von Willebrand Disease

	Normal	In Haemophilia	In von Willebrand
	Bleeding starts	Bleeding starts	Bleeding starts
Step 1	Blood vessels constrict	Blood vessels constrict	Blood vessels constrict
Step 2	Platelet plug forms	Platelet plug forms	Incomplete platelet plug; bleeding continues
Step 3	Fibrin clot forms; bleeding stops	Incomplete fribrin clot; bleeding continues	Incomplete or delayed fibrin clot; bleeding continues

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The factor that is missing or deficient in haemophilia (factor VIII in haemophilia A; factor IX in haemophilia B) is essential to the formation of a fibrin clot, the tough threads that hold the platelet plug in place. The factor that is missing, deficient or abnormal in von Willebrand disease, von Willebrand factor, is essential to the formation of the platelet plug itself.

Researchers have identified many variations of the disease, but most fall into the following classifications:

Type I: Most common and mildest form of von Willebrand disease. Levels of von Willebrand factor are lower than normal. Levels of factor VIII may also be reduced.

Type II: In these people, the von Willebrand factor itself has an abnormality. Depending on the abnormality, they may be classified as having Type IIA or Type IIB. In Type IIA, the level of von Willebrand factor is reduced as is the ability of platelets to clump together. In Type IIB, although the factor itself is defective, the ability of platelets to clump together is actually increased.

Type III: Severe von Willebrand disease. These people may have a total absence of von Willebrand factor and factor VIII levels are often less than 10%.

Pseudo (or platelet-type) von Willebrand disease: This disorder resembles Type IIB von Willebrand disease, but the defects appears to be in the platelets, rather than the von Willebrand factor

This disease, like haemophilia, is passed down through the genes. Unlike haemophilia, however, which usually affects only males, von Willebrand disease occurs in men and women equally. A man or woman with the disease has a 50% chance of passing the gene on to his or her child (see box). Types I and II are usually inherited in what is known as a “dominant” pattern. This means that if even one parent has the gene and passes it onto a child, the child gets the disease. Whether the child has no symptoms, mild symptoms, or, less commonly, severe symptoms, he or she definitely has the disease. Regardless of the severity of the symptoms, the child can still pass the gene on to his or her own offspring.

Type III von Willebrand disease, however, is usually inherited in a “recessive” pattern. This type occurs when the child inherits the gene from both parents. Even if both parents have mild or asymptomatic disease, their children are likely to be severely affected.

These patterns of inheritance differ from that of haemophilia, which is caused by a defect in one of the “sex-linked” chromosomes. A man with haemophilia cannot pass the gene on to a son, because the abnormality is carried on the X chromosome, and a man contributes only a Y chromosome to his male offspring.

Research concerning the inheritance of von Willebrand disease is still underway to clarify a great deal of information that is not yet understood about the disease.

Once in a while, people develop what appears to be von Willebrand disease later in life. When this occurs in those who have no family history of the disease, it is thought that they are probably producing antibodies that destroy or decrease the amount of von Willebrand factor. Some other people have “acquired” a form of the disease in association with another disorder, such as rheumatoid arthritis, systemic lupus erythematosus, kidney and certain cancers.

Despite progress in understanding this disorder, it is still sometimes difficult to diagnose. A physician may mistake its mild symptoms for those of other illnesses. For example, a woman with heavy menstrual bleeding might be advised to have a hysterectomy when the real cause of her disorder eventually proves to be von Willebrand disease. When a healtcare practitioner hears of recurrent nosebleeds, easy bruising, heavy menstrual periods, or longer than usual bleeding after such routine operations as tonsillectomy or tooth extraction, diagnostic tests should be performed to rule out the possibility of von Willebrand disease. Specific tests for von Willebrand factor must be conducted because people with a mild form of the disease may have normal results on the usual screening tests for bleeding disorders. The tests listed under section ‘Laboratory Tests for von Willebrand Disease‘ are considered the most useful.

Although the results of these tests can determine whether a person has von Willebrand disease, there are a few considerations that must be noted to make sure the diagnosis is correct. In certain situations, the amount of von Willebrand factor is temporarily increased; this could skew the results of laboratory tests. Examples include: newborns, people under stress (including a child who is crying), women who are pregnant or using birth control pills and individuals who have just had surgery or a blood transfusion. People who have recently taken aspirin or certain other medication can have an alteration in the function of their platelets. In these situations, laboratory tests may need to be repeated to assure the right diagnosis.

Various treatments are available for von Willebrand disease. Once a proper diagnosis has been made, the treating physician will decide whether therapy is required and, if so, will tailor the therapy to the case at hand.

In 1926, Erik von Willebrand, a Finnish internist, reported his studies of a family living on the Aland Islands, in the Gulf of Bothnia between Finland and Sweden. The proband was a 5-year-old girl with severe spontaneous bleeding. Three of her sisters had died before age 4 of severe bleeding. Both parents and many relatives had mild bleeding histories, and the disease clearly differed from both haemophilia and Glanzmann thrombasthenia. Severe disease was transmitted through males and females, among whom some were mildly symptomatic and others were asymptomatic. During the ensuing 70 years, our understanding of von Willebrand disease (VWD) has advanced to the point that we can discuss its pathogenesis in molecular detail. Nevertheless, VWD remains a clinical diagnostic problem for many of the reasons that were evident from the earliest reports. Chief among these are that no bleeding symptoms are specific for VWD, and heterozygous transmitters of VWD may be phenotypically normal. This presentation will consider the classification of VWD and some practical problems associated with its diagnosis.

Von Willebrand factor (VWF) is a large, multimeric protein that circulates in the blood plasma. VWF also is stored in granular of endothelial cells and platelets, and can be secreted from these sites in response to appropriate stimuli. VWF performs two major roles in hemostasis; it mediates the adhesion of platelets to sites of vascular injury, and it is a carrier protein for factor VIII. Defects in VWF, therefore, may cause bleeding by impairing either platelet adhesion or blood clotting.

This increasingly complex basic information has led to a simplified classification for VWD (Table 1). This includes three major categories: partial quantitative deficiency (type 1), qualitative deficiency (type 2), and total deficiency (type 3). Qualitative type 2 VWD is divided further into four variants – 2A, 2B, 2M, and 2N – based upon the nature of the phenotype. These six categories correspond to distinct pathophysiologic mechanisms with distinct clinical features and therapeutic requirements.

1.	All VWD is caused by mutations at the VWF locus.
2.	Type 1 VWD refers to partial quantitative deficiency of VWF. Type 2 VWD refers to qualitative deficiency of VWF. Type 3 VWD refers to virtually complete deficiency of VW
3.	Type 2A VWD refers to qualitative variants with decreased platelet-dependent function that is associated with the absence of high-molecular-weight VWF multimers.
4.	Type 2B VWD refers to qualitative variants with increased affinity for platelet GPIb..
5.	Type 2M VWD refers to qualitative variants with decreased platelet-dependent function that is not caused by the absence of high-molecular-weight VWF multimers.
6.	Type 2N VWD refers to qualitative variants with markedly decreased affinity for factor VIII.
7.	When recognised, a mixed phenotype caused by compound heterozygosity is indicated by separate classification of each allele, separated by a slash (/).
8.	For the description of mutations, numbering systems are suggested for amino acids and nucleotides.

If one parent has a defective gene:	If both parents have a defective gene:
Each parent contributes one of his/her genes for vWF to his/her child. As shown, there are four possible genetic combinations than can result from this union./td>	Again, there are four possible genetic combinations.
Odds:	Odds:
2 out of 4 children (50%) will be genetically normal. 2 out of 4 children (50%) will have the defective vWF gene.	1 out of 4 children (25%) will be genetically normal. 2 out of 4 children (50%) will have one defective vWF gene. 1 out of 4 children (25%) will have two defective vWF genes, which will result in severe von Willebrand disease.
	Von Willebrand types I and II have a “dominant” inheritance pattern. That means that in a child with one normal gene and one gene for either of these von Willebrand types, the defective gene in “stronger. So the child will actually have the disease.
	Von Willebrand type III has a recessive inheritance pattern. In a child with one normal gene and one gene for von Willebrand type III, the defective gene is “weaker”, so the child will be a carrier for the disease, but will not have it.
	In order to have von Willebrand type III, the child must have two genes for the disease.

Bleeding time

How long does it take to stop bleeding? This finding is related to both the number and function of platelets and the amount of von Willebrand factor.

Factor VIII clotting activity

This measurement, which is low or nonexistent in people with haemophilia A, is usually normal or only slightly lowered in people with von Willebrand disease. The measurement takes into account not just the level of Factor VIII, but also its ability to function.

vWF antigen

This measures the amount of von Willebrand factor. Those with mild disease usually have 25-35% of the normal amount. Those with severe disease have less than 5%. A person’s blood type may affects these levels.

Ristocetin cofactor activity

A measurement of how well the von Willebrand factor is working.

vWF multimers

Evaluates the structure of the von Willebrand factor molecule. Helps in correctly classifying the type of von Willebrand disease.

Platelet function tests

Measure how well platelets work. Helps identify the type of von Willebrand disease or other disorder.

Antifibrinolytic	Inhibiting the breakdown of fibrin, the blood component that forms the essential portion of a blood clot
Autosomal	Relating to any chromosome that is not a sex chromosome
Afibrinogenemia	The absence of fibrinogen from the blood
Coagulopathy	A disorder that prevents normal clotting of the blood
Dysfibrinogenemiac	Malfunction of fibrinogen in the blood
Fibrinogen	Factor I, a protein in the blood that is converted to fibrin by the action of thrombin
Glycoprotein	A protein compound that also contains carbohydrate
Hypofibrinogenemia	A low or deficient level of fibrinogen in the blood
Platelet	A component of blood that contributes to coagulation
Prothrombin	Factor II, a protein in the blood that is converted to thrombin in the coagulation process
Thrombin	An enzyme derived from prothrombin that converts fibrinogen to fibrin