Skip to content

Children's Health

Font Size

Hemophilia: Understanding Genetic Risk - Topic Overview

The genetic factors that cause hemophilia are passed down through the X chromosome. Every male has one X chromosome and one Y chromosome. Every female has two X chromosomes. Males inherit a Y chromosome from their father and an X chromosome from their mother; females inherit an X chromosome from each parent.

The chance that a child will inherit hemophilia depends upon whether he or she inherits an affected gene from one or both parents. Hemophilia affects men almost exclusively. Females may be a carrier of the gene that causes hemophilia but will not usually have any signs or symptoms of the disease. A female who is a carrier usually has one defective gene on the X chromosome and one normal gene on the X chromosome. When she has a normal working chromosome, she won't have symptoms. She has a 50% chance of passing on the defective gene to her children. If a woman who is a carrier is affected by hemophilia, the symptoms are usually very mild. In rare cases, a woman gets a defective gene from both her mother and her father and is born with hemophilia.

Hemophilia can also develop when the gene that is responsible for producing clotting factors changes (mutates). In this case, hemophilia is not inherited; the person in whom the gene changes will be the first person in a family to have hemophilia or will be a carrier. The person may pass this gene down to any children that he or she has.

Hemophilia genetics

Here are some examples of the genetics of hemophilia. The chance of having hemophilia depends on whether the parents have hemophilia or are carriers.

  • If the father has hemophilia and the mother is a carrier, sons will have a 50% chance of having hemophilia. Daughters will have a 50% chance of having hemophilia and a 50% chance of being a carrier. It is very rare for both parents to have these defective genes.
  • If the father does not have hemophilia and the mother is a carrier, sons will have a 50% chance of having hemophilia. Daughters will have a 50% chance of being carriers.
  • If the father has hemophilia and the mother has normal blood, all sons will be normal and all daughters will be carriers.

    This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at http:// cancer .gov or call 1-800-4-CANCER.

    WebMD Medical Reference from Healthwise

    Last Updated: March 12, 2014
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
    1
    Next Article:

    Hemophilia: Understanding Genetic Risk Topics

    Today on WebMD

    child with red rash on cheeks
    What’s that rash?
    plate of fruit and veggies
    How healthy is your child’s diet?
     
    smiling baby
    Treating diarrhea, fever and more.
    Middle school band practice
    Understanding your child’s changing body.
     

    worried kid
    fitArticle
    boy on father's shoulder
    Article
     
    Child with red rash on cheeks
    Slideshow
    girl thinking
    Article
     

    Loaded with tips to help you avoid food allergy triggers.

    Loading ...

    Sending your email...

    This feature is temporarily unavailable. Please try again later.

    Thanks!

    Now check your email account on your mobile phone to download your new app.

    babyapp
    New
    Child with adhd
    Slideshow
     
    rl with friends
    fitSlideshow
    Syringes and graph illustration
    Tool