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

In this article, we’ll break down how hemophilia A, B, and C are inherited and the chances of parents passing these conditions to their children. We’ll also briefly discuss the importance of genetic testing for hemophilia.

What Is Hemophilia?

Hemophilia is an inherited bleeding disorder caused by changes or mutations in clotting factor genes. These genes provide instructions for making clotting factor (coagulation factor) proteins that form blood clots. People with hemophilia can’t form these clots properly, which raises their bleeding risk.

There are several types of hemophilia, and each is defined by the missing clotting factor. Hemophilia A is caused by having little to no factor VIII (8). People with hemophilia B (Christmas disease) have little to no factor IX (9). An extremely rare form of this disease — known as hemophilia C (Rosenthal disease) — is due to a lack of factor XI (11).

Understanding Chromosomes and DNA

To better understand how people inherit hemophilia, it helps to first learn about chromosomes. These structures are made of your DNA and genes. Each human cell contains 46 chromosomes. You inherit one set of chromosomes from each parent — 23 from your mother and 23 from your father. The 23rd pair is known as the sex chromosomes. Sex assigned at birth is determined by the sex chromosomes a person inherits.

Females have two X chromosomes — one from the mother and one from the father — and males have one X and one Y chromosome, according to the Centers for Disease Control and Prevention (CDC). The X chromosome comes from the mother, and the Y chromosome comes from the father.

Inheritance of Hemophilia A and B

Hemophilia can be passed from both the mother and the father. This is because males and females both have at least one X chromosome, according to the CDC. Certain genes, like F8 and F9 (the genes for factors VIII and IX), are located on the X chromosome.

This is why you may hear that hemophilia A and B have an X-linked recessive inheritance pattern. It’s the scientific way of saying that you need both mutated copies of a gene to develop a condition in females and only one copy of the gene in males.

Having two sets of chromosomes means you also have two copies of each gene, one from each parent. For example, people assigned female at birth have two copies of the F8 gene because they have two X chromosomes. People assigned male at birth have only one copy because they have just one X chromosome.

Hemophilia in Males

A male develops hemophilia A and B if they inherit only one mutated copy of F8 or F9 from their mother, according to the CDC. Since they have only one X chromosome, there isn’t another healthy copy available to help make enough clotting factor proteins. This is why males with hemophilia have serious bleeding symptoms.

Hemophilia in Females

Since females have two X chromosomes, a few scenarios can happen. We’ll use an example with the F8 gene that causes hemophilia A.

In the first scenario, a female inherits a mutated F8 gene from their father and a healthy F8 gene from their mother. This person is known as a female carrier because they “carry” a mutated copy of a certain gene. Female carriers can have mild hemophilia A with some bleeding symptoms, but they’re not as severe. This is because the healthy F8 gene can make some clotting factor proteins.

In the second scenario, a female inherits two mutated copies of the F8 gene. This person develops hemophilia A because they can’t make any factor VIII protein. 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’s 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 inheritance pattern of hemophilia.

For example, according to the CDC, 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 from the CDC, 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)

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 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 your sex chromosomes (pair No. 23), you have 22 other pairs of chromosomes, known as autosomes. This means that unlike with hemophilia A and B, everyone is equally at risk of inheriting hemophilia C, regardless of sex assigned at birth.

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 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 children.

Genetic 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.

Talk With Others Who Understand

On MyHemophiliaTeam, the social network for people with hemophilia and their loved ones, more than 6,600 members come together to ask questions, give advice, and share their stories with others who understand life with hemophilia.

Do you have other questions about how hemophilia is inherited? Share them in the comments below, or start a conversation by posting on your Activities page.