Blood is carried throughout the body within a network of blood vessels. When tissues are injured, damage to a blood vessel may result in leakage of blood through holes in the vessel wall. The vessels can break near the surface, as in a cut. Or they can break deep inside the body, making a bruise or an internal hemorrhage.
Platelets are small cells circulating in the blood. Each platelet is less than 1/10,000 of a centimetre in diameter. There are 150 to 400 billion platelets in a normal litre of blood. The platelets play an important role in stopping bleeding and beginning the repair of injured blood vessels.
When a blood vessel is damaged, there are four stages in the normal formation of a clot.
Stage 1: The blood vessels is damaged and the bleedings starts.
Stage 2: The blood vessels constrict to slow the flow of blood to the injured area.
Stage 3: Platelets stick to, and spread on, the walls of damaged blood vessels. This is called platelet adhesion. These spreading platelets release substances that activate other nearby platelets which clump at the site of injury to form a platelet plug. This called platelet aggregation.
Stage 4: The surface of these activated platelets then provides a site for blood clotting to occur. Clotting proteins like factor VIII and IX circulating in the blood are activated on the surface of the platelets to form a mesh-like fibrin clot.
These proteins (factors I, II, V, VII, VIII, IX, X, XI, XII AND XIII and von Willebrand factor) work like dominos, in a chain reaction. This is called the coagulation cascade.
Platelet function disorders can affect clotting in several ways, depending on the type of disorder.
- The platelets don’t stick to the vessel walls at the site of an injury.
- The platelets don’t clump together (aggregate) to form a plug.
- The platelets don’t activate blood proteins to form a solid fibrin clot.
Serious hereditary platelet function disorders are quite rare. However, because the majority of people have very mild symptoms, many cases are not diagnosed. Doctors do not know the exact number of people who have these disorders. Some think as many as 1 person in 100 has a platelet function disorder.
Acquired platelet function disorders are even more uncommon.
Congenital platelet function disorders are hereditary diseases. This means that they are passed on from the parents to the child at the time of conception.
The heredity of platelet function disorders varies from disorder to disorder. There are even differences within the same disorder. Some families pass on the disorder in an autosomal dominant pattern. This means that only one parent carries the mutant gene.
Other types are autosomal recessive disorders. This means that both parents must carry the defective gene to be able to pass it on to their children.
The affected chromosome is an autosome. The sex chromosome is not affected in platelet function disorders. Therefore, platelet function disorders affect males and females in equal numbers.
Each family needs to be assessed individually to try to find out their inheritance pattern.
A person can get an acquired platelet function disorder in two ways:
- from taking certain medication or
- as a result of another medical condition.
(See Types of platelet function disorders for more information on the medications and the medical conditions that can affect platelet function.)
This depends on the type of disease.
The majority of people have mild symptoms. Many individuals have no symptoms at all unless they have a serious injury or an operation. In a few individuals, platelet function disorders can cause severe bleeding.
Surgeons should always be told about a person’s platelet function disorder before an operation. This way, proper precautions can be taken to prevent bleeding.