Why are most people with hemophilia male?

Hemophilia is an inherited genetic disorder caused by a deficiency in clotting proteins, specifically clotting factors VIII or IX. The genes that code for these clotting factors are located on the X chromosome. Since males have only one X chromosome and one Y chromosome, while females have two X chromosomes, hemophilia primarily affects males.

1. X-Linked Inheritance: The genes responsible for producing clotting factors VIII and IX are located on the X chromosome. In genetics, genes carried on the X chromosome are called X-linked genes. In the case of hemophilia, the altered genes that result in hemophilia are recessive. This means that a male needs to inherit only one copy of the altered gene to have hemophilia.

2. Females as Carriers: Females, on the other hand, have two X chromosomes. If they inherit one altered hemophilia gene and one normal gene, they become carriers of hemophilia. Carriers typically do not have symptoms of hemophilia themselves but can pass on the altered gene to their children. Males who inherit the altered hemophilia gene from their carrier mothers will have hemophilia, while females who inherit the altered gene will be carriers.

3. Male Predominance: Since males have only one X chromosome, they cannot "mask" the effects of an altered hemophilia gene with a normal copy, like females can. Hence, males with even a single altered hemophilia gene will express the disorder. This explains the higher prevalence of hemophilia in males compared to females.

4. Prevalence Rates: Hemophilia A, which is caused by a deficiency in clotting factor VIII, affects approximately 1 in 5,000 to 10,000 males. Hemophilia B, caused by a deficiency in clotting factor IX, occurs less frequently and affects about 1 in 20,000 to 30,000 males. These statistics further highlight the male preponderance of hemophilia.

It's important to note that while males are more commonly affected by hemophilia due to the X-linked inheritance pattern, carrier females can also play a crucial role in transmitting the altered hemophilia gene to offspring. Genetic counseling and prenatal testing are available for individuals with a family history of hemophilia to help manage the risk and ensure proper treatment and care.