Question

Women who were known to be carriers (heterozygous) of the X-linked, recessive, hemophilia gene were studied in order to determine the amount of time required for the blood clotting reaction.It was found that the time required for clotting was extremely variable from individual to individual. The values obtained ranged from normal clotting time at one extreme all the way to clinical hemophilia at the other extreme. What is the most probable explanation for these findings?

Answer 1

Hemophilia is a condition in which a person´s blood loses its capacity to coagulate, when it is necessary. This condition happens because of a genetic alteration in which the X chromosome, provided either by the mother, or both parents, possesses the recessive trait, wich affects the correct funtion of a gene known as FVIII. It is this gene which will activate the production of Factor VIII, basic for platelet cohesion, and one of the first steps in the coagulation cascade.

Hemophilia affects mostly males, given that the X chromosome of the mother is dominant. But in females, it is rare, and it takes the inheritance of the trait from the X chromosomes of both parents. However, there are cases in which females can inherit the trait from one of the parents, and they will not have hemophilia, but will present coagulation responses that are less rapid, than those who do not sport any mutation in their genetic coding. It is this reason given above that would explain why there have been cases in which it has been found that women have not just had slow coagulation response times, but have actually presented symptoms of clinical hemophilia.