Inheritance patterns in hemophilia
Last updated Aug. 18, 2025, by Lindsey Shapiro, PhD
Fact-checked by Joana Carvalho, PhD
Most cases of hemophilia — a group of rare bleeding disorders — are genetic, arising when children directly inherit disease-causing mutations from their biological parents.
These mutations result in deficiencies in important blood clotting proteins in the body, leaving people with hemophilia susceptible to the disease’s hallmark symptoms of spontaneous or excessive bleeding episodes.
Understanding how hemophilia is inherited is important for making family planning decisions and can help ensure prompt diagnoses that allow for early treatment and care.
Genetic causes of hemophilia
Hemophilia is usually caused by genetic mutations affecting the production or function of blood clotting factors, but the exact hemophilia inheritance pattern varies by the specific type of hemophilia.
A person inherits two copies of most genes — one from each biological parent. An exception is the genes found on the sex chromosomes, X and Y. Females have two X chromosomes, one inherited from each parent, while males have an X chromosome from their mother and a Y from their father. For genes on X chromosomes, women will have two copies, while men will have one.
Understanding the genetics of hemophilia relies on two important concepts related to genetic inheritance: X-linked versus autosomal, and dominant versus recessive.
- When affected genes are found on nonsex chromosomes, it’s called autosomal inheritance. An X-linked inheritance pattern means the implicated genes are located on the X chromosome.
- In a recessive disorder, having a healthy copy of an implicated gene is enough to compensate for a mutated one, so the disease will only develop if there are two mutated gene copies or no functioning copy is present. With dominant inheritance, one mutated gene copy is sufficient to cause the disease, regardless of the presence of other healthy copies.
Because they account for the vast majority of hemophilia cases, hemophilia A and B genetics explain why hemophilia as a whole primarily affects males.
These conditions are usually marked by X-linked, recessive inheritance, so males who inherit one copy of the disease-causing mutation on their only X chromosome won’t have a healthy copy to compensate and will certainly have hemophilia. But if women with one mutated gene copy have a healthy one on their other X chromosome, this often allows for sufficient production of the blood clotting protein to avoid symptoms.
Hemophilia A and B: X-linked recessive inheritance
Hemophilia A is caused by mutations in the F8 gene, encoding the production of clotting factor VIII. Hemophilia B, meanwhile, is caused by mutations in F9, encoding factor IX.
Both are X-linked recessive disorders. Male children can only inherit these hemophilia types from their mother, because that’s where they get their X chromosome from. Females can inherit a disease-causing mutation from either parent.
Hemophilia A or B will typically be present in males with one mutated copy and in females with two mutated copies of F8 or F9. In some cases, it’s also possible for females with a single faulty gene copy to develop the disease. This can happen if the healthy copy is found on the X chromosome that gets inactivated as part of a process that occurs early on in fetal development to ensure that only one X chromosome is active in each cell.
Females who carry only one copy of the mutated gene, along with a second healthy copy, are referred to as carriers. They often don’t have bleeding problems, but can still pass on the disease-causing mutation to their biological children. Carriers may also have symptoms of milder forms of hemophilia, depending on their levels of factor VIII or IX.
If a female carrier for hemophilia A or B has a child with a male who does not have hemophilia, there is a:
- 50% chance that any male child will have hemophilia
- 50% chance that any female child will be a carrier
If a female hemophilia A or B carrier has a child with a male who has the same type of the disease, there is a:
- 50% chance that any male child will have hemophilia
- 50% chance that any female child will have hemophilia, and a 50% any female child will be a carrier.
Should a male with hemophilia A or B have a child with a female who is not a carrier, no male children will have hemophilia. However, all female children will be carriers.
Hemophilia C: Autosomal recessive inheritance
Hemophilia C is caused by mutations in the F11 gene on chromosome 4, which lead to deficiencies in clotting factor XI. Hemophilia C inheritance typically is autosomal recessive, meaning that both inherited copies of F11 must be mutated for the disease to occur. With autosomal recessive inheritance, males and females are affected equally.
Either parent carrying one mutated copy of F11 and one healthy one is usually an asymptomatic carrier, and won’t show signs of the diease. But this parent can pass on the mutation to any biological children.
- If one parent is a carrier and the other is unaffected, there’s a 50% chance any of their children will be carriers, but none will develop hemophilia C.
- If both parents are carriers, there’s a 25% chance their children will have hemophilia C, a 50% chance they’ll be carriers, and a 25% chance they’ll be unaffected.
In rare cases, hemophilia C can be inherited in an autosomal dominant manner, which means that just one copy of the faulty gene is sufficient to cause the disease. If someone with this form of hemophilia C has a child, there’s a 50% chance the mutation will be passed on to any offspring.
Carrier status and genetic testing
Females in families with a history of hemophilia can undergo carrier testing to help them understand potential risks to their own health and make future family planning decisions.
Hemophilia carrier detection may be recommended for females who:
- have a child or other male family member with hemophilia
- are having symptoms of hemophilia
Genetic testing for hemophilia, which looks for a disease-causing mutation in a small blood or saliva sample, can play a role in diagnosing hemophilia and is the most definitive way to determine carrier status. A blood test to measure clotting factor levels might also be performed. However, this test may be unreliable on its own because a woman can carry a disease-causing mutation and have normal clotting factor levels.
Families with a history of hemophilia may be referred to a genetic counselor, who can help them understand who should be tested and when. Genetic counseling for hemophilia can also support families in understanding what their test results mean and the implications for future family planning decisions.
Other causes of hemophilia
While hemophilia is most often inherited from a person’s biological parents, there are a couple scenarios where hemophilia can happen without a family history.
Sometimes, disease-causing mutations arise spontaneously, or de novo, in an egg or sperm cell from a parent, or in the affected person during early development. Although the initial mutation isn’t directly inherited from a parent, any affected individuals can subsequently pass it on to their own children. Spontaneous mutations in hemophilia account for about a third of cases.
Very rarely, hemophilia is not caused by genetic mutations at all, but rather by autoimmune reactions in which the immune system mistakenly attacks its own blood clotting proteins. This is called acquired hemophilia. It isn’t known exactly what causes acquired hemophilia to develop, but it does not typically run in families.
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