Hemophilia

Hemophilia is the oldest known hereditary bleeding disorder. There are two types of hemophilia, A and B (Christmas Disease). Low levels or complete absence of a blood protein essential for clotting causes both. Patients with hemophilia A lack the blood clotting protein, factor VIII, and those with hemophilia B lack factor IX. A person with severe hemophilia has less than 1% of the normal amount of a clotting factor - either Factor VIII (8) or Factor IX (9). People without hemophilia have between 50-150% of the normal level of factor VIII or IX. There are about 20,000 hemophilia patients in the United States. Each year, about 400 babies are born with this disorder. Approximately 85% have hemophilia A and the remainder has hemophilia B.

The severity of hemophilia is related to the amount of the clotting factor in the blood. About 70% of hemophilia patients have less than one percent of the normal amount and, thus, have severe hemophilia. A small increase in the blood level of the clotting factor, up to five percent of normal, results in mild hemophilia with rare bleeding except after injuries or surgery.

This is not a problem when a person with hemophilia has a simple cut or scrape. He doesn’t bleed any faster than the average person. He can hold pressure on the cut and platelets in the blood will stop the bleeding.

The problem for people with hemophilia is bleeding inside the body, especially bleeding into joints like the knees, elbows, and ankles. When bleeding happens inside the joint, it becomes very swollen and painful. Repeated bleeding into a joint can cause a type of crippling arthritis. Bleeding inside other parts of the body, such as the brain, throat, and abdomen can be life-threatening. A person with mild hemophilia may only have problems with bleeding when he has surgery, major dental work, or a severe injury. A person with moderate hemophilia will have those problems plus bleeding problems with more minor injuries such as a hard bump to the knee. A person with severe hemophilia can have what are called spontaneous bleeds - bleeding that starts inside the body for no known reason.

Hemophilia is classified as mild, moderate or severe, depending on the amount of clotting factor a person has in his body. Severe hemophilia is actually the most common form. People with hemophilia are born with the disorder and have it all of their lives. You can't catch hemophilia from someone else. Hemophilia is a genetic disorder - it is passed down generation to generation through a family’s genes. Because the genetic defect occurs on the X chromosome, women are carriers of hemophilia but rarely have the disorder. Hemophilia occurs almost exclusively in men.

In about one-third of the babies born with hemophilia, the disorder is believed to be due to a spontaneous mutation of the gene. There is no family history of hemophilia. To determine a sex linkage inheritance of a defective trait, look at a family pedigree to notice the similarities and patterns of the trait throughout the family pedigree for example the pedigree below:

Normal Female Normal Male

Normal, but known carrier female Affected Male

The first generations are skipped, although Nicolas (1904-18) was a hemophiliac, neither his parents nor grandparents were. This pattern occurs in several other places of the pedigree, and indicates a recessive mode of inheritance. From the biochemical nature of the defect, scientists have determined that hemophilia is a recessive trait. All the affected individuals are sons, strongly suggesting that the defect is a sex linkage trait. Since males are hemizygous for the X chromosome, more males than females should have the phenotype of a sex-linked recessive trait because males do not have a second X chromosome that might carry the normal allele. The first prediction that we can make from this is that all males get their X chromosomes from their mothers; affected males should be the offspring of carrier, heterozygous, females. A female is automatically a carrier if her father had the disease. She has a 50% chance of being a carrier if her brother, but not her father, has the disease. In that case her mother was the carrier. There are several different inherited forms of hemophilia are known, each deficient on one of the steps in the steps in the pathway that forms fibrinogen, the blood clot protein. Two of these forms “classic” hemophilia A and hemophilia B, also called Christmas disease, are sex linked. Other hemophilia are autosomal.

Hemophilia is a very rare disorder. Very few people have it. There are about 17,000 people in the United States with hemophilia. One out of every 5,000 boys born has hemophilia. This makes it about as rare as triplets (three babies in one birth).

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