Hemophilia B is a bleeding disorder caused due to the lack of Factor IX. Factor IX is a coagulation factor (clotting factor) that causes the blood to clot and prevents excess bleeding at the injured site. The lack of Factor IX prevents blood from clotting at the bleeding site causing it to bleed further. Hemophilia is a genetic condition that is inherited through an X-linked recessive trait from parents to offspring.
Royal Disease
Hemophilia B is also referred to as a royal disease as it was found in royal families of England, Spain, Germany, and Russia. The Queen Victoria of England (1837) was the carrier of Factor IX deficiency due to spontaneous mutation. The son of Queen Victoria had hemophilia and all her daughters were carriers of this gene causing it to inherit in several royal families where they and their offspring were married off to. Hemophilia was passed for three generations in several royal families and then disappeared.
In 1991, a tomb containing the remains of the Czar Nicolas II family was found followed by a second tomb in 2007. By performing the genetic experiment in material obtained from Czar Alexis it was revealed that the royal disease was caused due to the substitution in the F9 gene in the splice acceptor site in exon 4 i.e Hemophilia B.
Genetics
Hemophilia is an inherited disorder that is passed from parents to offspring through X-linked recessive traits. As it is an X-linked disorder it is also known as a sex-linked disorder as X and Y chromosome determines the sex. It is a recessive trait because the female carries two X chromosomes whereas the male carries one X and one Y chromosome. The females inherit one X chromosome from their mother and one X chromosome from their father and the males inherit one X chromosome from their mother and one Y chromosome from their father. If the mother is the carrier of the gene then the son will inherit the disease (only when the son inherits a defective X chromosome from the mother) while the daughter will be the carrier as she has two X chromosomes (one chromosome carrying the defective gene and another healthy chromosome from the father) the healthy X chromosome will mask the effect of defect gene carrying chromosome but still will act as a carrier having the ability to pass it to next generation. If the father is the carrier of the gene then neither his son nor daughter will be affected but the daughter will still act as the carrier of the disease, the reason why the son is not affected is because he acquires the Y chromosome from his father. If the mother is the carrier of the gene and the father is affected then the daughter may or may not acquire the disease depending upon the X chromosome inherited from her mother but will act as a carrier and the son may or may not acquire the disease depending upon the X chromosome inherited from his mother.
Hemophilia is most commonly observed in males as they carry only one X chromosome whereas females are less likely to acquire it due to the presence of two X chromosomes but it is not impossible, if they inherit both the X chromosomes carrying the defective gene then they will be affected.
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