Accessible Search Form           Advanced Search

  • PRINT PAGE  |  PRINT ENTIRE TOPIC  |  SHARE

What Causes Hemophilia?

If you have inherited hemophilia, you're born with the disorder. It's caused by a defect in one of the genes that determine how the body makes blood clotting factor VIII or IX. These genes are located on the X chromosomes (KRO-muh-somz).

Chromosomes come in pairs. Females have two X chromosomes, while males have one X and one Y chromosome. Only the X chromosome carries the genes related to clotting factors.

A male who has a faulty hemophilia gene on his X chromosome will have hemophilia. A female must have the faulty gene on both of her X chromosomes to have hemophilia, which is very rare.

If a female has the faulty gene on only one of her X chromosomes, she is a "hemophilia carrier.” Carriers don't have hemophilia, but they can pass the faulty gene to their children.

Below are two examples of how the hemophilia gene is inherited.

Inheritance Pattern for Hemophilia—Example 1

The diagram shows one example of how the hemophilia gene is inherited. In this example, the father doesn't have hemophilia (that is, he has two normal chromosomes X and Y). The mother is a carrier of hemophilia (that is, she has one abnormal X chromosome and one normal X chromosome). Each daughter has a 50 percent chance of inheriting the abnormal gene from her mother and being a carrier. Each son has a 50 percent chance of inheriting the abnormal gene from his mother and having hemophilia.

The image shows one example of how the hemophilia gene is inherited. In this example, the father doesn't have hemophilia (that is, he has two normal chromosomes—X and Y). The mother is a carrier of hemophilia (that is, she has one faulty X chromosome and one normal X chromosome).

Each daughter has a 50 percent chance of inheriting the faulty gene from her mother and being a carrier. Each son has a 50 percent chance of inheriting the faulty gene from his mother and having hemophilia.

Inheritance Pattern for Hemophilia—Example 2

The image shows one example of how the hemophilia gene is inherited. In this example, the father has hemophilia (that is, his X chromosome is faulty). The mother isn't a hemophilia carrier (that is, she has two normal X chromosomes).  Each daughter will inherit the faulty gene from her father and be a carrier. None of the sons will inherit the faulty gene from their father; thus, none will have hemophilia.   

The image shows one example of how the hemophilia gene is inherited. In this example, the father has hemophilia (that is, his X chromosome is faulty). The mother isn't a hemophilia carrier (that is, she has two normal X chromosomes).

Each daughter will inherit the faulty gene from her father and be a carrier. None of the sons will inherit the faulty gene from their father; thus, none will have hemophilia.

Females who are hemophilia carriers usually have enough clotting factors from their one normal X chromosome to prevent serious bleeding problems. However, up to 50 percent of carriers may have an increased risk of bleeding.

Very rarely, a girl is born with hemophilia. This can happen if her father has hemophilia and her mother is a carrier.

Some males who have the disorder are born to mothers who aren't carriers. In these cases, a mutation (random change) occurs in the gene as it is passed to the child.

Rate This Content:

  
previous topic next topic
Hemophilia Clinical Trials

Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Hemophilia, visit www.clinicaltrials.gov.

Children and Clinical Studies Logo

Visit Children and Clinical Studies to hear experts, parents, and children talk about their experiences with clinical research.


 
July 31, 2013 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.