Haemophilia is a genetic disorder, which is usually inherited. It cannot be caught or transmitted. The Haemophilia gene is passed down from a parent to a child. Men with Haemophilia pass the gene on to their daughters, but not to their sons.

Women do not usually have Haemophilia, but they can be carriers of the gene. Women who are carriers have a 50 percent chance of having a boy with Haemophilia and a 50 percent chance of having a girl who is a carrier.

About one third of new cases are caused by a spontaneous mutation of the gene, which means that there was no history of Haemophilia in the family before.

The severity of Haemophilia is determined by the level of clotting activity of factor VIII or factor IX in the blood. There are three levels of severity: mild, moderate, and severe. The following table shows the range of factor VIII and factor IX activity:

People with severe Haemophilia usually bleed frequently into their muscles or joints. They may bleed one to two times per week. Bleeding is often spontaneous, which means the bleeding just happens with no obvious cause.

People with moderate Haemophilia bleed less frequently, usually after an injury, perhaps once a month. Cases of Haemophilia vary, however, and a person with moderate Haemophilia can bleed spontaneously.

People with mild Haemophilia usually bleed only as a result of surgery or major injury. They may never have a bleeding problem.

The life expectancy of someone with Haemophilia varies depending on whether they receive proper treatment. Without adequate treatment, many people with Haemophilia die before they reach adulthood. However, with proper treatment, life expectancy for people with Haemophilia is about 10 years less than that of males without Haemophilia.

Haemophilia usually only affects men, because the Haemophilia gene is carried on the same chromosome that determines whether a person is male or female.

The chromosomes that determine a person’s sex are called X and Y. Men have an X and a Y chromosome and women have two X chromosomes.

The genes for Haemophilia A and B are on the X chromosome. Because women have two X chromosomes, if one does not work properly, the other X chromosome makes up for it.

However, if a women has the Haemophilia gene on both X chromosomes, then she will have Haemophilia.

Most bleeding in Haemophilia occurs internally, into the joints or muscles. The joints that are usually affected are the ankle, knee, hip, elbow, and shoulder. Repeated bleeding without prompt treatment can damage the cartilage and the bone in a joint, leading to chronic arthritis and disability. Muscle bleeds most commonly occur in the upper arm, forearm, upper leg, calf, and iliopsoas muscle (the front of the groin area).

Some bleeds can be life-threatening and require immediate treatment. These include bleeds in the head, throat, gut, or iliopsoas.

Some people with Haemophilia do not exercise because they think it may cause bleeds, but exercise actually helps prevent bleeds. Strong muscles help protect someone who has Haemophilia from spontaneous bleeds and joint damage.

Sport is an important activity for young people. It not only helps build their muscles, it helps them develop mental concentration and coordination, and learn about being part of a team. However, some sports are riskier than others, and the benefits must be weighed against the risks. The severity of a person’s Haemophilia should also be considered when choosing a sport. Sports like swimming, badminton, cycling, and walking are sports that most people with Haemophilia can safely participate in, whilst sports like American football, rugby, and boxing are not recommended for people with Haemophilia.

In rare cases, a person can develop Haemophilia later in life. The majority of cases involve middle-aged or elderly people, or young women who have recently given birth or are in the later stages of pregnancy.

Acquired Haemophilia is usually caused by the development of antibodies to factor VIII.

This condition often resolves with appropriate treatment, which typically involves a combination of steroid treatment and the drug cyclophosphamide.

This is a very rare condition and affects between 1 and 4 people in every million. Pregnancy and autoimmune diseases such as rheumatoid arthritis and cancer may increase the risk of developing it. It can be a serious condition: many people develop severe bleeds and up to one in five may die from bleeding.

It is important that a carrier’s hematologist is involved in the supervision of the pregnancy and that there is some liaison with the obstetrician before delivery. It is not necessary to perform antenatal diagnosis just for management of the pregnancy: this is only done if termination of a pregnancy is being considered. The factor VIII level (but not factor IX)  tends to rise during pregnancy but it is sensible to check this sometime in the last couple of months of pregnancy. A normal vaginal delivery is perfectly acceptable even if the fetus is known to be male and at risk of Haemophilia. Epidural anesthesia does not usually present a problem and is generally permissible if the patient’s factor level is 40 percent or more. A cord blood sample after delivery will be used to check if a male baby does indeed have Haemophilia.