Understanding the difference between hemophilia A and B

Hemophilia A and hemophilia B are the two most common types of hemophilia.

Both are bleeding disorders that make it difficult for your blood to clot properly, due to a lack of certain proteins called clotting factors. They share similar symptoms, and both affect males more than females.

Despite their similarities, they have differences, including their specific genetic cause and, in some cases, how they’re treated.

What’s the difference between hemophilia A and B?

Hemophilia A, also called classical hemophilia, is the most common type of hemophilia. It accounts for about 80% of all cases and affects approximately 1 in 5,000 male births.

Hemophilia B is less common, affecting about 1 in 25,000 male births. It makes up 15% to 20% of all cases and is also known as Christmas disease, named after Stephen Christmas, a boy from Canada diagnosed with the condition in 1952.

Both types of hemophilia happen because of changes (mutations) in different genes on the X chromosome, which is one of the chromosomes that determine a person’s sex.

Do hemophilia A and B have different causes?

Regarding hemophilia A versus B causes, they differ based on the specific genes involved and the affected clotting factors in the blood.

• Hemophilia A is caused by mutations in the F8 gene, which leads to a deficiency of blood-clotting factor VIII, also known as coagulation factor VIII.
• Hemophilia B is caused by mutations in the F9 gene, leading to a deficiency of blood-clotting factor IX, another important protein for blood clotting.

Both types of hemophilia are passed down through families in an X-linked recessive way; this means the mutated gene is on the X chromosome.

Beacause males only have one X chromosome, they are more likely to have hemophilia if they inherit the mutated gene. Females, who have two X chromosomes, are usually carriers, meaning they can pass the gene to their children but often don’t have symptoms themselves.

While hemophilia inheritance is the most common reason for the disease’s occurrence, about one-third of cases do not have a family history of the disorder. Instead, the mutation happens spontaneously.

How do symptoms differ between hemophilia A and B?

While their genetic causes differ, the symptoms of hemophilia A versus hemophilia B are often similar.

People living with hemophilia may experience spontaneous bleeding, prolonged bleeding after injuries, and other bleeding-related complications.

The severity of symptoms depends on the level of your clotting factors. Hemophilia A and B can be diagnosed as mild, moderate, or severe, depending on these levels.

Mild hemophilia

People with mild hemophilia have factor levels between 5% and 40% of those considered normal.

In these individuals, the conditions may cause symptoms such as unusual bruising and excessive bleeding after dental procedures, trauma, or surgery.

Many people with mild disease may not be diagnosed with hemophilia until they experience bleeding after having a procedure.

Moderate hemophilia

Individuals with moderate hemophilia have factor levels ranging from 1% to 5% of normal.

Moderate hemophilia is usually diagnosed in young children and may cause prolonged bleeding after surgery or trauma.

Severe hemophilia

People with severe hemophilia have factor levels less than 1% of normal.

Severe hemophilia causes spontaneous bleeding episodes, including internal bleeding into the joints and muscles, which typically trigger pain and mobility issues.

Diagnosis is usually made during infancy or early childhood.

Is hemophilia A or B more severe?

The severity of both forms of hemophilia can vary, so it’s hard to say if one is worse than the other.

Some studies suggest that hemophilia B may be clinically less severe than hemophilia A, but there is no strong conclusive proof to confirm this. Both types can range from mild to severe, and each person’s experience is unique, making it difficult to compare their severity.

Researchers do know, however, that people with hemophilia A are more likely to develop an inhibitor, or a neutralizing antibody, to factor replacement therapy — the main type of hemophilia treatment, which involves replacing the missing or faulty blood-clotting factor.

Specifically, about 1 in 5 people with hemophilia A and about 3 in 100 people with hemophilia B develop an inhibitor. This can prevent the treatment from working properly, making it more challenging to stop bleeding.

Do treatments differ for hemophilia A and B?

Hemophilia A and B treatments may be similar, as both involve deficiencies in clotting factors.

However, the specific factor replacement therapies given to people with hemophilia A and B differ slightly.

• Hemophilia A therapies target factor VIII deficiency by replacing the missing or defective factor VIII.
• Hemophilia B treatments address factor IX deficiency, replacing the missing or faulty factor IX.

Factor replacement therapies for both types of hemophilia can be given regularly to prevent bleeding episodes or when bleeding occurs, such as after an injury. They may also be given before surgery to reduce the risk of bleeding.

These treatments are given intravenously, or directly into the bloodstream, to help restore blood clotting capacity.

Another possible treatment for both types of hemophilia is gene therapy. This method works by giving your body a healthy version of the defective gene.

How does life expectancy vary between hemophilia A and B?

In the 1950s and 1960s, there was no reliable treatment for hemophilia. Back then, males with severe hemophilia had an average life expectancy of 11 years. That changed when clotting factor replacement therapy began.

The availability of clotting factor therapies allows many people with the mild form of the disease to manage their condition, prevent major bleeds, and live normal lives.

Life expectancy depends on how severe the hemophilia is, with more severe cases being associated with a higher risk of bleeding complications.

According to estimates from the World Federation of Hemophilia, children diagnosed today — and who start treatment early — have a life expectancy comparable to that of the general population. However, adult men already living with hemophilia have a life expectancy that’s approxiately 10 years less than those without the disease.

A 2023 report suggested that in wealthier countries, life expectancy is about 30% shorter for people with hemophilia A and 24% shorter for people with hemophilia B. Life expectancy is lower in countries with more limited access to hemophilia treatments.

Ultimately, regular monitoring, early intervention, and advancements in treatment options can all contribute to a longer life expectancy for people with either hemophilia A or hemophilia B.