Myelodysplastic syndrome (MDS) is a group of disorders associated with dysfunctional and ineffective bone marrow that leads to decreased production of one or more types of blood cells. It can lead to anemia, recurrent infections, and/or excessive bruising and bleeding. MDS can arise spontaneously (also known as de novo or primary MDS) or develop after exposure to certain drugs, chemicals, radiation, and toxins (secondary MDS).
According to the American Cancer Society, there are 4-5 new cases of MDS each year for each 100,000 people in the U.S. This is about 13,000 new cases a year. The number is increasing as the population ages. MDS is more common in men than women, and more than 80% of cases occur in people who are older than 60 years.
Normal bone marrow is a fatty fibrous tissue found inside the body's larger bones. It contains stem cells that can differentiate and become one of three types of blood cells as needed. Stem cells commit to becoming a specific type of cell, go through several maturation stages while they develop in the bone marrow, and are then released as mature cells into the blood stream. They may become:
- Red blood cells (RBCs) – cells that contain hemoglobin and carry oxygen throughout the body
- White blood cells (WBCs) – five different kinds of cells that fight infections
- Platelets – special cell fragments that play a vital role in preventing bleeding
With MDS, an abnormal stem cell in the bone marrow begins to clone itself, making replicate copies of one of the cell types. As they replicate, the abnormal cells crowd out other normal bone marrow cells, leading to few normal cells. The cloned cells may be abnormal-looking (dysplastic) under the microscope and do not develop and mature as well as their normal counterparts. Because they are not normal, they may die more quickly and/or be targeted by the body's immune system for destruction. Consequently, the numbers of one or more types of blood cells (RBC, WBC, or platelet) will progressively decrease.
In some cases of MDS, chromosomes of the cloned cells may acquire one or more characteristic changes. Pieces of the genetic material may be deleted, duplicated, and/or translocated (transferred). Many DNA mutations have also been discovered in cases of MDS. These changes can alter the cells' behavior and the affected person's prognosis.
Some people with rare inherited syndromes are at an increased risk of developing MDS. These include Shwachman-Diamond syndrome, Fanconi anemia, dyskeratosis congenita, Diamond-Blackfan syndrome, familial platelet disorders, and familial myelodysplasia. Together, these are called inherited bone marrow failure syndromes.MDS is a group of disorders that can vary greatly. Some cases of MDS "smolder" for many years (so-called low-grade MDS). They may cause few symptoms and may go undiagnosed until significant cell shortages develop and/or until the disease begins to progress quickly. Other cases of MDS are more aggressive and advance rapidly (so-called high-grade MDS). Because of the wide range of types of MDS that exist, there are a few different ways that healthcare practitioners and other professionals classify them in order to better understand, diagnose, manage, and treat the disorders.