What is von Willebrand's Disease
von Willebrand's disease is a hereditary deficiency or abnormality of the von Willebrand factor in the blood, a protein that affects platelet function. It's the most common hereditary disorder of platelet function, affecting both women and men. The disease is estimated to occur in 1% to 2% of the population.
The disease was first described by Erik von Willebrand, a Finnish physician, who reported a new type of bleeding disorder among island people in Sweden and Finland.
In von Willebrand's disease, blood platelets don't stick to holes in blood vessel walls. Platelets are tiny particles in the blood that clump together at the site of an injury to prepare for the formation of a blood clot. von Willebrand factor causes them to bind to areas of a blood vessel that are damaged. If there is too little von Willebrand factor, or the factor is defective, platelets do not gather properly when a blood vessel is injured. von Willebrand factor is found in plasma, platelets, and blood vessel walls. When the factor is missing or defective, the first step in plugging a blood vessel injury (platelets adhere to the vessel wall at the site of the injury) doesn't take place. As a result, bleeding doesn't stop as quickly as it should, although it usually stops eventually.
There are no racial or ethnic associations with the disorder. A family history of a bleeding disorder is the primary risk factor.
Researchers have identified many variations of the disease, but most fall into the following classifications:
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.
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.
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.
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're 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 disease and certain cancers.
The life span of patients is usually normal length. Since the disease is genetically transmitted, genetic counseling may be recommended for parents.
von Willebrand disease can be more complicated for women because of obstetric and gynecological issues.
Like hemophilia, the disease is passed down through the genes. But unlike hemophilia, 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. 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 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 hemophilia, which is caused by a defect in one of the "sex-linked" chromosomes. A man with hemophilia 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. von Willebrand disease is found on the autosomal chromosomes and therefore can be inherited by either males or females. von Willebrand disease can often be traced through several generations in a family. Some have symptoms while others just carry the gene.
Symptoms & Diagnosis
Diagnosis can be difficult. When a healthcare 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.
Usually, a person with von Willebrand disease has a parent who has a history of bleeding problems. Typically, a child bruises easily or has prolonged bleeds excessively after a skin cut, tooth extraction, tonsillectomy, or other surgery. A woman may have increased menstrual bleeding. Bleeding may worsen at times. On the other hand, hormonal changes, stress, pregnancy, inflammation, and infections may stimulate the body to increase production of the von Willebrand factor and temporarily improve clot formation.
Laboratory tests may determine that the number of platelets is normal but bleeding time is abnormally long. Bleeding time is the amount of time elapsed before bleeding stops after a small cut is made on the forearm. To make the diagnosis, doctors may order tests that measure the amount of von Willebrand factor in the blood. Because the von Willebrand factor is the protein that carries factor VIII in the blood, the blood level of factor VIII may also be decreased.
Diagnostic signs can include:
- Normal platelet count
- Prolonged bleeding time
- Reduced von Willebrand factor level
- Reduced platelet adhesion may occur
- Reduced or increased platelet aggregation (platelet aggregation test)
- Ristocetin co-factor is reduced
There are a range of treatment choices, depending on whether the illness is mild or severe. Many people with von Willebrand disease never even need treatment.
Stimate, desmopressin acetate (DDAVP), a drug sprayed into the nose, is the treatment of choice for mild von Willebrand disease. Bleeding is usually controlled in individuals with mild von Willebrand disease by using this nasal spray to boost their own factor VIII and von Willebrand levels. DDAVP may be given to increase the amount of the von Willebrand factor long enough for surgery or dental procedures to be performed. DDAVP is a synthetic product that carries no risk of infectious disease.
For excessive bleeding, infusions of a viral inactivated factor VIII product rich in von Willebrand factor such as Humate-P, Alphanate, and Koate DVI may be required. If trauma occurs or surgery is scheduled, desmopressin acetate can be given to raise the levels of von Willebrand factor, which will decrease the tendency towards bleeding. Fresh plasma may also be used to decrease bleeding but the risk of viral infection can be high.
Children with von Willebrand disease should avoid unnecessary trauma, and those with severe disease should avoid certain contact sports. During menstruation, adolescent females may want to take extra precautions to avoid accidents. During bleeding episodes, elevate and apply cold compresses and gentle pressure to the area. During nosebleeds, apply pressure over the bridge of the nose, and have the child lean forward to prevent blood running down the back of the throat and being swallowed.
Aspirin and many of the drugs used for arthritis can aggravate bleeding because they interfere with platelet function. People who have von Willebrand's disease can take acetaminophen for pain relief because it doesn't inhibit platelet function.
The National Hemophilia Foundation's Medical and Scientific Advisory Council (MASAC) made recommendations for treatment of von Willebrand disease in November of 1999.They include:
- Stimate, desmopressin acetate (DDAVP), a nasal spray or injection.
- For patients who have become unresponsive to DDAVP or need surgical procedures, viral-inactivated factor VIII preparations rich in von Willebrand factor such as Alphanate, Humate-P and Koate DVI are recommended.
- Cryoprecipitate is not recommended except in life threatening emergencies because of the risk of HIV and hepatitis infection. Despite greatly improved screening and purification for viral inactivation in blood products, cryoprecipitate can still be infectious.