As a hematologist with a special interest in genetic bleeding disorders, I am often asked about the prevalence of hemophilia, particularly why it affects more males than females. Hemophilia is a hereditary bleeding disorder characterized by prolonged bleeding after injury, which is due to a deficiency or dysfunction of specific clotting factors in the blood. The most common forms of hemophilia are Hemophilia A and Hemophilia B, with Hemophilia A being the focus of your question.

Hemophilia A is caused by a deficiency in a clotting factor known as Factor VIII. This deficiency leads to an inability of the blood to clot properly, resulting in excessive bleeding, both externally and internally. The reason why more males are affected by Hemophilia A than females is rooted in the genetic nature of the disorder. The gene responsible for Hemophilia A is located on the X chromosome, which is one of the sex chromosomes.

In humans, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). This difference in sex chromosome composition plays a crucial role in the inheritance of X-linked recessive disorders like Hemophilia A. Since the gene for Hemophilia A is recessive, an individual must inherit two copies of the defective gene—one from each parent—to manifest the disorder. Females have two chances to inherit a normal gene from one of their parents, which would result in them being carriers of the gene but not affected by the disorder. However, males, having only one X chromosome, will exhibit the disorder if they inherit the defective gene from their mother, as there is no second X chromosome to potentially carry a normal gene.

This pattern of inheritance is known as X-linked recessive inheritance. It is the reason why Hemophilia A is predominantly seen in males, with females typically serving as carriers. Carrier females have a 50% chance of passing the defective gene to their offspring. If a carrier female has a son, there is a 50% chance that he will inherit the defective gene and develop Hemophilia A. Daughters of carrier females have a 50% chance of inheriting the gene and becoming carriers themselves.

It is important to note that while Hemophilia A is more common in males, females can also be affected, albeit rarely. This can occur in a few scenarios: if a female inherits two copies of the defective gene (one from each carrier parent), if there is a phenomenon known as "lyonization" where one of the X chromosomes is inactivated, or if there is a mutation in the gene on the second X chromosome.

In conclusion, the reason more males are affected by Hemophilia A than females is due to the X-linked recessive nature of the disorder. The genetic inheritance pattern dictates that males, with their single X chromosome, are more susceptible to manifesting the disorder when they inherit the defective gene. Females, with two X chromosomes, have a higher chance of having at least one normal gene that can prevent the disorder from manifesting, although they can still be carriers and pass the gene to their offspring.

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Males are affected more often than females, because the gene is located on the X chromosome. Hemophilia A. Hemophilia A is a disorder where the blood cannot clot properly due to a deficiency of a clotting factor called Factor VIII.read more >>