Hemophilia A

What Is Hemophilia A?

Hemophilia A, also called factor VIII (8) deficiency or classic hemophilia, is a genetic disorder caused by missing or defective factor VIII (FVIII), a clotting protein. Although it is passed down from parents to children, about 1/3 of cases found have no previous family history.

According to the US Centers for Disease Control and Prevention (CDC), hemophilia occurs in approximately 1 in 5,617 live male births. There are between 30,000 – 33,000 males with hemophilia in the US*.  More than half of people diagnosed with hemophilia A have the severe form. Hemophilia A is four times as common as hemophilia B. Hemophilia affects all races and ethnic groups.

Learn more about how blood clots at NBDF’s Steps for Living..

The Genetics of Hemophilia

A baseline understanding of hemophilia genetics is important for those individuals who have reason to suspect that a genetic predisposition for hemophilia exists in their family.

How is Hemophilia Inherited?

Hemophilia is passed down from parents to children.

Is Hemophilia Sex linked?

Yes, hemophilia is a sex linked disorder. The X and Y sex chromosomes help determine hemophilia inheritance patterns. The gene for hemophilia is carried on the X chromosome.

Is Hemophilia Dominant or Recessive?

Hemophilia is inherited in an X-linked recessive manner. 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). That means if a son inherits an X chromosome carrying hemophilia from his mother, he will have hemophilia. It also means that fathers cannot pass hemophilia on to their sons.

But because daughters have two X chromosomes, even if they inherit the hemophilia gene from their mother, most likely they will inherit a healthy X chromosome from their father and not have hemophilia. A daughter who inherits an X chromosome that contains the gene for hemophilia is called a carrier. She can pass the gene on to her children. Many women who carry the hemophilia gene also have low factor expression, which can result in heavy menstrual bleeding, easy bruising, and joint bleeds. Some women who have the hemophilia gene have factor expression low enough to be diagnosed with hemophilia.

For a female carrier, there are four possible outcomes for each pregnancy:
1.    A girl who is not a carrier
2.    A girl who is a carrier
3.    A boy without hemophilia
4.    A boy with hemophilia

Severity

(percentage breakdown of overall hemophilia population by severity)

•    Severe (factor levels less than 1%) represent approximately 60% of cases
•    Moderate (factor levels of 1-5%) represent approximately 15% of cases
•    Mild (factor levels of 6%-30%) represent approximately 25% of cases

What are the Symptoms of Hemophilia A?

People with hemophilia A bleed longer than other people. Bleeds can occur internally, into joints and muscles, or externally, from minor cuts, dental procedures, or injuries. How often a person bleeds and the severity of those bleeds depends on how much FVIII a person produces naturally.

Normal levels of FVIII range from 50% to 150%. Levels below 50% – or half of what is needed to form a clot – determine a person’s symptoms.

•    Mild hemophilia A:  6% up to 49% of FVIII in the blood. People with mild hemophilia A generally experience bleeding typically only after serious injury, trauma, or surgery. In many cases, mild hemophilia is not diagnosed until an injury, surgery or tooth extraction results in prolonged bleeding. The first episode may not occur until adulthood. Women with mild hemophilia often experience heavy menstrual bleeding, and can hemorrhage (bleed extensively) after childbirth.
•    Moderate hemophilia A: 1% up to 5% of FVIII in the blood. People with moderate hemophilia A tend to have bleeding episodes after injuries.
•    Severe hemophilia A.  <1% of FVIII in the blood. People with severe hemophilia A experience bleeding following an injury and may have frequent spontaneous bleeding episodes – bleeds that occur without obvious cause – often into their joints and muscles. Many males with severe hemophilia are diagnosed due to bleeding after circumcision.

Diagnosis of Hemophilia A

Doctors will perform tests that evaluate how long it takes for the blood to clot to determine if someone has hemophilia. A clotting factor test, called an assay, will show the type of hemophilia and the severity, or how much clotting factor the person produces on their own.

Because of our understanding of hemophilia genetics, most people who have a family history of hemophilia will ask that their baby boys be tested soon after birth to see if they have hemophilia. If there is no family history of hemophilia, people often notice bleeding that takes longer to stop or lots of bruising. Many babies born with severe hemophilia are diagnosed if there is prolonged bleeding after circumcision.

For girls, it often takes seeing worsening of symptoms for the diagnosis process to begin. Most girls are not tested for hemophilia before puberty. Heavy periods are a symptom of a bleeding disorder in women and girls. If there is a known family history, it is important to monitor for symptoms. It is recommended that women who have a family history of hemophilia get tested before getting pregnant, to help prevent complications during childbirth.

The best place for patients with hemophilia to be diagnosed and treated is at one of the federally funded hemophilia treatment centers (HTCs) that are spread throughout the country. HTCs provide comprehensive care from skilled hematologists and other professional staff, including nurses, physical therapists, social workers and sometimes dentists, dieticians and other healthcare providers, including specialized labs for more accurate lab testing.

Find a hemophilia treatment center near you.

How is Hemophilia A Treated?

Most treatments for hemophilia A focus on replacing the missing protein, FVIII (8), so a person can form a clot, and so reduce or eliminate the bleeds associated with the disorder. Treatments that work to prevent bleeding through new mechanisms have recently come to the market or are undergoing evaluation in research studies. People with hemophilia A have several different medication options for treatment.
 

Learn about treatment options for hemophilia.

Living with Hemophilia A

There's a lot to know about living with a bleeding disorder like hemophilia A. Visit NBDF’s Steps for Living to explore resources, tools, tips and videos on living with hemophilia A through all life stages. Organized by life stages, Steps for Living provides information on recognizing the signs of bleeds in children, help on navigating school issues, how to exercise safely, helping teens manage their bleeding disorder, information on workplace accommodations, and much more. There are downloadable checklists, toolkits, videos, and more.
 

Explore NBDF's Steps for Living to learn more about living with hemophilia A.

*"Occurrence rates of haemophilia among males in the United States based on surveillance conducted in specialized haemophilia treatment centres," Soucie et al