What Causes Myelodysplastic Syndromes?

This content has been reviewed and approved by

Hagop M. Kantarjian, MD
Chairman & Professor, Leukemia Department
MD Anderson Cancer Center
University of Texas

Myelodysplastic syndromes (MDS) occur when immature blood cells—called blasts—do not totally mature into red or white blood cells, or platelets. Why these cells do not mature is not fully understood. 

Individuals over the age of 60, men, smokers, and those with a specific congenital disease (such as Down syndrome) may be at greater risk for MDS. 

To better understand MDS and its treatment, a basic understanding of normal blood cell production is useful. Normal blood is made up of fluid called plasma and three main types of blood cells--white, red, and platelets. Each type of blood cell has a specific function. 

• White blood cells, also called leukocytes, help the body fight infection and other diseases. 
• Red blood cells, also called erythrocytes, make up half of the blood's total volume and are filled with hemoglobin, which picks up oxygen from the lungs and carries it to the body's organs. 
• Platelets, or thrombocytes, help form blood clots to control bleeding. 

Blood cells are produced inside the bones in a spongy space called the bone marrow. The process of blood cell formation is called hematopoiesis. All blood cells develop from one common cell type, called a stem cell. Stem cells become mature blood cells by a process called differentiation. Immature blood cells are called blasts. 

Blasts grow or differentiate into mature red blood cells, white blood cells, and platelets. Once they are fully developed, these cells are released into the blood where they circulate throughout the body and perform their respective functions. In healthy individuals, there are adequate stem cells to continuously produce new blood cells and mature blood cells are produced in a continuous and orderly fashion. MDS disrupts this normal process resulting in many blasts and few mature, healthy blood cells.