Skip to content
My WebMD Sign In, Sign Up

Children's Health

Font Size
A
A
A

Hemophilia and Genetic Risk

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.
By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer Brian Leber, MDCM, FRCPC - Hematology
Last Revised August 3, 2011

WebMD Medical Reference from Healthwise

Last Updated: August 03, 2011
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.

Today on WebMD

preschool age girl sitting at desk
Article
look at my hand
Slideshow
 
woman with cleaning products
Slideshow
young boy with fever
Article
 

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

babyapp
New
Child with adhd
Slideshow
 
rl with friends
fitSlideshow
Syringes and graph illustration
Tool
 
6-Week Challenges
Want to know more?
Build a Fitter Family Challenge – Get your crew motivated to move.
Feed Your Family Better Challenge - Tips and tricks to healthy up your diet.
Sleep Better Challenge - Snooze clues for the whole family.
I have read and agreed to WebMD's Privacy Policy.
Enter cell phone number
- -
Entering your cell phone number and pressing submit indicates you agree to receive text messages from WebMD related to this challenge. WebMD is utilizing a 3rd party vendor, CellTrust, to provide the messages. You can opt out at any time.
Standard text rates apply

WebMD Special Sections