Hemophilia A: Genetic Testing and What to Expect

Show Article Table of Contents

Genetic testing for Hemophilia A is widely available and includes carrier testing, direct DNA mutation testing, linkage testing, and prenatal testing. Affecting more than 20,000 Americans, hemophilia is a bleeding disorder caused by genetic defect where the body is unable to produce one of the factors crucial for clotting. Thus, when a blood vessel is injured, uncontrolled bleeding occurs.

There are two main types of hemophilia. Type A is due to a factor VIII deficiency while type B is due to a factor IX deficiency. Clinically, they are very similar conditions, causing unprompted bleeding into the joints and muscles and internal and external bleeding after an injury or surgery. Repeated bleeding eventually causes damage to the joints and muscles. Hemophilia A is four times more common than B according to the National Hemophilia Foundation.

Role of Genes

The X and Y chromosomes determine gender. Females inherit two X chromosomes, one from each parent, while males will inherit an X chromosome from their mother and a Y chromosome from their father.

Hemophilia A is an inherited condition through a chromosome X-linked recessive manner. This means the gene linked to hemophilia is found in the X chromosome, which means that if a son inherits the X chromosome carrying the hemophilia gene from his mother, he will have the condition. The son could also inherit the gene not carrying the genetic condition. Fathers cannot pass the condition to their children.

For females, even if they inherit an X chromosome carrying hemophilia from their mother, they could still get a healthy gene from her father and not have the condition. But getting the X chromosome carrying the gene makes her a carrier, and she can pass the gene to her children.

Genetic Testing

Genetic testing is available for people with hemophilia A and their family members. There are several methods of genetic testing to help women find out if they are carriers and to make decisions about family planning.

Carrier Testing

Carrier testing involves looking for clotting factors in blood. Women with the hemophilia A gene will have levels that are lower than normal, and some may even have levels so low they have bleeding issues.  

Carrier testing has an accuracy rate of up to 79 percent, but carrier testing alone is not enough to determine if a woman is a carrier. Family history, in addition to the testing, can confirm if a woman is carrying the hemophilia A gene.

Women who can benefit most from carrier testing include those who:

  • Have sisters with hemophilia A
  • Have maternal aunts and first cousins on their mother’s side, especially girl cousins, with hemophilia A

Direct DNA Mutation Testing

It's possible to look for and find mutations within the genes through DNA testing. A blood sample will first be taken from a male family member who has hemophilia A. The blood of the female looking to see if she is a carrier is next checked and compared for similar genetic mutations. DNA mutation testing tends to have high accuracy.

Linkage Testing

For some cases of hemophilia A, genetic mutations cannot be found. In these instances, linkage analyses, also called indirect DNA analyses, can track the gene mutation in the family. Blood samples are taken from various family members, especially affected males. 

Clinicians will then look for patterns of linked DNA in the person with hemophilia A and compare those patterns of the other family members. Unfortunately, linkage testing isn’t as accurate as other methods of testing, especially instances where affected males are distant relatives. 

Prenatal Testing

Women with a family history of hemophilia may want to have their unborn child tested. As early as ten weeks into pregnancy, chorionic villus sampling can be completed. This involves taking a small sample of the placenta and testing the DNA to look for genetic specific mutations.  

Another test that can be done later in the pregnancy–usually around 15 and 20 weeks into the pregnancy–is an amniocentesis. Using a fine needle inserted into the uterus via the abdomen, a small sample of amniotic fluid is taken. The cells found in the fluid are then analyzed for the hemophilia A gene.

What to Expect

Meeting with a genetic counselor is the first step in determining whether someone is a carrier of hemophilia A. Genetic counselors often work with parents who have affected newborns or with women who want to know if they are carriers. They may also meet with men who are assisting in testing of their sisters and daughters.

Meeting with a genetic counselor involves an initial consultation where family and personal history of hemophilia A are discussed. The counselor will then discuss the benefits, limitations, and possible outcomes of genetic testing.

Genetic testing is the next step in providing answers. The type of testing will depend on the family and/or patient’s needs and concerns. Family members who currently have hemophilia A are tested first and then any potential carriers.

Once test results come back, the genetic counselor will meet with the patient and family members to explain results. Discussion may include testing of other family members and getting appropriate medical care. 

Insurance may or may not cover the cost of testing. Some insurance providers will allow a physician to explain why testing is needed. Testing is generally approved after such requests.

Genetic counselors can also help patients and their families find necessary resources, including financial assistance and support groups.

A Word From Verywell

Being a carrier of hemophilia A can significantly affect a woman's life. Many carriers worry about the risk of passing the disease on. They may feel as if having children is not a possibility. 

Genetic counselors and hemophilia treatment centers can provide carriers with appropriate counseling, information, and support to help them make decisions and take control of their lives. Moreover, support groups with women in the same situation can be a great source of comfort and hope.

Was this page helpful?
View Article Sources