Hemophilia genotypes and genetics
» Hemophilia A and B are called X-linked recessive conditions, indicating the gene that induces hemophilia is on the X chromosome.
Males own one X chromosome (XY), and females have two X chromosomes (XX). Therefore, hemophilia usually affects males. When a male has received a gene that induces hemophilia on his X chromosome, he does not provide the clotting factor he requires because the Y chromosome does not store information for the production of factor VIII or IX.
When a female receives a gene that induces Hemophilia on one of her X chromosomes, she owns a second normal X chromosome. Therefore, the healthy gene produces the essential clotting factors and compensates for the hemophilia gene.
These women will be carriers of hemophilia.
» Men with hemophilia pass on hemophilia gene to all of their daughters, so they will be carriers.
But, their sons don’t receive the abnormal gene as they receive Y, not X chromosome, so they will not have hemophilia.
» Women who are carriers have a 50% opportunity to transfer the hemophilia gene to their kids.
Each son of a carrier has a 50% opportunity to have hemophilia, and each daughter has a 50% opportunity to be a carrier.
If a carrier woman is pregnant (gender unknown), she has a 25% opportunity to have a son with hemophilia, and a daughter who is a carrier. She may have a son or daughter who does not have hemophilia and is not a carrier with a 50% opportunity. If her first son is born without hemophilia, the subsequent male may have hemophilia with a 50% chance. The chance to transfer the hemophilia gene is the same with each pregnancy, regardless of her previous offspring conditions.
» Women who are carriers may suffer bleeding manifestations, as they may have low factor levels sufficient to be in the mild range of deficiency.
Females who carry hemophilia should have their factor (VIII or IX) levels monitored to ensure they have sufficient levels for natural blood clotting.
» If you are a carrier, women in your family may carry the gene for hemophilia. Therefore, there may be other family members at risk.
» Genetic examination is accessible for individuals with hemophilia and women at risk of being carriers.
» We should encourage our patients to make their family aware of hemophilia items. Knowledgable individuals take care of themselves and obtain proper treatment and information.
