Hemophilia is a bleeding disorder that can affect the blood’s ability to clot properly. In most cases, people inherit the gene variations for hemophilia in an X-linked recessive inheritance pattern.
Hemophilia is a condition that affects the blood’s ability to coagulate, or clot.
It occurs when people have low amounts of a certain type of protein in the blood known as clotting factors. Clotting factors are responsible for normal blood clotting.
Genes provide the instructions to produce clotting factors. People with hemophilia typically have a gene variation in the genes responsible for clotting proteins. These alterations cause the body to produce too little of these proteins, which causes problems with coagulation.
In most cases, people inherit the gene variations responsible for hemophilia from their parents. However, it is also possible for people without a family history of hemophilia to develop the condition.
This article explores the inheritance pattern of hemophilia, including how it passes through families and who can carry the gene variations.
In most cases, hemophilia is a
More specifically, it is an X-linked recessive condition. This is because hemophilia occurs due to problems with blood clotting factors, and the genes responsible for blood clotting factors are present on the X chromosome.
Male offspring usually inherit one X chromosome from their female parent and one Y chromosome from their male parent. Females typically inherit an X chromosome from each parent.
Due to being an X-linked recessive disorder, hemophilia is more common in males. This is because males typically have only one copy of an X chromosome.
As such, they only need to inherit a single nonworking gene variation from their female parent to develop a deficiency in a clotting factor.
While it is rarer, females can
If the male parent has hemophilia and the female parent is not a carrier of a gene variation, then none of the male children will develop hemophilia. However, all female children will be carriers of a gene alteration.
If the male does not have hemophilia and the female is a carrier, the chances of their offspring having hemophilia are
- 25% chance of having a son with hemophilia
- 25% chance of having a son with normal blood clotting
- 25% chance of having a daughter who is a carrier
- 25% chance of having a daughter who is not a carrier
If the male has hemophilia and the female is a carrier, the chances of their children having hemophilia are as follows:
- 25% chance of having a son with hemophilia
- 25% chance of having a son with normal blood clotting
- 25% chance of having a daughter who is a carrier
- 25% chance of having a daughter who has hemophilia
Most cases of hemophilia are genetic in nature. However, in rare cases, hemophilia can occur in a person with no personal or family history of diseases related to blood clotting.
This is known as acquired hemophilia. This type of hemophilia differs from the congenital types, as it is an autoimmune condition.
Instead of occurring due to genetic variations, it develops when the immune system produces antibodies that attack clotting factors, usually factor VIII.
Roughly half the cases of acquired hemophilia are idiopathic. This means the exact cause is unknown. The other 50% usually relate to other autoimmune conditions, cancer, or infections.
Both males and females can pass hemophilia gene alterations to their children.
A
As such, males with hemophilia are not known as carriers. They typically either present with symptoms of hemophilia or do not have a gene variation.
However, due to the inheritance pattern of hemophilia, females who are daughters of a male with hemophilia will be carriers or have the condition. Some health experts may refer to these people as obligate carriers.
Females who are daughters of a female carrier have a 50% chance of being a carrier, sometimes known as a potential carrier.
Different genes responsible for producing different clotting factors are responsible for the different types of hemophilia:
- Hemophilia A occurs from alterations in the F8 gene, which produces clotting factor VIII.
- Hemophilia B occurs due to variations in the
F9 gene , which produces clotting factor IX. - Hemophilia C occurs due to changes in the F11 gene, which produces clotting factor XI.
These genetic alterations lead to a deficiency of the respective clotting factors, causing the bleeding problems associated with hemophilia.
Genetic testing describes a medical test that can help identify genetic variations. As such, it can help determine the risk of potentially passing on genetic conditions, such as hemophilia.
Carrier testing is available to help identify females who carry gene variations for hemophilia. A genetic test is more accurate than a test measuring factor levels. This is because a person carrying a gene variation may still have normal factor levels.
A genetic test can help determine a person’s carrier status for either healthcare reasons or to know if they could pass it to their children. A doctor can also perform prenatal testing during pregnancy to determine whether the fetus has hemophilia.
Genetic counseling may be advisable for families with a history of hemophilia. A genetic counselor can provide valuable information and support for individuals and families affected by hemophilia. They can help people make informed decisions about family planning and healthcare.
In most cases, hemophilia is an inherited condition. It can occur if the child inherits a gene variation present on the X chromosome.
For male children, they only need to inherit one copy of the gene variation. For female children, either both X chromosomes will have the gene alteration, or one will have the variation and the other is missing or nonfunctioning.
If people with a known family history of hemophilia are considering pregnancy, they can undergo genetic testing and counseling. This can help individuals and families manage and make informed decisions about family planning.