Like hemophilia, von Willebrand Disease (vWD) is a hereditary deficiency or abnormality of clotting factor in the blood. In this case, it is the von Willebrand factor which is 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 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:
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.
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.
Inheritance Pattern (vWD)
Like hemophilia, the disease is passed down through the genes. But unlike hemophilia, which usually affects only males, von Willebrand disease occurs in males and females 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.