Macrothrombocytopenia (MTC) is a blood disorder in which blood cells called platelets are abnormally large. People with MTC also have thrombocytopenia, a low platelet count. MTC impairs blood clotting and can lead to severe bleeding.

Doctors associate various medical conditions with MTC, and a person may inherit the condition through certain mutated genes. Although MTC may not cause any symptoms, it can indicate a serious medical condition and may lead to complications.

This article looks at the symptoms, causes, diagnosis, and treatment of MTC. It also looks at the outlook for the condition.

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Platelets are blood cells that allow the blood to clot when a person has a wound. A person with MTC has fewer and larger platelets than a person without MTC.

Typical platelets are 1.5–3 microns in diameter. Giant platelets, which are present in the blood of people with MTC, are larger than 7 microns in diameter.

People with a normal platelet count have 150,000–450,000 platelets per microliter of blood, while those with thrombocytopenia have fewer than 150,000 platelets per microliter.

After a wound occurs, platelets travel to the site of the wound and bind together to form a plug. Platelets also release molecules to help hold the plug in place and form a clot, preventing excessive bleeding, until the body can repair the wound.

Giant platelets may not bind together or stick to the walls of the blood vessels properly due to their size. This means they cannot form an effective plug to stop excessive bleeding.

People who inherit MTC also typically have changes in certain genes that produce specific proteins, which form a complex called glycoprotein (GP)Ib-IX-V.

When a person experiences an injury, this complex binds to a protein inside the surface of the blood vessels, allowing clots to form. Mutations in the genes responsible for GPIb-IX-V complex formation can impair blood clotting.

Symptoms of MTC may include:

  • severe, prolonged bleeding after an injury
  • easy bruising
  • nosebleeds
  • spontaneous bleeding
  • petechiae, which are small spots on the skin due to bleeding under the skin
  • menorrhagia, which is heavy or prolonged menstrual bleeding

Changes in certain genes, which people can inherit from their parents, are the main cause of MTC.

MTC is often an indication of the bleeding disorder Bernard-Soulier syndrome. Changes in the GP1BA, GP1BB, or GP9 gene can cause this syndrome and MTC.

If a person inherits one changed copy of one of the three genes from each parent, they may have Bernard-Soulier syndrome from birth.

Each parent may have only one copy of one of the changed genes, so their platelets may be normal. However, when a person inherits a changed copy of one of the three genes from each parent, the presence of two copies of the changed genes may result in abnormal platelets.

Doctors also associate MTC with the following disorders:

  • May-Hegglin anomaly: This is a rare disease with characteristics that include large platelets and thrombocytopenia. Changes to the MYH9 gene, which a person may inherit, cause the disease.
  • Gray platelet syndrome: MTC is also a typical feature of gray platelet syndrome, a rare platelet disorder that results from changes to the NBEAL2 gene.
  • Myelodysplastic syndrome: This is a group of blood and bone marrow cancers in which blood cells in the bone marrow do not reach maturity. People with myelodysplastic syndrome may have thrombocytopenia and significant numbers of giant platelets.

When diagnosing MTC, a doctor may ask a person about their symptoms, such as excessive bleeding, and perform a physical examination.

They may also analyze the results of a variety of blood tests, including:

To help manage and prevent bleeding episodes, a person can:

  • register with an emergency center that can provide 24-hour treatment in case of a bleeding episode
  • carry a card or wear a bracelet that identifies their risk of excessive bleeding in case of an accident
  • avoid sports and activities that pose a high risk of injury
  • maintain good dental hygiene to prevent bleeding in the mouth
  • avoid taking medications that increase the risk of bleeding, such as some antibiotics, antihistamines, and nonsteroidal anti-inflammatory drugs (NSAIDs)
  • monitor their iron levels to prevent anemia
  • find out their human leukocyte antigen type through testing in case they need a transfusion

Doctors cannot cure MTC. Treatments may vary depending on the condition’s underlying cause.

Treatment may include:

  • Platelet transfusion: This is a type of blood transfusion that involves the intravenous replacement of blood. A person will receive a transfusion of healthy donor platelets to replace the abnormal platelets in their blood. Doctors may treat MTC with a transfusion when a person needs surgery or is at risk of a severe hemorrhage.
  • Antifibrinolytic agents: A doctor may prescribe an antifibrinolytic medication, such as tranexamic acid, to help reduce bleeding if a person experiences prolonged nosebleeds or after a minor surgical procedure.

The outlook for MTC may depend on the underlying reasons for the condition.

Doctors often associate MTC with Bernard-Soulier syndrome. People with this condition can often live nearly typical lives as long as they take preventive measures and have strategies in place in case of emergency.

The outlook for May-Hegglin anomaly is generally positive, and some people do not need treatment for it. Most people with this condition do not have significant bleeding issues.

People with gray platelet syndrome can also usually live typical lives and should prepare for emergency scenarios in the same way as those with Bernard-Soulier syndrome. The condition usually involves moderate but not severe MTC.

If a person’s MTC is due to myelodysplastic syndrome, the outlook can depend on a variety of factors, including the type and extent of myelodysplastic syndrome.

According to the American Cancer Society, a person can use the World Health Organization Prognostic Scoring System to determine median survival. According to that system, very low risk groups have a median survival time of 11.8 years and very high risk groups have a median survival time of 9 months.

In MTC, people have larger and fewer platelets than usual, and this interferes with blood clotting. People with MTC usually inherit changed genes.

Conditions doctors associate with MTC include Bernard-Soulier syndrome, May-Hegglin anomaly, gray platelet syndrome, and myelodysplastic syndrome.

Treatment for MTC mainly focuses on managing bleeding episodes. People with the condition can typically live as usual but should prepare for emergencies and try to prevent bleeding.