Understanding inheritance patterns
People with haemophilia are often concerned about passing the condition onto their children, or they want to understand how they developed it themselves. Inheritance patterns, as they are called, are notoriously difficult to understand, and you may need the help of a genetic counsellor to explain how you might have inherited the condition and/or to work out if you might pass it on.
Put as simply as possible, if you are a female ‘carrier’ of a ‘haemophilia’ X chromosome (i.e. you have one ‘haemophilia’ X chromosome and one normal one) and you have a baby with a male partner who has a normal X chromosome, you have a 50% chance of passing the ‘haemophilia’ gene to a girl (who will then also become a carrier) and a 50% chance of passing the ‘haemophilia’ gene to a boy (who will then have haemophilia).
If you are a male haemophilia sufferer (i.e. you have the haemophilia gene on your X chromosome) and you have a baby with a female partner who has normal X chromosomes, you have a 100% chance of passing the ‘haemophilia’ gene to a girl (who will then be a carrier) but no chance at all of passing the ‘haemophilia’ gene to a boy (because he will get your Y chromosome, not your X chromosome).
Occasionally, there may be no clear reason why an individual has haemophilia. There may be no obvious family history, and, when tested, neither parent appears to carry the ‘haemophilia’ gene. In these instances, it’s likely that the ‘haemophilia’ gene developed spontaneously while the baby was growing in the womb.
The severity of haemophilia tends to remain constant over generations. So if there is a family history of mild haemophilia, mild forms of the condition will be passed on. It is possible for the 'haemophilia' gene to remain hidden over several generations of a family because some carriers of the gene remain symptom free. If you or a member of your family is at all concerned about the possibility of inheriting or passing on 'haemophilia' genes, speak to your GP, who may refer you to a specialist haemophilia centre.