How is hemophilia inherited?
The abnormal gene is on the X chromosome. It can be carried by either the mom or dad or both.
The opportunity of a baby receiving a hemophilia mutated gene depends on which of their parents has the mutated gene.
If only the mother has the mutated gene
If a female with the mutated gene and a normal man has a kid, there is a:
- 1 in 4 opportunities of having a normal baby boy
- 1 in 4 chance of having a baby boy with hemophilia
- 1 in 4 chance of having a normal baby girl
- 1 in 4 chance of having a baby girl with an affected X chromosome
In the last state, the girl becomes a carrier of the mutated gene. The carrier girl may transfer it to her kids but may not have any severe manifestations of hemophilia herself.
However, female carriers may have bleeding problems, such as heavy.
If only the father has the changed gene
If a male with hemophilia has a son with a normal woman, there’s no opportunity the son will get hemophilia.
Because the boy always receives his X chromosome from his mother, who does not have the mutated gene.
However, any girls of the man will become carriers of the mutated hemophilia gene and may transfer it to their kids.
If both parents have the mutated gene
If a female with the mutated gene and a male with hemophilia have a kid, there’s a:
- 1 in 4 opportunities of having a normal baby boy
- 1 in 4 chance of having a baby boy with hemophilia
- 1 in 4 chance of having a baby girl who’s a carrier of hemophilia
- 1 in 4 chance of having a baby girl with hemophilia
So, females may have hemophilia, although it’s very uncommon.
When there’s no family history
A boy may be born with hemophilia, although there’s no family history of the disorder.
In such events, the gene mutation developed spontaneously, in the son’s mother, grandmother, or great-grandmother, but till then, a son of the family had never received it.
Some studies have shown, there’s no recognized family history of hemophilia in up to 1 in 3 new cases.
Genetic mutation
A human can acquire all genetic disorders spontaneously by mutation, rather than inheriting it, because of a new mutation in one of their parents’ gametes. Spontaneous mutations estimate about 33% of all cases of hemophilia A.
About 30% of states of hemophilia B are the outcome of a spontaneous gene mutation.
So, females may deliver a hemophiliac son, she is a carrier for the disorder or not, as a result of a spontaneous mutation.
Until modern direct DNA trial, however, it was difficult to determine if a female with only healthy kids was a carrier or not. Generally, the healthier sons she bore, the higher the probability that she was not a carrier.
Is hemophilia dominant or recessive
Hemophilia is an X-linked recessive condition.
It is a recessive disorder because the normal X chromosome dominates the diseased one in a carrier woman.
In the affected male, the mutated gene acts alone and causes the disorder.
