Published 22 August 2018 | 3 min read
Haemophilia B is a genetic disorder caused by missing or defective clotting factor IX (FIX, or factor 9), causing prolonged and often spontaneous bleeding externally and internally, into the muscles and joints.¹ Haemophilia B makes up 15–20% of all haemophilia cases, and 60% of cases are genetically inherited.²
The gene for haemophilia is located on the X chromosome. Females inherit two X chromosomes, one from their mother and one from their father (XX). Males inherit an X chromosome from their mother and a Y chromosome from their father (XY). So, if a son inherits an X chromosome carrying haemophilia from his mother, he will have haemophilia. A father with haemophilia B cannot pass it on to his sons, but will pass the gene to his daughters.
Because females have two X chromosomes, even if they inherit a haemophilia gene, they have another healthy X chromosome to compensate, instead they will be a carrier. Carriers have around half the normal amount of clotting factor and will also suffer symptoms. Haemophilia B can occur in females, but is rare.
FIX is a coagulation factor and is essential in forming blood clots. In response to injury, FIX interacts with other clotting factors to set off a chain of reactions that form a blood clot, sealing off damaged blood vessels.⁴
Normal levels of FIX vary between different people and range from 50–150%; however, in people with Haemophilia B, levels fall below 50%.¹
‘FIX concentrates’ are used to prevent and treat bleeding,⁵ which simply means replacing the person’s missing FIX with FIX that has been concentrated for use as a drug. Most people will use a ‘recombinant FIX’, that has been developed in a laboratory with DNA technology.⁵
People with severe haemophilia B will take FIX concentrates at regular intervals to prevent bleeds, prophylactically.¹ Research has suggested that the higher a person’s FIX level, the lower the risk of spontaneous bleeds. People with haemophilia B use FIX concentrates to raise their factor levels; the closer their factor levels get to normal, the lower the risk of bleeding.⁶^ ⁷
People sometimes avoid physical activity, thinking that it may cause bleeds. In fact, when carried out properly, regular activity can help reduce the risk of spontaneous joint bleeds⁸. Learn more on how to stay active and the best activities for people with haemophilia in our ‘Changing Haemophilia® Talking Joints’ toolkit.