mutation in the last two generations. In 82% (23/28), the carrier mothers had a de novo mutation where the X chromosome was of paternal origin in 74% (17/23). ddPCR is a potentially powerful and promising analysis for mosaicism in HA.

The spectrum of haemophilia B mutations reveals at least 65% of the families carry a unique mutation, but with more inhibitor patients than reported internationally, probably as a result of many 'null' mutations.