Why is XI clotting factor absent?

Answer 1

If the question is; what causes factor XI deficiency, also known as Hemophilia C, the answer is in the genetics of the individual. The gene sequence for the production of the factor XI protein in not on the X chromosome as it is with Hemophilia A and B. This means that Hemophilia C equally common in males and females alike. (If 1 in 100,000 can ever be considered common.)

Since the route cause of Hemophilia C is genetic, it is most often inherited from the parents. In communities such as people of Ashkenazi Jewish decent, the disorder is more common than in mass population. Due to their beliefs, they have practiced intermarrying which has increased the likelihood of the mutation being passed on. Combine this with the fact that the mutation for factor XI deficiency is a dominant trait, the disorder is easily passed generation to generation.

Of course there is always a chance that the mutation takes place at the time of conception or shortly thereafter and is not inherited from a parent.

As for the actual production of the factor protein molecule not being produced or being produced incorrectly, we have to take a closer look at the genetic sequence. In a person without the deficiency, when the body needs more factor XI, the genetic sequence that encodes the production of the protein molecule becomes RNA and acts like a factory, producing the protein on a production like. As the molecules move along the RNA structure, different pieces of the molecule are added and it moves to the next step in production.

If one of the manufacturing steps is being preformed incorrectly or never sends the molecule farther down the assembly line, the molecule never gets completed correctly. This is the case when a mutation in that specific sequence occurs, leading to the factor deficiency.