If you’re living with a genetic condition like hemophilia, you may worry about passing it on to your children. Hemophilia can be inherited in a few different ways, depending on the type.

In this article, we’ll explain how hemophilia A, B, and C are inherited and discuss the chances of passing these conditions to children. We’ll also briefly cover the role of genetic testing in hemophilia.

Understanding Chromosomes and DNA

To better understand how people inherit hemophilia, it helps to first learn about chromosomes. Chromosomes are structures that contain DNA and genes, which carry the body’s genetic instructions.

Most human cells contain 46 chromosomes, arranged in 23 pairs. One chromosome in each pair comes from each biological parent. The 23rd pair is called the sex chromosomes, which play a role in sex assigned at birth.

Most females have two X chromosomes (XX), and most males have one X and one Y chromosome (XY). However, not everyone fits this pattern, and some people have different chromosome combinations due to genetic variations or other biological differences.

Typically, an X chromosome is inherited from the mother, while either an X or a Y chromosome is inherited from the father.

Inheritance of Hemophilia A and B

Hemophilia A and hemophilia B can be inherited from either biological parent. These types of hemophilia are linked to genes on the X chromosome, including the F8 gene (which provides instructions for factor VIII) and the F9 gene (which provides instructions for factor IX).

This is why you may hear that hemophilia A and B have an X-linked recessive inheritance pattern. This means the inheritance pattern differs based on the number of X chromosomes a person has.

Most people assigned female at birth have two copies of the F8 gene and the F9 gene because they have two X chromosomes. Most people assigned male at birth have only one copy of each because they have one X chromosome.

Hemophilia in Males

A male typically develops hemophilia A or hemophilia B if they inherit a changed F8 or F9 gene on their X chromosome. Because most males have only one X chromosome, they don’t have a second copy of the gene that could help produce enough clotting factor protein.

Bleeding symptoms and severity can vary widely depending on clotting factor levels. In general, males with hemophilia are more likely to have more noticeable or severe bleeding symptoms than females with hemophilia.

Hemophilia in Females

Because most females have two X chromosomes, hemophilia inheritance can happen in several ways. Here’s an example using the F8 gene, which is linked to hemophilia A.

In the first scenario, a female inherits one mutated F8 gene from one parent and one healthy copy from the other parent. This person may be described as a carrier because they carry one mutated copy of the gene.

Female carriers may have no bleeding symptoms or experience a range from mild to significant bleeding episodes. Symptoms of hemophilia in female carriers are usually milder because the healthy F8 gene can make some clotting factor proteins. However, bleeding varies based on factor level and X-inactivation.

In the second (less common) scenario, a female inherits two mutated copies of the F8 gene. This person may develop hemophilia A due to reduced factor VIII levels, although severity depends on the specific mutation.

It’s also possible for a female to develop hemophilia A if they inherit one mutated gene and their other X chromosome doesn’t work or is missing.

People assigned female at birth with a rare genetic disorder known as Turner syndrome have only one copy of the X chromosome, so if that copy carries a mutated gene, they will develop hemophilia.

Chances of Passing Hemophilia A and B From Parents to Children

If you have hemophilia, you may be wondering what your chances are of passing the condition to your children. It all depends on whether your partner also has or is a carrier of hemophilia. Let’s break down the hemophilia inheritance pattern for variants A and B.

For example, a father without hemophilia and a mother who is a carrier have an overall 25 percent chance for each of these scenarios:

• Son without hemophilia (healthy gene from mother, healthy gene from father)
• Daughter without hemophilia who isn’t a carrier (healthy gene from mother, healthy gene from father)
• Son with hemophilia (mutated gene from mother, Y chromosome from father)
• Daughter who is a carrier (mutated gene from mother, healthy X chromosome from father)

In another example, a father with hemophilia and a mother who isn’t a carrier have a 50 percent chance that they’ll have a:

• Daughter who is a carrier (healthy gene from mother, mutated gene from father)
• Son without hemophilia (healthy gene from mother, Y chromosome from father)

In the very rare event that the father has hemophilia and the mother is a carrier:

• Each son has a 50 percent chance of having hemophilia (healthy or mutated gene from mother, Y chromosome from father).
• Each daughter has a 50 percent chance of being a carrier and a 50 percent chance of having hemophilia (mutated or healthy gene from mother, mutated gene from father).

It’s also worth noting that in about one-third of hemophilia A and B cases, there’s no family history of the condition. Instead, a person randomly acquires a new mutation, and they could pass the condition along to their children.

Inheritance of Hemophilia C

Hemophilia C (also known as Rosenthal disease) is different from hemophilia A and B. This is because the F11 gene (for factor XI) isn’t located on the X chromosome. Instead, it’s found on chromosome 4.

Besides their sex chromosomes (pair number 23), people typically have 22 other pairs of chromosomes, known as autosomes. This means that unlike with hemophilia A and B, people assigned male and female at birth are equally at risk of inheriting hemophilia C.

Is Hemophilia C Autosomal Dominant or Recessive?

To develop hemophilia C, a person needs to have two mutated copies of the F11 gene. This inheritance pattern is known as autosomal recessive because the gene is on an autosome. Recessive means you need two mutated copies of a gene to develop the condition.

Some families have autosomal dominant hemophilia C. Dominant means you need just one mutated copy of a gene to develop the condition.

Chances of Passing Hemophilia C From Parents to Children

People with recessive hemophilia C have a mutated F11 gene on chromosome 4 from both parents. You can also be a carrier of this disorder if you have one mutated gene and one healthy gene. Let’s break down a few scenarios to explain the chances of passing on hemophilia C.

Suppose you and your partner are both carriers for hemophilia C. You each have one healthy F11 gene and one mutated gene. When you have a child, chances are:

• 25 percent that they won’t have hemophilia and won’t be a carrier (two healthy genes)
• 50 percent that they’ll be a carrier (one healthy gene and one mutated gene)
• 25 percent that they’ll have hemophilia C (two mutated genes)

Now let’s say that you have hemophilia C and your partner is a carrier. In this case, there is a:

• 50 percent chance that your child will be a carrier for hemophilia C (one healthy gene and one mutated gene)
• 50 percent chance that your child will have hemophilia C (two mutated genes)

If you have hemophilia C but your partner doesn’t and isn’t a carrier, none of your children will have hemophilia. However, they’ll all be carriers who could pass the condition along to their own children.

Hemophilia Carrier Testing for Hemophilia

If you have a known family history of hemophilia, it’s a good idea to get genetic testing done. You can find out whether you’re a carrier for hemophilia A or hemophilia B. This will tell you whether you’re at risk of passing along hemophilia to your children.

Talk to your doctor or your child’s pediatrician if you’re interested in learning more about genetic testing.

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