Von Willebrand disease (VWD) is the most common type of bleeding disorder, affecting up to 1% of the world’s population. Unfortunately, bleeding symptoms are not always recognized as abnormal, so only a small number of affected individuals have been diagnosed.
In fact, it is not a single disease, but a family of related diseases. All the different types are caused by a problem with the von Willebrand factor (VWF). This is a protein in blood which is necessary for proper blood coagulation, or clotting. It helps platelets stick to the wall of a damaged blood vessel. In addition, the VWF carries factor VIII, another protein important to blood clotting, through the bloodstream.
When there is not enough VWF in the blood, or when it does not work the way it should, the blood takes longer to clot. (See von Willebrand disease: How does blood clot normally?)
Some people have such mild cases that they never know they have the disease. With all forms of VWD, however, bleeding episodes can be severe and may require treatment, particularly during or following surgery or dental work. The diagnosis of VWD is complex and should be made by physicians experienced in the treatment of bleeding disorders.
All types of VWD are inherited in an autosomal pattern. This means that men and women are affected in equal numbers.
Type 1 VWD is the most common. About 75% of women with VWD have Type 1. With this type, the VWF works normally, but there is less of it than normal. Type 1 is inherited through an autosomal dominant pattern. This means only one of the parents needs to be a carrier of the defective gene to pass it on to the child.
Type 2 VWD is the next most common. In fact, Type 2 VWD includes several sub-types. Together, they make up 20-25% of VWD cases. In Type 2 VWD, the VWF molecule may be present in normal quantity, but it does not work properly. The VWF does not play its role in binding platelets to the wall of the blood vessel; sometimes it binds to platelets in the bloodstream instead of at the site of the broken vessel wall. Type 2 VWD is also an autosomal dominant defect, meaning only one parent needs to be a carrier to pass on the disorder.
Type 3 VWD is the rarest, and the most serious, form. It affects about 1 in 250,000 women. People with Type 3 VWD have very little VWF in their blood. As a result bleeding can happen often and, if untreated, can be serious.
Type 3 follows an autosomal recessive pattern of inheritance. This means that the defective gene is inherited from both parents. However, in some cases, the disease can result from a combination of one parent passing on the defective gene and a new or spontaneous mutation in the child’s gene inherited from the other parent.
What’s more, because VWF transports factor VIII in the bloodstream, people with Type 3 VWD have very low levels of factor VIII as well. Factor VIII is another trace protein in the blood. It is important to the clotting process. People who lack only factor VIII have a bleeding disorder called hemophilia A. Women with Type 3 VWD have many symptoms similar to hemophilia A.
For more information, see von Willebrand disease.
Platelet function disorders may be as common as von Willebrand disease. However, because many of these disorders are mild, many women go undiagnosed.
Some types of platelet function disorder, such as Glanzmann Thrombasthenia, can be life-threatening.
Depending on the type of platelet function disorder…
- platelets do not stick to the walls of damaged blood vessels
- platelets do not clump together at the site of the injury to the blood vessel
- platelets do not form a proper surface so that other blood factors can make a fibrin clot. (See Platelet function disorders: How does blood clot normally?)
Platelet function disorders have variable inheritance patterns. Some follow an autosomal recessive pattern of inheritance. This means that both parents need to carry the defective gene for the child to be affected. Others follow an autosomal dominant pattern, meaning only one of the parents needs to carry the gene for it to be passed on to the child. Platelet function disorders affect men and women in equal numbers.
Platelet function can be affected by common drugs. These are:
- aspirin (ASA) and other drugs containing aspirin
- blood thinners such as warfarin or heparin
- non-steroidal anti-inflammatory drugs like indomethacin, ibuprofen and naproxen
Other drugs can also affect platelet function. These include:
- some antibiotics
- heart drugs
- blood thinners
Certain medical conditions can cause abnormal platelet function. These include
- chronic kidney disease
- heart bypass surgery
- some forms of leukemia.
For more information, see Platelet function disorders.
Hemophilia A (factor VIII deficiency) affects 1 in 5000 males. Hemophilia B (factor IX deficiency) affects 1 in 25,000 males. Severe hemophilia in women is extremely rare. However, women are carriers of hemophilia and many women who are carriers have bleeding problems.
The genes responsible for producing factors VIII and IX, the defective genes in hemophilia, are situated on the X chromosome. This makes hemophilia a sex-linked genetic disorder.
Carriers have one normal X chromosome and one abnormal X chromosome. The normal X chromosome produces a certain amount of factor VIII or IX clotting factor. This protects carriers from the most severe form of hemophilia in which the level of clotting factor is less than 1%.
However, the variation in clotting factor levels among carriers is very wide. In some carriers the level is much below normal. In other carriers, the level is closer to normal. This is because the two X chromosomes, one of which carries the hemophilia gene, are not equally functional. If the hemophilia X chromosome happens to be functional in most cells, then the carrier will have a very low level of clotting factor activity.
Many carriers have a clotting level between 30% and 70% of normal and do not usually suffer from severe bleeding, although they may suffer from the most common symptom – heavy menstrual bleeding. However, some carriers have less than 30% of the normal level of factor VIII or IX. These women are considered to have mild hemophilia. It is not known how many carriers of hemophilia A and B have bleeding problems. Estimates vary up to 60%.
For more information, see Hemophilia A and B.
There are a large number of other bleeding disorders caused by deficiencies in trace proteins in the blood. All these factor deficiencies are inherited in an autosomal recessive pattern. Both parents usually need to be carriers of the gene to pass on a severe form of the disorder to their children. Men and women are affected in equal numbers.
For more information, see Other factor deficiencies.